Vaughan P.,CMS Consulting |
Letey J.,University of California at Riverside
Agricultural Water Management | Year: 2015
Elucidation of interactions among these factors through modeling using the ENVIRO-GRO program to compute RY and N leaching from the root zone for corn (Zea mays) was our objective. Ten-year simulations included growing seasons and fallow periods. Simulation variables were applied water divided by potential evapotranspiration (AW/PET) equal to 0.9, 1.1, 1.3, and 1.42; irrigation water salinity (ECiw, dS/m) values of 0.5, 1, 2, 3, and 4; and inorganic N applications ranging from 270 to 350. kg/ha. RY for simulations that included winter precipitation were approximately 5% greater than identical simulations without precipitation for 2. ≤. ECiw. ≤. 4. Except for deficit irrigation, all AW/PET values resulted in RY equal to 100% for ECiw. ≤. 2 when N was not limiting. For ECiw. >. 2 progressively greater AW/PET was required for full yield. For less saline waters, water stress was limiting for the AW/PET = 0.9 treatment and RY was unaffected by the N application rate. For a given N application rate, increasing water application caused decreasing RY and increasing leached N. When N applications were greater than required for maximum RY, a decrease in N application resulted in an equal decrease in leached N. When decreasing N applications caused decreasing RY, the reduction in leached N was less than the reduction in N application. For the very saline waters (ECiw = 4), AW/PET = 1.1 was inadequate to leach the salts and water stress was the limiting factor rather than N application. Water flow below the root zone is controlled by both water application and N deficiency which reduces plant water uptake. Regulatory attempts to restrict N leaching to groundwater that prescribe management of N applications exclusively are likely to fail because N leaching depends on water flow as well as N application. © 2014 Elsevier B.V.
Letey J.,University of California at Riverside |
Vaughan P.,CMS Consulting
California Agriculture | Year: 2013
Many groundwater resources in California are degraded by high concentrations of nitrate, most of which was transported to the groundwater in water percolating below the root zone of agricultural fields. Factors that affect the rate of water percolation - including soil type, crop and irrigation - along with nitrogen application influence the probability of this type of groundwater degradation. UC scientists have developed several useful tools, including the Nitrogen Hazard Index (NHI) and the ENVIRO-GRO (E-G) model, for use in developing best management practices (BMPs) to achieve high crop yields while minimizing groundwater degradation. We report the results of E-G simulations that quantify the effects of irrigation, soil type and organic and inorganic nitrogen (N) application amounts to corn yield and the amount of leached N. Simulation results indicate that a nitrate management strategy that also includes water management will be more effective in reducing N loading to groundwater. The research findings are discussed in the context of the track and report concept in comparison to the BMP approach.