Kesuburan tanah Lanjutan

Kesuburan tanah Lanjutan Sub Topik: Besi (Fe) dan Seg (Zn) Oleh: Dr. Ir. Hamidah Hanum, MP Sekolah Pascasarjana USU

UNSUR MIKRO TANAH Fungsi fisiologis : dlm reaksi enzimatik Dlm tanaman : < 100 mg/g Diserap tanaman dlm btk ion dan senyawa kompleks organik alami/sintetik Bentuk dlm tnh: ion dlm larutan tnh, senyawa garam (mineral primer dan sekunder), kompleks dgn senyawa organik, bentuk organik dlm biomass mikroba Sumber : litosfer, batuan, mineral, pupuk, bahan organik Kadar dlm tnh : rendah Fe : 104 – 105 ppm Cl : 50 ppm Zn : 10 – 300 ppm Mo : 10 ppm Mn : 200 -300 ppm B : 7 – 10 ppm Cu : 10-80 ppm

Hubungan antara bentuk hara mikro dlm tnh Nutrient uptake by plants • Serapan tanaman • Eksudat akar • Adsorpsi • Desorpsi • Presipitasi • Pelarutan • Immobilisasi • Mineralisasi 1 2 Organic matter And Microorganism Soil Solution Exchange And Surface adsorption 3 4 8 7 6 5 Solid phase Minerals and precipitates

Siklus Unsur Mikro dlm Tanah • Bahan organik mrpkn sbr utama u.mikro tnh • Pelarutan mineral primer dan sekunder melepaskan P utk tan,mikroba, dan kompleks dgn BOT • Bentuk yg teradsorpsi kecil oerannya Plant Plant & Animal residues Plant uptake Primary And Secondary Zn minerals SOIL ORGANIC MATTER Dissolution Soil Solution Zn2+ Mineralization Precipitation Immobilization Adsorption Adsorbed or Labile Zn2+ Desorption

PerananFe • Fe deficiency symptoms and effects on growth • Interveinal yellowing and chlorosis of emerging leaves. • Whole leaves become chlorotic and then very pale. • The entire plant becomes chlorotic and dies if Fe deficiency is very severe. • Fe deficiency is very important on dryland soils but often disappears one month after planting. • Fe deficiency results in decreased dry matter production, reduced chlorophyll concentration in leaves, and reduced activity of enzymes involved in sugar metabolism. Function and mobility of Fe • Fe-utake as Fe2+ and Fe3+ • Iron is required for electron transport in photosynthesis and is a constituent of iron porphyrins and ferredoxins, both of which are essential components in the light phase of photosynthesis. • Fe is an important electron acceptor in redox reactions and an activator for several enzymes (e.g., catalase, succinic dehydrogenase, and aconitase), but inhibits K absorption. • On alkaline soils, immobilization of Fe in plant roots occurs because of Fe precipitation. Because Fe is not mobile within rice plants, young leaves are affected first.

Kadar Fe-sufficient : 50-250 ppm Kadar Fe-defisiensi : < 50 ppm Kadar Fe-toxic : > 300 ppm

Fe-Mineral Fe menyusun 5% kerak bumi, element terbanyak ke-4 Fe tnh ditemukan dlm mineral primer, liat, oxida, hidrousoksida Mineral Fe: olivin [(Mg,Fe)2SiO4], siderit (FeCO3), hematit (Fe2O3), magnetit (Fe3O4), limonit (Fe-OOH) Fe tnh yg mengontrol Fe3+ -larutan tanh : Presipitat Fe(OH)3 amorf Fe -tanah • Fe-Larutan tnh Fe(OH)3 + 3H+ Fe3+ + 3H2O Ca2+ Mg2+ Fe3+ Zn2+ Fe2+ Cu2+ Mn2+ Al3+ Fe2+ Fe3+ Defisiensi Fe pd tnh berpH tinggi,tnh berkapur >> tnh masam

Dinamika kelat unsur mikro • Selama serapan aktif, konsentrasi kelat dlm bulk soil > di permk. akar shg kelat berdifusi ke permukaan akar • Kelat terdisosiasi shg u.mikro dilepaskan kemudia kelat kembali ke bulk soil • Khelat mengikat logam/u. mikro lain di bulk soil Chelat ≈ claw : senyawa organik larut (as.sitrat, as.oksalat …) yg berikatan dgn logam seperti Fe, Zn, Cu, Mn shg kelarutan & ketersediaan unsur tsb meningkat krn  transport hara logam

