Infiltration Improvement for Prune and Walnut Orchard Soils

Water penetration in many California orchards and vinyards is a serious management problem. Chemical properties of soils related to their aggregate stability and crust strength were measured to determine if one or more properties could be used to predict crusting. None of the measured properties, including aggregate stability, texture, organic matter, and various forms of iron, aluminum, or silica were suitable for this purpose. A field trial in a prune orchard in Yuba county showed that 5 metric tons per hectare phosphogypsum applied to the soil surface greatly improved the final 24 hour infiltration rate and total water entering the soil in 24 hours. Deep disturbance of the soil was also effective, but only until irrigation water was added, after which the soil returned to its original slow water penetration. Two metric tons/hectare phosphogypsum incorporated into the soil did not improve water penetration. The length of time that 5mt/ha phosphogypsum is effective in improving infiltrationrates is unknown, and we do not know if the increased water infiltrationincreased tree growth or yield.