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BAHAN KAJIAN MK. DIT dan MAES KEMASAMAN TANAH DAN PENGAPURAN Soemarno – Maret 2012.

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Presentasi berjudul: "BAHAN KAJIAN MK. DIT dan MAES KEMASAMAN TANAH DAN PENGAPURAN Soemarno – Maret 2012."— Transcript presentasi:

1 BAHAN KAJIAN MK. DIT dan MAES KEMASAMAN TANAH DAN PENGAPURAN Soemarno – Maret 2012

2 EMPAT KOMPONEN TANAH Padatan An-organik: Mineral & Bukan mineral Padatan Organik : Bahan Organik Tanah (Senyawa organik mati) Organisme hidup Udara tanah …… Aerasi Tanah Air tanah = Larutan tanah Soil Solution, Elektrolit tanah Sifat fisiologik penting dari Larutan tanah adalah “REAKSINYA” (pH) ……. Kemasaman / kebasaan tanah

3 Apa itu pH Tanah? pH adalah kemasaman atau kebasaan relatif suatu bahan. Skala pH mencakup dari nilai 0 (nol) hingga 14. Nilai pH 7 dikatakan netral, di bawah nilai 7 dikatakan asam, sedangkan di atas 7 dikatakan basa. Asam menurut teori Bronsted dan Lewry adalah suatu bahan yang cenderung untuk memberi proton (H+) ke beberapa senyawa lain, demikian sebaliknya apabila basa adalah suatu bahan yang cenderung untuk menerimanya. Teori asam basa ini sangat baik untuk diterapkan dimedia cair termasuk larutan tanah. Teori asam basa lain yang sangat baik diterapkan dalam tanah adalah Arrhenius, yaitu asam adalah suatu bahan yang menghasilkan H+ atau menurunkan pH apabila terdisasosiasi dalam air, sebaliknya apabila basa dalam disosiasinya akan menghasilkan OH- atau menaikkan pH.

4 KEMASAMAN (pH) tanah Kemasaman di dalam tanah dapat dihitung berdasarkan kedudukan ion H+. Apabila yang diukur adalah ion H+ yang ada dilarutan tanah (sebelah kanan, bebas) dikatakan sebagai kemasaman aktual. Apabila ion H+ yang diukur terdapat di komplek jerapan tanah (sebelah kiri, tidak bebas) dikatakan sebagai kemasaman potensial, yang nilainya jauh lebih besar dari kemasaman aktual. Sedangkan apabila kedua kemasaman tersebut dijumlahkan disebut kemasaman total.

5 KEMASAMAN (pH) tanah Kemasaman pH tanah secara sederhana merupakan ukuran aktivitas H+ dan dinyatakan sebagai -log10[H+]. Secara praktikal ukuran logaritma aktivitas atau konsentrasi H+ ini berarti setiap perubahan satu unit pH tanah berarti terjadi perubahan 10 kali dari jumlah kemasaman atau kebasaan. Pada tanah yang mempunyai pH 6.0 berarti tanah tersebut mempunyai H+ aktif sebanyak 10 kali dibandingkan dengan tanah yang mempunyai pH 7.0

6 KEMASAMAN (pH) tanah Sebagian besar tanah tanah produktif, mulai dari hutan humid dan sub humid hingga padang rumput di semiarid, mempunyai pH bervariasi antara 4.0 hingga 8.0. Nilai di atas atau di bawah variasi tersebut disebabkan oleh garam Ca dan Na atau ion H+ dan Al+3 dalam larutan tanah. Pengaruh utama pH di dalam tanah adalah pada ketersediaan dan sifat meracun unsur seperti Fe, Al, Mn, B, Cu, Cd dll terhadap tanaman atau mikroorganisme.

7 pH = - log [H + ] [H + ] dlm larutan tanah ………. Kemasaman aktif [H + ] dijerap koloid tanah ………. Kemasaman potensial Total keduanya ………………….. Kemasaman total Kisaran Nilai pH tanah: pH = 7.0 : Tanah Netral pH < 7.0 : Tanah Masam pH > 7.0 : Tanah basa/ Alkalin/Alkalis Biasanya: Tanah masam : di daerah iklim basah Tanah alkalis: di daerah kering Misel -H [H + ] Ion H+ terjerap, H dd Ion H+ terlarut

8 Kation aluminium: MISEL Al Al 3+ Al 3+ + H 2 O Al(OH) 2+ + H + Al 3+ + OH - Al(OH) 2+ Al(OH) 2+ + OH - Al(OH) 2 + Al(OH) 2+ + H 2 O Al(OH) H + Al(OH) H 2 O Al(OH) 3 + H + SUMBER KEMASAM AN TANAH H dd H+ Bahan Organik Tanah:

9 pH & Ketersedia an Hara Ca dan Mg: Ketersediaan maksimum: pH = Ketersediaan minim pada tanah dg : pH < 4.0 N, K dan S: Ketersediaan maksimum: pH > 6 Ketersediaan minim pada tanah dg : pH < 4.0 Fosfat : Ketersediaan maksimum: pH = Ketersediaan minim pada tanah dg : pH < 4.0 Fe, Mn,Zn, Cu,Co : Ketersediaan maksimum: pH < 5.5 Ketersediaan minim pada tanah dg : pH > 7.5 Bakteri & Aktinomisetes : Ketersediaan maksimum: pH > 5.5 Ketersediaan minim pada tanah dg : pH < 4.0 Mo: Ketersediaan maksimum pd pH > 6.5

10 Problem Kemasam an Tanah Kesuburan tanah Ketersediaan Unsur Hara Suasana fisiologis larutan tanah tidak sesuai bagi proses-proses pertumbuhan akar tanaman Keracunan unsur hara mikro Gangguan akibat tingginya ketersediaan/kelarutan kation aluminium Menurunkan kemasaman tanah = Menaikkan pH tanah = ………….. Pengapuran Gangguan kehidupan jasad renik tanah

11 Al dd dan % KEJENUHAN Al 1. Sumber kemasaman tanah : H+, H dd, Al dd, 2. Al dd diendapkan pada pH > % kejenuhan Al dari KTK efektif menjadi ukuran kemasaman tanah 4. Kejenuhan basa (KB) = jumlah basa dibagi KTK 5. Al dd ditentukan dengan jalan ekstraksi tanah dg 1 N KCl, dan mentitrasi ekstraksnya dengn larutan basa 6.

12 HUBUNGAN pH dan KEJENUHAN Al % kejenuhan Al pH tanah Sumber: Abruna et al Ultisols & Oxisols

13 HUBUNGAN KEJENUHAN Al dan HASIL BEANS % kejenuhan Al % hasil maks Sumber: Abruna et al Ultisols & Oxisols r = 0.93**

14 1. Konsentrasi Al dlm larutan tanah > 1 ppm menyebabkan penurunan hasil tanaman 2.Tembakau dan kentang sangat peka thd Al +++ dlm tanah, terutama akarnya. Gejalanya akar menjadi tebal, kaku dan becak-becak jaringan mati 3.Pertumbuhan akar jagung mulai terganggu pada kondisi 60% kejenuhan Al. 4.Al cenderung terakumulasi dalam akar dan menghambat penyerapan dan translokasi Ca dan fosfat menuju tajuk, sehingga mendorong defisiensi Ca dan P.

15 1. Gangguan pertumbuhan tanaman pd tanah masam dapat juga disebabkan oleh defisiensi Ca dan/atau Mg 2.Gangguan akar tembakau pd Ultisol yg tidak dikapur disebabkan oleh keracunan Al dan defisiensi Ca. 3.Kalau Al diendapkan (dg menggunakan MgCO3) dan tidak ditambahkan Ca, pertumbuhan akar tembakau akan berhenti dalam waktu 60 jam. 4.Tanah masam di daerah tropis defisien Ca tanpa menunjukkan masalah toksisitas Al. 5.Misalnya Tanah masam di Hawaii, pH < 5.0, namun Al dd nya sedikit; pengapuran berfungsi seperti pemupukan Ca 6.Tanah masam di Brazil sangat miskin Mg dan respon positif thd pupuk Mg.

16 TOKSISITAS Al & DEFISIENSI Ca thd AKAR TEMBAKAU waktu (hari) % maks. pemanjangan akar Sumber: Abruna et al Ultisols & Oxisols Dikapur CaCO3, pH 5.8, 4.4 meq Ca++ Dikapur MgCO3, pH 5.6, 0.4 meq Ca++ Tdk Dikapur, pH 4.2, 0.4 meq Ca++

17 EFEK Al thd PERTUMBUHAN AKAR TanahpHAl dd % Kejenuhan Berat kering akar tanaman: me/100 g AlJagung (mg/pot)Sorghum Ultisol Oxisol Sumber: Brenes & Pearson, 1973.

18 MENGUKUR KEMASAMAN (pH) tanah Ada 2 metode yang paling umum digunakan untuk pengukuran pH tanah yaitu kertas lakmus dan pH meter. Kertas lakmus sering di gunakan di lapangan untuk mempercepat pengukuran pH. Penggunaan metode ini di perlukan keahlian pengalaman untuk menghindari kesalahan. Lebih akurat dan secara luas di gunakan adalah penggunaan pH meter, yang sangat banyak di gunakan di laboratorium. Walaupun pH tanah merupakan indikator tunggal yang sangat baik untuk kemasaman tanah, tetapi nilai pH tidak bisa menunjukkan berapa kebutuhan kapur. Kebutuhan kapur merupakan jumlah kapur pertanian yang dibutuhkan untuk mempertahankan variasi pH yang di inginkan untuk sistem pertanian yang digunakan. Kebutuhan kapur tanah tidak hanya berhubungan dengan pH tanah saja, tetapi juga berhubungan dengan kemampuan menyangga tanah atau kapasitas tukar kation (KTK).

19 PENGELOLAAN KEMASAMAN (pH) tanah Tanah masam adalah tanah ber-pH rendah (pH di bawah 6), semakin rendah pH tanahnya maka semakin ekstrim kemasamannya. Kendala Tanah Masam 1.Unsur hara makro (terutama N,P,K,Ca,Mg) tidak tersedia dalam jumlah cukup, efektifitas dan efisiensi pemupukan makro (urea, TSP, KCl) juga rendah. 2.Beberapa unsur (terutama Al dan Fe) tersedia berlebih sehingga sering meracun pada tanaman. 3.Menghambat perkembangan mikroorganisme tanah.

