PENYERAPAN UNSUR HARA OLEH AKAR TUMBUHAN Penyunting: Soemarno PM-PSLP PPSUB MALANG-2011

PENYERAPAN UNSUR HARA OLEH AKAR TUMBUHAN Cetakan : I – Malang Program Pascasarjana, Universitas Brawijaya, Malang Viii : 60 hlm : 20 cm x 25 cm Penyunting: Soemarno Tata Letak : Grafis & Desain Sampul : Soemarno Hak Cipta pada penulis. Cetakan Pertama Agustus 2011 Penerbit : PPSUB Jl. Mayjen MT. Haryono 165, Malang Tel. 0341-571260

KATA PENGANTAR Dengan memanjatkan puji syukur kehadirat Allah swt, atas segala karunia-Nya, penyusunan buku Bahan Kajian mengenai “PENYERAPAN UNSUR HARA OLEH AKAR TUMBUHAN” ini dapat diselesaikan. Buku memori ini menyajikan data, informasi dan konsep-konsep tentang “Pengelolaan Hara Tanaman” yang relevan dengan filosofi “Sustainable Crop Management”. Data dan infromasi yang disajikan dalam tulisan ini dihimpun dari beragam pengalaman dan dari berbagai sumber yang dianggap valid, termasuk hasil-hasil pengkajian yang tersebar di berbagai referensi . Dengan telah selesainya Buku ini, perkenankanlah kami mengucapkan terima kasih yang sebesar-besarnya kepada semua pihak yang telah membantu, terutama kepada rekan-rekan sejawat yang telah secara tulus ikhlas memberikan informasi yang ada kaitannya dengan penyusunan buku ini. Semoga informasi yang terkandung dalam buku ini dapat dimanfaatkan sebagaimana mestinya bagi pengembangan pembelajaran pada program pascasarjana di Universitas Brawijaya. Malang, Agustus 2011 Penyunting Soemarno

DAFTAR ISI Pendahuluan …….. 1 Unsur Hara Tanaman …….. 2 Sistem Perakaran Tanaman ….. 7 Penyerapan air dari tanah ….. 10 Penyerapan Hara Tanaman ….. 19 Mekanisme Penyediaan Unsur Hara ….. 22 Mekanisme Penyerapan Hara ….. 29 Mikorizha ………………….. 34 Serapan Hara Tanaman (Nutrient Uptake) ……… 41 Hubungan Kandungan N dengan Hasil …….. 47 Efisiensi Pupuk N pada Padi …….. 48

KETERSEDIAAN UNSUR HARA

ZONE UJUNG AKAR Plants absorb water through the entire surface - roots, stems and leaves. However, mainly the water is absorbed by roots. The area of young roots where most absorption takes place is the root hair zone. The root hairs are delicate structures which get continuously replaced by new ones at an average rate of 100 millions per day. The root hairs lack cuticle and provide a large surface area. They are extensions of the epidermal cells. They have sticky walls by which they adhere tightly to soil particles. As the root hairs are extremely thin and large in number, they provide enormous surface area for absorption. They take in water from the intervening spaces mainly by osmosis.

PERTUKARAN ION Ion exchange theory Both cations and anions have a tendency to get adsorbed on the surfaces of the cell walls, and exchange with ions present in the soil solution. This process of exchange between the adsorbed ions and ions in solution is known as ion exchange.

Biogeochemical cycle of mineral nutrients in agricultural ecosystems SIKLUS UNSUR HARA Biogeochemical cycle of mineral nutrients in agricultural ecosystems

Types of roots: . Seminal root - from a seed Adventitious root - from a stem First order lateral root - from a seminal or adventitious root Second order laterals, etc. - from first order laterals, which in turn produce third order laterals, and so on . . . Feeder roots - fine, relatively short-lived roots that acquire nutrients and water in the topsoil Primary roots - from primary growth by the apical meristem Secondary roots - mature, thicker "woody" roots with bark and additional vascular tissue Coarse roots - may live for a long time and have roles in transport and mechanical support

Iron Uptake and Translocation KETERSEDIAAN UNSUR HARA  Iron Uptake and Translocation Iron is primarily taken up by plants as the ferrous (Fe2+) iron. However, because most agricultural soils contain iron in the ferric (Fe3+) form, plant must somehow first solubilise the Fe3+ and then reduce it to Fe2+ so that it can pass through the root hair plasma membrane (plasmalemma).  In dicotyledoneous species (ie most crops), iron uptake is an active, energy, requiring process.

THE UPTAKE OF WATER FROM THE SOIL TO THE LEAVES The cytoplasm of root hair cells is usually hypertonic to the surrounding soil water. Hence, water enters the root hair cells by osmosis. The root hair cells are now hypotonic to the adjacent root cortex cells. Water then diffuses into these cells until it reaches the cortex region. Water flows through the parenchyma cells (cortex) until it reaches the endodermis through either the apoplastic pathway or the symplastic pathway . The Casparian strips (impermeable to water) prevent water from moving through the cell wall of the endodermal cells. The water concentration gradient which exists across the cortex creates a transpiration pull to direct water into the xylem vessels. Water finally reaches the mesophyll cells in the leaves where it will be lost through the stomata into the surroundings

Ion homeostasis: plants feel better with proper control The model plant species, thale cress (Arabidopsis thaliana, right) and rice (Oryza sativa, left), are displayed as a chimera. (A) OsHKT2;1 functions as a transporter for Na+ uptake. (B) QSO2, a flavoprotein quiescin sulphydryl oxidase, is a new component in ion homeostasis at the root symplast–xylem interface. (C) Downregulation of OST2/AHA1 H+-ATPase activity is a prerequisite for ABA-induced stomatal closure. ABA, abscisic acid; OST2/AHA, OPEN STOMATA 2. http://www.nature.com/embor/journal/v8/n8/fig_tab/7401040_F1.html