Optimization of application of nitrogen fertilizers to increase the yield and improve the quality of Chinese cabbage heads

The study investigates the effects of nitrogen fertilizers on the characteristics of the autumn crop of Chinese cabbage. The rates applied varied from 0 to 225 kg ha(-1) ( N-0, N-45, N-90, N-135, N-180, N-225); the supply of phosphorus and potassium fertilizers was similar in the all trials, 90 and 150 kg ha(-1), respectively. It was found that the optimum nitrogen fertilization rate for the autumn crop of Chinese cabbage was N-135. In the case of lower nitrogen rates the yield decreased and the cabbage heads were smaller. Further increase in fertilizer rate (>N-135) resulted in a higher percentage of non-standard cabbage heads, while the yield remained almost unchanged compared with N-135. The total plant mass of cabbage crop fertilized with N-135 was 76 t ha(-1); plant residues constituted 33 t ha(-1) ( 43% of the total mass). The yield of market quality cabbage heads was 30 t ha(-1) ( 70% of all the heads produced); the rest of heads were loose, not formed or rot-infected. The optimal amount of total mineral nitrogen ( the sum of nitrogen present in the 0-60 cm soil layer and the nitrogen supplied with fertilizers) before planting was 260 kg ha(-1). When nitrogen rates were higher than N-180 the quality of cabbage heads in terms of the content of vitamin C, nitrates, soluble solids, total solids and sugars decreased.