New protocol developed under a multi-year, multi-disciplinary fertilizer management project funded in part by the Almond Board of California and led by UC Davis pomologist Patrick Brown, is refining the way almond growers and other farmers make decisions about fertilizing their crops.

As a result of this research, almond growers now have new tools for making in-season adjustments to nitrogen (N) fertilizer applications based on current leaf tissue analysis and updated crop load projections.

Almond growers already have one of the highest rates of nitrogen use efficiency among California specialty crop producers. Still, they have been clamoring for some time for predictive tools that would allow them to sample leaf nitrogen levels early in the season and make adjustments for the current crop year.

Nitrogen Protocol

One of the most significant outcomes of this new research is the development of a nitrogen budgeting protocol that provides specific guidelines for almond growers to analyze April leaf tissue samples and then make adjustments beginning in May based on those lab numbers and an adjusted in-season crop load projection.

Prior to the development of this new protocol, growers used July leaf tissue samples to adjust nitrogen rates for the crop in the following year.

This comes at an important time as the Central Valley Regional Water Board prepares new waste discharge requirements under the Irrigated Lands Regulatory Program that will mandate all San Joaquin Valley growers on irrigated farmland to be more deliberate about their nitrogen use and reporting procedures.

The Regional Board is currently in the process of drafting separate orders for all watershed coalitions within the San Joaquin Valley. The first order was adopted in December of 2012 for the Eastern San Joaquin River Watershed Coalition. Additional orders for other coalitions, which are expected to closely model the East San Joaquin Coalition order, are expected to be adopted by 2014.

Groundwater Requirements

A key component of the new orders is the regulation of discharges to groundwater in addition to current surface water requirements. Under those groundwater requirements, growers will be expected to file nitrogen management plans and farm evaluations for each farm that outline potential water quality issues and practices to minimize potential discharges of nitrates to the groundwater.

This means not only increased reporting, but also doing everything possible to enhance the efficient and sustainable application of nitrogen fertilizers and other inputs.

Brown and his team, Sebastian Saa, Saiful Muhammad and Emilio Laca, at UC Davis, and Blake Sanden, UC Cooperative Extension, Kern County, have developed a new protocol designed to ensure N fertilization rates are more closely matched to individual orchard productivity in the current year.

The detailed protocol can be found on the Almond Board website at http://bit.ly/YLM9z1.

Under this new nutrient management protocol, growers establish a preseason nitrogen fertilization plan based on predicted yields and all potential sources of N. In April, they take tissue samples for all elements. Newly developed predictive models compare those tissue analysis results with UC critical values. Those results, along with early-season yield estimations, are used to fine-tune the nitrogen budget and make in-season adjustments for the remainder of the crop year. By May, growers will have received lab results from April leaf tissue analysis and can make adjustments through July according to those results.

N Rate Formulas

Brown lays out very simple formulas to make in-season nitrogen application rate adjustments based on whether April tissues levels are adequate, low or high, and whether visual field estimates for yield in April and May differ from preliminary predicted yields.

The protocol also lays out four different scenarios for leaf tissue analysis and expected yield, and specific recommendations for how to make in-season adjustments. In years of lower-than-expected yield with adequate April tissue N analysis, a specific reduction in mid-season N fertilization is suggested, while higher-than-expected yields might require an increase in N applications. Similar adjustments can be made in accordance with sampling results.

In addition, the research team has created a spreadsheet and other resources for these calculations, which can be downloaded at http://bit.ly/10YkoAc. Under “What’s New,” choose “Nitrogen Prediction Models for Almond.”

Together, these resources create a valuable set of new tools for further fine-tuning nitrogen applications in almonds and other crops at a time when nitrogen fertilizers are under the regulatory microscope.

By Bob Curtis, Associate Director, Agricultural Affairs and Gabriele Ludwig, Associate Director, Environmental Affairs, Almond Board of California.

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