Influence of irrigation system and fertilization management on seasonal distribution of N in the soil profile and on N-uptake by citrus trees

Understanding the fate of nitrogen (N) in agricultural soils as affected by crop N uptake is important in order to develop management practices that maximize nitrogen uptake efficiency by minimizing N losses. The aim of this work was to analyze the effect of two different N-management techniques, low frequency of N application combined with flood irrigation (LFFI) and high frequency of N application with drip irrigation (HFDI), on the seasonal dynamics of fertilizer-N in the soil profile and N-uptake by citrus. Eight-year old citrus trees were cultivated in lysimeters containing 3.5 m3 sandy-loam texture soil and fertilized with 15N enriched (%) potassium nitrate. Throughout the vegetative cycle, the initial accumulation of NO3-N from fertilizer in the surface layers of the soil leached towards deeper layers later on, under LFFI and HFDI treatments. This movement of NO3− in soil profile was lower under HFDI than in LFFI. At the end of the trial, total 15N recovery in the plant–soil system was 92.3 and 85.4% for drip and flood irrigation, respectively. Whole tree N-use efficiency was significantly higher under HFDI (75.1%) than under LFFI (62.7%). The amount of N retained as NO3-15N in the soil profile was significantly greater under flood irrigation (7.1%) than under drip irrigation (0.9%). Nevertheless, no significant differences appeared in the amount of organic-15N for both treatments. Improved management of fertilizer and irrigation thus contributed to enhance N uptake efficiency and reduced potential nitrate leaching. Appropriate use of fertigation under drip irrigation thus may facilitate more efficient use of both water and nutrients and could be part of Best Management Practices (BMP) for citrus.