Study examines how to keep nitrates out of groundwater
process in which soil microbes transform nitrates into gaseous forms of nitrogen. “Those denitrifying microbes need to be stimulated to do the work,” said Dahlke. “What we have found is that if you do a little bit of irrigation before you start the flooding, increasing the soil moisture can get those microbes started, and they can take out more nitrate from the soil.” The timing and quantity of fertiliz- er applications are also major factors in reducing leaching. Although more growers are following high-frequency,
low-concentration practices to max- imize uptake by crops, Dahlke said there needs to be more emphasis on incorporating nitrogen transformation processes such as denitrification in the nutrient management guidelines that farmers follow. “Implementing thoughtful nutrient management plans will play a partic- ularly important role in participating farms,” Fidelibus added. (This article was originally published by the University of California, Davis, College of Agricultural and Environmental Sciences.)
With California enduring re- cord-breaking rain and snow and Gov. Gavin Newsom recently easing restric- tions on groundwater recharge, interest in “managed aquifer recharge” has nev- er been higher. One concern for farmers is ensuring that recharge doesn’t push nitrates from fertilizer into the ground- water supply. “Many growers want to provide farm- land to help recharge groundwater, but they don’t want to contribute to nitrate contamination of the ground- water, and they need to know how on- farm recharge practices might affect their crops,” said Matthew Fidelibus, a University of California Cooperative Extension specialist in the department of Viticulture and Enology. A recent study by UC scientists sheds new light on how nitrates move through an agricultural recharge site and how growers might reduce potential leach- ing. The study, published in the journal Science of the Environment, researchers analyzed data from two grape vineyards at the Kearney Agricultural Research and Extension Center in Fresno County—one flooded for two weeks, the other for four. A key factor in mitigating contamina- tion is understanding how much nitrate is in the soil at the outset, said study au- thor Helen Dahlke, a UC Davis hydrol- ogist and leader of UC Agriculture and Natural Resources’ strategic initiative on water. (See related commentary on groundwater recharge on Page 2.) In areas with little precipitation and cropping systems that require greater amounts of synthetic fertilizer, the accu- mulation of residual nitrate—resulting from nitrogen in the fertilizer not taken up by the plants—can be quite high. “The percentage of nitrates in some soils can really increase over the years, particularly if you have many dry years in a row where you don’t have access to irrigation water or natural precipitation flushing some of those nitrates out of the soil,” Dahlke said. While intense rains in recent weeks have helped dilute nitrate concentra- tions naturally, farmers looking to par- ticipate in recharge during the dry years ahead should consider flooding their fields with greater volumes of water. “If you’re doing this for the first time— on-farm recharge in the winter—check your residual soil nitrate levels because if they’re very high, you should apply a lot of water in order to make sure that the residual nitrate is diluted down,” said Dahlke, who added that growers should check their soil properties for suitability of recharge projects. She recommended using, as a “good first approximation,” the online Soil Agricultural Groundwater Banking Index map, a project led by Toby O’Geen, a UCCE soil resource specialist. Even before flooding the fields for recharge, there are several practices that
can lower initial nitrate levels and risk of leaching. Cover crops such as alfalfa and triticale, for example, can help take up residual nitrates that accumulate from fertilizing a main crop over time. Dahlke and Fidelibus—a co-author of the San Joaquin Valley vineyard study —both pointed to pre-flooding irriga- tion that encourages denitrification, a
The decisions you make here
Pay off here
Some of the most important work you’ll do all season is happening now — researching new and better ways to tackle the challenges you know are coming. At UPL, we’re opening new doors to productivity with an integrated portfolio that includes both conventional crop protection solutions like VIGILANT ® insecticide and innovative BioSolutions like PH-D ® fungicide , which can be used in a customized ProNutiva ® program to optimize crop quality and yield while reducing residue levels. One more way UPL is helping meet the challenges of today and tomorrow.
SMART SOLUTIONS FROM PREBLOOM TO POSTHARVEST UPLTreeNutPortfolio.com
Always read and follow label directions. VIGILANT, PH-D, ProNutiva, UPL, OpenAg and the UPL logo are registered trademarks of a UPL Corporation Limited Group Company. ©2023 UPL Corporation Limited Group Company. TREE-2301
April 12, 2023 Ag Alert 11
Powered by FlippingBook