Critical Compositional Nutrient Indexes for Sweet Corn at Early Growth Stage

It would be instrumental to define nutrient norms from small‐size crop databases at the V4–V6 corn (Zea mays L.) growth stage for in‐season N fertilizer recommendations. Our objective was to derive Compositional Nutrient Diagnosis (CND) and Diagnosis and Recommendation Integrated System (DRIS) nutrient index ranges from a sweet corn database and to relate nutrient concentration and indexes to ear yield. A sweet corn database of 240 observations on commercial yields and N, P, K, Ca, and Mg concentrations in 30‐cm high corn seedlings were divided at random between survey ( n = 200) and validation ( n = 40) subpopulations. The proportion of low‐yield specimens in the survey population was computed at inflection point of a cubic cumulative variance 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 nutrient 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 imbalance index for high‐yield targets (>6.7 Mg ha −1 ). Nutrient concentration values were little to closely related to CND indexes ( R 2 = 0.34–0.87). The 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.