Improving nitrogen management in potatoes through crop rotation and enhanced uptake

Impact on water quality due to nutrient loading of our finite water resources is a growing concern. Nitrate and phosphates originating from agricultural operations have been identified as the primary contributors to such non-source point pollution of water. The Ti-County Agricultural Area (TCAA) in north-east Florida is predominantly dedicated to intensive potato production system with producers often resorting to over-fertilization, particularly with N sources. Best management practices (BMPs) including crop rotation and enhanced N uptake have been proposed as options to minimize the risk of nitrate contamination of the surface and groundwater in the St. Johns River watershed. To evaluate the effect of NO3-N concentration on shallow water table and to determine optimum N requirement for an economically successful potato crop (var. Atlantic), a 3-year field study with four potato-cover crop rotations and five N rates was conducted in the TCAA. Increased NO 3-N concentrations in the shallow water table were recorded immediately after N application at planting but not after the side dressing. At the end of potato season an increase in soil NO3-N resulting from residual effect of N side-dress was found. While nitrate concentrations produced linear and quadratic increase of sorghum N uptake across N rates, cowpea did not exhibit any response. Rotation with green bean in the fall increased soil NO3-N concentration at potato planting in the next season, and a high rainfall between during the intervening period increased the potential for nitrate leaching and run-off. Potato in rotation with sorghum produced higher yields than in rotation with cowpea. Sorghum was found to be a more efficient catch crop for residual NO3-N.;A study of potato root distribution under the effect of three N rates was done in the third year. There was no effect of N rate on root length density, specific root length, root surface area density, and specific root surface. Observations suggested that potato root system was constrained due to soil compaction, and increased soil bulk density recorded at the study site. A soil region where the potato root system showed highest activity was identified which could guide precise fertilizer placement.