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1 AIR,TANAH & TANAMAN (Prof.Dr.Ir.Soemarno, M.S.) Oktober 2008.

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Presentasi berjudul: "1 AIR,TANAH & TANAMAN (Prof.Dr.Ir.Soemarno, M.S.) Oktober 2008."— Transcript presentasi:

1 1 AIR,TANAH & TANAMAN (Prof.Dr.Ir.Soemarno, M.S.) Oktober 2008

2 2 Proses fotosintesis memerlukan air

3 3 Air dari tanah CO2 dari Udara Fotosintesis: CO2 + H2O ---- Karbohidrat (Glukosa) Glukosa Pati dan senyawa organik lain dalam buah dan biji

4 4 Stomata: Pintu lalulintas CO2, O2, dan H2O Fotosintesis: CO2 + H2O Karbohidrat (Glukosa) CO2 dari Udara Glukosa Pati dan senyawa organik lain dalam biji Air dari tanah

5 5 Budidaya tanaman padi sawah memerlukan banyak air

6 6 Kurva Penggunaan Air Musiman oleh Tanaman KEBUTUHAN AIR TANAMAN A plant has different water needs at different stages of growth. While a plant is young it requires less water than when it is in the reproductive stage. When the plant approaches maturity, its water need drops. Curves have been developed that show the daily water needs for most types of crops.

7 7 Komposisi tanah menurut volume Tanah subur yg ideal: Mineral 45% Organic matter 5% Water 25% Air 25%

8 8 Tiga komponen tanah The soil system is composed of three major components: solid particles (minerals and organic matter), water with various dissolved chemicals, and air. The percentage of these components varies greatly with soil texture and structure. An active root system requires a delicate balance between the three soil components; but the balance between the liquid and gas phases is most critical, since it regulates root activity and plant growth process.

9 9 Ilustrasi tentang penurunan potensial air untuk suatu tanaman Plants develop the tension, or potential, to move soil water from the soil into the roots and distribute the water through the plant by adjusting the water potential, or tension, within their plant cells. The essence of the process is that water always moves from higher to lower water potential. For water to move from the soil, to roots, to stems, to leaves, to air the water potential must always be decreasing.

10 10 HUB. Tanah- Air-Tanaman Hub.TAT mrpk sistem dinamik dan terpadu dimana air mengalir dari tempat dengan tegangan rendah menuju tempat dengan tegangan air tinggi. Serapan bulu akar Penguapan Hilang melalui stomata daun (transpirasi) Air kembali ke atmosfer (evapo-transpirasi) Air dikembalikan ke tanah melalui hujan dan irigasi

11 11 Kekuatan ikatan antara molekul air dengan partikel tanah dinyatakan dengan TEGANGAN AIR TANAH. Ini merupakan fungsi dari gaya-gaya adesi dan kohesi di antara molekul - molekul air dan partikel tanah Partikel tanah H2O Adesi Kohesi Air terikatAir bebas

12 12 Air Tersedia untuk pertumbuhan tanaman

13 13 ). Fine textured soils with small pores can hold the greatest amounts of PAW. Coarse textured sandy soils with large pores can hold the least amounts of PAW.

14 14 Status Air Tanah Perubahan status air dalam tanah, mulai dari kondisi jenuh hingga titik layu Jenuh Kap. Lapang Titik layu 100g 8g udara Padatan Pori 100g 20g udara 100g 10 g udara 100g air 40g tanah jenuh air kapasitas lapang koefisien layu koefisien higroskopis

15 15 TEGANGAN & KADAR AIR PERHATIKANLAH proses yang terjadi kalau tanah basah dibiarkan mengering. Bagan berikut melukiskan hubungan antara tebal lapisan air di sekeliling partikel tanah dengan tegangan air Bidang singgung tanah dan air Koef. Koef. Kapasitas padatan tanah higroskopis layu lapang atm 31 atm 15 atm 1/3 atm atmMengalir krn gravitasi Tegangan air 1/3 atm tebal lapisan air

16 16 Representasi bola air yang menyelubungi partikel padatan tanah

17 17 JUMLAH AIR DALAM TANAH The amount of soil water is usually measured in terms of water content as percentage by volume or mass, or as soil water potential. Water content does not necessarily describe the availability of the water to the plants, nor indicates, how the water moves within the soil profile. The only information provided by water content is the relative amount of water in the soil. Soil water potential, which is defined as the energy required to remove water from the soil, does not directly give the amount of water present in the root zone either. Therefore, soil water content and soil water potential should both be considered when dealing with plant growth and irrigation. The soil water content and soil water potential are related to each other, and the soil water characteristic curve provides a graphical representation of this relationship.

18 18 TEGANGAN vs kadar air Kurva tegangan - kadar air tanah bertekstur lempung Tegangan air, bar 31Koefisien higroskopis Koefisien layu Kapasitas lapang 0.1 Kap. Lapang maksimum persen air tanah Air kapiler Air Air tersedia higros- kopis Lambat tersedia Cepat tersedia Air gravitasi Zone optimum

19 19 Hubungan antara kadar air tanah dan tegangan air tanah untuk tekstur lempung

20 20 STRUKTUR & CIRI POLARITAS Molekul air mempunyai dua ujung, yaitu ujung oksigen yg elektronegatif dan ujung hidrogen yang elektro-positif. Dalam kondisi cair, molekul-molekul air saling bergandengan membentuk kelompok-kelompok kecil tdk teratur. Ciri polaritas ini menyebabkan plekul air tertarik pada ion-ion elektrostatis. Kation-kation K+, Na+, Ca++ menjadi berhidrasi kalau ada molekul air, membentuk selimut air, ujung negatif melekat kation. Permukaan liat yang bermuatan negatif, menarik ujung positif molekul air. Kation hidrasiTebalnya selubung air tgt pd rapat muatan pd per- mukaan kation. Rapat muatan = Selubung air muatan kation / luas permukaan

21 21 STRUKTUR & CIRI IKATAN HIDROGEN Atom hidrogen berfungsi sebagai titik penyambung (jembatan) antar molekul air. Ikatan hidrogen inilah yg menyebabkan titik didih dan viskositas air relatif tinggi KOHESI vs. ADHESI Kohesi: ikatan hidrogen antar molekul air Adhesi: ikatan antara molekul air dengan permukaan padatan lainnya Melalui kedua gaya-gaya ini partikel tanah mampu menahan air dan mengendalikan gerakannya dalam tanah TEGANGAN PERMUKAAN Terjadinya pada bidang persentuhan air dan udara, gaya kohesi antar molekul air lebih besra daripada adhesi antara air dan udara. Udara Permukaan air-udara air

22 22 ENERGI AIR TANAH Retensi dan pergerakan air tanah melibatkan energi, yaitu: Energi Potensial, Energi Kinetik dan Energi Elektrik. Selanjutnya status energi dari air disebut ENERGI BEBAS, yang merupakan PENJUMLAHAN dari SEMUA BENTUK ENERGI yang ada. Air bergerak dari zone air berenergi bebas tinggi (tanah basah) menuju zone air berenergi bebas rendah (tanah kering). Gaya-gaya yg berpengaruh Gaya matrik: tarikan padatan tanah (matrik) thd molekul air; Gaya osmotik: tarikan kation-kation terlarut thd molekul air Gaya gravitasi: tarikan bumi terhadap molekul air tanah. Potensial air tanah Ketiga gaya tersebut di atas bekerja bersama mempengaruhi energi bebas air tanah, dan selanjutnya menentukan perilaku air tanah, ….. POTENSIAL TOTAL AIR TANAH (PTAT) PTAT adalah jumlah kerja yg harus dilakukan untuk memindahkan secara berlawanan arah sejumlah air murni bebas dari ketinggian tertentu secara isotermik ke posisi tertentu air tanah. PTAT = Pt = perbedaan antara status energi air tanah dan air murni bebas Pt = Pg + Pm + Po + ………………………… ( t = total; g = gravitasi; m = matrik; o = osmotik)

23 23 Hubungan potensial air tanah dengan energi bebas Energi bebas naik bila air tanah berada pada letak ketinggian yg lebih tinggi dari titik baku pengenal (referensi) Poten- sial positif Poten- sial negatif Energi bebas dari air murni Potensial tarikan bumi Menurun karena pengaruh osmotik Menurun karena pengaruh matrik Energi bebas dari air tanah Potensial osmotik (hisapan) Potensial matrik (hisapan)

24 24 POTENSIAL AIR TANAH POTENSIAL TARIKAN BUMI = Potensial gravitasi Pg = G.h dimana G = percepatan gravitasi, h = tinggi air tanah di atas posisi ketinggian referensi. Potensial gravitasi berperanan penting dalam menghilangkan kelebihan air dari bagian atas zone perakaran setelah hujan lebat atau irigasi Potensial matrik dan Osmotik Potensial matrik merupakan hasil dari gaya-gaya jerapan dan kapilaritas. Gaya jerapan ditentukan oleh tarikan air oleh padatan tanah dan kation jerapan Gaya kapilaritas disebabkan oleh adanya tegangan permukaan air. Potensial matriks selalu negatif Potensial osmotik terdapat pd larutan tanah, disebabkan oleh adanya bahan-bahan terlarut (ionik dan non-ionik). Pengaruh utama potensial osmotik adalah pada serapan air oleh tanaman Hisapan dan Tegangan Potensial matrik dan osmotik adalah negatif, keduanya bersifat menurunkan energi bebas air tanah. Oleh karena itu seringkali potensial negatif itu disebut HISAPAN atau TEGANGAN. Hisapan atau Tegangan dapat dinyatakan dengan satuan-satuan positif. Jadi padatan-tanah bertanggung jawab atas munculnya HISAPAN atau TEGANGAN.

