Abstract

                                A unique methodology of two-directional creation of fertility gradient with chemical fertilizers in one direction and organic manures in the opposite direction of the experimental field (60 x 40 m) was devised by Dr. B. Ramamoorthy for soil test - crop response (STCR) correlation research. This unique methodology has been adopted in the All India Coordinated Soil Test - Crop Response Correlation project of the Indian Council of Agricultural Research (ICAR) for over 4 decades at 25 Cooperating centres in the country at present on a range of soils and crops and validated through hundreds of demonstration trials in farmers’ fields. The “Law of optimum” propounded by Ramamoorthy and Velayutham (2011) as the unifying concept in plant nutrition, is an experimentally proven concept for soil test based major plant nutrients (N, P and K) applications to crops for desired targeted yields, based on the derivation of three parameters from standard soil test - crop response factorial field experiments, namely 1) per cent contribution (efficiency) from the soil available nutrients (Cs) as estimated by chemical soil tests in soil testing laboratory, 2) per cent contribution of nutrients from added fertilisers (Cf) and manures (Cm) and 3) nutrient requirement of the crop (kg/ton) as estimated from yield and plant nutrient uptake data from STCR field experiments. The principles underlying the “Law of minimum”, “Law of diminishing returns” and “Law of the maximum” governing plant nutrition are not only embedded in the “Law of optimum” but also provides a basis for “Balanced fertilisation”. The scope for extensive use of the “Targeted yield” approach on the basis of derivation of the efficiencies of soil and fertilizer nutrients is discussed.

Key words : Law of Optimum, STCR, Balanced fertilization, Soil health