Production of Chinese cabbage in relation to nitrogen source, rate, and leaf nutrient concentration
Obreza, T.A.; Vavrian, C.S.
Communications in Soil Science and Plant Analysis 24(13-14): 1465-1479
Chinese cabbage (Brassica rapa L. Chinensis group) production is expanding in the U. S., and guidelines regarding its production under Western 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 estimate 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 subsurface 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 Chinese cabbage wrapper leaf concentrations of P, Ca, and Mg increased with increasing N rate, while leaf-K concentration decreased. Leaf-N concentration increased in response to N rate, but was not affected by N source or harvest data. Leaf-P, K, Mg, and B concentrations were sufficient or high according to established standards, but leaf-Ca was low. Leaf-Ca and Mg concentrations were lowest with N source containing only urea, and highest where at least part of the N was applied as NO-3. Chinese cabbage head weight and percentage marketable heads increased as N rate increased. Yield and quality were highest with N sources which contained NO-3, and were smallest where N was applied entirely as urea, which may have been due to plant sensitivity to NH-4+. The critical value of mature cabbage wrapper leaf-N concentration above which yield or marketability was not limited was estimated to be 36 to 41 mg/g, which agrees well with established standards.