25 25 Cara Menyatakan Tegangan Energi Tegangan: dinyatakan dengan “tinggi (cm) dari satuan kolom air yang bobotnya sama dengan tegangan tsb”. Tinggi kolom air (cm) tersebut lazimnya dikonversi menjadi logaritma dari sentimeter tinggi kolom air, selanjutnya disebut pF. Tinggi unit Logaritma BarAtmosfer kolom air (cm) tinggi kolom air (pF)

26 26 KANDUNGAN AIR DAN TEGANGAN KURVA ENERGI - LENGAS TANAH Tegangan air menurun secara gradual dengan meningkatnya kadar air tanah. Tanah liat menahan air lebih banyak dibanding tanah pasir pada nilai tegangan air yang sama Tanah yang Strukturnya baik mempunyai total pori lebih banyak, shg mampu menahan air lebih banyak Pori medium dan mikro lebih kuat menahan air dp pori makro Tegangan air tanah, Bar Liat Lempung Pasir Kadar air tanah, %70

27 27 Tekstur tanah dan air tersedia

28 28 Hubungan antara kadar air tanah dengan tegangan air tanah

29 29 Jelaskan bagaimana tektur tanah mempengaruhi jumlah air tersedia bagi tanaman? Sebanyak 250 kata

30 30 Jelaskan tanah-tanah yang tekturnya halus mampu menahan lebih banyak air dibandingkan dgn tanah-tanah yang teksturnya kasar? Sebanyak 250 kata

31 31 Kapasitas air tersedia dalam tanah yang teksturnya berbeda-beda

32 32 Gerakan Air Tanah Tidak Jenuh Gerakan tidak jenuh = gejala kapilaritas = air bergerak dari muka air tanah ke atas melalui pori mikro. Gaya adhesi dan kohesi bekerja aktif pada kolom air (dalam pri mikro), ujung kolom air berbentuk cekung. Perbedaan tegangan air tanah akan menentukan arah gerakan air tanah secara tidak jenuh. Air bergerak dari daerah dengan tegangan rendah (kadar air tinggi) ke daerah yang tegangannya tinggi (kadar air rendah, kering). Gerakan air ini dapat terjadi ke segala arah dan berlangsung secara terus-menerus. Pelapisan tanah berpengaruh terhadap gerakan air tanah. Lapisan keras atau lapisan kedap air memperlambat gerakan air Lapisan berpasir menjadi penghalang bagi gerakan air dari lapisan yg bertekstur halus. Gerakan air dlm lapisan berpasir sgt lambat pd tegangan

33 33 Gerakan Jenuh (Perkolasi) Air hujan dan irigasi memasuki tanah, menggantikan udara dalam pori makro - medium - mikro. Selanjutnya air bergerak ke bawah melalui proses gerakan jenuh dibawah pengaruh gaya gravitasi dan kapiler. Gerakan air jenuh ke arah bawah ini berlangsung terus selama cukup air dan tidak ada lapisan penghalang Lempung berpasir Lempung berliat cm 0 15 mnt4 jam jam24 jam jam48 jam cm 60 cm Jarak dari tengah-tengah saluran, cm

34 34 Pola Penetrasi dan Pergerakan Air pada tanah Berpasir dan tanah Lempung-liat

35 35 Pola pergerakan air gravitasi dalam tanah

36 36 Pengaruh struktur tanah terhadap pergerakan air tanah ke arah bawah

37 37 PERKOLASI Jumlah air perkolasi Faktor yg berpengaruh: 1. Jumlah air yang ditambahkan 2. Kemampuan infiltrasi permukaan tanah 3. Daya hantar air horison tanah 4. Jumlah air yg ditahan profil tanah pd kondisi kapasitas lapang Keempat faktor di atas ditentukan oleh struktur dan tekstur tanah Tanah berpasir punya kapasitas ilfiltrasi dan daya hantar air sangat tinggi, kemampuan menahan air rendah, shg perkolasinya mudah dan cepat Tanah tekstur halus, umumnya perkolasinya rendah dan sangat beragam; faktor lain yg berpengaruh: 1. Bahan liat koloidal dpt menyumbat pori mikro & medium 2. Liat tipe 2:1 yang mengembang-mengkerut sangat berperan

38 38 LAJU GERAKAN AIR TANAH Kecepatan gerakan air dlm tanah dipengaruhi oleh dua faktor: 1. Daya dari air yang bergerak 2. Hantaran hidraulik = Hantaran kapiler = daya hantar i = k.f dimana i = volume air yang bergerak; f = daya air yg bergerak dan k = konstante. Daya air yg bergerak = daya penggerak, ditentukan oleh dua faktor: 1. Gaya gravitasi, berpengaruh thd gerak ke bawah 2. Selisih tegangan air tanah, ke semua arah Gerakan air semakin cepat kalau perbedaan tegangan semakin tinggi. Hantaran hidraulik ditentukan oleh bbrp faktor: 1. Ukuran pori tanah 2. Besarnya tegangan untuk menahan air Pada gerakan jenuh, tegangan airnya rendah, shg hantaran hidraulik berbanding lurus dengan ukuran pori Pd tanah pasir, penurunan daya hantar lebih jelas kalau terjadi penurunan kandungan air tanah Lapisan pasir dlm profil tanah akan menjadi penghalang gerakan air tidak jenuh

39 39 Gerakan air tanah Gerakan air tanah dipengaruhi oleh kandungan air tanah Penetrasi air dari tnh basah ke tnh kering (cm) 18 Tanah lembab, kadar air awal 29% Tanah lembab, kadar air awal 20.2% Tanah lembab, kadar air awal 15.9% Jumlah hari kontak, hari Sumber: Gardner & Widtsoe, 1921.

40 40 GERAKAN UAP AIR Penguapan air tanah terjadi internal (dalam pori tanah) dan eksternal (di permukaan tanah) Udara tanah selalu jenus uap air, selama kadar air tanah tidak lebih rendah dari koefisien higroskopis (tegangan 31 atm). Mekanisme Gerakan uap air Difusi uap air terjadi dlm udara tanah, penggeraknya adalah perbedaan tekanan uap air. Arah gerapan menuju ke daerah dg tekanan uap rendah Pengaruh suhu dan lengas tanah terhadap gerapan uap air dalam tanah Lembab Dingin Kering Dingin Kering Panas Lembab Panas

41 41 RETENSI AIR TANAH KAPASITAS RETENSI MAKSIMUM adalah: Kondisi tanah pada saat semua pori terisi penuh air, tanah jenuh air, dan tegangan matrik adalah nol. KAPASITAS LAPANG: air telah meninggalkan pori makro, mori makro berisi udara, pori mikro masih berisi air; tegangan matrik bar; pergerakan air terjadi pd pori mikro/ kapiler KOEFISIEN LAYU: siang hari tanaman layu dan malam hari segar kembali, lama-lama tanaman layu siang dan malam; tegangan matrik 15 bar. Air tanah hanya mengisi pori mikro yang terkecil saja, sebagian besar air tidak tersedia bagi tanaman. Titik layu permanen, bila tanaman tidak dapat segar kembali KOEFISIEN HIGROSKOPIS Molekul air terikat pada permukaan partikel koloid tanah, terikat kuat sehingga tidak berupa cairan, dan hanya dapat bergerak dlm bentuk uap air, tegangan matrik-nya sekitar 31 bar. Tanah yg kaya bahan koloid akan mampu menahan air higroskopis lebih banyak dp tanah yg miskin bahan koloidal.

