Contribution of Cover Crop Residue Decomposition to Peach Tree Nitrogen Nutrition

Cover crop nitrogen (N) cycling has an important role in agricultural production and contributes to peach [Prunus persica (L.) Batsch] N nutrition. This study evaluated black oat (Avena strigosa Schreb) and ryegrass (Lolium multiflorum L.) residue decomposition dynamics, N recovery from cover crop residues, and N compartmentalization in peach tree organs. A 2-year field trial was developed with labeled (3.6–4.0 atom% 15N excess) cover crop shoot biomass application in a 5-year-old peach orchard. The region’s climate is warm temperate (Cfb), and the soil is classified as a Typic Hapludalf. Litter bags with unlabeled shoot residues were also deposited in the orchard to assess biomass, carbon (C), N, lignin, cellulose, and non-structural biomass decomposition dynamics. After 13 months, the leaves, trunk, and roots showed the greatest proportion of N derived from residues (Ndfr) (35.4, 25.1, and 22.4%, respectively) while the greatest concentrations of 15N and Ndfr occurred in roots <2 mm (0.0376 and 0.94%, respectively). The N derived from cover crop shoots in the second production cycle was similar among tree organs. Ryegrass residues presented the highest decomposition constant (k) values for dry matter, total organic carbon (TOC), cellulose, and lignin. Hence, black oat residues presented a higher half-life (t½) for dry matter, TOC, total N, cellulose, and lignin. The N derived from black oat and ryegrass residues in mature trees was expressively low (<1%) and similar between species. Within organs, the highest Ndfr occurred in peach leaves during the flowering stage, when the greatest residue decomposition rate also occurred. Soil N and plant internal N reserves are the major N sources for newly formed organs, but greater contributions to tree N nutrition may occur with long-term cover crop residue deposition and different plant species.