Chinese yam yield is affected by soil nutrient levels and interactions among N, P, and K fertilizers.

Objective: The current fertilization methods for Chinese yam are uneconomic and unfriend to environment. A rational one is very important to achieve desired balance of high yield of Chinese yam, economic and friend to environment. Here, we studied the effects of nitrogen (N), phosphorus (P), and potassium (K) fertilizers on the yield of 'Qinfeng' Chinese yam in shallow-groove directional cultivation.

Methods: The experiments were conducted in Dehua County, Fujian Province, China using a "3414" optimal design. Overall, three fertilizer factors (N, P, and K) were evaluated at the following four levels: 0, no fertilizer; 1, 0.5-fold the typical rate; 2, typical fertilization rate; and 3, 1.5-fold the typical rate. There were 14 different fertilization treatments.

Results: Treatment 6 (NPK) produced the longest (75.6 cm) and thickest tubers (4.9 cm) with the highest tuber fresh weight (1311.9 g) and yield (41 015.9 kg/hm), whereas, treatment 1 produced the shortest (65.6 cm) and thinnest tubers (3.9 cm) with the lowest fresh weight (953.4 g) and yield (28 532.8 kg/hm) among the 14 fertilizer combinations. The experimental data could be fitted to single-variable quadratic and binary quadratic models but not to a ternary quadratic polynomial model. Appropriate N, P, and K fertilizer application rates increased Chinese yam yield. However, excessive fertilization lowered the yield. Chinese yam yield was significantly and strongly correlated with the amounts of N, P, and K fertilizer applied.

Conclusion: Based on the single variable quadratic and binary quadratic models, we propose that the quantities of N, P, and K fertilizer used to grow 1 hm 'Qinfeng' Chinese yam should be 360-388.3, 90-100.95, and 416.3-675 kg, respectively.