The harvest season is winding down, and in the next few weeks many orchards will be receiving their last irrigations. After the final irrigation of the season, growers should conduct soil sampling to determine any potential issues with sodium, chloride, or boron. These salts are “imported” onto the farm through fertilizers and soil amendments, with the largest amount coming through irrigation water.
There are several videos online that go through the procedure of collecting a soil sample. Here is a link to an article containing this series. When soil sampling for salinity management, varying depths of soil must be collected to determine where the salts have accumulated. Suggested depths are in one foot increments (down to
four five feet), but 18 inch increments may also be used. If dealing with soil infiltration issues, it may be of value to sample the top 6″ to determine if there is a soil imbalance.
Almond trees are relatively sensitive to salt. 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 is due to the osmotic effects of the salts, which basically makes the tree “work harder” for water. If excess salts continue to accumulate within the rooting zone, trees will ultimately uptake the salts and cause tissue toxicity.
If the salt levels within the soil are high, they must be leached from the soil. This process is typically done with applications of water during dormant when evapotranspiration rates are low. More on this topic will be written later, but a great source of information on salinity, management, and leaching programs can be found in “Agricultural Salinity and Drainage” written by Hanson and colleagues (1993), UC ANR publication #3375.