Soil test crop response studies on coleus (Solenostemon rotundifolius Poir J.K Morton) in the laterite soils of Kerala

Abstract

Investigation entitled" Soil Test crop response studies on coleus in laterite soil of Kerala" consisting of two experiments namely fertility gradient experiment and STCR experiment was conducted during 2002 in the farm attached to the College of Horticulture, Vellan ikkara. Objective of the study was to develop soil test based balanced fertilizer recommendation for specific yield targets of coleus in laterite soils of kerala and provide a basis for fertilizer recommendation for maximum and economic tuber yield at varying soil test values. The fertility gradient experiment was conducted to create desired gradient in soil fertility in one and the same field by applying graded doses ofN, P, and K fertilizers and raising fodder maize var.Co.l. After development of fertility gradient, the STCR experiment was conducted in the same field with the test crop, coleus variety Nidhi.The treatment structure consisted of four levels of N (0,20,40, and 80 kg ha'), three levels of P20S (0,45 and 90 kg ha-I) and five levels of K (0, 25, 50, 100, 200 kg ha-I) along with three levels of FYM (0, 7.5 and 15 t ha-I) The nutrient requirement of coleus, variety Nidhi were estimated to be 9.15,1.38 and16.38 kg ha-I N, P20S and K20 respectively to produce one tonne of tuber. The soil efficiencies worked out as 21,46.85 and 40.85 per cent for N, . , P205 and K20 respectively for coleus in laterite soil. The contribution of nutrients from the fertilizers for coleus was calculated as 61.6,9.57 and 56.60 per cent for N, P205 and K20 respectively. From the above basic data, fertilizer prescription equation for specific yield targets of coleus variety Nidhi in the laterite soil were derived as follows, Without rVM FN =14.85T-0.34SN FP205 =14.42T-l J.21SP FK20 =28.98T-0.87SK FN, F P20S, F K20 - Fertilizer N, P20S and K20 respectively T - Target yield of tuber in t ha-I SN, SP, SK - Soil available N, P and K in' kg ha-I respectively . WithFYM FN 14.85 T - 0.34 SN - 0.34 ON 14.42 T - 11.21 SP - 3.25 OP F K20 = 28.93 T - 0.87 SK - 1.22 OK Where, ON, OP and OK are quantities ofN, P and K supplied through organic manure in kg ha" Multiple regression models calibrated with yield as dependent variable and STVs for available N, P and K and applied nutrients as independent variables had 67.4 per cent predictability. Among the three fertilizer nutrients, FN only showed the normal type (+, -, -) of response. The fertilizer adjustment equation fur v,!rying levels of soil available N for maximum tuber yield (t ha") of coleus in laterite soil was derived as FN= 168 SN, where FN is fertilizer N (kg ha"): SN is available N (kg ha-I) is soil. The behavior of applied p and K was found to produce responses other than normal and hence optimization coula not be done for fertilizer P and K at varying soil test values. Simple correlations coefficient was worked out for Nutrient uptake, soil available nutrients, applied nutrients with yield of coleus. Available nutrients -! showed higher positive correlation" than that of allied nutrients. The uptake of nutrients (N, P and K) also significantly correlated with yield of coleus. This study is useful to adjust fertilizer doses based on the specific objective and available resources of coleus farmers of the state.