Biosolids for field crops in the San Joaquin Valley: What do we know?
Jun 3, 2006 12:00 PM, By Blake Sanden
We all know the saying, “You can have too much of a good thing.” and the more Spartan corollary, “All things in moderation.” We also know that any amount of a bad thing is no good. So what about using biosolids (sewage sludge) as fertilizer to grow grain and animal feed crops? Is this flat out just a “bad thing,” or is it a “good thing that needs moderation/regulation” for recycling nutrients that shouldn't be concentrated in the landfill or dumped in the ocean? Or do we really know?
And this is where we have a big problem. Qualified researchers line up on both sides of the issue; some pointing to why the stuff can be really good and others saying applying sludges to farmland is like parking nuclear waste containers in your backyard and waiting for them to leak. The mix of biosolids, soils, crops, groundwater and farming practices is a very complex system with a lot of variation from one field to the next. It is easy to find holes and “what if's” in all sides. So what do we know for sure?
Since 1993, more than 10 million tons of biosolids, digested wastewater treatment plant sewage sludge, has come over the Tehachapi Mountains into the southern end of the San Joaquin Valley. Until 1998, controls and oversight of application were too loose and several instances of gross dumping (Mojave) and excessive applications causing crop damage (Maricopa Highway) were seen. Field applications were made to nearly 40,000 acres across Kern. The general interest for growers was the equivalent of more than $100 per acre of fertilizer value in the material. Local ordinances were passed with stricter permitting that sharply reduced the applied acreage to 12,000 acres to 15,000 acres. Annual tonnage dropped even more starting in 2003 when the Kern County Board of Supervisors instituted a ban on the application of “Class B” biosolids. The application of “Class A/EQ” (sludge with a lower pathogen count) was still permitted. Treatment plants and farm appliers changed practices and land was reduced to about 8,000 acres.
The biggest problem has been lack of documented impact on local soils. The University of California Cooperative Extension, Kern County, stepped up to the plate to try and find out what we know locally. Good ag Extension programs and research are supposed to work like detective Joe Friday from the old television series Dragnet: “Just the facts, ma'am.” So starting in fall 1998, four years of field trials tried to dig out the facts on biosolids applications to wheat and cotton and the fate of selected heavy metals. The biosolids applications were compared to standard fertilizer programs. The results of these trials showed a consistent benefit to wheat production under moderate sludge applications of 8 dry tons/acre to 12 dry tons per acre. Wheat yields on a very poor salty alkali soil doubled when only 1 irrigation was applied (0.35 to 0.7 ton per acre) and protein content increased from 11.1 to 14.3 percent. On a fully irrigated saline/alkali field, grain yield increased from 3.0 ton per acre to 3.2 ton per acre the first year and 3.65 ton per acre to 3.75 ton per acre the second year. These differences are not statistically significant, but the 2.0 percent and 1.5 percent increase in protein content was significant.
For the 2002 season, Ultima cotton was planted to the 40-acre field with adequate water supply. The biosolids treatment had a significant one-third bale (166 lb) per acre lint yield increased over the standard fertilized control for a total yield of 3.4 bales per acre. Percent turnout for the control was higher due to slightly smaller plants. Another 80-acre field planted to Ultima compared a standard nitrogen fertilizer application to Class B biosolids, a straight, biosolids compost and a biosolids/dairy manure co-compost. This field had received Class B biosolids over the entire acreage for the three prior seasons. Yields in this very nonuniform field averaged 3.1 bales per acre with no significant difference between treatments.
In general, surrounding production fields to which Class B biosolids have been applied over the previous five to eight years had excellent yields compared to the long-term ranch average. However, a field of pima cotton suffered severe defoliation and loss of bowls over the lower 10 nodes to 12 nodes. This field yielded quite poorly; suffering similar symptoms found in another Pima field in southwest Kern County in 1996. Other fields have also exhibited occasionally yield loss in staging areas where the biosolids are dumped prior to spreading. In some fields the effect lasts four years. The exact cause of this problem is not known at this time but is clearly related to high application rates.
The change of organic nitrogen in the biosolids to nitrate nitrogen (which plants can use) was highly variable across all fields; ranging from a minimum of 4 percent to as high as 85 percent in one year. The overall average was 42 percent. The standard industry calculation is 20 percent. Consistent high applications of organic materials (like biosolids and dairy manure) year after year containing significant nitrogen can lead to groundwater contamination. This was the case resulting from the high dairy concentration in Chino, east of Los Angeles.
Applied metals over the test were 20 pounds per acre to 50 pounds per acre for copper and zinc. For heavy metals like arsenic, cadmium, lead and chromium, for which EPA has a concern, this was about 0.5 pound per acre to 9.9 pounds per acre. A very slight increase of copper and chromium was measured in the second foot of soil. These additional amounts were significant increases but still close to amounts found in many of our native Westside soils.
Unfortunately, nothing can be said about the fate of pathogens in these trials as this was beyond the scope of the available funding and local expertise. Questions regarding the long-term fate of pathogens, secondary organic chemical breakdown products and the movement of heavy metals are the main issues that continue to cause significant public concern over this practice. There is, however, no evidence to suggest that pathogen survival in sludge applied to the soil is greater than many of the pathogens in animal manures that can also infect humans.
This June 2006, Kern County voters are being asked to vote on Measure E, which “prohibits the land application of any (bulk materials containing any form of) biosolids in the unincorporated area of Kern County.” This is a local measure meant to help reduce the amount of sludge imported to Kern County. California Senate Bill 926, introduced by Dean Florez and now stalled in committee, would require all counties do deal with their own sludge within their county borders. Legal challenges, policy ‘maneuvering’ and hypocrisy swarm around these measures and the use of the material like flies on … well, you know what!
Measure E still allows for homeowners to use your favorite bag of Kellog's Nitrohumus or Gromulch to improve the soil in your vegetable garden, but the same type of biosolids containing compost in a bulk form would be illegal for the large farmer to apply to his alfalfa, cotton or corn. Bakersfield, Tehachapi and other incorporated city “sewer farm” acreage will still be allowed to use their own sludge residues to grow crops.
So what do we know? Fact 1: We will all keep eating, digesting and … go on to No. 2. Fact 2: The material has good fertilizer value and has improved crop yields in many areas across the country when applied at proper rates on an occasional basis. Fact 3: Big city sanitation departments often had “I don't care” attitudes and poor oversight of sludge applications in the 1990s that caused problems in certain fields and showed contempt for the local farming community. This lead to Fact 4: Instituting ultra restrictive laws force sludge applications to small acreages where over application will almost certainly lead to groundwater contamination of some kind. Fact 5: You will be killed in an accident on a Los Angeles freeway before you die of cancer from tomatoes grown with Kellog's Nitrohumus. (No, that's not really a scientific fact I can back up, but you get my point!)
We need real answers and management for real problems. The bluster of “banning bills” may work against us in the long run.
Blake Sanden is a UC Extension farm advisor
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