20 PENGELOLAAN KEMASAMAN (pH) tanah Pengapuran untuk Meningkatkan pH Tanah Perbaikan pH tanah bisa diakatakan menyelesaikan 50% masalah kesuburan tanah. Salah satu cara meningkatkan pH tanah dengan pengapuran menggunakan kapur pertanian (kaptan) atau dolomit. Beberapa hal yang perlu diperhatikan : 1.Idealnya paling lambat pengapuran dilakukan 2 minggu sebelum tanam, karena bahan kapur termasuk bahan yang lambat bereaksi dengan tanah. 2.Setelah pengapuran sebaiknya tanah dicangkul (dibajak) agar kapur bisa merata masuk dekat zona perakaran. 3.Pengairan setelah pengapuran sangat diperlukan. 4.Peningkatan pH tidak bisa terjadi seketika, melainkan pelan dan bertahap. 5.Dosis kapur disesuaikan pH tanahnya, tetapi sebagai pedoman praktis dosis berkisar 500 kg/Ha 2 ton/Ha. Catatan : Dolomit juga harus secara rutin digunakan pada tanah pH normal, karena unsur Ca dan Mg pada dolomit sangat dibutuhkan tanaman.

21 PENGELOLAAN KEMASAMAN (pH) tanah Kapur pertanian merupakan mineral yang berasal dari alam yang merupakan sumber hara kalsium. Kaptan yang mempunyai reaksi basa dapat menaikkan pH tanah. Kaptan yang banyak digunakan dalam pertanian adalah kalsit (CaCO3) Manfaat : Untuk menetralkan pH tanah pada tanaman sayuran⁄hortikultura dll. Untuk menanggulangi beberapa jenis jamur ⁄bakteri pada tanah. Untuk menetralkan tanah gambut sehingga menambah tingkat kesuburan tanah dll Spesifikasi : Kadar CaCO3 + MgCO %, Kadar CaO + MgO 58.8 %, Kadar Air Saat dikemas 1.00 %, Mesh 40 – 100, Berat bersih kemasan 50 kg

22 KAPTAN Kapur Pertanian (Kaptan) memiliki kandungan kalsium dan magnesium yang tinggi, ukiran butiran (mesh) yang halus dan sesuai dengan standar yang telah ditetapkan oleh SNI (Standar Nasional Indonesia) KAPTAN dapat diproduksi dengan menggunakan mesin crusher dan milling yang mampu memproduksi kaptan sekitar ton per bulan. Spesifikasi Kaptan Kadar CaCO3 + MgCO3 : 91.53% Kadar CaO + MgO : 50.23% Kadar air saat dikemas : 1.00% Mesh 40 – 100 : 82.01% Berat bersih perkemasan 50 Kg Kapur Pertanian merupakan mineral yang berasal dari alam yang merupakan sumber hara kalsium. Kaptan yang mempunyai reaksi basa dapat menaikkan PH tanah. Kaptan yang umum banyak digunakan dalam pertanian adalah Kalsit (CaCo3)

23 KAPTAN Dosis Kaptan 1. Sebelum melakukan pengapuran, sebaiknya terlebih dahulu dilakukan pemeriksaan PH tanah dengan menggunakan kertas lakumus atau PH soil tester, dapat meminta bantuan penyuluh terdekat dari dinas pertanian/ perkebunan/ perikanan 2. Pengapuran dengan dosis tersebut untuk jangka panjang atau 3 tahunan keatas, baru dilakukan pengapuran ulang. Ada anjuran para ahli sebaiknya dilakukan penambahan KAPTAN sebanyak 10% – 20% dari dosis diatas pada setiap 6 bulan sekali atau bersamaan dengan waktu pemupukan dilakukan 3. Untuk tanah marginal, umumnya berwarna terang atau pada tanah podsolik merah dan kuning atau pada tanah yang miskin kandungan bahan organik, dianjurkan pemberian kompos, bokasi atau pupuk organik 4. Mutu KAPTAN yang tepat selain kandungan kalsium (CaCO) yag tinggi kisaran 42% sampai 51%, tingkat kehalusan dan kelembutan (mesh) yang terbaik adalah 60 sampai 100 mesh 5. KAPTAN berkualitas tinggi bereaksi lebih cepat dan sempurna, sedangkan KAPTAN berkualitas renddah memerlukan waktu sangat lama untuk dapat merubah PH tanah, bahkan bisa sampai tahunan. Adapun KAPTAN yang memenuhi standar, dapat langsung bermanfaat dengan cara pemberian yang tepat

24 KALSIUM KARBONAT Kalsium karbonat adalah bahan aktif dalam kapur pertanian, dan biasanya merupakan penyebab utama air keras. Hal ini biasanya digunakan secara medis sebagai kalsium suplemen atau sebagai antisida, namun konsumsi yang berlebihan dapat membahayakan Kalsium karbonat memunyai beberapa sifat khas khususnya : 1. Bereaksi dengan asam yang kuat, dan melepaskan karbon dioksida CaCO3(s) + 2HC1(aq) ---- CaC12(aq) + CO2(g) + H2O(1) 2. Ia melepaskan karbondioksida pada pemanasan (diatas 840 C dalam kasus CaCO3), untuk membentuk kalisum oksida, yang biasa disebut kapur, dengan reaksi 178 KJ/ Mol CaCO CaO + CO2

25 KALSIUM KARBONAT Kalsium karbonat akan bereaksi dengan air yang penuh dengan karbon dioksida untuk membentuk larut kalsium bikarbonat CaCO3 + CO2 + H2O ? Ca(HCO3)2 Reaksi ini penting dalam erosi dari batuan karbonat, membentuk gua gua, dan menyebabkan air keras di berbagai daerah Sebagian besar dari kalsium karbonat yang digunakan dalam industri diekstraksi dengan pertambangan atau penggalian. Kalsium karbonat murni (misalnya untuk keperluan makanan atau farmasi), dapat dihasilkan dari sumber yang digali murni (biasanya marmer) atau kalisum karbonat disusun oleh kalsinasi mentah oksida kalsium. Air ditambahkan untuk memberikan kalsium hidroksida, dan karbon dioksida dilewatkan untuk mengendapkan kalsium karbonat yang diinginkan, sebagaimana dimaksud dalam industri sebagai endapan kalsium karbonat

26 KALSIUM KARBONAT Karbonat sering ditemukan dalam pengaturan geologi, kalsium karbonat terjadi sebagai polimor aragonit dan kalsit. Polimorf adalah mineral dengan rumus kimia yang sama tetapi struktur kimia yang berbeda. Mineral karbonat membentuk jenis batu : kapur, marmer, travertine, tufa, dan lain lain. Kalsit umumnya terjadi sebagai sedimen dalam pengaturan laut. Kalsit biasanya ditemukan di sekitar lingkungan tropis yang hangat. Endapan kalsit di lingkungan dangkal hangat lebih dari itu tidak dalam lingkungan yang lebih dingin karena lingkungan lebih hangat tidak mendukung pembubaran CO2. Hal ini dianalogikan dengan CO2 yang larut dalam soda. Ketika anda mengambil tutup botol soda, CO2 bergegas keluar. Sebagai soda menghangat, & karbon dioksida dilepaskan. Prinsip yang sama dapat diterapkan pada kalsit di laut

27 SUPER DOLOMITE Super Dolomite adalah pupuk magnesium berkadar tinggi, digunakan baik untuk tanah pertanian, tanah perkebunan, kebutuhan industri dan bahkan untuk perikanan /tambak. Bahan baku Super Dolomit berasal dari batuan dolomit yang ditambang dari kawasan pertambangan di Gresik. Menurut pusat Penelitian dan Pengembangan Geologi Direktorat Jenderal Pertambangan Umum Bandung, batuan dolomit di Gresik adalah jenis batuan dolomit yang berkualitas tinggi, yakni dengan kadar MgO 18% - 21%

28 Keunggulan Pupuk Super Dolomit 1. Ukuran butir seragam, dan minimal 95% lolos ayakan 100 mesh Kadar MgO minimal 18% Daya larut dalam air cepat, sehingga cepat tersedia bagi tanaman Sebagai pupuk Mg memiliki efektifitas tinggi Daya tangkal pengasaman cepat Untuk mencapai produktifitas yang sama hanya memerlukan 60% super dolomit bila dibandingkan dengan dolomit biasa, sehingga mengurangi biaya aplikasi pemupukan dan biaya pengiriman 2. Pemakaian Kieserite dapat digantikan oleh super dolomit, jika super dolomit telah dicampur dengan ZA. Selain itu dapat memberikan manfaat lebih tinggi sebagai berikut : Pemakaian kombinasi super dolomit + ZA mampu memasok hara Magnesium (Mg) dan Sulfat Nitrogen pada tanaman dan tidak mengasamkan tanah Penghematan biaya produksi karena pemakaian Super Dolomit + ZA harganya lebih murah dibandingkan dengan Kieserite Penghematan devisa, karena import Kieserite dapat ditiadakan.

