C A L I F O R N I A
Vegetables A SPECIAL GROWERS’ REPORT OF AG ALERT ®
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University of California farm advisors say they are trying to develop a fuller understanding of how much nitrogen is contained in lettuce and dozens of other vegetable crops, in order to make more accurate recommendations on use of fertilizer and irrigation, to help farmers comply with government water-quality regulations.
Advisors discuss strategies to meet water standards ByBob Johnson
“This is going to be a very important issue in the Central Coast region because of Ag Order 4.0,” Smith said. “Some portion of the nitrogen left behind is subject to leaching, which is why we are concerned with this. But it is a little more complicated, because some of the nitrogen is taken up by the next crop or by cover crops, or is sequestered in soil organic matter.” The challenge of meeting ever more strict standards by applying only a little more nitrogen than is removed with the crop will be complicated by the fact that even re- searchers do not fully understand howmuch nitrogen is in each of the dozens of veg- etables widely harvested in the Salinas Valley. “Cooperative Extension is working on coefficients for more than 30 different crops, and even just romaine lettuce can vary from 47 to 70 pounds of nitrogen removed for a 30,000-pound crop,” Smith said. “These are things that are going to have to be recon- ciled in the regulations.” Farmers and pest control advisors can access fertilizer and irrigation recommen- dations based on years of UC research intended to give a crop as much nitrogen as it needs and little more, through an app on a laptop or smartphone. “We’ve been working the last 10 years to take our research and put it into a software program, CropManage,” said Michael Cahn, a Salinas-based UCCE irrigation farm
Salinas Valley vegetable growers are looking at tools and management strategies available to reduce nitrate leaching, as water-quality regulatorsmove toward adoption of nitrogen restrictions. But specialists say theproposed regional water quality board regulationswill be tough andmight actually discourage practices such as using compost tobuildhealthy soil that sequesters carbon and nitrogen, ignore the importance of rotating to deeper-rooted vegetables such as broccoli, and count nitrates in irrigation water to germinate seeds and start plants too small to take up the water. The rules would limit Salinas Valley nitrogen applications in fertilizer and irrigation water combined in 2022 to 500 pounds more than is removed at harvest; ramp down in the early years to targets of 300 pounds in 2026 and 200 pounds in 2030; and then would drop allowable nitrogen applications to 150 pounds in 2035, 100 pounds in 2040 and to just 50 pounds over crop removal in 2050. “Itmoves alongpretty quickly toanumber that will bepretty challenging for a grower,” said University of California Cooperative Extension farm advisor Richard Smith, who has been studying cool-season vegetable nitrogenmanagement for decades. Smith and other Cooperative Extension advisors discussed the fertilizer limits in the proposed Ag Order 4.0, and strategies for reaching the standards, during a Vegetable Production on the Central Coast webcast.
See QUALITY, Page 16
December 16, 2020 Ag Alert 15
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