Nitrogen-rich animal and plant wastes as fertilizer improve the soil carbon/nitrogen ratio and plant branching and thickening of young walnut trees under deficit irrigation conditions

To investigate the physiological status of plant following the application of a mixture of organic residues, nitrogen-rich meat powder and alfalfa (Medicago sativa L.) powder mixed in different proportions as fertilizers were applied to the soil of a hilly area to cultivate young walnut trees under drought and wet soil conditions, respectively. The results showed that the nitrogen-rich fertilizer treatments could significantly increase the soil water content (SWC), soil organic matter (SOM), soil organic carbon (SOC), and soil organic nitrogen (SON), total nitrogen (TN), total phosphorus (TP), total potassium (TK), available nitrogen (AN), available P (AP), available K (AK), a high soil organic carbon/nitrogen ratio under soil drought conditions. Moreover, they also significantly improved the soil nutrients contents of Ca, Mg, Fe, Mn, Cu and Zn, especially Ca and Mg in dry soil. Consequently, this nutrient-rich soil greatly promoted the plant branching and thickening with a high net leaf photosynthesis rate (Pn), water use efficiency (WUE), a low transpiration (Tr) under soil drought conditions. We proposed that high soil carbon/nitrogen ratio improved by applying nitrogen-rich fertilizers might weaken top shoot growth and regulate the plant branching and thickening of young walnut trees under deficit irrigation conditions.