What Will It Take To Protect Groundwater Quality Under California Central Valley Dairies?
University of California Cooperative Extension
There is ample evidence of elevated nitrate concentrations in groundwater under dairies in the Central Valley of California, however solutions to this issue have been elusive. Regulations put in place may have raised awareness among dairy operators, and may have resulted in improved nutrient management, but have not resulted in the level of improvement necessary to protect groundwater quality. Work done in a 10-year study showed that while decreasing the amount of manure applied did result in a decrease in shallow groundwater nitrate concentrations, yields could not be maintained unless the amount of manure and other nitrogen applied exceeded what is now the regulatory limit of 1.4 times crop removal. Many dairy producers now find themselves in the position of being unable to maintain their production levels and still stay within the regulatory limits. Without access to improved nutrient management techniques and technologies, additional education and potentially changes in the regulatory system, dairy operators face the real possibility of being forced to move their dairies out of state or leave the dairy business.Many factors limit a dairy operator’s ability to maintain production using only manure nitrogen forms. They include sandy soils with poor ability to retain nutrients, irrigation systems that cannot apply water at rates that minimize leaching of nitrates, fluctuating lagoon nitrogen concentrations, difficulty and complexity of measuring, recording and calculating application rates, uncertainties in predicting and accounting for manure and soil organic nitrogen availability, inadequate land base for the amount of manure generated, and limited economic resources to implement improvements even where proven technology exists.Solutions to these issues will be different for different regions and dairies within regions; there is no one approach that will fit all situations. However, in general, an effective nutrient management system on a dairy would include these essential components: • Reasonable irrigation efficiency and uniformity to prevent excessive leaching. • Accurate measurements of irrigation water and nutrient inputs, and nutrient harvest removal• Ability to apply specific amounts of manure nutrients at the target rates and times they are needed• On-farm record keeping which provides timely in-season computation of application amounts • Decision support for estimating organic N release, expected leaching losses and other dynamic nitrogen processes throughout the year both to make an application plan and to identify the need for in-season adjustments.Implementation of each of these components has significant challenges, and in many cases the technology and science are currently inadequate or nonexistent. In addition, our experience is that there are many additional unforeseen issues that will need to be addressed on an individual basis for each dairy. Even when the best technology is implemented to minimize leaching through irrigation improvements, groundwater quality may not improve enough to meet regulatory expectations because some leaching is unavoidable and necessary to prevent salt buildup in the soil, and the nitrate and salt concentration in the reduced amount of leachate would be expected to be high.