29 Kegunaan Super Dolomite 1. Penyembuhan Untuk tanaman, kekurangan Magnesium (Mg) berakibat sangat fatal. Tanaman yang menderita kekurangan Magnesium ditandai dengan daun yang menguning, sehingga kehilangan kemampuan menghasilkan CO2, dengan demikian, pemberian pupuk Super Dolomite akan mampu menambah unsur hara Magnesium yang diperlukan tanaman, sehingga warna daunnya menjadi hijau lagi 2. Amelioran Pada tanah masam atau PH rendah, selain pertumbuhan tanaman akan terganggu, juga keracunan A1 dan Fe sering terjadi. Dengan pemberian Super Dolomit, selain dapat menetralisir A1 dan Fe, juga menaikkan PH tanah sehingga penyerapan unsur unsur hara, N Fosfor (P), K oleh tanaman menjadi baik 3. Pembenah Pemberian pupuk berbentuk Amonium (UREA/DAP) dan kalcium (KCl) yang terlalu banyak, dapat mengakibatkan kekurangan Magnesium (Mg). Selain itu pupuk nitrogen mempunyai kecenderungan menciptakan suasana masam. Pemberian pupuk Super Dolomit mampu menetralisir reaksi tanah yang bersifat masam akibat pemberian pupuk yang berlebihan

30 CARA PENGGUNAAN SUPER DOLOMITE 1. Disebar/ Dicampur merata Cara ini dilakukan apabila pupuk super dolomit digunakan untuk memperbaiki tanah yang buruk. Pupuk ini disebar/ dicampur merata diatas tanah pada waktu tanah terakhir yang bisanya dilakukan sebelum tanaman ditanam atau benih ditabur 2. Dimasukkan pada lubang tanaman Bila sebagai pupuk dasar pada tanaman perkebunan, Super Dolomit ditempatkan pada dasar lubang tanaman, kemudian diaduk merata dengan pupuk dan tanah pada dasar lubang, setelah itu ditimbun sedikit dengan tanah, baru diatas timbunan ditempatkan bibit tanaman 3. Super Dolomit dicampur dengan ZA / Pupuk lainnya Bila super dolomit diperlukan dalam pencampuran pupuk maka cara pemberiannya dilakukan dengan cara sebar merata dalam larikan sejajar baris tanaman, sekeliling batang tanaman atau ditempatkan pada lubang yang dibuat dikanan – kiri tanaman Untuk meniadakan reaksi tanah masam, Pupuk Super Dolomit dicampurkan pada waktu pengolahan tanah secara merata dan dilakukan 2 minggu sebelum tanam.

31 BENTUK BAHAN KAPUR Kapor Oksida: Kapur Sirih Kemurniannya: % Pembuatannya: CaCO3 + panas CaO + CO2 CaMg(CO3)2 + panas CaO +MgO + CO2 Reaksinya dlm tanah: MISEL - H + CaO MISEL - Ca + H2O CaO + H2O Ca(OH)2 Ca(OH)2 + 2 H 2 CO 3 Ca(HCO 3 ) H2O % Oksida CaO : 77% Ekuivalen oksida Ca: 102 Daya netralisasi : (kesetaraan CaCO3) Persentase unsur Ca: 55 % Oksida MgO : 18% Persentase unsur Mg: 10.8

32 BENTUK BAHAN KAPUR Kapor Hidroksida: Kapur Tembok Kemurniannya: % Pembuatannya: CaO + MgO + H2O Ca(OH)2 + Mg(OH)2 Reaksinya di udara lembab terbuka: Ca(OH)2 + CO2 CaCO3 + H2O Mg(OH)2 + CO2 NgCO3 + H2O Reaksinya dlm tanah: MISEL - H + Ca(OH)2 MISEL - Ca + 2H2O Ca(OH)2 + 2 H 2 CO 3 Ca(HCO 3 ) H2O % Oksida CaO : 60% Ekuivalen oksida Ca: 76.7 Daya netralisasi : (kesetaraan CaCO3) Persentase unsur Ca: 42.8 % Oksida MgO : 12% Persentase unsur Mg: 7.2

33 BENTUK BAHAN KAPUR Kapor Karbonat : Kapur Kalsit = CaCO3 Kapur Dolomitik = CaMg(CO3)2 Dolomit= MgCO3 Kemurniannya : % Pembuatannya: Batuan CaCO3 digiling Kapur giling Reaksinya dlm tanah: MISEL - H + CaCO3 MISEL - Ca + H2O + CO2 Oksida CaO = 44.8%; MgO = 6.70% Ekuivalen oksida Ca: Daya netralisasi : 96.6 (kesetaraan CaCO3) Persentase unsur Ca = 32; Mg = 4.03 Karbonat: CaCO3 = 80%; MgCO3 = 14% Total = 94%

34 PENGARUH KAPUR PADA TANAH Pengaruh Fisik: - Membantu granulasi - agregasi - Memperbaiki struktur tanah - Tata Udara (Aerasi) - Tata Air / Pergerakan air Pengaruh Kimia: (Bila tanah dg pH= 5.0 dikapur hingga ph naik menajdi 6.0) - Kepekatan kation hidrohen menurun - Kepekatan anion hidroksil meningkat/ naik - Daya larut Fe, Mn dan Al akan menurun - Ketersediaan fosfat dan Mo akan diperbaiki - Ca dd dan Mg dd akan naik - Persentase kejenuhan basa (KB) akan naik - Ketersediaan kalium berubah tgt keadaan. Pengaruh Biologik: 1.Merangsang kegiatan jasad tanah, termasuk mikroba tanah 2.Membantu pembentukan humus 3.Aminisasi, amonifikasi, oksidasi belerang dipercepat 4.Fiksasi nitrogen dari udara secara biologis dirangsang 5.Nitrifikasi dipercepat

35 JENIS TANAMAN yg SESUAI TANAH MASAM dg KEBUTUHAN KAPUR MINIMUM Kebutuhan Kejenuhan pHVarietas tnm yg toleran kapurAl (t/ha)(%) Gogo, ubikayu, mangga, mente Jeruk, Nanas, Desmodium, Cen- trosema, Paspalum Cowpea, Plantain Jagung, Black bean Sumber: Spain et al. 1975

36 MEKANISME TOLERANSI / KEPEKAAN TANAMAN thd Al dlm TANAH 1. Morfologi akar. Varietas yg toleran Al mampu menumbuhkan dan tidak mengalami kerusakan ujung-ujung akar pd kondisi tanah masam kaya Al 2.Perubahan pH rhizosfer. Varietas yg toleran Al mampu menaikkan pH zone rhizosfernya, sdg varietas yg peka menurunkan pH tsb. Perubahan pH ini diduga akibat dari penyerapan anion diferensial-selektif, sekresi asam organik, CO 2 dan HCO Lambatnya translokasi Al ke tajuk. Varietas yg toleran Al mengakumulasikan Al dlm akar, dan mentranslokasikan ke tajuk secara lebih lambat dp jenis yg peka.

37 MEKANISME TOLERANSI / KEPEKAAN TANAMAN thd Al dlm TANAH 4. Al dalam akar tidak menghambat penyerapan dan translokasi Ca, Mg dan K dlm varietas yg toleran Al. 5. Toleransi varietas kedelai thd Al berhubungan dengan penyerapan dan translokasi Ca. 6. Toleransi varietas keNTANG thd Al berhubungan dengan translokasi Mg dan K. 7.Toleransi varietas padi thd Al berhubungan dengan tingginya kandungan Si dlm tanaman. 8.Varietas yg toleran Al tidak mengalami hambatan penyerapan dan translokasi fosfat; tdk dmk varietas yg peka.

38 1. Tujuan utama pengapuran adalah menetralisir Al dd, dan biasanya diikuti oleh kenaikan pH hingga Kalau diduga ada keracunan Mn, maka pH dinaikkan Faktor-faktor yg harus diperhatikan: 1. Jml bahan kapur yg diperlukan untuk menetralkan Al dd hingga tingkat yg sesuai bagi tanaman 2. Kualitas bahan kapur 3. Cara penempatan / aplikasi bahan kapur ke tanah.

39 RESPON TANAMAN thd PENGAPUR AN Umumnya pertumbuhan tanaman menjadi lebih baik. Tnm kacang-kacangan menyukai kapur, termasuk kedelai dan kacang tanah Alasan terjadinya respon tanaman: 1. Pengaruh langsung unsur hara Ca dan Mg 2. Dinetralkannya senyawa-senyawa toksik 3. Penekanan gangguan penyakit tanaman 4. Ketersediaan beberapa unsur hara meningkat 5. Rangsangan kegiatan jasad mikro akan meningkatkan ketersediaan hara 6. Beberapa tanaman tertentu tidak senang pengapuran, misalnya semangka. 7. ……. Dll.

40 1. Kamprath (1970): Dosis kapur = 1.5 x ( me Al dd topsoil) = m.e. Ca yg harus diaplikasikan sbg kapur 2. Dosis kapur yg dihitung dg cara ini mampu menetralkan % Al dd dlm tanah yg mengandung 2 - 7% bahan organik 3.Faktor 1.5 digunakan untuk menetralkan H+ yg dilepaskan oleh bahan organik atau hidroksida Fe dan Al kalau pH tanah meningkat 4.Dalam tanah yg kaya bahan organik, faktor tersebut menjadi 2.0 atau 3.0, karena adanya H dd. 5.Untuk setiap satu m.eq. Al dd dlm tanah diperlukan aplikasi 1.5 meq Ca atau setara dg 1.65 ton CaCO3 per ha. 6.Faktor penting lain adalah kandungan Al dd dlm tanah yang dapat ditolerir oleh tanaman tertentu 7.Jagung sensitif terhadap kejenuhan Al 40-60%. Pengapuran hingga kejenuhan Al = 0% dapat menguntungkan, namun pengapuran untuk menurunkan kejenuhan Al menjadi 20% dapat lebih ekonomis.

41 RESPON HASIL TERHADAP PENGAPURAN % kejenuhan Al % Hasil maks Sumber: Abruna et al Oxisols & Ultisols Rumput gajah Sorghum Jagung

42 1. Kapur biasanya dibenamkan sedalam 15 cm beberapa hari sebelum tanam. 2.Tanah Oksisol sangat masam yg topsoilnya telah dikapur hingga pH 5.5, sebagian besar akar jagung tumbuh dalam topsoil. Tingginya kandungan Al dd dalam subsoil mencegah pertumbuhan akar lebih dalam. 3.Penempatan kapur pada lapisan tanah yg lebih dalam mengakibatkan perakaran tanaman tumbuh lebih dalam dan hasil tanaman lebih baik 4.Deep placement kapur dimungkinkan pada tanah- tanah berpasir yang strukturnya baik. 5.

