Patrick Brown of the University of California ANR
Almond growers pay close attention to nitrogen applied to their orchards, and so do researchers with the University of California. Over the years, advances in knowledge have come from research on nitrogen levels in almonds, thanks in large part grants from the Almond Board.
For UC researchers and growers alike, the nitrogen balance is a worthy topic, year in and year out.
That’s why growers gathered round on a rainy day in March to hear about the accumulated research and advice for growers from Patrick Brown.
Brown’s team of researchers ran a trial at four sites in Kern County comparing traditional grower practices to improved “Best Management Practices” or BMP developed by the UC team.
The nitrogen management of the side-by-side plots were done differently: on one side was the traditional method of using tissue samples and predicted yield and timing nitrogen so that 30% would be deployed each month in March, April, and May, with 10% in June.
The BMP approach used a nitrogen rate determined by bloom yield estimate, reduced the application for nitrogen in irrigation water, and reduced it for residual nitrogen in soil. That revised approach deployed 20% of nitrogen in March, 30% in April, 30% on June 11, and 20% on August 30.
The modified approach meant more nitrogen in July, Brown said.
“This grower backed off for fear of hull rot,” he said, explaining the difference between the BMP and traditional grower approach. The grower also backed off after harvest.
The end of bloom in Chowchilla
“The modified (practice) gets closer to the predicted yield than traditional grower practice,” Brown said. “We jump efficiency of nitrogen by 20-30% because of (credits applied for irrigated and residual nitrogen).”
Irrigation water nitrogen “is every bit as good as applied nitrogen, and should be offset against it,” Brown told the growers.
In fact, in the second year of the study, the grower saw the UC team’s results alongside his own and backed off his nitrogen use, narrowing the gap between the new BMP methodology and the traditional.
Brown tipped his hat to Ash Slough Farms, which hosted the event in Chowchilla, saying that their fertigation practice of fertigating with every irrigation is ideal.
The opposite, fertigating only rarely, in richer applications, is a “big slug” of nitrogen that’s not ideal, Brown said.
Other advice Brown had for growers included that new orchards should have split fertigation systems for different cultivars, so that optimum nitrogen can be applied to nonpareils without oversupplying other types of almonds. Existing orchard may want to consider a retrofit to accomplish this goal.
Growers will need to keep a close eye on nitrogen as new Irrigated Lands Regulatory Program rules are formed, Brown said.
“It’s important to think about how you manage nitrogen,” he said. “The real goal is to keep nitrogen in the root zone when the tree is hungry.”