Soil Salinity and Leaching for Almonds

An earlier post discussed proper soil sampling methods. By now, those results should have been received and reviewed.Almond trees are relatively sensitive to sodium, chloride, and boron. Yields are impacted when average root system salinity increases above 1.5 dS/m, with research indicating a 19% decrease in potential yield with every 1.0 dS/m increase. This yield reduction is due to the osmotic effects of the salts, which basically makes the tree “work harder” for water reducing growth and vigor. If excess salts continue to accumulate within the rooting zone, trees will ultimately uptake the salts and cause tissue toxicity. The salts of primary concern are sodium, chloride, and boron. A leaching program should be implemented when EC of the entire rooting depth exceeds 1.5 dS/m or sodium, chloride, and boron exceed  an exchange saturation percentage of 5%, 5 meq/l, and 0.5 mg/l, respectively.If the salt levels within the soil are high, they must be leached from the soil. This process is typically done with either an application of a leaching fraction in-season or  applications of water during dormant when evapotranspiration rates are low. If planning to leach during the dormant period, it is important to begin this process early in the dormant period in order to complete it before root expansion (mid-January). Enough water must be applied to fill the soil profile. Once the profile is full, smaller quantities of water applied either through rain or irrigation more frequently is the best way to move salts below the root-zone.  In developing a program, its best to refill the profile early with irrigation water as all subsequent rainfall will aid the leaching program. Be careful not to saturate the soil for prolonged periods as this may increase the risk of root diseases.Growers using single or double line drip may want to also consider to irrigate during rain events. Applications of water during this time will help "push" the salt out of the rootzone. It will also aid in filling the profile or leaching. This practice is a concern for drip irrigation systems since the volume of wetted soil and root zone are diminished.Calcium amendments are also a benefit when trying to leach sodium and boron. Calcium competes for the exchange sites within the soil. This keeps sodium and boron in the soil water, allowing it to be leached. Calcium is sourced through a variety of products, but the cheapest and most effective for leaching programs are either lime or gypsum. Lime should only be used when pH is below  7, while gypsum can be used at any pH. If the soil is alkali and has high amounts of calcium, acidifying the soil will free up calcium. When determining the amount of calcium or acid to apply, a soil analysis is required. Once this analysis is in hand, please contact your local farm advisor or agronomist for a recommended amendment rate and application procedure for your soil type.