43 PENGAPURAN & HASIL JAGUNG Dosis kapur ( ton/ha) Hasil biji, t/ha Sumber: Gonzales, 1973 Tanah Oxisols Zone pengapuran cm Zone pengapuran cm

44 1. Efek residu pengapuran tergantung pada seberapa cepat Ca dan Mg digantukan oleh residu kemasaman dari pupuk nitrogen. 2.Pada tanah Hydrandept Selama lima tahun sejak aplikasi 2 ton kapur/ha ternyata nilai Al dd dalam tanah dipertahankan sekitar 1 meq, semula sebesar 3 m.eq, meskipun sebagian besar Ca++ telah tercuci. Setelah lima tahun efek residu pengapuran lenyap. 3.Pada Oxisol berpasir. Jagung dan kedelai respon positif terhadap kapur enam tahun setelah aplikasi, respon hasil meningkat dg waktu, diduga karena pelarutan partikel kasar kapur.

45 KELEBIHA N Pemberian KAPUR Kelebihan: penambahan kapur yg mengakibatkan meningkatan pH tanah melebihi yang diperlukan untuk pertumbuhan optimum tanaman. Tanaman akan menderita, terutama pada tahun pertama aplikasi kapur Biasanya terjadi pada tanah berpasir / berdebu yg miskin bahan organik Pengaruh buruk pengapuran yg berlebihan: 1. Kekurangan Fe, Mn, Cu dan Zn 2. Ketersediaan fosfat mungkin menurun karena pembentukkan senyawa kompleks dan tidak larut 3. Serapan fosfat dan penggunaannya dlm metabolisme tanaman dapat terganggu 4. Serapan B dan penggunaannya dapat etrganggu 5.Perubahan pH yang terlalu melonjak dapat berpengaruh buruk 6. ………dst. 7. ……. Dll.

46 Apakah KAPUR perlu diberikan? Penggunaan kapur harus didasarkan pada : Kemasaman Tanah dan Kebutuhan Tanaman 1. Sebelum mengapur tanah, karakteristik kimia tanah perlu diteliti 2. pH tanah dan Kejenuhan Basa harus ditentukan secara akurat : Lapisan atas dan Lapisan bawah 3. Cara lain adalah menentukan Al dd 4. ………. 1. Kebutuhan kapur untuk tanaman secara umum atau untuk tanaman tertentu 2. Pengelompokkan respon tanaman thd kapur : - Tanaman Senang Pengapuran - Tanaman tidak senang Pengapuran - Tanaman netral

47 Bentuk KAPUR yg dipakai Lima faktor unt menentukan bentuk kapur : 1. Jaminan mutu kimia bahan kapur 2. Harga bahan 3. Kecepatan reaksi dengan tanah 4. Kehalusan bahan kapur 5. Hal lain-lain (penyimpangan, pembungkusan dsb. Kecepatan Reaksi: 1. Kapur kaustik (kapur tohor dan tembok) lebih cepat bereaksi dg tanah dp kapur giling 2. Kapur dolomitik bereaksi lebih lambat dp kapur kalsitik 3. Bentuk tepung halus lebih cepat bereaksi dg tanah 4. …. Dll. Pertimbangan biaya: 1. Harga bahan kapur 2. Biaya angkut ke lahan usaha 3. Biaya aplikasi bahan kapur ke lahan usaha 4. ….. dll

48 Jumlah KAPUR yg diaplikasikan Enam faktor penting unt menentukan jumlah kapur : 1. Karakteristik tanah: Lapisan atas: pH, Al dd, Tekstur & Struktur, BOT Lapisan bawah: pH, Al dd, Tekstur & Struktur 2. Tanaman yg akan ditanam 3. Lamanya pergiliran tanaman 4. Macam bahan kapur dan komposisi kimianya 5. Kehalusan bahan kapur 6. Pengalaman praktis Karakteristik Tanah : 1. Tekstur dan BOT menentukan besarnya kapasitas jerapan 2. Semakin tinggi Kapasitas jerapan dan Al dd, semakin banyak kapur diperlukan 3. Kemasaman dan Al dd tanah lapisan bawah ikut menentukan jumlah kapur Contoh: Jml kapur giling unt tanah mineral setebal 20 cm seluas 1 ha: Untuk menapai pHJumlah kapur, ton/ha x me Al dd

49 Teknologi Aplikasi KAPUR Cara Aplikasi : 1.Kapur disebar di permukaan tanah yg baru dibajak, kemudian dicampur rata dengan tanah olahan 2.Kapur disebar di permukaan tanah, tanah dibajak (diolah) dan dicampur rata Waktu Aplikasi : 1. Biasanya sebelum tanam 2.Kapur diberikan bila diperkirakan tidak turun hujan pd saat aplikasi 3. …… 1. Pertanaman tunggal 2. Pertanaman majemuk: Pola pergiliran tanaman Kapur diberikan pd tanaman yg paling memerlukan pengapuran

50 TEKNOLOGI PENGAPURAN TERPADU Prinsip utama pengelolaan tanah masam adalah menaikkan pH tanah dan mengurangi kejenuhan Al yang meracun, serta meningkatkan ketersediaan hara tanaman, terutama unsur hara P sehingga sesuai dengan pertumbuhan tanaman yang optimal. Pengapuran merupakan teknologi yang paling tepat dalam pemanfaatan tanah masam di dasarkan atas beberapa pertimbangan: 1.Rekasi kapur sangat cepat dalam menaikkan pH tanah dan menurunkan kelarutan Al yang meracun. 2.Respons tanaman sangat tinggi terhadap pemberian kapur pada tanah masam. 3.Efek sisa kapur atau manfaat kapur dapat dinikmati selama 3 sampai 4 tahun berikutnya. 4.Bahan kapur cukup tersedia dan relatif murah

51 PENGELOLAAN KEMASAMAN (pH) tanah Teknologi pengapuran terpadu meliputi topik- TOPIK : 1.Kapur pengendali kemasaman tanah 2.Peranan kapur dalam meningkatkan serapan P 3.Penetapan kebutuhan kapur 4.Manfaat kapur bagi pertumbuhan dan hasil tanaman 5.Pengaruh sisa pupuk P bersama kapur 6.Jenis kapur dan cara penggunaannya 7.Pengapuran harus di sertai dengan pemupukan 8.Peran bahan organik pada tanah masam 9.Integrasi kapur, bahan organik, dan pupuk 10.Efek kapur berlebihan 11.Pengapuran dan pengaturan pola tanam 12.Budidaya lorong "Alley cropping" memantapkan pengapuran 13.Perhitungan keuntungan penggunaan kapur

52 PENGELOLAAN KEMASAMAN (pH) tanah TEKNOLOGI PENGAPURAN TERPADU: Teknologi pengapuran yang diintegrasikan dengan penggunaan bahan organik dan pupuk buatan yang disertai dengan budidaya lorong dengan pola tanam yang menguntungkan.

53 WHEN TO APPLY LIME AND FERTILIZER Kenneth Wells Department of Agronomy Diunduh 27/2/2012 When lime and fertilizers are applied to soils, many chemical reactions take place — some immediately, and some over long periods of time. These reactions have a great influence on when lime and fertilizer can be applied and how efficiently fertilizer is taken up by growing crops, and this influences the economic returns from lime and fertilizer use. When applied to soil, the liming material reacts with soil moisture to release particles of calcium or, in the case of dolomitic lime, magnesium. The rate at which the lime material dissolves to release these particles is largely controlled by how finely it is ground and the chemical form of the material (carbonate, oxide or hydroxide). The finer the material, the more rapidly it dissolves. Oxides (burned lime) and hydroxides (hydrated lime) are more soluble in water and react much more quickly than carbonate forms of lime (calcitic aglime or dolomitic aglime).

54 APLIKASI KAPUR Diunduh 27/2/2012 Timing Lime Application for Best Results In general, follow these guidelines to achieve the best results with our Superfine formulation: 1.in a rotation, apply before the crop with the greatest acid sensitivity 2.if you plan on reducing tillage, apply one year before the most acid sensitive crop, and in a greater quantity 3.make sure that the root disease Take-All has been controlled before applying lime fertiliser ahead of a wheat or critical crop 4.lime fertiliser application is generally not recommended for permanent pastures, due to issues of incorporation GUIDE TO LIME APPLICATIONS IGC Document 143/08/E

55 MENGUKUR KEMASAMAN ….. Diunduh 27/2/2012 The term pH stands for the potential (p) of the hydrogen ion (H + ) in water. It is actually a way of reporting the concentration of H + in solution using an electrical "potential" to measure H +. The pH of any solution is one of the easiest laboratory measurements to make using a pH meter and an electrode specifically designed to measure hydrogen (pH electrode). Color indicators and litmus paper are a quick alternative for less precise measurements. By mixing a quantity of soil with demineralized or distilled water (usually a 1:1 mixture), we can measure the pH of the water solution in equilibrium with the soil. The pH measurement is based on a scale from 1 to 14 (pH is reported as the negative logarithm of the hydrogen ion activity). At a pH of 7.0, there is an equal balance of hydrogen (H + ) ions and hydoxyl (OH - ) ions, and the soil (actually the soil-water suspension) is said to be neutral. Because the pH measurement is logarithmic, each unit change in pH represents a ten-fold increase in the amount of acidity or basicity. That is, a soil solution with a pH of 6.0 has 10 times as much active H + as one with a pH of 7.0.

