PRODUCTION OF CHINESE-CABBAGE IN RELATION TO NITROGEN-SOURCE, RATE, AND LEAF NUTRIENT CONCENTRATION

Chinese cabbage (Brassica rapa L. Chinensis group) production is expan ding in the U. S., and guidelines regarding its produCtion under Weste rn cultural practices are needed. The objectives of this study were to investigate the effects of N source and rate on Chinese cabbage yield , marketability, and wrapper leaf nutrient concentrations, and to esti mate the critical wrapper leaf-N concentration associated with maximum yield and marketability. Chinese cabbage was grown in five sequential plantings using raised-bed, polyethylene mulch culture with subsurfac e irrigation on a sandy soil. Nitrogen fertilizer was applied at rates of 0. 67, 112, and 157 kg/ha using the following sources: 1) ammonium nitrate. 2) calcium nitrate, 3) urea-ammonium nitrate solution (Uram, 32% N), 4) urea, and 5) a urea-calcium solution (18% N). Mature Chine se cabbage wrapper leaf concentrations of P, Ca, and Mg increased with increasing N rate, while leaf-K concentration decreased. Leaf-N conce ntration increased in response to N rate, but was not affected by N so urce or harvest date. Leaf-P, K, Mg, and B concentrations were suffici ent or high according to established standards, but leaf-Ca was low. L eaf-Ca and Mg concentrations were lowest with N sources containing onl y urea, and highest where at least part of the N was applied as NO3-. Chinese cabbage head weight and percentage marketable heads increased as N rate increased. Yield and quality were highest with N sources whi ch contained NO3-, and were smallest where N was applied entirely as u rea, which may have been due to plant sensitivity to NH4+. The critica l value of mature cabbage wrapper leaf-N concentration above which yie ld or marketability was not limited was estimated to be 36 to 41 mg/g, which agrees well with established standards.