Cotton has long been known as a salt tolerant crop, but despite many small-scale field and laboratory trials over 30 years almost no marginally saline water of more than 1,000 ppm salt in the San Joaquin Valley is used for long-term production.
Over this same period, however, water costs have increased four- to tenfold while cotton prices have actually declined to those seen in the early 1960s. Farmers are looking for more secure water supplies and converting acreage to more profitable permanent orchard and vine crops.
For permanent crops only pistachios have been shown to be tolerant of the salinity often found on the Westside of the San Joaquin Valley, especially when soluble boron levels go above 1 ppm. Work in Iran, salt tank studies at the USDA Salinity Lab, Riverside, and a nine-year small plot study in northwest Kern County indicate pistachios may have the same level of salt tolerance as cotton. However, this has not been proven on a large commercial scale in California under our high-yield production conditions.
Enter one of the “old salts” of Kern County cotton, Fred Starrh of Starrh & Starrh Farming. Like many of the Westside Kern water districts, a 100 percent allocation of surface water in the Belridge Water District only gets Starrh about two acre feet each season. It takes 2.6 to 3 acre feet to grow cotton and about four acre feet to grow almonds, pistachios or alfalfa. It's been more than 5 years since the last 100 percent allocation. The choices have been simple; either fallow acreage or buy more expensive supplemental water elsewhere.
Groundwater in this area had previously been marked as “unusable” by the Central Valley Regional Water Quality Control Board. However, recent testing of old wells and historical data indicated salinity ranged from 2 to 6 dS/m with 1 to 10 ppm boron.
Not known for taking the timid approach in finding solutions for big problems, Starrh decided that it would be economically beneficial to utilize this groundwater. Seven wells were drilled from the end of 2002 through 2003. The eventual goal is to convert much of this acreage to pistachio production. With this end in mind, the six quarter section fields outfitted with drip tape are laid out to accommodate pistachios planted on a 22-foot row spacing and still allow for rows of interplanted cotton for the first three years that pistachios are growing.
In two of these fields Starrh is working with the University of California Cooperative Extension in one of the largest salinity field trials ever installed in the San Joaquin Valley to get detailed information comparing the fresh Aqueduct water to the 50/50 blend and full strength well water.
In the first year of this trial (2004) cotton was planted to the entire field. Total salts applied in the 32 inches of irrigation water were 1,898 pounds of salt per acre for the Aqueduct water, 11,680 pounds of sale per acre for the 50/50 blend, and 17,285 pounds of salt per acre from the well water.
It is essential to have adequate drainage when handling this amount of additional salt. Drainage plus the application of six to eight inches of Aqueduct water in the spring for leaching and crop establishment is the key to maintaining yield.
Test plot findings
In 2004, large-scale replicated test plots (19.4 acres each) using drip-tape buried 10 inches below the top of the bed were set up over 310 acres to test the impact of saline well water on cotton yields. A 2,015 pounds of lint per acre of Pima cotton (DP340) on a 38-inch row spacing was achieved using this well water (3,000 ppm TDS or 4.5 dS/m EC). A 50/50 blend of well and California Aqueduct water (1,900 ppm or 3.0 dS/m) yielded 1,930 pounds of lint and the Aqueduct water (262 ppm or 0.41 dS/m) yielded 1,935 pounds of cotton. Yields were not statistically different.
Another 600 production acres under drip tape and 600 acres using hand-move sprinklers were irrigated with the 50/50 water using additional wells. The mixture of Acala and Pima fields all yielded between three and four bales per acre. This conjunctive use program provided the grower with 2,000 acre feet of well water at an average cost of about $60 per acre foot of water; a savings of $30-$60 per acre foot compared to the cost of the water from the district or other sources.
In the pistachio trial, rootstock seedlings (PG1) were planted March 2005. Four 38-inch rows of cotton were interplanted in April when the weather warmed up. Plant mapping of cotton shows no treatment growth differences for 2005. Boll loads look similar and yields may be close to 3 bales per acre, not bad considering the very late spring. Trunk circumference, shoot growth and bud take in the pistachios show no difference as of the end of September.
Crop water use (ET) is slightly reduced for the saline well water, which actually helps prevent rank cotton growth.