56 KETIDAK-SUBURAN TANAH MASAM When the pH falls below 6.0, the availability of nutrients such as phosphorus, potassium, calcium, and magnesium decreases. The availability of the metallic micronutrients, however, like zinc, manganese, copper, and iron increases as the pH decreases. Plants don't need aluminum to grow. It's not an essential plant nutrient. Aluminum, however, is one of the prominent mineral components of silt and clay. Therefore, the earth's crust is naturally high in aluminum. Like zinc, manganese, copper and iron, the more acid the soil, the more aluminum will be dissolved into the soil solution. If the pH is allowed to drop much below 5.5, the availability of manganese and aluminum is increased to the point that they could become toxic to plants. Aluminum toxicity to plants is the main concern we have with acid soils in our region. Charles C. Mitchell. Extension Agronomist-Soils & Professor Auburn University ….. Diunduh 27/2/2012

57 PROBLEM TANAH MASAM DAN TANAH ALKALIS Problems in very acid soilsProblems in alkaline soils *Aluminum toxicity to plant roots *Iron deficiency *Manganese toxicity to plants *Manganese deficiency *Calcium & magnesium deficiency *Zinc deficiencies *Molybdenum deficiency in legumes *excess salts (in some soils) *P tied up by Fe and Al*P tied up by Ca and Mg *poor bacterial growth *bacterial diseases in potatoes *reduced nitrogen transformations Charles C. Mitchell. Extension Agronomist-Soils & Professor Auburn University ….. Diunduh 27/2/2012

58 FAKTOR pH TANAH Parent material. Soils of the Piedmont and Sandstone Plateau regions of Alabama are very acid because of the acid nature of the rocks (granites and sandstones, respectively) which formed these soils. Limestone valley soils were formed from basic rocks (limestones) but may be acid on the surface because of time and weathering. Some Black Belt Prairie soils may be alkaline because the Selma chalk (soft limestone) which formed the soils is alkaline. Rainfall/leaching. Rainfall also affects soil pH. Water passing through the soil leaches basic cations such as calcium (Ca 2+ ), magnesium (Mg 2+ ), and potassium (K + ) into drainage water. These basic cations are replaced by acidic cations such as aluminum (Al 3+ ) and hydrogen (H + ). For this reason, soils formed under high rainfall conditions are more acid than those formed under arid conditions. Fertilizers. Both chemical and organic fertilizers may eventually make the soil more acid. Hydrogen is added in the form of ammonia-based fertilizers (NH 4 + ), urea-based fertilizers [CO(NH 2 ) 2 ], and as proteins (amino acids) in organic fertilizers. Transformations of these sources of N into nitrate (NO 3 - ) releases H + to create soil acidity. Therefore, fertilization with fertilizers containing ammonium or even adding large quantities of organic matter to a soil will ultimately increase the soil acidity and lower the pH. NH O NO H + + H 2 O Bacteria Plant uptake. Plants take up basic cations such as K +, Ca ++, and Mg ++. When these are removed from the soil, they are replaced with H + in order to maintain electrical neutrality. Charles C. Mitchell. Extension Agronomist-Soils & Professor Auburn University ….. Diunduh 27/2/2012

59 PENGAPURAN TANAH MASAM Soils are limed to reduce the harmful effects of low pH (aluminum or manganese toxicity) and to add calcium and magnesium to the soil. The amount of lime needed to achieve a certain pH depends on (1) the pH of the soil and (2) the buffering capacity of the soil. The buffering capacity is related to the cation exchange capacity (CEC). The higher the CEC, the more exchangeable acidity (hydrogen and aluminum) is held by the soil colloids. As with CEC, buffering capacity increases with the amounts of clay and organic matter in the soil. Soils with a high buffering capacity require larger amounts of lime to increase the pH than soils with a lower buffering capacity. Most soil testing laboratories use a special buffered solution to measure the exchangeable acidity. This is the form of soil acidity that must be neutralized for a change in soil pH. By calibrating pH changes in the buffered solution with known amounts of acid, the amount of lime required to bring the soil to a particular pH can be determined. Lime reduces soil acidity (increases pH) by changing some of the hydrogen ions into water and carbon dioxide (CO 2 ). A Ca ++ ion from the lime replaces two H + ions on the cation exchange complex. The carbonate (CO 3 - ) reacts with water to form bicarbonate (HCO 3 - ). These react with H + to form H 2 O and CO 2. The pH increases because the H + concentration has been reduced. H + Soil Colloid + CaCO Soil Colloid-Ca ++ + H 2 O + CO 2 Remember, the reverse of the above process can also occur. An acid soil can become more acid as basic cations such as Ca 2+, Mg 2+, and K + are removed, usually by crop uptake or leaching, and replaced by H +. Charles C. Mitchell. Extension Agronomist-Soils & Professor Auburn University ….. Diunduh 27/2/2012

60 BAHAN PENGAPURAN The most common liming materials are calcitic or dolomitic agricultural limestone. These are natural products made by finely grinding natural limestone. Since natural limestone is relatively insoluble in water, agricultural limestone must be very finely ground so it can be thoroughly mixed with the soil and allowed to react with the soil's acidity. Calcitic limestone is mostly calcium carbonate (CaCO 3 ). Dolomitic limestone, according to most state laws, must have at least 6 percent magnesium, and is made from rocks containing a mixture of calcium and magnesium carbonates. Either will neutralize soil acidity. Dolomitic limestone also provides magnesium. Charles C. Mitchell. Extension Agronomist-Soils & Professor Auburn University ….. Diunduh 27/2/2012 Some common soil liming materials. Material Relative Neutralizing value % Comment pure CaCO 3 100not generally available Calcitic agricultural lime, (calcium carbonate, CaCO 3 +impurities) easily available Dolomitic agricultural lime, CaCO 3 + MgCO easily available; provides Mg Ground oyster shells Selma chalk/marl, CaCO 3 + clay contains clay; keep dry Burned lime, CaO very caustic; don't use Hydrated lime or builders' lime, Ca(OH) caustic; use with caution; no Mg Basic slag contains some P & micronutrients; byproduct Wood stove or fireplace ashes provides some plant nutrients Boiler wood ash provides some plant nutrients By-productsVariableuse as specified by manufacturer Gypsum and/or ground drywall, CaSO 4 0NOT A LIMING MATERIAL

61 Liming to Increase Soil pH A.M. JOHNSTON¹ and R. DOWBENKO² ¹ Potash & Phosphate Institute of Canada, Saskatoon, Saskatchewan ² Agrium Inc., Calgary, Alberta The desirable pH range for optimum corn production is 6.0 to 6.5. Soils with a pH 0.2 to 0.3 units below the recommended level should be considered for liming. Liming to maintain an optimum soil pH has several benefits. It reduces the risk of toxicity from aluminum (Al) and other metals, improves the physical condition of the soil, stimulates microbial activity, increases the cation exchange capacity (CEC) in some variable charge soils, increases the availability of several nutrients such as N, P, and molybdenum (Mo), supplies Ca and Mg for plants, and improves symbiotic N fixation by legume rotation crops such as alfalfa and soybeans. Calcitic and dolomitic aglime are the most common lime sources. Diunduh 27/2/2012 Yield response of corn to soil pH. (From Lathwell and Reid In F. Adams, ed. Soil Acidity and Liming- Agronomy Monograph 12, 2nd Edition. American Society of Agronomy).

62 BENTUK-BENTUK KEMASAMAN TANAH (i) Kemasaman aktif Refers only to H + and not Al 3+ in the soil solution (ii) Kemasaman-tukar = Exchangeable acidity Includes exchangeable Al 3+ Includes exchangeable H. Usually there is a small amount in acid mineral soils but it is more abundant in organic soils It is extracted with a neutral unbuffered salt solution, such as KCl, CaCl 2 or NaCl (iii) Kemasaman residual atau Non-exchangeable This is comprised of weak acids not replaced by neutral unbuffered salt solution and H + which bonds with OH -. This is the type of acidity caused by organic matter and bound Al. Bound Al occurs in soils primarily as Al polymers (long chain compounds) and is denoted as Al (OH) x x+ Al (OH) x x+ + OH Al (OH) x x+ COOH + OH COO - + H 2 O Diunduh 27/2/2012

63 TAPAK PERTUKARAN KATION Al-tukar dan Kation-tukar Soil chemists have defined exchangeable cations in acid soils as those cations extracted with a neutral unbuffered salt solution. The sum of these cations is termed the effective cation exchange capacity. A neutral unbuffered salt solution will extract only cations that are held at active exchange sites at a particular pH of the soil. The exchangeable acidity extracted from soils with a neutral unbuffered salt is Al. Acid mineral soils at pH 5.0 have their active exchange sites occupied by Al and at pH 6.0 these sites are countered by exchangeable bases. The relative cation saturations have an important effect on the cation composition of the soil solution and in turn on plant growth. Diunduh 27/2/2012 Cation composition of the exchange sites as related to the soil pH value. pHAlCa + Mg + KCEC meq/100g

64 KOMPOSISI LARUTAN TANAH Aluminum The concentration of Al in the soil solution is related to pH of the soil, the Al saturation of effective cation exchange capacity, and the salt concentration of the system. At a pH of 5.5 the concentration of Al in the soil solution is quite low. However, as the pH drops from 5.0 to 4.5, the Al concentration increases markedly. The Al concentration of the soil solution is related to the Al saturation of the effective CEC of the soil. The concentration of Al in the soil solution is low until the exchangeable Al saturation exceeds 60% and then increases rapidly. When the Al saturation is greater than 60%, the soil solution concentration of Al is greater than 1 ppm and may be as high as 5 or 6 ppm. ….. Diunduh 27/2/2012 Manganese Water-soluble Mn content of acid soils is closely related to the soil pH, being high below pH 5.0 but decreasing rapidly as the pH value increases to 6.0. Calcium The predominant cation in the soil solution of most acid soils is Ca. Concentrations of soil solution Ca are increased considerably when acid soils are limed.

65 PEMBENTUKAN Al dd Clays with hydrogen ion on the exchange complex are not stable. The aluminosilicate structure decomposes to form Al saturated clays. Aluminum and basic cation content of different soils. Notice the difference in aluminum saturation even though the pH values are approximately the same. Soi1pH Al Ca + Mg +K %Alsatura tion meq/100g Norfolk Lynchburg Portsmouth Diunduh 27/2/2012

66 ASAL-USUL KEMASAMAN TANAH Serapan Ca dan Mg oleh Tanaman Rainfall in excess of evapotranspiration (leaching) removes Ca and Mg from the soil. Soils of humid regions usually contain little weatherable Ca and Mg minerals. Diunduh 27/2/2012

67 ORIGIN OF SOIL ACIDITY SERAPAN TANAMAN Calcium and magnesium composition of some crops. Crop CaMg lbs/ton of crop Dicots Alfalfa Lespedeza Red clover Soybean Monocots K. bluegrass Timothy Corn stover Wheat straw Diunduh 27/2/2012

68 ASAL-USUL KEMASAMAN TANAH Penambahan Hidrogen i.) From the decomposition of organic matter ii.) Roots take up basic cations and exchange them with H iii.) Acid forming fertilizers 2NH 4 + (ammonium) + 4O 2 2NO 3 - (nitrate) + 4H + (acidic hydrogen) + 2H 2 O Estimates of 1.8 to 3.6 lb of CaCO 3 is required to neutralize the acidity generated from 1 lb of NH 4 + nitrogen: Acidity generated from common N sources Nitrogen Source lb CaCO3/lb N needed to neutralize the acidity Anhydrous ammonia 1.8 Urea 1.8 Ammonium nitrate 1.8 Ammonium sulfate 5.4 Monoammonium phosphate 5.4 Diammonium phosphate 3.6 Diunduh 27/2/2012

69 MANFAAT PENGAPURAN Diunduh 27/2/2012 Liming will provide the following benefits: 1.reduces the possibility of Mn2+ and Al3+ toxicity; 2.improves microbial activity; 3.improves physical condition (better structure); 4.improves symbiotic nitrogen fixation by legumes; 5.improves palatability of forages; 6.provides an inexpensive source for Ca2+ and Mg2+ when these nutrients are deficient at lower pH; 7.improves nutrient availability (availability of P and Mo increases as pH increases at 6.0 – 7.0, however, other micronutrients availability increases as pH decreases).

