Effect of drip irrigation and nitrogen application rates on soil nitrogen and potassium movement and nitrogen uptake and accumulation in vegetable crops

Water movement is a major process that affects solute transport in the soil profile under Florida sandy soils conditions. Therefore, understanding the impact of current irrigation and N fertilization practices will have on leaching of water and nutrients below the crop root zone, and on crop yield is important for developing best management practices (BMPs). The BMPs should aim at minimizing water and nutrients leaching below the root zone while optimizing crop yield. Two field experiments were conducted in Spring 2002 in a sandy soil cropped with bell pepper and watermelon crops at North Florida Research and Education Center (NFREC) near Live Oak, Florida, to estimate the potential of leaching of N and K from the soil profile using calculated water fluxes over time, to measure biomass accumulation, N accumulation, and crop yield as affected by irrigation and N rates. The main goal of the study was to select BMPs that reduce nutrient leaching below the root zone from vegetable crops grown on plastic mulched beds under drip fertigation. The experimental design consisted of three irrigation treatments: 66, 100, and 133% of crop evapotranspiration (ETC) and two rates of N fertilizer: 100 and 125% of IFAS recommended rate. Each treatment was replicated four times and the experiments were laid out in a completely randomized block design. At the beginning of each experiment calcium bromide was injected with the fertilizers to trace water and fertilizer movement through the soil profile. Soil samples were collected throughout the growing season, to characterize the storage and distribution of water, N-forms, and potassium in the root zone and below the root zone. Cumulative uptake and distribution of N and biomass accumulation were also monitored by taking plant samples at different stages of crop growth. Increasing irrigation rates, increased soil water content above Field Capacity (FC) and water flux was fast during crop establishment and flowering. Therefore soil water, Br, and NO3-N, moved below root zone under both crops. The amount of soil NO3-N leached below the root zone increased with increasing N rate. Most of the applied NH4-N remained within the root zones for both crops and the amounts of soil NH4-N in the root zones increased with increasing N rate. Similarly, most of soil K remained within the root zone of both crops. At harvest, soil water content was close to FC but water was still moving soil nutrients such as NO3-N below the root-zone. Increasing N-rate increased N uptake but did not significantly increase crop yield. However, nitrate leaching below the root-zone also increased. Based on currently recommended crop factors used to calculate irrigation treatments, the BMPs for the bell pepper crop would be 66% of ETC irrigation rate and 100% of the IFAS recommended N rate. For the watermelon crop the BMPs would be 100% ETC irrigation rate and 100% of the IFAS recommended N rate. The above BMPs for both crops would optimize crop yield while minimizing nutrient leaching below the root zone.