Critical compositional nutrient indexes for sweet corn at early growth stage

It would be instrumental to define nutrient norms from small-size crop data bases at the V4-V6 corn (Zea mays L.) growth stage for in-season N fertiliz er recommendations. Our objective was to derive Compositional Nutrient Diag nosis (CND) and Diagnosis and Recommendation Integrated System (DRIS) nutri ent index ranges from a sweet corn database and to relate nutrient concentr ation and indexes to ear yield. A sweet corn database of 240 observations o n commercial yields and N, P, K, Ca, and Mg concentrations in 30-cm high co rn seedlings were divided at random between survey (n = 200) and validation (n = 40) subpopulations. The proportion of low-yield specimens in the surv ey population was computed at inflection point of a cubic cumulative varian ce ratio function and was associated with a chi-square value (CND r(2)) of 3.9 that was confirmed in the validation subpopulation. Critical CND nutrie nt indexes were found to be symmetrical about zero as follows: -0.70 to +0. 70 for N, -0.45 to +0.45 for P, -1.14 to +1.14 for K, -0.63 to +0.63 for Ca and Mg, and -1.05 to +1.05 for the residual filling value. Summing squared critical nutrient indexes also gave a CND r(2) of 3.9, the minimum CND imb alance index For high-yield targets (>6.7 Mg ha(-1)). Nutrient concentratio n values were little to closely related to CND indexes (R-2 = 0.34-0.87), T he DRIS and CND indexes were highly related to each other (R-2 = 0.91-0.99) , For N at V4-V6 growth stage, the CND N index was the most closely related to ear yield.