How We Grow

2021 March/April How We Grow

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Nitrogen Best Management Practices Founded in Research, Strategy Nitrogen management is a balancing act. While on one hand growers are careful to fully satisfy the nutrient demands of their crop, excess nitrogen not only wastes money but can lead to nitrate leaching, susceptibility to hull rot and difficulty in shaking. To help guide growers through the nitrogen decision-making process – how much to apply, when to apply, etc. – the Almond Board of California (ABC) released the new Nitrogen Best Management Practices (Nitrogen BMPs), a resource infused with insights from decades of research that reflects a deeper understanding of almond trees' nitrogen needs. "I think this research in nitrogen management is incredibly valuable, not just to help us be better stewards but also to increase our efficiencies, which comes down to our bottom line," said Modesto-area almond grower Garrett Bowman. "It is important to emphasize that adopting these practices is not a compromise," said University of California (UC), Davis plant scientist Patrick Brown, Ph.D., who has been researching nitrogen management in almonds for over 20 years. "It's not a cost. It's an opportunity." The Nitrogen BMPs weave together a framework for applying the learnings of decades of planning, research and experimentation to fit the needs of each individual almond orchard. Used properly, these BMPs will equip growers to maximize profit and productivity while minimizing the negative effects of applying too much or too little nitrogen. "This resource is an excellent example of how years of research – all the way from basic research to applied science – and long-term strategic planning can be combined and communicated to the grower via outreach and extension efforts," said Sebastian Saa, associate director for Agricultural Research at the Almond Board. "This is a role that ABC is uniquely positioned to fill." More nitrogen ≠ more kernels Many in the industry are aware of the 4Rs of nutrient management, which state that nitrogen must be applied at the Right Rate and the Right Time, in the Right Place using the Right Source of nutrients. But the precise meaning of "Right" has not always been easy to define – what is "Right" for each grower? What is the optimal way to determine the appropriate rate and time to apply nitrogen to an almond orchard? The 4Rs framework, explained in detail in the Nitrogen BMPs, provides a clear, science-based method to answer those questions and a solid starting point for addressing nutrient management in almonds. Before determining the right amount of nitrogen to apply in any given orchard, growers need an accurate method to estimate the amount of nitrogen they must replace: For every 1,000 pounds of almond kernels produced, 68 pounds of nitrogen is removed from the orchard. "It's always tempting to think that if you want more kernels, you should just apply more nitrogen," said Brown. "But that's not how it works. The amount of kernels on the tree determines how much nitrogen will be used; not the other way around." This is why it's important to estimate yield in order to accurately calculate nitrogen needs. Yield estimates made early in the season are valuable even if they aren't precise. In fact, the Nitrogen BMPs recommend adjusting those estimates throughout the growing season as the crop develops and using frequent, small fertilizer applications based on changes in anticipated yield. Another important consideration for calculating nitrogen needs is to estimate existing supply, which may be found in residual nitrogen left over in the soil from the prior crop year, nitrogen that has been released from soil organic matter, or nitrogen in irrigation water. The needs of the trees themselves will also vary with age and vegetative growth. The Nitrogen BMPs account for these considerations and can be used along with the Almond Nitrogen Calculator, a tool included in ABC's California Almond Sustainability Program (CASP). 1 This tool makes it easy to enter the variables necessary to estimate your crop's nitrogen demand for the growing season. When uptake occurs (and when it doesn't) Calculating crop needs is an important element of nitrogen management and yet only part of the larger equation. Growers must not only balance the amount of nitrogen applied, but also be very deliberate on the timing of their applications as tree roots take up limited amounts of nitrogen during very specific times of year. "The trees uptake nitrogen following a demand curve, so of course you need to understand that curve," said Saa. "For example, the remobilization of nitrogen RESEARCH UPDATE "I think this research in nitrogen management is incredibly valuable, not just to help us be better stewards but also to increase our efficiencies, which comes down to our bottom line." — Garrett Bowman 1 For more on CASP, visit SustainableAlmondGrowing.org. 9

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