70 Crops require different pH levels (adapted from Tisdale et al., 1993). Diunduh 27/2/2012

71 BAHAN KAPUR PERTANIAN Liming materials are usually Ca and or Mg carbonates, oxides, and hydroxides. Liming materials are effective when they: remove H+ and Al+ off of exchange sites (potential acidity); neutralize H+ in solution (active acidity); are economical. In order for liming material to be economical, it generally has to be a salt. A strong base and strong acid such as NaCl (sodium chloride) or CaSO4 (gypsum) are not effective in raising pH levels because a hydroxyl (OH-) is not released to neutralize H+ by forming water (H2O). A salt of a strong base and a weak acid is required to raise pH as shown by the equation below. CaCO3 + H2O ↔ Ca2+ + HCO3- + OH- The Ca2+ displaces H+ and Al3+ on exchange sites where OH- neutralizes the H+ in solution. The effectiveness of liming material is based on two factors: Calcium Carbonate Equivalent (CCE) and fineness of material These two factors when combined are called the Effective Calcium Carbonate (ECC). Diunduh 27/2/2012

72 MENENTUKAN NILAI CCE Diunduh 27/2/2012 The CCE is a way to relate all liming materials to CaCO3 as a standard. The molecular weight of CaCO3 is 100 (Ca = 40, C =12, and O =16 x 3). The CCE of CaCO3 has been theoretically established at 100. When using other materials other than CaCO3, the molecular weight of CaCO3 is divided by the other material’s molecular weight. For example, the calculation for the use of wood ash as a liming material is as follows: Wood ashes (K2CO3) molecular weight = 138 CaCO3 = /138 = 0.72 (CCE) or 72% effective compared to CaCO3 So if a recommendation from a soil called for 1,000 lbs. of agricultural lime (CaCO3), then you would divide the CCE of 0.72 (K2CO3) into the rate needed to determine the amount of K2CO3 needed. 1,000 lbs. CaCO3 / 0.72 = 1,389 lbs. of K2CO3 In this case 1,389 lbs. of K2CO3 are needed to achieve the same effect as 1,000 lbs. of calcium carbonate. Neutralizing Value (CCE) of Liming Materials (Tisdale et al., 1993)

73 BAGAIMANA KAPUR MENAIKKAN pH TANAH ….. Diunduh 27/2/2012 Limestone is calcium carbonate and magnesium carbonate: CaCO 3 and MgCO 3 The limestone dissolves in water to form carbonic acid (H 2 CO 3 ) and calcium hydroxide (Ca(OH) 2 ): CaCO 3 + H 2 O ↔ H 2 CO 3 + Ca(OH) 2 Carbonic acid is unstable and converts to carbon dioxide (CO 2 ) and water; the CO 2 gas escapes: H 2 CO 3 ↔ CO 2 + H 2 O The remaining calcium hydroxide dissociates: Ca(OH) 2 ↔ Ca OH - The Ca 2+ replaces 2H + from the soil, increasing the soil base saturation The hydroxide anion (OH - ) reacts with the soil acid cation (H + ), forming water: OH - + H + ↔ H 2 O

74 REAKSI KAPUR DALAM TANAH ….. Diunduh 27/2/2012

75 PENGAPURAN MENINGGKATKAN KETERSEDIAAN HARA ….. Diunduh 27/2/2012 Soil pH affects nutrient availability by changing the form of the nutrient in the soil. Adjusting soil pH to a recommended value can increase the availability of important nutrients. Plants usually grow well at pH values above 5.5. Soil pH of 6.5 is usually considered optimum for nutrient availability. Lower pH increases the solubility of Al, Mn, and Fe, which are toxic to plants in excess. A critical effect of excess soluble Al is the slowing or stopping of root growth. Extreme pH values decrease the availability of most nutrients. Low pH reduces the availability of the macro- and secondary nutrients, while high pH reduces the availability of most micronutrients. Microbial activity may also be reduced or changed.

76 REAKSI KAPUR DALAM TANAH ….. Diunduh 27/2/2012 Lime supplies a surplus of the basic cations Ca2 + and/or Mg 2+ in a carbonated, hydroxide, or oxide form (CaCO 3, MgCO 3, CaOH, MgOH, CaO). As the compounds dissolve in soil solution, the carbonate (CO 3 2- ), hydroxyl (OH - ), or oxide (O 2- ) react with active acidity (H + ) to form carbonic acid (H 2 CO 3 ) or water (H 2 O). Also, because H + is being removed from soil solution, free Al 3+ reacts with OH - to form an insoluble compound. Hydrogen held by soil-clay (potential acidity) is released into soil solution to maintain chemical equilibrium as active acidity is neutralized, and Al 3+ is released from the soil to form insoluble compounds. The H + released into the soil solution is then neutralized until the CO 3 2-, OH -, and O 2- are exhausted. Ultimately, most of the carbonic acid will dissociate to form water and carbon dioxide. Thus, excess H + is converted into water, and free Ca 2+ and/or Mg 2+ replace the released H + and Al 3+ on the soil exchange sites

77 TNP = Total Neutralizing Power ….. Diunduh 27/2/2012 Total Neutralizing Power (TNP) is a measure of the ability of a liming material to raise the pH. The percentage of calcium, percentage of magnesium, and impurities, such as silt and clay, determine TNP. Pure calcium carbonate has a neutralizing power of 100: other liming materials are compared on a percentage basis with it. The two major liming materials are dolomitic and calcitic limestone. Both are sources of calcium and magnesium, but the percentage of each varies and thus the TNP varies. Dolimitic limestone contains approximately 20 to 22% calcium and 11 to 13% magnesium. Because of molecular weight differences, magnesium carbonate on a pound for pound basis is 16% more effective in raising the pH than calcium carbonate. Therefore the TNP will normally range from 100 to 110 for dolomitic limestone. Calcitic or hical lime contains approximately 32 to 35% calcium, 2 to 5% magnesium, and has a TNP of 90 to 99.

78 ENP = effective neutralizing power In Ohio, liming materials are labeled based on their effective neutralizing power (ENP), which is reported in lbs/ton. The ENP considers the total neutralizing power (TNP), fineness of grind, and percent moisture of a liming material (Ohio Aglime Council, 2003), and may be calculated by Equation 1. Equation 1: ENP (lbs/ton) = TNP/100 * FI/100 * %DW/100 * 2000 lbs/ton ….. Diunduh 27/2/2012 Total neutralizing power (TNP), fineness, water content, and ENP of common liming materials. GradeTNP (%) Fineness Water (%) ENP (lbs/ton) % passing mesh size 82060FI Aglime superfine Dolomitic hydrated aglime Calcitic aglime Dolomitic aglime Waste water lime Pelletized lime These are liming materials available in the state of Ohio. Depending upon source, lime characteristics will vary.

79 REKOMENDASI KAPUR ….. Diunduh 27/2/2012 Once it has been determined that liming is necessary by soil pH and the buffer pH measurement, a lime recommendation can be made. Reported lime rates assume an effective neutralizing power (ENP) of 2000 lb/ton and an incorporation depth of 8 inches. To compute the application rate of a lime source with an ENP different from 2000 lb/ton use Equation : Tons of material / A = LR * (2000 / ENP) If depth of incorporation is different than 8 inches, divide the lime recommendation by 8 and multiply by the new depth. For example, assume the lime rate needed is 1.6 t/A from Table 4. The lime will be incorporated into the top 6 inches, so the new rate of lime is 1.2 t/A, (i.e., 1.6/8 x 6 = 1.2). Tons of liming material (ENP of 2000 lbs/ton) needed to raise the soil pH to the desired pH level based on the SMP (Shoemaker-McLean-Pratt) buffer and an incorporation depth of 8 inches (adapted from Tri-State Fertilizer Recommendations, 1996) Buffer pH 1 Desired pH levels Mineral soilsOrganic soils Soil pH5.3 tons agricultural limestone/acre tons/acre To compute LTI multiply buffer pH by For desired pH of 6.8: lime recommendation = -6.8*buffer pH For desired pH of 6.5: lime recommendation = -5.6*buffer pH For desired pH of 6.0: lime recommendation = -4.6*buffer pH

80 Lime Recommendations for Field Crops Diunduh 27/2/2012 Lime recommendations depend on: 1. Current and desired pH. 2. Exchangeable acidity. 3. Base saturation of the soil at the current and at the desired pH. 4. Tillage depth. Base saturation is the amount of basic cations divided by the total cation exchange capacity (total number of cation exchange sites). So, if the base saturation is 0.75, 75% of the cation exchange capacity is occupied by Ca2+, Mg2+, K+ and/or Na+ while 25% is exchangeable acidity. For soils with a pH of 6.0 or lower, the lime recommendation is determined by the exchangeable acidity, base saturation at the original pH and at the desired pH, and the tillage depth (TD, inches): (BSdesired-BSoriginal) Lime Req. = EA*0.5* * (TD/6) (1-BSorginal) Where the pH of the soil is 6.1 or higher, the exchangeable acidity is negligible but there is still residual acidity. For these soils, the exchangeable acidity measurement needs to be replaced by estimated cation exchange capacity (CEC).

