Alternative Nutrient Sources: Compost and agricultural by-products

With increasing fertilizer prices, many have considered other materials to source major and minor nutrients. These products include manures, composts, and other agricultural by-products such as grape pomace, and even almond hulls and shells. These materials provide additional organic matter to the orchard, which may be of additional value. Each of these materials, however, may differ in their nutrient content, and analysis should be conducted to determine if they are suitable price replacements for conventional fertilizer sources. Below is a brief overview of three consistently available by-products that can be applied in almond orchards.Composts and manures. These by-products were discussed in this previous post. Due to the high variability of these products, an analysis is needed to determine the nutrient content. Specifically, the water content of the compost or manure must be taken into account prior to estimating nutrient use. Products with high moisture will reduce the benefit of application and the cost of applying the material. Additionally, composts and manures are often out-of-balance with tree nutrient needs. These products tend to have more phosphorus and micronutrients, but lower potassium and nitrogen, than what almond trees require. This can lead to increase soil phosphorous levels, increasing the risk of run-off pollution into water ways.  Lastly, the material applied must meet food safety standards expected by the handler/processor of the crop.Grape pomace. This product is a bit more difficult to source due to its multiple uses. Grape pomace tends to have high amounts of potassium (1.2-2.0%) and calcium (~1%), and both these nutrients are needed in high levels within orchards. Nitrogen will vary, but typically ranges form 1.5-2.5%. There are also additional micronutrients such as iron, copper, and zinc that are at high levels. This link provides an overview of the feed components. Although this product can be tricky to distribute, it has considerable value as it contains high amounts of sugars that help stimulate the soil ecosystem.Almond hulls and shells. Often overlooked due to its diversion into the dairy industry, almond hulls and shells should be considered for orchard application. Nutrient content is more stable than other by-products, and generally the product is delivered with low moisture content. A study in 2016 analyzed multiple sources of almond hull/shell mix, which is a lower grade product than almond hulls. Through its sampling, it found that almond hulls contain 2.0-3.0% potassium, ~1% nitrogen, 0.1% phosphorus, and 0.2% calcium in addition to boron, zinc, and other micronutrients. The amount of nutrients provided by a short ton (2000 lbs) of material was estimated to be $46.10 at 2016 prices.In the same study, application of the products were made in March at either a 1- or 2-ton rate. The product was applied directly to the irrigation pattern of the tree as delivered from the processing facility. By July, the product was reduced to small enough pieces that it did not interfere with harvest. There was no impact on nutrient status of the trees, yields, or interference with operations. As such, the study concluded that the almond hull /shell mix is a suitable product for almond orchard applications. More on this study can be found here. Furthermore, additional studies have found that hull/shell applications increased stable aggregates within sand and clay loam soils, while also increasing soil microbial activity, increasing the perceived value of these products.Within our operations, we have utilized hulls and shells for applications to newly developed fields. We have found that this by-product can be easily applied with a manure spreader, and can be incorporated at very high rates ( 2.5-5 tons/acre, or 5-10 metric tons/ha). When compared to working with manure, it is easier to handle, and it delivers more value due to reduced moisture content and increased nutrient levels. Essentially, we are paying more for the product with less handling, leading to a reduction in costs. We will continue this practice as long as we can buy the product for under $60/ton, based on current fertilizer prices.Other products. There are several waste products available that can serve as a source of nutrients for orchards. These products should be evaluated for their ability to be integrated into orchard operations. This includes the application, timing, and possible interference with other practices, such as winter sanitation and pre-emergent herbicide treatments. Always consider an analysis of the material prior to making the purchase decision to determine the fertility value. This will also provide insight if it is a good deal to purchase and pay for the application of this material to your orchard.