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2. Maintain continuous and diverse organic inputs Not only can soil organic matter address compaction, continuous inputs of carbon and nutrients in organic forms such as amendments, mulches, animal manure and plant residues are essential to enhancing soil ecosystem functions and reaping the benefits of healthy soil. In fact, soil organisms like bacteria, fungi and earthworms require carbon and nutrients to live and perform essential soil ecosystem functions. There are many creative ways to increase organic inputs in agriculture. For example, researchers documented almond growers using compost, recycled almond shells, growth of resident weeds in the winter, planted cover crops and animal manures. Although we did not work with growers who utilized whole orchard recycling (WOR), this practice recycles carbon and nutrients from aboveground biomass back into the soil ecosystem and is a useful long-term strategy for supporting healthy soil. However, one of the most effective ways to introduce more continuous and diverse organic inputs is to maintain living plant roots, which leads to the third principle of building healthy soil: 3. Maximize the presence of living cover in almond orchards Living root systems provide an effective way to supply resources directly into the soil. Although there are multiple management constraints to increasing living roots in almond orchards, interesting strategies that are effective and feasible for management exist. For example, resident vegetation and planted cover crops like ground clover and triticale – which have shorter stands – can be effectively managed where frost is a concern to almond growers. Additionally, planting and termination can be optimized to take advantage of winter rainfall when almond trees are dormant and competition is low. Further, appropriate selection of plants and their growth periods can help ensure that residues left on the surface are able to sufficiently decompose before harvest. Ultimately, finding what works for any given almond orchard will take time and experimentation – a recurrent comment from growers we spoke with who are increasing the presence of living roots in their orchards. Introducing more organic inputs – especially living covers – in almond orchards also helps promote the fourth principle of healthy soil: 4. Keep the soil covered as much as possible Although this principle may require adjustments to management, maintaining a surface cover is essential to building healthy soil. Covering the soil physically protects it from the environment, which can reduce soil loss by wind erosion and surface runoff. In addition, covering the soil allows for greater sunlight interception and moderation of soil temperature, both of which could help reduce water evaporation from the soil surface. The degree to which residues are kept on the surface influences how management needs to be adjusted. For example, one grower's cover crop was terminated early enough to allow the residue to decompose well ahead of harvest, posing no challenges. Another grower, who left a small residue layer on the soil surface, said slowing down during harvest – moving equipment through the orchard at a slower pace – allowed for sufficient nut collection. Adoption of an off-ground harvesting system would allow for the maintenance of a thick residue layer – where residues can build up over years to protect the soil surface and provide organic inputs. (Figure 3) Enhancing biodiversity in almond orchard soil is also essential, and leads to the final principle of healthy soil: 5. Support soil biodiversity through diversification There is growing consensus amongst the scientific community that soil biodiversity can promote a wide range of soil ecosystem functions. Finding ways to support soil biodiversity – such as diversifying the plants growing in the soil – can be an effective strategy to build healthy and well-functioning orchard soils. For example, growers can plant cover crops mixes in their orchard middles that contain multiple species such as grasses, legumes and brassicas. Integrating animals to manage vegetation has also shown great potential as a beneficial diversification strategy for building healthy soils. However, uncertainties remain regarding best management practices, management logistics and concerns over food safety – questions that the Almond Board of California will be researching in the upcoming years 1 . Building healthy soils in almond orchards is essential and enables growers to not only address current management challenges but also ensure RESEARCH UPDATE 1 The integration of animals and use of animal manure is not currently recommended by the Almond Board of California due to food safety concerns and uncertainties regarding best management practices. To comply with food safety regulations, animals must be removed from the orchard or manures applied more than 90 days before harvest if almonds are harvested off-ground and more than 120 days before harvest if almonds are shaken onto the ground. Figure 3 Continued from page 18 Figure 3 This young orchard has built a thick layer of plant residue to protect the soil surface. A mixture of resident vegetation and planted cover crops grow across the orchard middle and berm then is mowed to build a residue without terminating plant growth. 19