Ammonium and Nitrate Distribution in Soil Using Drip and Microsprinkler Irrigation for Citrus Production

Good management of N is critical for improved citrus production and environmental sustainability on Florida sandy soils. Thus, understanding N movement in the root zone is important to devise appropriate nutrient management strategies. Field experiments were conducted on citrus at two sites in Florida to: (i) determine the soil moisture distribution in the irrigated and unirrigated zones as a function of time and depth; (ii) determine NH 4 + –N and NO 3 − –N distribution patterns in the irrigated and unirrigated zones as a function of depth, lateral distance, and fertilizer application method; and (iii) determine NH 4 + sorption in a fertilizer mixture due to cation exchange. The treatments were (i) a simulated conventional grower practice, irrigated periodically with a large‐pattern microsprinkler; (ii) a simulated open hydroponic system, drip irrigated and fertigated daily in small pulses; and (iii) a simulated open hydroponic system irrigated using a small‐pattern microsprinkler. The experiment was arranged in a randomized complete block design with four replicates. Soil moisture contents varied between 5 and 15%, remaining close to field capacity. Approximately 16 to 100% greater NH 4 + –N and NO 3 − –N concentrations were observed in the irrigated zones of the intensively managed drip or restricted microsprinkler irrigation than conventional practice. Ammonium adsorption followed a linear isotherm, with sorption coefficients varying between 1 and 2.2 L kg −1 . The results suggest the possibility of promoting nutrient retention and availability with intensive fertigation, thereby decreasing the potential for N leaching beyond the root zone.