42 42 Klasifikasi Air Tanah Klasifikasi Fisik: 1. Air Bebas / air gravitasi (drainase) 2. Air Kapiler 3. Air Higroskopis Air Bebas (Drainase): a. Air yang berada di atas kapasitas lapang b. Air yang ditahan tanah dg tegangan kurang dari atm c. Tidak diinginkan, hilang dengan drainase d. Bergerak sebagai respon thd tegangan dan tarika gravitasi bumi e. Hara tercuci bersamanya AIR KAPILER: a. Air antara kapasitas lapang dan koefisien higroskopis b. Tegangan lapisan air berkisar atm c. Tidak semuanya tersedia bagi tanaman d. Bergerak dari lapisan tebal ke lapisan tipis e. Berfungsi sebagai larutan tanah AIR HIGROSKOPIS : a. Air diikat pd koefisien higroskopis b. Tegangan berkisar antara atm c. Diikat oleh koloid tanah d. Sebagian besar bersifat non-cairan e. Bergerak sebagai uap air

43 43 Agihan air dalam tanah Berdasarkan tegangan air tanah dapat dibedakan menjadi tiga bagian: Air bebas, kapiler dan higroskopis Koef. Higroskopis Kap. Lapang Jml ruang pori kurang lebih 31 atm kurang lebih 1/3 atm Lapisan olah Air higros- Air Kapiler Ruang diisi udara kopik Peka thd gerakan Biasanya jenuh uap air Hampir tdk kapiler, laju pe- Setelah hujan lebat menunjukkan nyesuaian me- sebagian diisi air, sifat cairan ningkat dg me- tetapi air cepat hi- ningkatnya ke- lang krn gravitasi lembaban tanah bumiLapisan bawah tanah Karena pemadatan ruang pori berkurang Strata bawah (jenuh air) Kolom tanahJumlah ruang pori

44 44 Klasifikasi Biologi Air tanah Klasifikasi berdasarkan ketersediaannya bagi tanaman: 1. AIR BERLEBIHAN: air bebas yg kurang tersedia bagi tanaman. Kalau jumlahnya banyak berdampak buruk bagi tanaman, aerasi buruk, akar kekurangan oksigen, anaerobik, pencucian air 2. AIR TERSEDIA: air yg terdapat antara kap. Lapang dan koef. Layu. Air perlu ditambahkan untuk mencapai pertumbuhan tanaman yang optimum apabila % air yg tersedia telah habis terpakai. Kalau air tanah mendekati koefisien layu, penyerapan air oleh akar tanaman tdk begitu cepat dan tidak mampu mengimbangi pertumbuhan tanaman 3. AIR TIDAK TERSEDIA: AIR yg diikat oleh tanah pd TITIK LAYU permanen, yaitu air higroskopis dan sebagian kecil air kapiler. KH KL KP 100 % pori 31 atm 15 atm 1/3 atm Air Air Ruang udara dan Higroskopis Kapiler air drainase Tdk tersedia Tersedia Berlebihan Daerah Optimum

45 45 Faktor yg mempengaruhi Air Tersedia Faktor yg berpengaruh: 1. Hubungan tegangan dengan kelengasan 2. Kedalaman tanah 3. Pelapisan Tanah TEGANGAN MATRIK : tekstur, struktur dan kandungan bahan organik mempengaruhi jumlah air yg dapat disediakan tanah bagi tanaman TEGANGAN OSMOTIK: adanya garam dalam tanah meningkatkan tegangan osmotik dan menurunkan jumlah air tersedia, yaitu menaikkan koefisien layu. Persen air Sentimeter air setiap 30 cm tanah Kap. Lapang Air tersedia Koef. Layu 5 6Air tidak tersedia Pasir Sandy loam Loam Silty-loam Clay-loam Liat Tekstur semakin halus

46 46 SUPLAI AIR ke TANAMAN Dua proses yg memungkinkan akar tanaman mampu menyerap air dlm jumlah banyak, yaitu: 1. Gerakan kapiler air tanah mendekati permukaan akar penyerap 2.Pertumbuhan akar ke arah zone tanah yang mengandung air LAJU GERAKAN KAPILER LAJU PERPANJANGAN AKAR Selama masa pertumbuhan tanaman, akar tanaman tumbuh memanjang dengan cepat, sehingga luas permukaan akar juga tumbuh terus. Jumlah luas permukaan akar penyerap yang bersentuhan langsung dengan sebagian kecil air tanah (yaitu sekitar 1-2%) Bulu akar menyerap air Jumlah air tanah berkurang Tegangan air tanah meningkat Terjadi perbedaan Tegangan dg air tanah di sekitarnya Terjadi gerakan kapiler air menuju bulu akar Laju gerakan tgt perbedaan tegangan dan daya hantar pori tanah Gerakan kapiler 2.5 cm sagt penting

47 47 KEHILANGAN UAP AIR DARI TANAH HADANGAN HUJAN OLEH TUMBUHAN Tajuk tumbuhan mampu menangkap sejumlah air hujan, sebagian air ini diuapkan kembali ke atmosfer. Vegetasi hutan di daerah iklim basah mampu menguapkan kembali air hujan yg ditangkapnya hingga 25%, dan hanya 5% yg mencapai tanah melalui cabang dan batangnya. Awan hujan Pembentukan Awan Tanah permukaan Groundwater Batuan Sungai - laut presipitasi infiltrasi perkolasi Run off transpirasi evaporasi

48 48 Hadangan hujan oleh tanaman semusim Sekitar % dari curah hujan dihadang tanaman dan dikembalikan ke atmosfer. Besarnya tergantung pada kesuburan tanaman dan stadia pertumbuhan tanaman. Dari curah hujan 375 mm, hanya sekitar mm yang mencapai tanah. Hadangan curah hujan oleh jagung dan kedelai Keadaan hujan Persen dari curah hujan total untuk: JagungKedelai Langsung ke tanah Melalui batang Jumlah di tanah Yang tinggal di atmosfer Sumber: J.L.Haynes, 1940.

49 49 HUBUNGAN ENERGI LTTA: Perubahan tegangan air pd saat bergerak dari tanah melalui akar, batang, daun, ke atmosfer Potensial negatif air (Tegangan air) Tanah berkadar air rendah Tanah berkadar air tinggi Tanah Akar Batang Daun Atmosfer

50 50 EVAPO- TRANSPIRASI Kehilangan uap air dari tanah: 1. EVAPORASI: penguapan air dari permukaan tanah 2. TRANSPIRASI: Penguapan air dari permukaan tanaman 3. EVAPOTRANSPIRASI = Evaporasi + Transpirasi Laju penguapan air tgt pd perbedaan potensial air = selisih tekanan uap air = perbedaan antara tekanan uap air pd permukaan daun (atau permukaan tanah) dengan atmosfer Faktor Iklim dan Tanah: 1. Energi Penyinaran 2. Tekanan uap air di atmosfer 3. Suhu 4. Angin 5. Persediaan air tanah Air tanahEvapotranspirasi (cm: JagungMedicago sativa Tinggi Sedang Sumber: Kelly, 1957.

51 51 Ketersediaan Air Tanah vs Evapotranspirasi Ketersediaan air di daerah perakaran sangat menentukan besarnya evapotranspirasi. Kedalaman daerah perakaran tanaman cm. Air tanah pada lapisan olah mengalami pengurangan karena evaporasi permukaan Air tanah pd lapisan bawah mengalami pengurangan karena diserap akar tanaman Kedalaman tanah (cm)Evapotranspirasi (cm): JagungPadang RumputHutan Sumber: Dreibelbis dan Amerman, 1965.