81 Lime and Nutrient Recommendations Diunduh 27/2/2012 Soil pH and Lime Recommendations Soil-water pH provides a measure of active acidity in soil, and soil-buffer pH provides a measure of reserve acidity in soil. Soil-water pH can be lower than expected in the fall after a dry growing season due to salts from fertilizer not being leached out. To avoid the lower than expected soil-water pH, active acidity is measured in a solution with a high salt concentration (1 M KCl), which removes variable soil-salt levels occurring at much lower concentrations in the soil. The soil pH measured in 1 M KCl is about 1 pH unit lower than soil-water pH. Since soil-water pH is a much more familiar value in relationship to optimum plant growth, the measurement of 1 M KCl soil pH is converted to soil-water pH for presentation on soil test reports. Lime recommendations, however, are based on 1 M KCl soil pH. To determine how much lime is required to raise soil-water pH, see tables 6, 7, or 8 with the target pH of 6.4, 6.6, or 6.8 in the heading. The soil-water pH is shown as the first column, and the buffer pH is shown as the top row of pH values. To determine the appropriate lime rate, read down the first column to the samples soil-water pH then read across to the samples buffer pH. The lime rates were determined from a lime response curve using 1 M KCl soil pH and buffer pH with a correction factor for field application. The resultant lime rates are rounded to the nearest 0.25 tons/acre.

82 Lime and Nutrient Recommendations Diunduh 27/2/2012 Soil pH and Lime Recommendations Rate of 100% effective limestone (tons/acre) needed to raise soil pH to 6.4. Rate of 100% effective limestone (tons/acre) needed to raise soil pH to 6.6.

83 PENGARUH PENGAPURAN TERHADAP BIOLOGI TANAH ….. Diunduh 27/2/2012 Mean millipede and snail abundance (number per 25 m2) with SE bars on lime- treated and control sites with model lines. Lime treatment was applied between 2003 and 2004 in central Pennsylvania. *Confidence intervals of the time-by- treatment interaction excluded zero, indicating a significant effect of liming on that variable.

84 PENGARUH PENGAPURAN TERHADAP HASIL TANAMAN ….. Diunduh 27/2/2012 Effects of Liming on Canola Yields at 27 Alberta Sites on Soils with Different pH Ranges. The canola yields on acid soils can be substantially increased by lime application. The increase in soil pH resulting from lime application provides a more favourable environment for soil microbiological activity that increases the rate of release of plant nutrients, particularly nitrogen. Reduced soil acidity following liming also increases the availability of several other plant nutrients, notably phosphorus. One of the benefits of liming acid soils is the increased utilization of residual fertilizer phosphorus by crops. On slightly acid (pH 6.1 to 6.5) and moderately acid (pH 5.6 to 6.0) soils, liming will have a minor effect on canola yields

85 PENENTUAN KEBUTUHAN KAPUR ….. Diunduh 27/2/2012 Soil acidity consists of active and reserve acidity. Most of the acid-causing elements (hydrogen and aluminum) are held by the cation exchange sites of the soil particles and organic matter. This is referred to as reserve acidity. Soils with large amounts of clay and organic matter have high potential for reserve acidity. Soil pH is a measure of active acidity, the hydrogen ion concentration in the soil solution. The higher the concentration of hydrogen ions in soil solution, the lower the pH (i.e., greater acidity). The active acidity is present in the immediate environment of roots and microbes. The total acidity is the sum of the reserve and active acidity. Lime neutralizes both the active acidity and some of the reserve acidity. As active acidity is neutralized by the lime, reserve acidity is released into the soil solution, maintaining the active acidity or the pH. The ability of a soil to resist changes in pH is called buffering capacity and is largely due to the reserve acidity. More lime is required to neutralize acidity on a highly buffered soil compared to a less buffered soil

86 Examples of approximate lime required to raise the pH of soils of different textural classes. (Source: Nutrient Management for Agronomic Crops in Nebraska, EC155, UNL Extension.) Soil texture CEC (meq/100 g) Soil pH Buffer pH Lime rate (tons/acre) Loamy sand Silt loam Silty clay loam ….. Diunduh 27/2/2012

87 KUALITAS BAHAN KAPUR Two factors determine the effectiveness (ECCE) of liming materials: 1.neutralizing value or purity, also referred to as calcium carbonate equivalent (CCE) 2.particle size or fineness of the liming material. The neutralizing value, or CCE, is the amount of acid on a weight basis that a given quantity of lime will neutralize when dissolved. It is expressed as a percentage of the neutralizing value of pure calcium carbonate or calcite (100 percent CCE). A lime that neutralizes 80 percent as much acid as pure calcium carbonate is said to have a CCE of 80. Table III shows the CCE of different liming materials. Calcium carbonate equivalent (CCE) of liming materials. Material %CCE* Pure calcite Calcitic lime Dolomitic lime Hydrated lime Burned lime Pel-lime (finely ground ag-lime) Fly ash** Wood ash *These values only consider the purity of the material, however, the fineness also must be considered to determine the effectiveness of the lime (i.e., ECCE = CCE times fineness). **Based on UNL research on ash from power plants in Nebraska. Fly ash CCE values and other chemical analyses should be done due to variation caused by source of coal, collection procedures and other factors. ….. Diunduh 27/2/2012

88 BENEFICIAL EFFECTS FROM LIMING ….. Diunduh 27/2/2012 Soil acidity has a direct effect upon availability of most essential plant nutrients. The general effect of pH on plant nutrient availability. The best pH range for most nutrients is between 6.0 and 7.0. Deficiencies can be observed at both low and high pH's. Manganese and iron exhibit toxicity at low pH's and deficiency at high pH levels. Although aluminum is not an essential nutrient, it is important because it rapidly increases in solubility as the soil pH drops below 5.0. Too much aluminum in solution will restrict root and plant development. Effects of change in soil pH on the availability of plant nutrients.

89 KEBUTUHAN pH TANAMAN Normal crop growth occurs over a range in pH values and the range varies by crop. In a soil testing laboratory, the necessity for limestone is based on crops to be grown, soil pH, and soil organic matter (mineral soil vs. organic soil). The goal of a liming program is to apply enough aglime to raise the soil pH to the middle of the range for normal growth and then reapply when it drops below the range. Mineral soil pH ranges for crops. ….. Diunduh 27/2/2012

90 BENEFITS PROVIDED BY LIMING SOILS INCLUDE: 1.Improved availability of soil nutrients such as phosphorus, potassium, nitrogen, calcium, magnesium, sulfur, boron, and molybdenum. 2.Increased efficiency of fertilizers applied to the soil. 3.Reduced availability of aluminum and manganese, which may cause toxicity problems in acid conditions. 4.More favorable microbial activity in the soil. 5.Better soil structure and tilth. 6.Increased longevity of legume stands such as alfalfa and clovers. 7.Improved activity of certain herbicides, providing better weed control. Diunduh 27/2/2012 Effect of soil acidity on soybean yields. Missouri Agricultural Experiment Station Bulletin 947. T.R. Fisher.

91 Pasture responses to lime over five years are limited and highly variable A.E. Crawford and C.J.P. Gourley Agriculture Victoria Ellinbank, Department of Natural Resources and Environment, Victoria. Diunduh 27/2/2012 Effect of lime on soil pH(H 2 O), exchangeable Al (KCl), available P (Olsen) and extractable cations at Wyelangta in October 1999, five years after application. Depths shown are 0-5 cm (), 5-10 cm (), cm () and cm ().

92 Grain yield responses to liming obtained at Rutherglen, North-east Victoria, 1984 season. Diunduh 27/2/2012

93 EFEK PENGAPURAN TERHADAP HASIL Diunduh 27/2/2012 Effect of calcium carbonate on dry matter output from a surface seeded grass-clover sward (source O’Toole 1968) Liming to neutral state is expensive and unnecessary. It may affect the availability of trace elements and over-liming may influence denitrification, producing toxic levels of nitrate-nitrogen. O’Toole (1968) showed that where an adequate supply of nitrogen fertilizer is applied to pasture the pH can be maintained at lower levels than where no applications are given. The influence of liming on the dry matter output of a mixed grass-clover sward.

94 PENGAPURAN TANAMAN JAGUNG Diunduh 27/2/2012 Cumulative yields of maize over three years at a site in Brazil, as affected by lime rates and depth of lime incorporation (CPAC 1976). A yield increase in corn after lime incorporation to 30 cm compared to 15 cm

95 Responses of Corn and soybeans to liming on mineral soils Diunduh 27/2/2012 A major reason for crop response to lime is due to the precipitation of exchangeable Al The beneficial effects of liming on crop growth are often related to neutralization of Al and not directly to the change in pH. pH % Al Saturation Yield CornSoybeans bu/a

96 METODE KEBUTUHAN KAPUR Diunduh 27/2/2012 The Adams and Evans buffer (used by Alabama, Florida, Georgia, Tennessee, South Carolina, and Virginia) was developed for soils with low cation exchange capacity and containing primarily kaolinitic clays. These soils usually have relatively low lime requirements and the possibility of overliming exists. The Adams and Evans buffer is very reliable for soils with relatively small amounts of exchangeable acidity and provides a fairly high degree of accuracy of estimating lime requirements to reach pH 6.5 or less. Sensitivity of the lime requirement by this method is within 500 lb/A of limestone. The Adams and Evans lime requirement method is based on separate measurements of soil pH in water and a buffer solution (pH 8.0) The soil pH determination is used as a measure of acid saturation of the soil (H-sat 1 ) according to the following equation: Measured soil pH = 7.79 ­ 5.55 (H-sat 1 ) (H-sat 1 ) 2 Where H-saturation is expressed as a fraction of the CEC. Buffer pH is used as a measure of soil acids (Soil H) according the following equation: Soil H = 8(8.00 ­ buffer pH) The desired soil pH is expressed in terms of acid saturation of the soil (H-sat 2 ) according to the following equation: Desired soil pH = 7.79 ­ 5.55 (H-sat 2 ) (H-sat 1 ) 2 The Adams-Evans buffer method assumes that agricultural-grade limestone is about 2/3 effective in neutralizing soil acidity up to a soil pH of about 6.5, and allows for this by using a correction factor of 1.5. Thus, the lime requirement is the product of the following equation: Soil H/H-sat 1 x (H-sat 1 ­ (H-sat 2 ) x 1.5 or for 10 cm 3 soil in 10 ml water + 10 ml buffer solution, the lime recommendation is: Limestone (lbs/A) = 8000[( buffer pH)/H-sat 1 ] x (H-sat 1 - H-sat 2 ) x 1.5

97 METODE KEBUTUHAN KAPUR Diunduh 27/2/2012 As noted above lime requirement calculations using the Adams-Evans method is based on two pH determinations, soil pH and buffer pH. With this information and the formulas above the lime requirement of a soil can be calculated. The following table is an abbreviated example of the lime requirement for a soil depth weighing 2,000,000 pounds per acre to increase soil pH to 6.5. Soil pH in Buffered Solution Soil pH in water *Note: The depths of soil it takes to weigh 2,000,000 pounds will vary with the bulk density of the soil. For example, a sandy loam soil with a bulk density of would weigh 2,001,232 pounds per 6 inch-depth, whereas, a loam soil with a bulk density of would weigh 2,001,504 pounds per 6.8 inch-depth.