pH dan Bicarbonat . Bicarbonat terbtk pd tnh berkapur. pH yg tinggi (> 7) berkaitan dgn akumulasi HCO3- CaCO3 + CO2 + H2O Ca2+ + 2HCO3- 2. Air berlebih dan aerase yg jelek Tanah yg kompak, bertekstur berat, berkapur berpotensi defisiensi Fe. 3. Bahan organik Aplikasi bahan organik pd tanah berdrainase baik meningkatkan ketersediaan Fe karena: Tersedianya agen pengkelat Meningkatnya struktur tnh bertekstur halus shg aerase menjadi baik 4. Interaksi dgn hara lain Defisiensi Cu dpt disebabkan kelebihan Cu, Mn, Zn dan Mo, interaksi Fe-P. Jk tanaman menyerap NH4+ mk kelarutan dan ketersediaan Fe meningkat, krn terbtknya kondisi masam Jk tanaman menyerap NO3- mk terjadi stress Fe, krn NO3- mengganti HCO3- mk pH rhizosfer meningkat shg kelarutan Fe menurun 5. Faktor tanaman Setiap tanaman berbeda (faktor genetik) kemampuannya dlm uptake dan translokasi Fe Mekanisme toleransi dan adaptasi Fe : Ekskresi H+ dari akar Ekskresi senyawa kelat dari akar Tingkat reduksi meningkat di akar Meningkatnya anion organik as. Sitrat pd tudung akar. Transfor Fe dari akar ke bagian atas tan. Kurangnya akumulasi P di akar dan tajuk atau kadaP yg sgt tinggi pd media tumbuh Faktor yg mempengaruhi ketersediaan Fe

Suppression: Mg K, Ca, Mn Ca  K, Mg K N, Mg, Ca, B N Fe, Cu NH4-N  K, Ca, Mg NO3-N P, S P  Zn, Ca S  B, Mo, Fe Cu Zn Zn  Fe B, Cu, Mn, Fe compete Enhancement: NO3-N  Ca P  Mo K  Fe S  N B  Ca Competition between nutrients for uptake: IOWA STATE UNIVERSITY University Extension

Causes of Fe deficiency Preventive strategies for Fe management • Low concentration of soluble Fe2+ in upland soils. • Inadequate soil reduction under submerged conditions (e.g., low organic matter status soils). • High pH of alkaline or calcareous soils following submergence (i.e., decreased solubility and uptake of Fe because of large bicarbonate concentration). • Wide P:Fe ratio in the soil (i.e., Fe bound in Fe phosphates, possibly because of excess application of P fertilizer). • Excessive concentrations of Mn, Cu, Zn, Mo, Ni, and Al. • In upland soils, cultivars with low potential for excretion of organic acids to solubilize Fe. • Increased rhizosphere pH after the application of large amounts of NO3-N fertilizer (rare case and is relevant for upland crops only). Varieties: Screen and breed for tolerance for low soil Fe availability. Grow Fe-efficient cultivars. Selection of high-Fe rice cultivars is in progress to improve Fe nutrition in children and pregnant women in developing countries. Soil management: Apply organic matter (e.g., crop residues, manure). Apply waste materials from mining and other industrial operations provided that they do not contain other pollutants at toxic concentrations. Fertilizer management: Use acidifying fertilizers (e.g., ammonium sulfate instead of urea) on high-pH soils. Use fertilizers containing Fe as a trace element

Treatment of Fe deficiency Fe deficiency is the most difficult and expensive micronutrient deficiency to correct. Soil applications of inorganic Fe sources are often ineffective in controlling Fe deficiency, except when application rates are large. • Fe deficiency should be treated as follows: - Apply solid FeSO4 (about 30 kg Fe ha-1) next to rice rows or broadcast (larger amount needed). - Foliar applications of FeSO4 (2–3% solution) or Fe chelates. Because of low Fe mobility in the plant, two or three repeated applications at 2-wk intervals starting at tillering are necessary to support new plant growth.

Function and mobility Plant roots absorbs Zn as Zn2+ and asa componento synthetic and natural organic complexes. Cytochrome and nucleotide synthesis Auxin metabolism Chlorophyll production Enzyme activation Membrane integrity Zn accumulates in roots and can be translocated from roots to developing plant parts. Because little retranslocation of Zn occurs within the leaf canopy, particularly in N-deficient plants, Zn deficiency symptoms are more common on young or middle-aged leaves. Description of Zn deficiency symptoms and effects on growth Dusty brown spots on upper leaves of stunted plants starting 2–4 wk after planting. Symptoms appear between two to four weeks after transplanting, with uneven plant growth and patches of poorly established hills in the field, but the crop may recover without intervention. Under severe Zn deficiency, tillering decreases and can stop completely and time to crop maturity increases. Zn deficiency can also increase spikelet sterility in rice. Midribs, particularly near the leaf base of younger leaves, become chlorotic and leaves lose turgor and turn brown as brown blotches and streaks appear on lower leaves, enlarge, and coalesce. A white line sometimes appears along the leaf midrib. Plant growth is stunted and leaf blade size is reduced. In Japan, Zn deficiency is the cause of the "Akagare Type II" disorder in rice PerananZn

