Nutrient Management Research Database

Many groundwater resource 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.

• Nitrate leaching through the soil and polluting groundwater is a serious environmental concern.
• The rate of nitrate leaching is affected by fertilization rates, soil type, crop species, and irrigation practices.
• This modeling study investigated the relative importance of irrigation practices on nitrate groundwater pollution

• The study showed that corn is effective at accessing large amount of soil N, and that mineral N is an appropriate form of N fertilization for this crop.
• Crops grown on sandy soils are more likely to result in nitrate leaching than those grown on finer textured soils.
• Targeted irrigation systems help prevent nitrate leaching.
• The total amount of water that extends beyond the root zone was found to be more important than total N applied in driving nitrate leaching.