52 52 PEMAKAIAN KONSUMTIF (PK) Pemakaian Konsumtif merupakan jumlah kehilangan air melalui evaporasi dan transpirasi. Lazim digunakan sebagai ukuran dari seluruh air yg hilang dari tanaman melalui evapotranspirasi Ini merupakan angka-praktis untuk keperluan pengairan Dua faktor penting yg menentukan PK adalah: 1. KEDALAMAN PERAKARAN TANAMAN 2. FASE PERTUMBUHAN TANAMAN PK dapat berkisar cm atau lebih: 1. Daerah basah - semi arid dg irigasi: cm. 2. Daerah panas dan kering dg irigasi: cm. EVAPORASI vs TRANSPIRASI Faktor yg berpengaruh adalah: 1. Perbandingan luas tutupan tanaman thd luas tanah 2. Efisiensi pemakaian air berbagai tanaman 3. Perbandingan waktu tanaman berada di lapangan 4. Keadaan iklim Di daerah basah : EVAPORASI  TRANSPIRASI Di daerah kering: 1. EVAPORASI  % dari seluruh hujan yg jatuh 2. TRANSPIRASI  % 3. RUN OFF  5%

53 53 WUE : Water Use Efficiency WUE  Produksi tanaman yg dapat dicapai dari pemakaian sejumlah air tersedia WUE dapat dinyatakan sbg: 1. Pemakaian konsumtif (dalam kg) setiap kg jaringan tanaman yg dihasilkan 2.Transpirasi (dalam kg) setiap kg jaringan tanaman yg dihasilkan ……… NISBAH TRANSPIRASI Jumlah air yg diperlukan untuk menghasilkan 1 kg bahan kering tanaman NISBAH TRANSPIRASI Untuk tanaman di daerah humid: , di daerah arid duakalinya TanamanNisbah Transpirasi Beans Jagung Peas Kentang Sumber: Lyon, Buckman dan Brady, 1952.

54 54 FAKTOR WUE Faktor yang mempengaruhi WUE: Iklim, Tanah, dan Hara WUE tertinggi lazimnya terjadi pd tanaman yg berproduksi optimum; Adanya faktor pembatas pertumbuhan akan menurunkan WUE Nisbah evapo-transpirasi tanaman di lokasi yg mempunyai defisit kejenuhan dari atmosfer 800 Kentang Kacang polong 400 Jagung 0 0 Defisit kejenuhan dari atmosfer (mm Hg) Jumlah air unt menghasilkan 1 ton bahan kering 30 Kadar air tanah rendah 15 Kadar air tanah tinggi 0 0 Pupuk P, kg/ha600

55 55 Pengendalian Penguapan MULSA & PENGELOLAAN Mulsa adalah bahan yg dipakai pd permukaan tanah untuk mengurangi penguapan air atau untuk menekan pertumbuhan gulma. Lazimnya mulsa spt itu digunakan untuk tanaman yang tidak memerlukan pengolahan tanah tambahan MULSA KERTAS & PLASTIK Bahan mulsa dihamparkan di permukaan tanah, diikat spy tdk terbang, dan tanaman tumbuh melalui lubang-lubang yg telah disiapkan Selama tanah tertutup mulsa, air tanah dapat diawetkan dan pertumbuhan gulma dikendalikan MULSA SISA TANAMAN Bahan mulsa berasal dari sisa tanaman yg ditanam sebelumnya, misalnya jerami padi, jagung, dan lainnya Bahan mulsa dipotong-potong dan disebarkan di permukaan tanah Cara WALIK DAMI sebelum penanaman kedelai gadu setelah padi sawah MULSA TANAH  Pengolahan tanah Efektivitas mulsa tanah dalam konservasi air-tanah (mengendalikan evaporasi) masih diperdebatkan, hasil-hasil penelitian masih snagat beragam

56 56 Olah Tanah vs Penguapan Air Tanah Alasan pengolahan tanah: 1. Mempertahankan kondisi fisika tanah yg memuaskan 2. Membunuh gulma 3. Mengawetkan air tanah. Pengendalian Penguapan vs Pemberantasan Gulma PerlakuanHasil jagung (t/ha) Kadar air tanah (%) hingga kedalaman 1 m Tanah dibajak dg persiapan yg baik 1. Dibebaskan dari gulma Gulma dibiarkan tumbuh Tiga kali pengolahan dangkal Persiapan Buruk 4. Dibebaskan dari gulma Sumber: Mosier dan Gutafson, Pengolahan tanah yg dapat mengendalikan gulma dan memperbaiki kondisi fisik tanah akan berdampak positif thd produksi tanaman Pengolahan tanah yg berlebihan dapat merusak akar tanaman dan merangsang evaporasi, shg merugikan tanaman

57 57 Beberapa proses penting dalam siklus air: Precipitation is condensed water vapor that falls to the Earth's surface. Most precipitation occurs as rain, but also includes snow, hail, fog drip, graupel, and sleet. Approximately 505,000 km³ of water fall as precipitation each year, 398,000 km³ of it over the oceans.

58 58 Canopy interception is the precipitation that is intercepted by plant foliage and eventually evaporates back to the atmosphere rather than falling to the ground.

59 59 LIMPASAN = Runoff includes the variety of ways by which water moves across the land. This includes both surface runoff and channel runoff. As it flows, the water may infiltrate into the ground, evaporate into the air, become stored in lakes or reservoirs, or be extracted for agricultural or other human uses. Infiltration is the flow of water from the ground surface into the ground. Once infiltrated, the water becomes soil moisture or groundwater.

60 60 Subsurface Flow is the flow of water underground, in the vadose zone and aquifers. Subsurface water may return to the surface (eg. as a spring or by being pumped) or eventually seep into the oceans. Water returns to the land surface at lower elevation than where it infiltrated, under the force of gravity or gravity induced pressures. Groundwater tends to move slowly, and is replenished slowly, so it can remain in aquifers for thousands of years.

61 61 Evaporation is the transformation of water from liquid to gas phases as it moves from the ground or bodies of water into the overlying atmosphere. The source of energy for evaporation is primarily solar radiation. Evaporation often implicitly includes transpiration from plants, though together they are specifically referred to as evapotranspiration. Approximately 90% of atmospheric water comes from evaporation, while the remaining 10% is from transpiration. Total annual evapotranspiration amounts to approximately 505,000 km³ of water, 434,000 km³ of which evaporates from the oceans.

62 62 SUBLIMASI is the state change directly from solid water (snow or ice) to water vapor. ADVEKSI is the movement of water — in solid, liquid, or vapour states — through the atmosphere. Without advection, water that evaporated over the oceans could not precipitate over land. KONDENSASI is the transformation of water vapour to liquid water droplets in the air, producing clouds and fog.

63 63 Aktivitas manusia yang dapat mempengaruhi siklus air : Pertanian Alteration of the chemical composition of the atmosphere Construction of dams Deforestation and afforestation Removal of groundwater from wells Water abstraction from rivers Urbanization.

64 64 KAPASITAS PENYIMPANAN AIR: WATER HOLDING CAPACITY Soil "holds" water available for crop use, retaining it against the pull of gravity. This is one of the most important physical facts for agriculture. If the soil did not hold water, if water was free to flow downward with the pull of gravity as in a river or canal, we would have to constantly irrigate, or hope that it rained every two or three days. There would be no reason to pre-irrigate. And there would be no such thing as dryland farming.

65 65 Soil Moisture Level (Depletion, %) vs. Soil Moisture Tension (Bars).

66 66 Hubungan antara Potensial Air Tanah dnegan Air Tersedia pada tiga macam tekstur tanah

67 67 The soil's ability to hold water depends on both the soil texture and structure. Texture describes the relative percentages of sand, silt, and clay particles. The finer the soil texture (higher percentage of silt and clay), the more water soil can hold. Gravity is always working to pull water downwards below the plant's root zone. To counteract the pull of gravity, soil is able to generate its own forces, commonly called "matric forces" ("matric" because of the soil "matrix" structure that forms the basis for the forces).

68 68 An important fact about the soil's water-holding forces is that as the level of soil moisture goes down, the soil generates more force. This is the reason that some water will move up into the root zone from a shallow ground water table. As the plant extracts water in the root zone, the soil pulls water up from the area with more water to the area with less. As you would expect, the rate at which the water-holding forces go up with decreasing soil moisture is different for different soils. In a coarse soil, they will go up slowly. This means that plants can extract a great amount of water from coarse soils before they stress. In contrast, these forces rise quickly in finer soils.

69 69 Graphically, the relationship can be described by the Figure SWP-1. Looking at the lowest line for a coarse soil. You can see that at A, the soil moisture level is very high and the water-holding forces are low. This means that the plant can extract water easily from the soil. At B, the soil moisture level is lower but the water-holding forces haven't gone up that much. The plant can still extract water easily. However at C, the soil moisture level is very low and the water- holding forces have increased greatly. The plant cannot extract water easily and will be stressed.

