Optimization of growth and production parameters of walnut (Juglans regia) saplings with response surface methodology

Straw mulching is an effective conservation tillage tool that utilizes waste resources and reduces environmental pollution. To determine the optimal levels of quality, placement and quantity of straw mulching, we performed a field experiment that used the Box-Behnken design combined with response surface methodology. The treatments designed for walnut saplings (Juglans regia) considered three independent variables: quality, placement, and quantity of straw mulching. Tree height of walnut saplings (THW) and net photosynthesis rate (NPR) were used as the response variables in a full, quadratic polynomial model. Analysis of variance (ANOVA) results showed that the selected models were significant (P < 0.05), expressing ideal relationships between the independent and dependent variables (R² ≥ 0.9225). The optimum conditions for the THW and NPR responses were determined to be a straw mulching quality which mixed rice and rapeseed straws, a straw mulching placement which covered the entire soil surface of experimental plots, and a straw mulching quantity applied as 3 kg/m² (i.e., the low level). This optimized scheme of straw mulching combinations offers an alternate choice for optimizing the growth and potential yield of walnut saplings, but practical field experiments should also be carried out to obtain more site-specific results.