Over the last 15 years almonds and pistachios have become the major cash crop commodity alternatives to cotton in the San Joaquin Valley. California’s bearing almond acreage has increased from 418,000 acres in 1995 to 710,000 acres in 2009, while over the same period cotton acreage declined from 1.6 million acres to less than 200,000 in 2009.
Total pistachio acreage went from 75,000 to 190,000 acres over the same period. At the same time, Kern County has seen its almond acreage double from 68,000 to 132,000 bearing acres. This rapid conversion of acreage has been fueled by stagnant cotton prices with only moderate yield increases, drastically increasing water costs and significant increases in almond yields (1,329 pounds per acres 1995-1999 average increasing to 1,994 pounds per acre 2005-2009 average). Excellent marketing and wide-ranging product alternatives have contributed to a reasonably stable profitable rate of return even with total California tonnage more than doubling.
Substituting pistachios for cotton in marginal soils has generally been a favorable alternative as University of California Cooperative Extension research in the late 1990s showed they are as salt-tolerant as cotton. The final and largest study in this series (covering 240 acres) started in 2004 will take newly planted pistachios all the way to bearing under saline conditions. These very current field and USDA Salinity Lab studies have given pistachio growers good tools for salinity management in real field conditions in the 21st century.
Almonds are another story, however. They are a much more sensitive tree than pistachios, but the studies we have on almond salt tolerance are more than 50 years old. Growers have tended to “push the limits” on these old standards and as water has become more expensive and cotton acreage less profitable, almonds have been the preferred crop over pistachios; providing a commercial crop in the third year instead of waiting the usual seven years for pistachios. But many orchards have gone from being on the edge to heading over the cliff in terms of salt toxicity.
A combination of hydrologic and “judicial” drought (The latter includes restrictions of state and federal project pumping out of the Delta due to Endangered Species Act listing of the Delta Smelt.) has drastically cut the import of fresh water to the San Joaquin Valley over the last three to five years. Growers and water districts have responded by pumping more groundwater, buying “emergency pool” water and other market trades; improving field irrigation efficiency where possible; and finally reducing applied water.
With insufficient rainfall in the SJV for natural winter leaching the result has been a steady increased trend in the number of almond (and even pistachio) orchards showing marginal leaf burn, yield decline and other obvious signs of excess salinity in the rootzone. Of course this damage is often compounded by additional deficit irrigation and declining groundwater quality as water table levels drop.
Much of this damage makes sense based on the commonly used 50-year-old threshold for almond root zone salinity. However, there are other orchards that should be in much worse condition based on soil and water analyses, resulting in much lower yields than they actually have. The contention of those of us helping growers deal with these problems is that they are rootstock, soil, sodium/calcium ratio and chloride/boron/bicarbonate/sulfate interactions that can mitigate or exacerbate the damage beyond the limited data we have at hand.
The most recent almond salinity field study was conducted on the UC Westside Field Station in western Fresno County (an area of prime concern for this issue) from 1980 to 1987. But even the best control treatments and resulting tree performance was far below 21st century industry standards and offered little in the way of management thresholds and guidelines.
We are facing a growing crisis for perhaps 25 percent to 30 percent of the almond industry that is frequently having to make due with declining water quality, water supply and increasing root zone salinity. Our data is old and incomplete, lacking comprehensive understanding of the mitigating effects of field soils, solute and specific ion interactions and current rootstock tolerance under the high performance yield expectations of 21st century almonds in the SJV. A group of salinity, water management and almond physiology specialists and farm advisors with the university have just begun serious discussions that will lead to the formation of an Almond Salinity Management Taskforce with sufficient funding to initiate field, greenhouse and rootstock trials to deal with this growing problem.