SOIL BASED PLANT NUTRIENT MANAGEMENT PLAN FOR AGRO-ECOSYSTEMS OF KERALA

SOIL ACIDIFICATION Acid soil infertility is a major limitation to crop production on highly weathered and leached soils of tropics. The problem of acidity has aggravated to extreme levels in soils of crop lands due to heavy inputs of acid producing fertilizers (ammonia, urea, phosphates). It is evident that the practice of liming to ameliorate soil acidity is either non-existent or ineffective.

Strong and extreme soil acidity seriously impairs plant availability of nutrients and microbial process responsible for organic matter decomposition and nitrogen mineralisation and fixation. In strongly acid soils (pH < 5.5) Aluminium ion concentration in soil solution is high enough to seriously affect plant roots. Bacteria based bio-fertilizers are ineffective in strongly acid soils.

Most plant nutrients are available and microbial activity is favoured within a pH range of 6.0 to 7.5. Acid soils are stressed environments for microorganisms and beneficial species are normally absent at pH values below 4.5. Pathogenic fungi thrive best in acid soils, causing many diseases.

ACTION Regular application of liming materials to raise the pH to safe levels (pH >5.5); say around 600 kg/ha annually. Make available cheap liming materials (burnt lime, finely powdered limestone, dolomite, slags etc.)

AVAILABLE NITROGEN ACTION Though Kerala soils are rich in organic matter, mineralisation of OM and yield of nitrogen is constrained by soil acidity. Correction of soil acidity can lead to better microbial activity and consequently to better utilization of applied nitrogen fertilizer and possibly reduction in their use. ACTION Restrict the use of nitrogenous fertilizers to recommend dose and lime the soils.

AVAILABLE PHOSPHORUS Heavy inputs of phosphatic fertilizers (Factamphos, DAP, bone meal etc.) lead to build up of very high levels of the nutrient in soils. IMPLICATIONS Impairs nutrient balance Affects micronutrient absorption by plants even when they are present in adequate levels in soils Possible leaching of phosphorus into water bodies, gradual build up in sediments and eventual eutrophication of water bodies. ACTION Immediate reduction of P fertilizers to the tune of 50 per cent (or through soil test) “Every kilogram of P costs Rs.100/- and its reduction alone can provide money to meet the cost of lime”.

AVAILABLE POTASSIUM ACTION Absence of K build up is a consequence of low retention by the highly weathered soils and consequent leaching loss under high rainfall. ACTION Application of potassium fertilizers in as many splits as possible.

AVAILABLE CALCIUM Substantial areas under crop production systems are deficient in secondary plant nutrient Calcium. IMPLICATION Seriously impair plant growth and productivity by affecting absorption of other nutrients and through elements direct effect on cellular functions. ACTION Regular application of lime.

AVAILABLE MAGNESIUM ACTION Serious deficiency in soils Application of a quarter of the lime requirement with dolomite or application of 80 kg magnesium sulphate per hectare

Thirty per cent of the soil samples tested deficient for sulpur. AVAILABLE SULPHUR Thirty per cent of the soil samples tested deficient for sulpur. Application of magnesium sulphate shall ensure the availability of the nutrient.

AVAILABLE ZINC Plant available zinc was adequate in most samples. However, when soil phosphorus levels are very high, zinc absorption by plants is impaired. ACTION Application of zinc as foliar spray (0.2 % solution of zinc sulphate)

AVAILABLE COPPER Soils were found to be adequate in available copper

Widespread deficiency AVAILABLE BORON Widespread deficiency ACTION Apply borax as foliar spray (0.1 % solution of Borax: two times, first 30 days after planting and second at flower initiation) Soil application @ 10 kg borax per hectare is also recommended. However, in the light of very high levels of phosphorus in soils, soil application may not ensure plant uptake of boron.

Soils of Kerala suffer from very unfavourable reaction: strongly to extremely acid suffer from multi-nutrient deficiencies: Calcium, magnesium and boron available phosphorus levels high enough to impair plant absorption of zinc and boron.

SIMPLE SOLUTIONS TO A COMPLEX WORLD Application of lime/dolomite to raise the pH above 5.5: annual application @600 kg/ha. Reduction in use of phosphatic fertilizers to the tune of 50% of the recommended dose. Application of Magnesium sulphate @80 kg/ha. Application zinc and boron as foliar spray.

RICE YIELDS CAN BE IMPROVED! Rice yield obtained in a field experiment at Kizhakkancherry, Palakkad by amelioration of soil acidity and soil test based input of plant nutrients (major, secondary and micro-, except Boron): 7 tonnes/ha Yield realised with additional application of Borax @5 kg/ha: 8 tonnes/ha Best farmer yield in the local area: 4 tonnes/ha Santhosh, C. 2013. Chemistry and Transformation of Boron in Soils of Kerala, Ph.D thesis, Kerala Agricultural University, Thrissur, 182 p.