Main soil fertility factors and their critical ranges for Chinese walnut (Carya cathayensis Sarg.) production

Objectives Soil fertility is the foundation of healthy plant growth and production. The soil fertility factors and their importance to soil productivity in the main producing area of Chinese walnut (Carya cathayensis Sarg.) were investigated, to provide scientific basis for sustainable and profit production of Chinese walnut.

Methods Fifty-eight Chinese walnut stands were randomly selected as the research objects in typical main production areas (Lin’ an, Zhejiang). Soil samples were collected, and twelve fertility factors were analyzed, including pH, organic matter, available contents of N, P, K, Ca, Mg, Fe, Mn, Cu, Zn and B. Based on the analysis of twelve fertility factors and growth vigor, disease susceptibility and yield, the leading influencing factors of soil productivity and the critical range of some key factors were explored through principal component analysis and regression analysis.

Results The cumulative contribution rate of the first 5 principal components (PC1, PC2, PC3, PC4, PC5) was 78.49%. The main loading factors in PC1 were pH, available Ca and Mg, in PC2 were available trace elements and P, in PC3 were organic matter and alkali-hydrolyzable N N, and in PC4 and PC5 were available B and K. The growth vigor grade was significantly and negatively correlated with pH, available K, Ca, Mg, Cu, and Zn (P < 0.01). The canker disease grade was significantly and negatively correlated with pH, available Ca, Mg (P < 0.01). Yield grade was significantly and positively correlated with pH, available Ca, Mg, P, Zn (P < 0.01). The soil pH, available K, Ca, Mg, Cu and Zn were the key fertility factors affecting the Chinese walnut ’ s growth and soil productivity. Of the tested stands, the comprehensive fertility of soil in 57% of the studied area was lower than the average fertility level.

Conclusions The top factors affecting the soil comprehensive productivity of Chinese walnut woodland are pH, exchangeable Ca and Mg contents, the second important factors are available trace elements and P contents, and then are organic matter and available K contents. The critical ranges of some key factors in Chinese walnut production area are: pH 5.19–5.70, available K 87–129 mg/kg, exchangeable Ca 817–1374 mg/kg, exchangeable Mg 93–145 mg/kg, available Cu 1.36–4.39 mg/kg and available Zn 0.78–2.33 mg/kg.