Annual and residual urea nitrogen contribution to the nutrition of peach trees (Prunus persica L.) grown under subtropical climate

Nitrogen (N) fertilizers such as urea are applied to peach orchards worldwide whenever the soil cannot meet plants’ N demand. However, the actual nutritional contribution of different N supply modes applied to peach crops, or the contribution of residual N in the subsequent cycle, is yet to be fully known. The current study aims to assess the annual and residual urea N contribution to the nutrition of peach trees grown under subtropical climate. Forty kilograms of N per hectare supplied as enriched urea (3.0 at. % ¹⁵N), were applied to peach in full production at a single rate (100 % at budding) or split in two rates (50 % at budding and 50 % at flowering). Total ¹⁵N and N concentrations in the application year and in the year after treatments were assessed in peach leaves throughout the cycle, in fruits (pulp and stone) at harvest and in stratified soil samples. Total ¹⁵N, N concentrations and total dry mass were measured in annual and perennial tree organs in the year after treatment application. Peach trees evidenced higher N deriving from fertilizer (NDFF) in leaves and fruits (pulp and stone) in the year N was applied to the soil, as well as in the following year when N application was split into two rates. The highest NDFF amounts recorded in the year following N application were observed in leaves and fruits (annual organs) and thick roots (perennial organ), mainly when N was splitted. However, mainly in the year following its application, due to the small residual N, the N found in trees derived from sources other than N fertilizer; this justifies annual N applications, whenever necessary. The cultivation of cover crops and the preservation of organic matter could help N peach nutrition that seems to take advantage more of residual N in soil than on fertilizers.