70 70 Looking at the top line for a finer soil. At A, as with the coarse soil, the water-holding forces are low when the soil moisture level is high. However, at B, the soil moisture level has dropped somewhat but the water-holding forces have gone up greatly. And at C, where the soil moisture level is low, the water-holding forces have gone up very high. We will be coming back to this idea of increasing soil water- holding forces with decreasing soil moisture many times

71 71 HUBUNGAN TANAH-AIR The role of soil in the soil-plant-atmosphere continuum is unique. It has been demonstrated that soil is not essential for plant growth and indeed plants can be grown hydroponically (in a liquid culture). However, usually plants are grown in the soil and soil properties directly affect the availability of water and nutrients to plants. Soil water affects plant growth directly through its controlling effect on plant water status and indirectly through its effect on aeration, temperature, and nutrient transport, uptake and transformation. The understanding of these properties is helpful in good irrigation design and management.

72 72 The soil system is composed of three major components: solid particles (minerals and organic matter), water with various dissolved chemicals, and air. The percentage of these components varies greatly with soil texture and structure. An active root system requires a delicate balance between the three soil components; but the balance between the liquid and gas phases is most critical, since it regulates root activity and plant growth process.

73 73 The amount of soil water is usually measured in terms of water content as percentage by volume or mass, or as soil water potential. Water content does not necessarily describe the availability of the water to the plants, nor indicates, how the water moves within the soil profile. The only information provided by water content is the relative amount of water in the soil. Jumlah air tersedia dipengaruhi tekstur tanah

74 74 Soil water potential, which is defined as the energy required to remove water from the soil, does not directly give the amount of water present in the root zone either. Therefore, soil water content and soil water potential should both be considered when dealing with plant growth and irrigation. The soil water content and soil water potential are related to each other, and the soil water characteristic curve provides a graphical representation of this relationship.

75 75 The nature of the soil characteristic curve depends on the physical properties of the soil namely, texture and structure. Soil texture refers to the distribution of the soil particle sizes. The mineral particles of soil have a wide range of sizes classified as sand, silt, and clay. The proportion of each of these particles in the soil determines its texture. All mineral soils are classified depending on their texture. Every soil can be placed in a particular soil group using a soil textural triangle. For example a soil with 60% sand and 10% clay separates is classified as a Sandy loam

76 76 Kapasitas Lapangan Field Capacity There are limits on the amount of water that soil holds for crop use. The upper limit is termed "field capacity". During an irrigation, or whenever excess water is added to soil, water drains down through the soil due to the pull of gravity. At first, this internal drainage is relatively rapid. However, it soon slows to almost nothing. (The increasing soil water-holding forces finally start to counteract gravity.) At this point we would say the soil is at field capacity.

77 77 You can demonstrate field capacity using a visualization of a sponge (like soil, a porous material that will hold water). Using a pan of water, hold a sponge under water until it is saturated. Now, pull the sponge out of the water. It will immediately start to drip water, quickly at first, then slower and slower. At some point it will essentially stop dripping. The internal drainage has stopped and the sponge is at field capacity. It is very important to note that you can soak more water into soil that is already at field capacity. There will be open soil pores that will take the water. However, the excess water will not be held. It will just drain down until the soil moisture returns to field capacity.

78 78 You can use the sponge again to demonstrate this important fact. With the sponge at "field capacity", use a cup to pour water on it. The water will soak in, there will be open pores in the sponge that will take in water. But you will see that the sponge starts dripping again as the excess water starts to drain off the bottom. Because of this ability to hold water against the pull of gravity, soil does not act like a bathtub during irrigations. That is, irrigation water does not have to go to some "bottom" and then fill back up to the top. Rather soil fills to field capacity from the top down.

79 79 Field capacity is a soil-based concept. That is, it depends on the texture and structure of the soil as well as the physical conditions in the field. Coarse soils have lower field capacities than fine soils. If there is a high water table or severe stratification that would restrict drainage, the field capacity would be higher than normal.

80 80 AIR TERSEDIA & ZONE AKAR EFEKTIF The water held by the soil between field capacity and permanent wilting point is termed the "available water holding capacity" of the soil. It is water that is "available" for the plant to use. Water added to the soil in excess of field capacity will drain down, below the active root system. Water held by the soil that is below the permanent wilting point is of no use, the plant has died. As a crop manager you are concerned with the soil moisture throughout the depth of the plant's active root system, the "effective root zone".

81 81 The effective root zone is that depth of soil where you want to control soil moisture (just as you control fertility and weed/pest pressures). The effective root zone may or may not be the actual depth of all active roots. It may be shallower because of concerns for crop quality or development (as with many vegetable crops). For a pre-irrigation though, you may want to consider the maximum potential root zone as the effective root zone for that irrigation. For example, with cotton you may estimate the effective root zone as 6 feet for a preirrigation, 2 feet for the first seasonal irrigation, 4 feet for the second seasonal, and 6 feet thereafter. For an almond orchard, you may estimate the effective root zone as four feet for the entire season. With onions, the major concern is with the top 2 feet.

82 82 Hubungan Air – Tanah The soil is composed of three major parts: air, water, and solids. The solid component forms the framework of the soil and consists of mineral and organic matter. The mineral fraction is made up of sand, silt, and clay particles. The proportion of the soil occupied by water and air is referred to as the pore volume. The pore volume is generally constant for a given soil layer but may be altered by tillage and compaction. The ratio of air to water stored in the pores changes as water is added to or lost from the soil. Water is added by rainfall or irrigation, as shown in Figure 2. Water is lost through surface runoff, evaporation (direct loss from the soil to the atmosphere), transpiration (losses from plant tissue), and either percolation (seepage into lower layers) or drainage.

83 83 The pore volume is actually a reservoir for holding water. Not all of the water in the reservoir is available for plant use. Figure 3 represents a "wet" (saturated) soil immediately after a large rainfall. Note that all of the pores are filled with water. Gravity will pull some of this water down through the soil below the crop's root zone. The water that is redistributed below the root zone due to the force of gravity is gravitational water. In general, gravitational water is not available to plants, especially in sandy soils, because the redistribution process occurs quickly (in two days or less).

84 84 Kapan tanah perlu ditambah air agar tanaman tidak terganggu pertumbuhannya? Jelaskan pendapat Saudara dnegan 250 kata?

85 85 Sumber dan perilaku air yang ditambahkan ke tanah

86 86 Saturated (wet) soil. All pores (light areas) are filled with water. The dark areas represent soil solids.

87 87 Water distribution in a soil at field capacity. Capillary water (lightly shaded areas ) in soil pores is available to plants. Field capacity represents the upper limit of plant-available water.

88 88 Water distribution in a soil at thw wilting point. This water is held tightly in thin films around soil particles and is unavailable to plants. The wilting point represents the lower limit of plant-available water.

89 89 Plant-available water, PAW, adalah volume air yang disimpan dalam tanah yang dapat digunakan oleh tanaman. It is the difference between the volume of water stored when the soil is at field capacity and the volume still remaining when the soil reaches the permanent wilting point (the lower limit), as shown in Figure 6.

90 90 Figure 6. HUBUNGAN ANTARA AIR-TERSEDIA DAN DISTRIBUSI AIR DALAM TANAH.

91 91 Kapasitas tanah menyimpan air

92 92 Jumlah air tanah pada tiga macam tekstur tanah

93 93 Tabel 1. Jumlah air tersedia dalam tanah yang teksturnya berbeda-beda

94 94 AIR-TANAH dan CEKAMAN (stres) TANAMAN Kalau tanaman menyerap air dari tanah, jumlah air tersedia yang tersisa dalam tanah menjadi berkurang. The amount of PAW removed since the last irrigation or rainfall is the depletion volume. Irrigation scheduling decisions are often based on the assumption that crop yield or quality will not be reduced as long as the amount of water used by the crop does not exceed the allowable depletion volume. The allowable depletion of PAW depends on the soil and the crop. For example, consider corn growing in a sandy loam soil three days after a soaking rain. Even though enough PAW may be avai1able for good plant growth, the plant may wilt during the day when potential evapotranspiration (PET) is high.

95 95 AIR-TANAH dan CEKAMAN (stres) TANAMAN Evapotranspiration merupakan proses hilangnya air tanah ke atmosfer, melalui evaporasi dari permukaan tanah dan proses transpirasi dari tanaman yang tumbuh di tanah. Potential evapotranspiration is the maximum amount of water that could be lost through this process under a given set of atmospheric conditions, assuming that the crop covers the entire soil sur- face and that the amount of water present in the soil does not limit the process. Potential evapotranspiration is controlled by atmospheric conditions and is higher during the day. Plants must extract water from the soil that is next to the roots. As the zone around the root begins to dry, water must move through the soil toward the root (Figure 7). Daytime wilting occurs because PET is high and the plant takes up water faster than the water can be replaced.

