Effects of Nitrogen Fertilization on a Chinese Cabbage Hybrid

Brassica spp. may be used advantageously during forage‐deficit periods, particularly for late‐season grazing in the northern USA. This study evaluated the influence of N fertilization on the yield and N metabolism and distribution in ‘Tyfon’ [B. rapa L. × B. pekinensis (Lour.) Rupr.], a Chinese cabbage hybrid. Field experiments were conducted in August through November of 1983 and 1984 on a Woodbridge fine sandy loam soil (coarse‐loamy, mixed, mesic Aquic Dystrochrept). Tyfon was no‐till seeded into a herbicide‐suppressed sod, followed by broadcast N at rates of 0, 56,112,168, and 224 kg ha−1. Foliage yields, N uptake, and concentrations of total N and NO3−N increased with applied N. Root yields, concentrations of dry matter, and N use efficiencies were reduced as N rate increased. The amount of N partitioned into the foliage was much greater than in the roots. Once total N uptake reached approximately 100 kg ha−1, no significant increases in yield were observed. Total N recovery, averaged over years, exceeded 75% at the 56 to 168 kg N ha−1 treatments. These data suggest that N fertilization of Tyfon is beneficial only when the amount of N available to plants results in N uptakes of less than 100 kg ha−1. Excessive N fertilization is accompanied by accumulation of NO3–N in the plant.