Effect of potassium and phosphorus on yields and quality of cash crops

Potassium (K) is one of the major factors influencing cash crop quality and yield in apple, grape, cotton, and several vegetables grown on loess soils [available K ranging from 100 to 271 parts per million (ppm)]. Locally it is believed that K has no effect on crop yields if available K is more than 100 ppm. The objective of this experiment is to change that perception.

Hot pepper (chili) yield increased from 8 to 39 percent with 300 kg K₂O/ha (104 ppm available K). Smaller yield increases were observed in celery, cabbage, and Chinese cabbage (150 ppm available K). No substantial yield improvement was observed in grape due to K application (200 ppm available K); however, weight per grape, vitamin C, and soluble solids increased, while sugar and total acidity decreased. Application of K improved apple coloration and subsequent commercial value while farmer practice (no K) resulted in small fruit with rust spots. Potassium use also increased numbers of flowers for Chinese rose and improved ornamental colorfulness.

A significant decline (36 percent) in nitrate (NO₃^–) concentration within the 0 to 400 cm soil depth was observed when nitrogen (N) and phosphorus (P) were used along with K in chili fields, thus reducing contamination risks to ground water. Chili yield was also increased by 13 percent when the P rate was increased from 45 to 135 kg P₂O₅/ha in combination with 300 kg/ha of both N and K₂O. Nitrate concentrations of cabbage, Chinese cabbage, and celery also declined from 1,250 to 580, 1,250 to 1,055, and 895 to 800 mg/kg, respectively, compared to NP application alone. Great potential for both K and P markets exists in Shaanxi province. SHAANXI-NMS01