96 96 Gambar. Kalau tanaman menyerap air, tanah di sekitar perakaran menjadi mengering. If the rate of water movement from moist zones is less than the PET, the plant temporarily wilts.

97 97 Pada malam hari, pada saat PET menurun hingga mendekati nol, air tanah bergerak dari tanah yang lebih basah memasuki zone tanah yang lebih kering di sekitar akar tanaman. The plant recovers turgor and wilting ceases (Figure 8). This process of wilting during the day and recovering at night is referred to as temporary wilting. Proper irrigation scheduling reduces the length of time a crop is temporarily wilted.

98 98 Gambar. At night when the PET is low, the plant recovers from wilting as water moves from moist zones (dark areas) to eliminate the dry zones around the roots.

99 99 Hubungan antara distribusi air dalam tanah dan konsep jadwal irigasi ketika 50 percent air tersedia telah habis

100 100 FAKTOR TANAMAN Three plant factors must be considered in developing a sound irrigation schedule: the crop's effective root depth, its moisture use rate, and its sensitivity to drought stress (that is, the amount that crop yield or quality is reduced by drought stress). KEDALAMAN EFEKTIF AKAR Rooting depth is the depth of the soil reservoir that the plant can reach to get PAW. Crop roots do not extract water uniformly from the entire root zone. Thus,the effective root depth is that portion of the root zone where the crop extracts the majority of its water. Effective root depth is determined by both crop and soil properties.

101 101 PENGARUH TANAMAN thd KEDALAMAN EFEKTIF AKAR Different species of plants have different potential rooting depths. The potential rooting depth is the maximum rooting depth of a crop when grown in a moist soil with no barriers or restrictions that inhibit root elongation. Potential rooting depths of most agricultural crops important in North Carolina range from about 2 to 5 feet. For example, the potential rooting depth of corn is about 4 feet. Water uptake by a specific crop is closely related to its root distribution in the soil. About 70 percent of a plant's roots are found in the upper half of the crop's maximum rooting depth. Deeper roots can extract moisture to keep the plant alive, but they do not extract suffficient water to maintain optimum growth. When adequate moisture is present, water uptake by the crop is about the same as its root distribution. Thus, about 70 percent of the water used by the crop comes from the upper half of the root zone (Figure 10). This zone is the effective root depth.

102 102 JUMLAH AIR YANG DAPAT DISERAP TANAMAN DIPENGARUHI OLEH DISTRIBUSI AKAR DLAMA TANAH

103 103 PENGARUH TANAH thd KEDALAMAN EFEKTIF AKAR. The maximum rooting depth of crops in North Carolina is usually less than their potential rooting depth and is restricted by soil chemical or physical barriers. North Carolina subsoils have a pH of about 4.5 to 5.0, which presents a chemical barrier to root growth, as shown in Figure 11. Liming practices rarely improve soil pH below the 2-foot depth. Shallow soils (Carolina slate belt soils) or soils with compacted tillage pans (coastal plain soils) are examples of soils with physical barriers that restrict root penetration below the plow depth (usually less than 12 inches unless subsoiling is practiced). Thus, for example, while corn has a potential rooting depth of 4 feet, when grown under North Carolina conditions, its maximum rooting depth is about 2 feet. Maximum rooting depths for several crops under North Carolina conditions are given in Table 2.

104 104 CIRI-CIRI TANAH YANG MEMPENGARUHI KEDALAMAN PERAKARAN TANAMAN

105 105 The effective root depth is the depth that should be used to compute the volume of PAW in the soil reservoir. The effective root depth for a mature root zone is estimated to be one-half the maximum rooting depth listed in Table 2. For example, under North Carolina conditions corn has a maximum rooting depth of 2 feet; thus, the maximum effective root depth is estimated to be 1 foot. Effective root depth is further influenced by the stage of crop development. Effective root depths for most aops inaease as top growth inaeases until the reproductive stage is reached. After this time, effective root depth remains fairly constant.

106 106 Kedalaman perakaran tanaman jagung pada berbagai umur pertumbuhannya. Jadwal irigasi harus didasarkan pada kedalaman efektif akar dan bukan pada kedamalan maksimum perakaran.

107 107 LAJU PENGGUNAAN AIR TANAMAN Often, irrigation scheduling requires an estimate of the rate at which PAW is being extracted. A "checkbook" approach is often used to keep a daily accounting of water additions and removal. Traveling irrigation systems usually require several days to complete one irrigation cycle. Soil-water measurements should be used to schedule irrigation for these systems, but continued PAW extraction during the irrigation cycle must also be estimated so that the last part of the field does not get too dry. In the above situations, the crop's water use rate must be estimated. Estimates of the water use rate for most crops are available from county Extension Service or Soil Conservation Service offices. As with rooting depth, water use rate is a function of the crop's stage of development, as shown in Figure 13. For example, corn uses water three times as fast during the pollination period (65 to 75 days after planting, 0.25 inch per day) as during the knee- high stage (35 to 40 days after planting, 0.08 inch per day).

108 108 Penggunaan air harian tanaman jagung dipengaruhi oleh fase pertumbuhan tanaman. Jadwal irigasi harus disesuaikan dengan perubahan konsumsi air tanaman selama musim pertumbuhannya

109 109 KEPEKAAN TANAMAN TERHADAP KEKERINGAN The reduction in crop yield or quality resulting from drought stress depends on the stage of crop development. For example, corn is most susceptible to stresses caused by dry conditions at the siLicing stage (Figure 14). For a given level of stress, the yield reduction for corn would be four times greater at the silking stage than at the knee-high stage. From the yield standpoint, applying irrigation water at silking would be worth four times more than if the same amount of water was applied during the knee-high stage. Knowledge of this relationship is most useful when the irrigation capacity or water supply is limited. When water is in short supply, irrigation should be delayed or cancelled during the least susceptible crop growth stages. This water can then be reserved for use during more sensitive growth stages.

110 110 Kepekaan tanaman jagung terhadap kekeringan dipengaruhi oleh fase pertumbuhannya. Semakin besar tingkat kepekaannya, maka pengaruh kekeringan terhadap hasil semakin besar.

111 111 Kepakaan tanaman jagung terhadap kekeringan dipengaruhi oleh umur tanaman. This relationship is typical for most agricultural crops irfigated. The most critical irrigation period typically begins just before the reproductive stage and lasts about 30 to 40 days to the end of the fruit enlargement or grain development stage. Because the root system is fully developed by the beginning of the reproductive period, irrigation amounts should be computed to replace the depleted PAW within the effective root zone (12 inches). Exceptions include tobacco and other transplanted crops where irrigation is often scheduled immediately after transplanting to ensure stand establishment.

112 112 When if rigation is scheduled before the crop root system is fully developed, the amount of irrigation to apply should be based on the depleted PAW within the actual effective root depth at the time of irrigation. For example, irrigation scheduled when corn is at the knee-high stage (35 to 40 days after planting) should apply only about two- thirds as much water as an irrigation scheduled during the tasseling stage (65 days after planting) because the effective rooting depth at the knee-high stage is only two-thirds as deep (8 inches compared to 12 inches). For soils that have an abrupt textural change within the effective root depth, such as a loamy sand surface texture overlying a sandy clay loam, a correction may be necessary to account for the different amounts of PAW within each soil texture.

113 113

114 114 Jumlah air tanah tersedia dalam berbagai tipe tanah

115 115

116 116

117 117 Bagaimana mycorrhiza dapat membantu penyerapan air dari dalam tanah? Uraian 250 kata

118 118 Jelaskan mengapa air bergerak dari akar menuju daun tanaman ? 250 kata

119 119 Jelaskan klasifikasi biologis air tanah, dengan 250 kata

120 120 Pengaruh Potensial Air tanah thd konduktivitas hidraulik tanah

121 121 Pengaruh ketersediaan air terhadap pertumbuhan tanaman

122 122 Pola penyerapan air oleh tanaman yang tumbuh pada profil tanah yang tidak mempunyai lapisan penghambat dan suplai air tersedia cukup di seluruh zone perakaran tanaman

123 123 Sistem Perakaran Serabut dan Perakaran Tunggang pada Tanaman umur dua bulan

124 124 Penyerapan air BAWANG PUTIH (Allium cepa) Tanaman mempunyai sistem perakaran yang dangkal dan akar-akar terkonsentrasi pada tanah klapisan atas sedalam 0.3 m. Pada umumnya 100% penyerapan air terjadi dari lapisan tanah atas sedalam m (D= m ). Untuk memenuhi sekuruh kebu­tuhan air tanaman (ETm) tanah harus dijaga tetap lembab; pada laju evapotranspirasi 5-6 mm/hari ternyata laju penyerapan air mulai menurun kalau sekitar 25% dari total air tanah tersedia telah habis (p = 0.25).

