How to Control Soil Leaching with Precision Irrigation Management

Every state in the contiguous United States is experiencing some level of nitrate contamination that is causing chemical buildup in rivers, lakes, oceans and groundwater. Those states showing the most widespread drinking water contamination to date are California, Illinois, Iowa, Kansas, Maryland, Nebraska, Oklahoma, Pennsylvania, Texas and Wisconsin. Many states in river headland areas have started educational programs with regional growers so they are better informed about how to avoid soil runoff and soil leaching using process control and precision irrigation management techniques.


California leads the nation in total agriculture, producing a third of the country’s vegetables. California has battled groundwater contamination for many years. A 2012 report commissioned by the state and developed by UC Davis focused on heavy agricultural areas within the state, and showed that groundwater contamination by nitrates from agriculture had exceeded safe levels in groundwater for many communities. The report further determined that mitigation of nitrogen by pumping and cleaning was not economically feasible, and that it would take decades to produce meaningful reductions of nitrates in the groundwater.

Chemical nitrogen reporting requirements matched to harvest estimates are now required for all of California’s Central Valley. The state is recommending that growers pumping groundwater for irrigation should minimize excess water not taken up by plant roots and that growers should make efforts to reduce application of excess chemical nitrogen past the needs of plants for optimal yield for the nitrates invested.


Farms and ranches comprise 92% of Nebraska’s total land area. Over 1/3 of the farmland produces annual crops (corn, wheat, soy etc.). For many years the University of Nebraska—Lincoln has studied the effects of nitrate on groundwater and the mechanics of soil leaching, resulting in many of the nitrate-conserving practices in general use. The Nebraska water Center at UNL conducts regular surveys, develops reports/seminars and advises growers on best conservation practices.

Recent legislation being considered by the State would incentivize growers to “implement a program to incentivize farmers to switch from synthetic fertilizers to sustainable alternatives, such as nitrogen-fixing bacteria.”


For states like Mississippi that enjoy adequate although uneven average rainfall, waterlogging can prevent water from draining down to the water table, carrying nitrate with it, and as a result nitrogen loss is largely due to ammonification and denitrification. Mississippi does not yet have a problem, but with climate change, drought conditions in the upper Mississippi River valley and longer than usual local droughts the situation requires monitoring. The National Center for Alluvial Aquifer Research operated jointly by Mississippi State and The USDA’s Agricultural Research Service works to ensure water quality for the state.


Colorado’s Agricultural Chemicals and Groundwater Protection Program (Groundwater Program) has sampled groundwater from wells in Colorado since 1992. Colorado has 250,000 wells, four out of five of which are small residential wells. The Groundwater Program focuses primarily on wells in agricultural areas of the state. Results from 1992 to 2015 show that 23% of wells sampled had nitrate contamination over the EPA recommended standard.

Colorado’s program for groundwater management is voluntary, and based on a vulnerability score that considers many factors including water table depth and soil composition. Colorado’s Best Management Practices for controlling agricultural nitrate contamination are based on the Four R’s (Right rate, Right source, Right time and Right place).

Aside from legislative action, growers are being concerned over their own wells and soil health. One measure that growers can take to monitor and prevent soil leaching in their own fields is precision irrigation management.

Precision irrigation management

Controlling the timing and amount of irrigation water applied during the growing cycle can prevent irrigation water from leaching, that is, seeping down through the vados zone into the water table, as the available water is completely taken up by the plants. Successful management to prevent soil leaching depends on knowledge of root depth at any given time to ensure that roots receive water, but leachate is controlled.

Precision irrigation management is essential for maintaining the right amount of moisture at the crop’s roots, in addition to monitoring salinity and soil temperature. Correct irrigation management combined with appropriate regenerative practices can produce long-term benefits for soil health. Learn more here.

Monitoring root depth and water uptake with AquaSpy® Crophesy™ Soil Intelligence

AquaSpy’s unique layer by layer view into the soil and the crop’s active root zone gives growers detailed insight into how far each irrigation is reaching with relationship to the crop’s roots. Since soil leaching takes place when irrigation pushes nutrients below the roots where it can’t be readily consumed by the crop, this wastes fertilizer as well as leaving it deep in the soil layers where it can accumulate and/or seep further into the ground water table.

AquaSpy’s Fuel Gauge shows growers exactly where crops roots are so that:

  • They can precisely time fertilizer applications
  • They can precisely control irrigation amounts so as to provide as much water as the crop can consume


Agricultural states are seeing the amounts of nitrate in groundwater push past EPA approved levels, largely because of soil leaching from overuse of nitrogen fertilizers. Most of these states have programs in place to monitor nitrogen by sampling well water and other sources. Monitoring and Best Management Practices programs have been put into place, mostly voluntary because growers care about the safety of the water they drink.

Regenerative farming may have answers, as these programs advocate no-till, minimal fertilizer and cover cropping to pull out excess nitrogen and encourage microbial growth to supply nitrogen the plants need naturally. Paired with consistent sensor-based precision irrigation management, regenerative practices may be the best answer to prevent soil leaching for the future.