Pre-sidedress Soil Nitrate Test Is Effective for Fall Cabbage

The pre-sidedress soil nitrate test (PSNT) was evaluated in 27 fields in New Jersey, 6 in Connecticut, 5 in Delaware, and 2 on Long Island in New York for its ability to predict whether sidedress N is needed to grow fall cabbage ( Brassica oleracea var . capitata ) as a double crop. Soil NO 3 -N concentrations measured on 20 field sites on the day of transplanting and 14 days after transplanting indicated that NO 3 -N concentrations over this time period increased, and that residues from the previous crop were not causing immobilization of soil mineral N. The relationship between soil NO 3 -N concentration measured 14 days after transplanting and relative yield of marketable cabbage heads was examined using Cate-Nelson analysis to define the PSNT critical level. Soil NO 3 -N concentrations ≥24 mg·kg -1 were associated with relative yields >92%. The success rate for the PSNT critical concentration was 84% for predicting whether sidedress N was needed. Soil NO 3 -N concentrations below the PSNT critical level are useful for inversely adjusting sidedress N fertilizer recommendations. The PSNT can reliably determine whether fall cabbage needs sidedress N fertilizer and the practice of soil NO 3 -N testing may be extendable to other cole crops with similar N requirements.