125 125 Penyerapan air tanaman LOMBOK (Capsicum annum dan Capsicum frutescens) Tanaman lombok mempunyai akar utama yang patah pada saat trans­ planting dan kemudian menumbuhkan banyak akar-akar lateral. Kedalaman akar dapat meluas hingga 1 m tetapi pada kondisi irigasi ternyata akar terkonsentrasi pada lapisan tanah atas seda­lam 0.3 m. Pada kondisi evapoytranspirasi maksimum 5-6 mm/hari, 25-30% total air tersedia dapat dihabiskan sebelum terjadi reduksi penyerapan air (p= ). Biasanya 100% penyerapan air terjadi dalam keda;laman lapisan tanah m (D = m).

126 126 Penyerapan air tanaman jeruk Tanaman jeruk menumbuhkan satu akar tunggang utama. Akar-akar cabang membentuk semacam jaring horisontal yang dilengkapi dengan bulku-bulu akar. Perkembangan akar snagat tergantung pada tipe batang bawah yang digunakan dan karakteristik profil tanah. Kedalaman perakaran beragam antara 1.20 dan 2.0 m. Pada umumnya 60% akar berada pada lapisan tanah atas 0.5 m, 30% dalam lapisan tanah 0.5 m ke dua, dan 10% pada lapisan tanah di bawah 1 meter. Kalau persediaan air irigasi mencukupi, biasanya 100% air diekstraks dari lapisan tanah atas m (D = m) tetapi pada kondisi kering ternyata kedalaman ek­straksi air lebih dalam lagi. Selama periode defisit air yang panjang, air dalam tanah yang kedalaman efektifnya tebal dan drainasenya bagus dapat digunakan oleh tanaman hingga kedalaman 2 atau 3 meter.

127 127 Pergerakan air dari lapisan tanah basah ke lapisan tanah kering dengan bantuan sistem perakaran tanaman

128 128 BAGAIMANA TANAMAN MENGAMBIL AIR? Apa kebutuhan tanaman? Plants need water. We all know that. Why do they need water? For the following reasons: Firstly, they need water in order to stand up. Some will eventually make woody tissue to help this process, but basically plants are full of pressurised water which makes them turgid. The leaves offer themselves to the sun....their stomata (pores) open....and moisture evaporates. Water is drawn upward from the roots and through the stems to replace this lost water. This process is called "evapotranspiration". The more sun, the greater the pressure to take up water. This process takes energy from the plant, and obviously requires a healthy root system and the presence of AVAILABLE water in the root zone (I'll explain the "availability" shortly). If it's not there, the plant will wilt. In cases of root disease and diseases like Fusarium, you will see whole crops crash down.

129 129 Secondly, they need water to carry nutrients into themselves which are dissolved in the soil water. They can't munch on dry fertiliser. No water.....or I should say, "no passage of water into the plant" and no nutrient uptake. If the plant can't take up water, it will become starved of nutrients. It's not so uncommon to see high nutrient soils and pale, nutrient- starved crops because of an inability of the plant to take up water. Thirdly, plants need water to photosynthesize. To summarise a fairly complex process, photosynthesis is the synthesis of sugar (energy) from light, carbon dioxide and water, with oxygen as a by-product. Take away any of those factors, and the plant won't grow. It has no energy.

130 130 Apa lagi kebutuhan tanaman ? They need oxygen, and they need it in the root zone. Like all aerobic organisms (including us), they need to respire as part of the process of utilising the sugars they created in photosynthesis, and this requires oxygen. No oxygen, and no respiration. No respiration, and no functionality. The roots can't grow....and can't take up water....and can't supply the plant with the nutrients and water that it needs. This is why we talk about a plant needing DRAINAGE. The problem in a waterlogged situation is not too much water......it's too little oxygen!

131 131 AIR DALAM TANAH Soil is made up of soil particles in crumb-form (peds), and pore spaces around the soil crumbs. In a well-structured soil, these crumbs are nice and stable....but in a poorly structured soil, the crumbs are unstable which often limits pore-space. The pore-spaces are necessary for holding water, and for the free gaseous exchange of oxygen and carbon dioxide between the plant roots and the soil surface (respiration process). There are three types of soil water (ie. water in the soil).

132 132 AIR GRAVITASI This is the water which is susceptible to the forces of gravity. It exists after significant rainfall, and after substantial irrigation. This is the water which fills all the pore-space, and leaves no room for oxygen and gaseous exchange. In "light" soils, this tends to drain away quickly. In heavy soils, this can take time. AIR KAPILER This is the water which is held with the force of SURFACE TENSION by the soil particles, and is resistent to the forces of gravity. This is the water which is present after the gravitational water has drained away, leaving spaces free for gaseous exchange. When the soil is holding it's MAXIMUM capillary water (after the gravitational water has drained), this is called FIELD CAPACITY. At this point, the plant is able to take up water easily, and has the oxygen that it needs in the root zone.

133 133 AIR HIGROSKOPIS This is the water which is held so tightly (by surface tension) to the soil particles that the plant roots can't take it up. It's there but it's unavailable. At this stage there's generally sufficient oxygen, but there just isn't enough available water. The plant wilts, and will eventually die if it doesn't get water. When the plant wilts and is unable to recover, this is called the TITIK LAYU PERMANEN Titik layu permanen merupakan sifat tanah yang penting bagi pertumbuhan tanaman. Mengapa demikian? Jelaskan dengan 250 kata

134 134 TITIK LAYU PERMANEN The closer to the soil particle the water is held, the tighter it's held. And the further from the particle, the looser it's held. It takes little energy for the plant roots to take up the water that's far from the particle and is present at the field capacity point. By contrast, as the water is used up (or evaporates), it takes more and more energy for the plant to take up water. I often use the analogy of drinking through a straw. A short straw, ie. when a cup is 15 cm away from you, is easy to use. A one-metre long straw takes a lot of energy to suck up a drink. A twenty-metre straw is impossible to use. It works much the same with plants. The more the soil dries out, the more energy the plant needs to output in order to get a decent drink. The effect of increased soil salinity (due to high soil salinity, high soil-water salinity, or both) has basically the same effect as a soil drying out. Salt in the soil has as osmotic effect, and causes the water to be held more tightly around the soil particles. The higher the salinity level, the harder it is for a plant to take a drink, despite apparently sufficient moisture present.

135 135 Jelaskan pendapat Saudara mengenai pentingnya sirkulasi air dalam sistem Tanah-Tanaman 250 kata

136 136 Bibit tanaman tomat yang baru ditanam ini memerlukan cukup banyak air dari dalam tanah. Mengapa demikian? Jelaskan dengan 250 kata

137 137 Struktur Sistem Tanah- Tanaman. Jelaskan bagaimana air dari tanah memasuki sistem tanah- tanaman. 250 kata

138 138 Bagaimana peranan tumbuhan dalam siklus air di alam? Jelaskan pendapat Saudara 250 kata

139 139 Representasi ketersediaan air dalam tanah bagi pertumbuhan tanaman

140 140 AIR TERSEDIA BAGI TANAMAN In other words, Plant Available Water (PAW) is the amount of water held in a soil between the limits of Field Capacity and Permanent Wilting Point.Plant Available Water (PAW) However, only the water near to Field Capacity may be Readily Available Water (RAW). This is particularly so for fine textured, clayey soils because a high proportion of PAW is held in small pores and as thin films and plants need to 'do more work' to extract this fraction of water from soils.

141 141 RAW - Readily Available Water (Air Mudah Tersedia) Not all PAW is equally available to plants. As soils dry out and PAW approaches PWP, plants will come under water-stress and wilt. It is the objective of irrigators to avoid this situation. They prefer to irrigate when the soil water content is about 50% of FC or about 100kPa. These limits, however, are set by the irrigator to suit the business enterprise. For example, if growth rates are to be restricted then the trigger for an irrigation event may be 300kPa. As the name suggests, Readily Available Water or RAW is the amount and availability of water in soils that is readily available to plants.