Mineral Zn Zn di litosfer sekitar 80 ppm, di tnh 10-300 ppm dgn rata-rata 50 ppm Mineral-Zn: franklinite (ZnFe2O4), smithsonite(ZnCO3), Willemit (Zn2SiO4) Zn – larutan tanah Zn –larutan tanah: 2-70 ppb Jk pH > 7.7 : ZnOH+ Kelarutan Zn menurun 100x per kenaikan 1 unit pH Soil-Zn + 2H+ Zn2+ Zn-larutan diserap tanaman mlli difusi dgn bantuan kelat dari eksudat akar/dekomposisi residu organik

1. pH . Ketersediaan Zn2+ menurun dgn meningkatnya pH krn terbentuk Zn-amorf yg tdk larut ZnFe2O4 dan atau Zn2SiO4 Pengapuran pd tnh masam yg rendah Zn akan menurunkan serapan Zn krn: Efek peningkatan pH Adsorpsi Zn pd CaCO3 Adsorpsi Zn2+ oleh mineral liat/Al-Fe oksida/Bahan organik 2. Adsorpsi Zn Adsorpsi Zn pada permukaan oksida terjadi mlli ikatan spesifik atau mlli pertukaran kation Adsorpsi Zn pada magnesit (MgCO3) lebih kuat dari dolomit dan kalsit Faktor-faktor yg mempengaruhi ketersediaan Zn

4. Interaksi dgn hara lain Ketersediaan P yg tinggi menyebabkan defisiensi Zn karena terjadi reaksi P-Zn membtk Zn3(PO4)2 4H2O Mikoriza meningkatkan serapan u.mikro 5. Penggenangan Jk tnh masam digenangi ketersediaan hara meningkat kecuali Zn Jk tnh berkapur digenangi meningkatkan ketersediaan Zn 6. Kondisi Iklim Defisiensi Zn sering terjadi pd musim hujan dan hilang pd musim panas. Jk temperatur tnh meningkat mk ketersediaan Zn meningkat krn meningkatnya kelarutan dan difusi Zn2+ 7. Faktor tanaman Terdapat perbedaan toleransi tanaman thdp ketersediaan Zn yg rendah kn perbedaan kemampuan setiap kultivar dlm menyerap Zn, translokasi dan penggunaan Zn, perbedaan akumulasi hara yng berinteraksi dgn Zn, perbedaan eksploitasi akar terhadap Zn-tanah Faktor yg mempengaruhi ketersediaan Zn

Causes of Zn deficiency • Formation of Zn-phosphates following large applications of P fertilizer. High P content in irrigation water (only in areas with polluted water). • Formation of complexes between Zn and organic matter in soils with high pH and high organic matter content or because of large applications of organic manures and crop residues. • Precipitation of Zn as ZnS when pH decreases in alkaline soil following flooding. • Excessive liming. • Wide Mg:Ca ratio (i.e., >1) and adsorption of Zn by CaCO3 and MgCO3. Excess Mg in soils derived from ultrabasic rocks. • Small amount of available Zn in the soil. • Planted varieties are susceptible to Zn deficiency • High pH (close to 7 or alkaline under anaerobic conditions). Solubility of Zn decreases by two orders of magnitude for each unit increase in pH. Zn is precipitated as sparingly soluble Zn(OH)2 when pH increases in acid soil following flooding. • High HCO3- concentration because of reducing conditions in calcareous soils with high organic matter content or because of large concentrations of HCO3- in irrigation water. • Depressed Zn uptake because of an increase in Fe, Ca, Mg, Cu, Mn, and P after flooding.

Treatment of Zn deficiency Preventive strategies for Zn management • Zn deficiencies are most effectively corrected by soil Zn application. Surface application is more effective than soil incorporation on high pH soils. • If Zn deficiency symptoms are observed in the field, immediately apply 10–25 kg ha-1 ZnSO4.7 H2O. Uptake of ZnSO4 is more efficient when broadcast over the soil surface (compared with incorporated) particularly in direct-sown rice. To facilitate more homogeneous application, mix the Zn sulfate (25%) with sand (75%). • Apply 0.5–1.5 kg Zn ha-1 as a foliar spray (e.g., a 0.5% ZnSO4 solution at about 200 L water ha-1) for emergency treatment of Zn deficiency in growing plants. Start at tillering (25–30 DAT), two or three repeated applications at intervals of 10–14 d may be necessary. Zn chelates (e.g., Zn-EDTA) can be used for foliar application, Varieties: Screen and breed for tolerance for low soil Fe availability. Grow Fe-efficient cultivars. Selection of high-Fe rice cultivars is in progress to improve Fe nutrition in children and pregnant women in developing countries. Soil management: Apply organic matter (e.g., crop residues, manure). Apply waste materials from mining and other industrial operations provided that they do not contain other pollutants at toxic concentrations. Fertilizer management: Use acidifying fertilizers (e.g., ammonium sulfate instead of urea) on high-pH soils. Use fertilizers containing Fe as a trace element

Kesuburan tanah Lanjutan