Effects of Nitrogen and Potassium Rates on Yield of Summer Chinese Cabbage

Potassium chloride (KCl) and potassium sulfate (K₂SO₄) are the two commonly used K fertilizers for vegetable production in China. However, vegetable growers fear that KCl may affect vegetable yield and quality as many field vegetables are sensitive to chloride (Cl^-), especially in early growth stages. We conducted field experiments in Jiulongpo District of Chongqing to verify the effects of KCl and K₂SO₄ on yields and quality of lettuce and Chinese cabbage. The experiment had nine treatments with two K sources (KCl and K₂SO), two K application rates (0 and 100 kg/ha), and four different application timings (with or without splitting - viz., one basal application, basal + top dressing at rosette stage in a 50:50 ratio, basal + top dressing at cupping or head forming stage in a 50:50 ratio, and two top dressings at rosette stage and cupping stage in a 50:50 ratio) on the basis of 300-90-100 kg N-P₂O₅-K₂O/ha.

Potassium application significantly increased the yields of lettuce and Chinese cabbage by 10 to 15% over the K omission treatment. However, no yield differences were observed between the two K sources used (KCl and K₂SO₄). Maximum lettuce yield was obtained for the treatment with split K application as basal + top dressing at cupping stage in a 50:50 ratio, while maximum Chinese cabbage yield was obtained with two top dressings at rosette stage and cupping stage in a 50:50 ratio. Contents of Vitamin C, amino acids, and soluble sugar varied with fertilizer sources and application timings for both vegetable crops. Nitrate content decreased with splitting KCl application, but increased significantly with splitting K₂SO₄ application in lettuce. Potassium use efficiency was much higher when KCl was split applied during later growth stages of the two vegetables. On the other hand, with K₂SO₄, K use efficiency was higher when it was applied during early crop growth stages and regardless of whether it was applied as basal or in splits. The results indicated that KCl and K₂SO₄ are almost equally good for the production of lettuce and Chinese cabbage when used properly. Chongqing-BFDP-2011-01