142 142 PAW - Plant Available Water Following rainfall, or irrigation, all the pores in soil will be filled with water; this is the Saturation Water Content (SWC). With time the water in the largest pores will drain to depth due to gravitational forces. In coarser textured, sandy and loamy soils this drainage will take place in less than a day and will, therefore, be unavailable to plants. Fine-textured, clayey soils, however, may be somewhat poorly drained and all pores may remain filled with water for several days. In these cases some of the SWC may be available for EvapoTranspiration and would need to be considered in calculations of soil water balances and irrigation scheduling. Poorly drained soils, however, are less suitable for irrigation. They are difficult to manage and may be waterlogged for times that can cause damage to plants for reasons of anaerobic root environments.

143 143 Jelaskan bagaimana hubungan antara Evapotranspirasi dan Irrigasi Dengan 250 kata

144 144 Evapotranspirasi dan Irrigasi Evapotranspiration (ET) is the combined process of plant transpiration and soil evaporation. Plant transpiration is the movement of moisture from the plant to the air through tiny pores in the leaves known as stomates. The water enters the plants through the roots in a liquid form and leaves the plants through the stomates in a gaseous form. Soil evaporation is the direct evaporation of water from the surface of the soil into the atmosphere.

145 145 Hubungan antara profil tanah dengan air tanah. Jelaskan pendapat Saudara tentang hal ini 250 kata

146 146 Hubungan antara kadar air tanah dnegan nilai pF, pada tiga macam tekstur tanah. Jelaskan pendapat Saudara tentang hal ini 250 kata

147 147 Transport air dalam tanaman Plants need raw materials like CO2, water and minerals for photosynthesis and for various other purposes such as making of proteins. For plants soil is the richest source of water and minerals. Roots absorb these substances and transport to the various parts of the plant. The water and minerals dissolved in it move through special tissue present in plants called xylem. Xylem consists of two kinds of elements called tracheids and vessels. Vessels and tracheids of the roots, stems and leaves are interconnected to form a continuous system of water conducting channels reaching all parts of the plant.

148 148

149 149 Struktur jaringan pembuluh tanaman

150 150 Struktur jaringan pembuluh tanaman

151 151 PERGERAKAN AIR TANAH During long-continued heavy rains, infiltration of soil water continues under the force of gravity, carrying the water down to successively greater depths. Soil pores become filled with water, with only a small amount of free air remaining entrapped in bubbles. The soil may, for a time, become almost completely saturated with water. Downward percolation continues beyond the soil water belt into the intermediate belt, a zone too deep to be reached by plat roots. Water may ultimately reach the ground-water zone below. After the rain has ceased, water continues to drain downward under the influence of gravity, but some remains held in the soil, clinging to the soil grains in thin films, by the force of capillary tension. This is the same force that causes ink to be drawn upward in a piece of blotting paper and which permits small water droplets to cling to the side of a vertical pane of glass. Films of capillary water in the soil remain held in place until gradually dissipated by evaporation or drawn into root systems.

152 152 PERGERAKAN AIR TANAH After soil has been saturated by prolonged rains and then drains until no more water moves downward under the force of gravity, the soil is said to be holding its field capacity of water. Most excess water drains out in a day’s time; usually not more that two or three days are required for gravity drainage to cease. Soil-moisture content can be stated in terms of the equivalent depth in inches of water in a given thickness of soil. At field capacity, soil-moisture content ranges from 1 to 4 inches per foot of soil, depending upon soil texture. Sandy soils have low field capacity, which is rapidly reached because of the ease with which the water penetrates the large openings (macro pores). Clay soils, on the other hand, have a high field capacity, but require much longer periods to attain it because of the slow rate of water penetration due to the much smaller openings (micro pores). A comparable, but lower value of soil moisture is the wilting point, below which foliage wilts because of the inability of the plants to extract the remaining moisture.

153 153 A few points to consider: Only after heavy rainfall does the water “flow” through the soil. This is especially true in our area where evapotranspiration exceeds precipitation. During most of the growing season the water can be said to be “pulled” through the soil by capillarity. Field Capacity can be thought of as “all the water a soil can hold against the pull of gravity”. When the field capacity of a particular soil is exceeded, water begins to flow downward. One last point to consider is that available water to the plant is only the water held in the soil at tensions between field capacity and wilt point, or realistically, the water held at tensions less than wilt point. The characteristic annual cycle of changes in soil moisture content deserves study because it leads to a better understanding of the principles of ground-water movement, surface runoff, and various aspects of the sculpturing of the land by running water.

154 154 Hubungan Air – Tanah – dan Tanaman Suatu sistem yang kontinum. Jelaskan pendapat Saudara mengenai hal ini (sebanyak 250 kata)

155 155 Air tanah pada berbagai kondisi kelengasan (kadar air)

156 156 Struktur Tanaman Tanaman menyerap air dari dalam tanah melalui akar- akarnya, kemudian diangkut ke daun untuk fotosintesis Jelaskan bagaimana akar tanaman menyerap air dari dalam tanah? dengan 250 kata

157 157 AKAR TANAMAN Often roots are overlooked, probably because they are less visible than the rest of the plant. However, it's important to understand plant root systems because they have a pronounced effect on a plant's size and vigor, method of propagation, adaptation to soil types, and response to cultural practices and irrigation. Roots typically originate from the lower portion of a plant or cutting. They have a root cap, but lack nodes and never bear leaves or flowers directly. Their principal functions are to absorb nutrients and moisture, anchor the plant in the soil, support the stem, and store food. In some plants, they can be used for propagation.

158 158 Struktur akar tanaman

159 159 Penampang melintang akar tanaman

160 160 Pengolahan tanah sawah memerlukan banyak air Pengolahan tanah sawah untuk menanam padi memerlukan banyak air. Mengapa demikian? Jelaskan dengan 250 kata

161 161 Penanaman bibit padi juga memerlukan banyak air

162 162 How Rice Is Grown The two major types of rice, indica (long-grain) and japonica (medium- and short-grain) do well in different environments. Long-grain indica rices (basmati and jasmine, for example) do well in hot, equatorial climates. Medium- and short-grain japonica rices grow well in temperate and mountainous regions. Rice cultivation has traditionally been well-suited to countries and regions with low labor costs and high rainfall. Without modern technology, rice is very labor-intensive to cultivate; either way it requires plenty of water for irrigation.

163 163 Kebutuhan air tanaman : "kedalaman (jumlah) air yang diperlukan untuk memenuhi kehilangan air melalui evapotranspirasi (ETtanaman) tanaman yang sehat, tumbuh pada sebidang lahan yang luas dengan kondisi tanah yang tidak mempun­yai kendala (kendala lengas tanah dan kesuburan tanah) dan mencapai potensi produksi penuh pada kondisi lingkungan tumbuh tertentu".

164 164 AIR TANAMAN Water is essential in the plant environment for a number of reasons. Water transports minerals through the soil to the roots where they are absorbed by the plant. Water is also the principal medium for the chemical and biochemical processes that support plant metabolism. Under pressure within plant cells, water provides physical support for plants. It also acts as a solvent for dissolved sugars and minerals transported throughout the plant. In addition, evaporation within intercellular spaces provides the cooling mechanism that allows plants to maintain the favorable temperatures necessary for metabolic processes.

165 165 HUBUNGAN TANAH-AIR The role of soil in the soil-plant-atmosphere continuum is unique. It has been demonstrated that soil is not essential for plant growth and indeed plants can be grown hydroponically (in a liquid culture). However, usually plants are grown in the soil and soil properties directly affect the availability of water and nutrients to plants. Soil water affects plant growth directly through its controlling effect on plant water status and indirectly through its effect on aeration, temperature, and nutrient transport, uptake and transformation. The understanding of these properties is helpful in good irrigation design and management.

166 166 Komponen Neraca Air pada Suatu Lahan Air Irigasi

167 167 Hubungan antara Kadar Air Tanah dan Pertumbuhan Tanaman Growth of most agricultural crops is favored by a soil water content that is high enough to encourage crop growth and development, but not so high that aeration becomes restrictive. If soil water is plant- extracted to levels approaching the PWP, water is held so tenaciously by the soil that plants can no longer obtain sufficient water to meet the potential for transpiration. Transpiration is restricted and yield losses take place.

168 168 IRRIGATION A. Definition: Supplying water to plants in an artificial manner. (39% of all freshwater in the US is used to irrigate crops) 1. Ancient practice – first irrigation used ditches to divert rivers and streams. 2. California agriculture relies on irrigation. a. Mediterranean climate b. Crop diversification c. Economics

169 169 Pola pergiliran tanaman berdasarkan curah hujan Jelaskan mengapa demikian? Dengan 250 kata

170 170 Soil Water and Groundwater (1)


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