Much permanent crop acreage in the San Joaquin Valley has penetration problems. Studies documenting the benefits of cover crops, manures and gypsum have been carried out for over 50 years. But much of these materials can only be applied to surface irrigated orchards during the dormant season. The soil surface reseals by the summer when water demand peaks and stress/defoliation result. Crop load makes it impossible to using spreading equipment mid-season. A four year trial using a 75% purity pit gypsum was carried out from 2001 through the 2004 season in one such block of surface irrigated almonds on a Wasco Sandy Loam irrigated with low salinity canal water. About 100 kg of the gypsum material was piled by the alfalfa valves at the head of the check in May and again in July to simply be dissolved into the water as it flowed by.

The uniformity of infiltration down the check was 95% even though the concentration of gypsum declined dramatically. Infiltration evaluations at the time of gypsum application showed no difference between treated or untreated checks the first two years, but showed increases of 10 to 47% for the last two years. Soil moisture readings using the neutron probe showed only a 15% improvement in stored soil moisture. Some defoliation was still seen in treated checks in 2004. The three year average yield increase for the gypsum treatment on was statistically significant at 318kg/ha/yr, a 10% increase over the untreated trees. Nut size increased by 3.8%. Cost of this treatment was about $30/ha – much less than retrofitting the system with a gypsum solutionizer machine.