98 METODE MEHLICH Diunduh 27/2/2012 The Mehlich buffer method (used by North Carolina) was developed to determine the amount of lime required to neutralize the acidity extracted with an unbuffered salt solution. This approach was based on neutralizing the acidity that is limiting crop growth and not trying to achieve a given pH. A buffer solution of pH 6.6 is used to measure extractable acidity (Ac). The buffered solution extracts both exchangeable Al and the pH dependent acidity (H) which becomes ionized up to pH 6.6. The lime rate to apply is calculated with the following equation: CaCO 3 tons/acre = Ac (desired pH - soil pH) (6.6 - soil pH) The desired pH for a soil is the pH at which the activity of Al is neutralized. The effect of soil organic matter in decreasing the activity of Al has been taken into account by establishing desired pH's for three classes of soils based on their organic matter content: mineral, mineral-organic and organic. The desired pH at which exchangeable Al is essentially neutralized is 6.0 for mineral soils, 5.5 for mineral-organic soils and 5.0 for organic soils.

99 REAKSI KAPUR DALAM TANAH Diunduh 27/2/2012 When lime (i.e., CaCO3) is added to a moist soil, the following reactions will occur: (1)Lime is dissolved slowly by moisture in the soil to produce Ca2+ and OH- CaCO3 + H2O (in soil) ==> Ca2+ + 2OH- + CO2 (gas) (1)Newly produced Ca2+ will exchange with Al3+ and H+ on the surface of acid soils 2Ca2+ + soil-Al ===> soil-Ca + Al3+ + soil-H soil-Ca + H+ (1)Lime-produced OH- will react with Al3+ to form Al(OH)3 solid and with H+ to form water. Al3+ + 3OH- ===> Al(OH)3 (solid) H+ + OH- ===> H2O

100 Diunduh 27/2/2012 Relationships between permanent and pH dependent charge

101 Diunduh 27/2/2012 At low soil pH Aluminum ions make up a large fraction of the cations. As soil pH approaches 4.5, exchangeable Aluminum ions per se, disappear, and above pH 6 there are few Aluminum ions potentially available. The table below reports data from a Bordeaux study on the affects of Aluminum ions on growth of Cabernet Sauvignon (V. vinifera) grapevines. Note that only 10 ppm (mg/l) in solution reduced vine growth almost in half. The aluminum ions are not absorbed by the roots, and they do not enter the vine. Aluminum ions directly inhibit root growth. Thus aluminum toxicity cannot be detected from petiole mineral element analysis. Vine roots must be inspected. EFEK pH dan Al terhadap tanaman

102 EFEK PENGAPURAN thd Al Diunduh 27/2/2012 the addition of lime to an acid soil raises the pH and decreases aluminum availability. Effects of Lime Addition on Extractable Aluminum of a Bordeaux, France Soil Soil TreatmentSoil pH Extractable Aluminum (mg/kg) Control tons/acre CaO tons/acre CaO tons/acre CaO6.1Trace Source: Delmas, Pont-de-la-Maye, 1984

103 SOURCE OF ELECTROSTATIC CHARGE Diunduh 27/2/2012 Isomorphic substitution Al 3+ for Si 4+ in the tetrahedral sheet and Mg 2+ for Al 3+ in the dioctahedral sheet. These substitutions occur during formation of the clay mineral and are permanent to the structure. Both lead to net negative charge within the crystal lattice that is balanced by adsorbed cations. pH-dependent charge Loss of ionizable H + from certain sites on mineral colloids or from certain functional groups in humus leads to negatively charged sites. Protonation of other sites leads to positively charged sites. pH-dependent negative charge increases with increasing pH but pH-dependent positive charge increases with decreasing pH.

104 Muatan negatif yang trgantung pH Diunduh 27/2/2012

105 MUATAN NEGATIF TANAH B3EF&article_id=377C1F0CB5E518C97B90EAB21FEA1D74 ….. Diunduh 27/2/2012 Influence of pH on CEC of smectite and SOM. Below pH 6 the charge for clay minerals is relatively constant (permanent CEC charge); above pH 6, contribution of the variable charge from clay minerals is evident (ionisation of H + from hydroxy groups). By comparison, almost all of the charges on the organic colloid are considered to be pH dependent, i.e. variable charge (modified from Brady 1990).

106 The permanent negative charge on a clay mineral as a result of isomorphous substitution does not change with pH. Why? Because the charge was created when the mineral was formed sand is locked inside the crystal structure. Increased negative charge, or pH dependent charge, is caused by ionization of H + ions (deprotonation) attached to -OH ions on the surface and edges of the crystal lattice. Therefore at higher soil pH's the clay minerals have increased capacity to hold basic cations. ….. Diunduh 27/2/2012 pH dependent charge on clay minerals

107 pH Dependent Charge ….. Diunduh 27/2/2012 The negative charge on clay minerals generally increases with a rise in the pH of soil solution. This is a result of deprotonation. Deprotonation is the removal of H + from anions such as OH bound at the edges of 2:1 clay minerals or the surface of 1:1 minerals such as kaolinite. The reaction can be represented as follows: In soils there are many other sources of pH dependent negative charge: from dissociation of H + from functional groups on organic matter and also from OH groups attached to amorphous hydrous metal oxides which often coat the surfaces of clays and link to organic matter.

108 ISOMORPHOUS SUBSTITUTION ….. Diunduh 27/2/2012 During clay formation, the central cation of a silica tetrahedra Si 4+ can be replaced (substituted) by similar sized ions such as, Al 3+ aluminum or Fe 3+ iron (How? See previous section). Similarly, replacement of the central cation, Al 3+, in aluminum octahedra can also occur. In this case Mg 2+ magnesium or Fe 2+ iron are the most common substitutes. This phenomenon is called isomorphous substitution (literally: "same shape"). 2:1 Crystal lattice showing isomorphous substitution and net negative charge

109 Electric Double Layer dd7efefd6f1bd6b9974b3a66990f….. Diunduh 27/2/2012 Electric Double Layer is the phenomenon playing a fundamental role in the mechanism of the electrostatic stabilization of colloids. Colloidal particles gain negative electric charge when negatively charged ions of the dispersion medium are adsorbed on the particles surface. A negatively charged particle attracts the positive counterions surrounding the particle. Electric Double Layer is the layer surrounding a particle of the dispersed phase and including the ions adsorbed on the particle surface and a film of the countercharged dispersion medium. The Electric Double Layer is electrically neutral. dispersion mediumdispersed phase An Electric Double Layer consists of three parts: Surface charge - charged ions (commonly negative) adsorbed on the particle surface. Stern layer - counterions (charged opposite to the surface charge) attracted to the particle surface and closely attached to it by the electrostatic force. Diffuse layer - a film of the dispersion medium (solvent) adjacent to the particle. Diffuse layer contains free ions with a higher concentration of the counterions. The ions of the diffuse layer are affected by the electrostatic force of the charged particle.

110 REAKSI PERTUKARAN KATION Diunduh 27/2/2012 The interchange between a cation in solution and another cation on the surface of any negatively charged material such as clay or organic matter. What determines if a cation is on the exchange complex or in the soil solution? Cation exchange is influenced by: 1) strength of adsorption--->Strong adsorption » Al+3 > Ca2+ > Mg2+ > K+=NH 4 + > Na+ >H+ »Weak adsorption 2) the relative concentration of the cations in the soil solution. At any one time the quantity of ions on the exchange compared to what is in the soil solution is determined by the kind of ions present and the quantity of ions present in the soil.

111 KTK = KAPASITAS TUKAR KATION Diunduh 27/2/2012 Cation Exchange Capacity (CEC) is the ability of the soil to hold onto nutrients and prevent them from leaching beyond the roots. The more cation exchange capacity a soil has, the more likely the soil will have a higher fertility level. When combined with other measures of soil fertility, CEC is a good indicator of soil quality and productivity. The cation exchange capacity of a soil is simply a measure of the quantity of sites on soil surfaces that can retain positively charged ions by electrostatic forces. Cations retained electrostatically are easily exchangeable with other cations in the soil solution and are thus readily available for plant uptake. Thus, CEC is important for maintaining adequate quantities of plant available calcium (Ca++), magnesium (Mg++) and potassium (K+) in soils. Other cations include Al+++( when pH < 5.5), Na+, and H+. Cation Exchange Capacity can be expressed two ways: 1.the number of cation adsorption sites per unit weight of soil or, 2.the sum total of exchangeable cations that a soil can adsorb. Soil CEC is normally expressed in units of charge per weight of soil. Two different, but numerically equivalent sets of units are used: meq/100 g (milliequivalents of element per 100 g of dry soil) or cmolc/kg (centimoles of charge per kilogram of dry soil).

112 REAKSI PERTUKARAN KATION Diunduh 27/2/2012 BULU AKAR – KOLOID TANAH


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