Improving soil conditions has been an increasingly important issue in degraded hilly areas; however, the effects of plant manure on soil nutrient and plant dry matter accumulation are poorly understood. We studied the effects of alfalfa powder, decomposed chicken manure and drought in a nonplanted group (NPG) and planted walnut group (PG) soil to explore the regulatory mechanisms of plant growth and dry matter accumulation in response to soil nutrients in hilly areas. Alfalfa fertilizer increased the soil water content and organic nutrient content, and drought resulted in a high carbon to nitrogen ratio and carbon to phosphorus ratio in NPG and PG soil. In addition, fertilization changed the available nutrient content of the soil in the nonirrigated NPG and PG. Alfalfa fertilizer altered the soil micro‐element contents and leaf mineral nutrient contents, promoted the net photosynthetic rate and relative water content, and inhibited the transpiration rate, resulting in high water use efficiency in leaves. Moreover, the coupling effect of soil organic matter and soil water content affected the correlations between the organic composition and mineral nutrients and maintained leaf mineral element contents as well as the net photosynthetic rate and water use efficiency, resulting in dry matter accumulation in the leaves, shoots and roots. This study highlights that plant manure can improve soil properties and the accumulation of plant dry matter in hilly areas. Core Ideas Alfalfa powder enhanced soil fertility in mountainous/hilly areas. Alfalfa powder improved leaf nutrient contents, leaf photosynthesis and water use efficiency (WUE) in drought. Soil environmental factors were correlated with plant growth and dry matter accumulation.