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V. NAGARJUNA* AND D. MUTHUMANICKAM
Department of Soil Science and Agril. Chemistry, Tamil Nadu Agricultural University, Coimbatore, India
A mathematical model, based on the first order rate equation derived to determine the critical nutrient level in soil and plants. The model has been used to determine the critical level by characterizing plant growth as a function of nutrient concen-tration in plant tissues or content of the soil. A field experiments was conducted to establish critical limit to DTPA extractable Cu with graded levels of Cu (0, 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0 kg Cu ha-1) as adopted during 2012-13 for onion growing soils in Tamil Nadu. The curve linear equation was developed based on the Bray’s percentage yield (Y) and soil available Cu (x). The extrapo-lated Bray’s per cent yield values at varying definite interval (0.1 mg kg-1) of DTPA extractable Cu in the soil were determined from the equation. The estimated Bray’s per cent yield was started to decline after the increasing the DTPA level of 3.00 mg kg-1 and upto this extrapolated Bray’s percentage yield was considered for estimation of ã. The critical concentration of available Cu in soil worked out to be 0.625 mg kg-1 below which appreciable responses to Cu application was expectable.
DTPA extractable Cu, Mitscherlich method, Onion growing soils, Onion leaf, Plant growth model.