Is it time for a closer look at alternative nutrient sources?

Franz Niederholzer, UCCE Farm Advisor, Colusa and Sutter/Yuba Counties

Consistent, positive net return/acre to the grower is the key to sustainable farming. In 2022, hitting that goal is tougher due to 1) lower almond prices and 2) increases in major input costs including nitrogen (N) and potassium (K) fertilizer. With the real possibility of continued tight nut markets and high input costs, it’s worth considering all nutrient input options in an effort to lower costs and maintain production. This short article briefly presents and discusses a few alternative nutrient (re)sources. Growers may already be working with some or all of these materials and practices.

Nitrogen (N) and potassium (K) cost was roughly 17% of total cash costs to grow almonds in the 2019 UC Cost to Establish and Produce Almonds in the Sacramento Valley. High yielding almond orchards export large amounts of these nutrients in the harvested nuts (hull, shell and kernel). In most conventional orchards, these nutrients are provided by soluble, mineral fertilizers such as nitrogen (N) fertilizers containing urea, nitrate, and/or ammonium. As well as potassium (K) fertilizers such as potassium sulfate (SOP), potassium chloride (MOP), potassium thiosulfate (KTS) and potassium carbonate. These materials can be directly injected into irrigation water and delivered into the active root zone. When carefully managed, use of these fertilizers is highly efficient. However, as stated above, current price and perhaps future availability of conventional fertilizers challenge a grower’s bottom line. Alternative nutrient sources are locally available and, also, may be part of a sustainability program.

Except for irrigation water nitrate, all the alternative nutrient sources presented below are largely insoluble or slowly degradable soil amendments that contain low (<5% by dry weight) levels of essential nutrients. Application rates must be in tons/acre to deliver even partial crop nutrient requirement(s). In addition, the amendment must be incorporated (tilled) into the orchard soil or left on the soil surface for rain or irrigation (sprinkler) water to move nutrients into the soil. Availability of N-P-K from these materials generally ranks K = P > N. Growers should consider working with their CCA to trial different sources and practices to determine what practices might best fit their operation.

Irrigation water nitrate can be a significant source of N to an orchard. No extra effort is needed to “use” this N source except to include irrigation water nitrate-N (from lab test result) in the orchard N budget and reduce fertilizer N to match that applied with the irrigation water. See page 5 of the new Almond Board of CA publication Nitrogen Best Management for details on ground water as a nitrogen source.

Composted manure can be a significant source of phosphorus and potassium (up to 90% of the total P or K in that compost) compared to <10% of the total N if no runoff/erosion losses occur. In general, manure compost contains roughly 2x the N and 3-6x the P or K as composted municipal yard waste.

N fixing cover crops can capture as much as 80-120 lbs N/acre and some of that can be available to almond trees. The amount of N available to almond trees from cover crops varies with cover crop growth, composition (grains vs legumes), crop termination timing and method (mowing or tilling). See a Cover Crop Research Review post in The Almond Doctor and The Almond Board of California’s Cover Crop Best Management Practices for more information.

Almond shells contain significant amounts of K (1.5% on dry wt basis). Shells release K rapidly with rain or irrigation water. Shell/hull mixtures from shell piles can contain more than 2% K (roughly 50-60 lbs K2O/ton). Spreading almond hulls and shells, preplant or in young orchards, is a way to preload soil K ahead of crop need and dispose of a crop residue at the same time. A research update on shells and hulls in almond orchards will post in the near future in the Sacramento Valley Orchard Source. Growers are experimenting with application of shells in the Sacramento Valley.

There are costs and tradeoffs with the materials and practices listed above. Compost and crop residue (hulls and/or shells) must be hauled to the orchard and spread. Cover crops must be planted, require rain or irrigation water to grow, mowed down ahead of frost threat, and finally mowed or tilled to terminate. However, the benefits from these locally available nutrient sources may be a worthwhile consideration for growers, especially if there is an added benefit of improving rainwater infiltration by increasing orchard floor surface cover (spread or grown) in the fall.

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