Background: The Fe toxicity is a perpetual problem of low lying poorly drained acid soils. It also affects the solubility and availability of most of the plant nutrients, by reducing toxic concentrations of iron, aluminum and manganese. To overcome these constraint, application of lime is inevitable but high cost of liming materials necessitate the use of low-cost, internally sourced, environmentally friendly and adoptable organic sources. In present study rice husk ash was used as a soil ameliorant in lieu of liming. Methods: A field experiment was conducted at Rice Research Station, Moncompu during 2017-2018 with nine treatments replicated thrice in RBD using rice variety Uma. A customized formulation with composition of K (8.9 %), Mg (3.2 %), Ca (3.7 %), Zn (2.1 %), Mn (0.23 %), B (3.5 %) and Cu (0.96 %) was developed based on the available nutrient status of the region and crop requirement and used for supplementary foliar nutrition. Result: It was found that treatment comprising of Soil test based RDF + Rice husk ash @ lime (based on pH) + foliar spray of 0.5 % solution of customized formulation @ 5 kg ha-1 as foliar application of 0.5 % solution in two splits at maximum tillering and panicle initiation stage was the best treatment in increasing yield by 23 % compared to recommended dose of lime and fertilizer application and B:C ratio increased from 1.53 to 1.91. Effect of rice husk ash in ameliorating soil acidity was found to be on par with application of lime based on pH in acid sulphate soils of Kuttanad zone.

A study was conducted in the typic ustipsamments of Kerala in India to assess the available micronutrient status of the region to develop a multi micronutrient mixture for balanced crop nutrition and to evaluate the effect of multi micronutrient mixture on growth and yield of okra. Chemical analysis of 200 georeferenced soil samples from the region revealed deficiencies of boron (77%), zinc (66%) and copper (53%). A customized micronutrient mixture with a composition of Zn (9.5%) + B (2.6%) +Cu (1.2%) +Mg (2.4%) +N (0.46%) @ 20kg ha -1 was developed based on the available micronutrient status of the region and crop requirement. Effect of micronutrient mixture was assessed in field experiments using okra variety Varsha Uphar as the test crop with nine treatments in three replications. Growth, yield and quality of okra increased significantly due to multi micronutrient mixture. Application of soil test based NPK and secondary nutrients + foliar application of 0.5 per cent solution of computed dose of micronutrient mixture @ 5 kg ha -1 in two splits at 15 DAS and 30DAS (T 7 ) yielded significantly higher (11.3 t ha -1 ) with a B: C ratio of 3.02. Application of micronutrient mixtures customized for soil and crop ensures increased yield and sustain soil health.

Kuttanad is a unique wetland ecosystem lying 0.6 to 2.2 m below the mean sea level. The soil of Kuttanad is characterised by extreme acidity and accumulation of salts and the cultivation of paddy in this area faces problems due to water logging, acidity and metal toxicities of iron and aluminium. Iron toxicity can cause nutrient disorders and deficiencies of several elements like P, K, Ca, Mg, Mn, and Zn and primarily affects the production of lowland rice. Management strategies such as liming and additional multi nutrient supply (P, K, Mg, Zn, Cu and B) have proven to enhance the rice productivity of soils prone to Fe toxicity by correcting the multi nutrient deficiencies. Therefore, this study was undertaken with the objectives to evaluate the effect of soil amelioration with rice husk ash in abating iron toxicity and supplementary foliar application of a customized nutrient formulation in increasing rice yield in the low lands of Kuttanad. A customized nutrient formulation was developed based on the available nutrient status of the region and crop requirement and applied as foliar spray of 0.5 per cent solution in two splits at maximum tillering and panicle initiation stage. The field experiment was done at Rice Research Station, Moncompu using rice variety Uma. The experiment was laid out in RBD with nine treatments and three replications. The results indicated that use of rice husk ash as soil ameliorant along with soil test based RDF and supplementary foliar nutrition improved rice yield in Kuttanad and reduced the nutritional constraints due to iron toxicity.

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