A key issue for organic tomato farmers is the “fertility gap,” which is informally defined as the time just before harvest when testing shows the nutrients that were placed in the soil before the growing season are exhausted but the plants need a little more to achieve peak yields. Conventional growers have it easy: They can fill the irrigation lines with urea, a technique called fertigation, and the plants will immediately respond. While organically registered liquids can help fill the gap, they tend to cost a little more, they are not as fast-acting as urea, and they can sometimes clog the tiny pores in drip irrigation lines.
Olam, an agricultural firm active in 16 major commodities and 65 countries, buys organic tomatoes for their canneries in Williams and Lemoore, Calif., and cans them under the Muir Glen label and others. Olam wanted their growers to produce the highest-quality organic tomatoes possible.
At the same time, Olam’s two California canneries create a fair amount of waste—thousands of tons of skins and seeds per year—as well as the 2 to 3 percent of all incoming tomatoes that hit the floor or for other reasons do not end up in a can. Some of those tomatoes were going to feed cows, and others were going back to the field, but to Zach Bagley and others at Olam, they looked like an underutilized asset.
Bagley, a Purdue University alumni who did his masters work through the Peace Corps Masters International Program at UC Davis, wanted to do something entrepreneurial that would help growers. Olam was also interested in value-added solutions.
Enter GO Compost, conceived in 2012 and now making up to 15,000 tons per year of compost from tomato skins and seeds, known as pomace, and other locally sourced materials. GO stands for the partners in the project, General Mills and Olam.
“I didn’t really know anything about compost, but I became the person to figure out how to do it right,” said Bagley who now manages the composting project in his role as an Olam agricultural operations supervisor. “Thankfully, Olam and General Mills have given us the runway to get up to speed.”
That runway included purchasing a straddle-type compost windrow turner and a front-end loader, and the use of roughly 25 acres on a 600-acre property near Williams, in Colusa County, where the company pipes cannery water and grows sorghum and Sudan grasses and winter rye. The pomace is wet and contains nitrogen, so Bagley struck deals to bring on carbonaceous materials such as rice hulls and almond shells, as well as some local chicken and horse manure.
The tomato growers were happy to have a locally produced soil amendment that could help them build their soil and fulfill their organic production plans. Despite costing significantly more than green waste compost, the first year’s production of just under 3,000 tons sold out, with two-thirds of it going to Olam growers and about 90 percent overall going back to tomato fields. Most tomato farmers add compost and/or manure to their soils in the fall, after the harvest.
To prove the value of its compost to tomato farmers, Olam worked with Tom Rabaey, an agronomist with General Mills, to design a series of field trials. Completed in five different fields, the trials showed statistically significant yield increases in four of the five fields. Fields at the lower end of the yield spectrum received as much as a 25 percent boost from using the compost, while the increased yield for those at the upper end of the spectrum was closer to 10 percent. Interestingly, the peak yields occurred when compost was used at 6 tons per acre; 3 tons per acre often had a lesser impact, and an application of 12 tons per acre did not result in a higher yield than did 6 tons per acre.
OLAM also worked with agronomist Tim Hartz of UC Davis to study the “fertility gap.” In 1999, Hartz had put together information on early-season macronutrient-level indicators in soils that would affect yields in conventional tomatoes. In 2011 he wanted to replicate that effort with organic tomatoes. He collected soil, petiole, and leaf samples from 47 organic fields immediately following transplant and in weeks 5, 8 and 11 afterward. Growers then had the opportunity to follow up with Hartz on their specific test results and devise a corrective action plan. These efforts, jointly promoted by UC Cooperative Extension with funding from General Mills, did not specifically consider the impact of compost.
“One organic field in three needs in-season augmentation of nitrogen,” said Hartz. “We are able to describe what predicts that. The biggest determinant is how much nitrate nitrogen was in the soil profile when they planted. In this context, what you did in the fall can have an impact.”
Olam compost is also part of a series of trials at Russell Ranch, UC Davis’ long-term agricultural experimentation farm. Several types of compost, including green materials, chicken manure, and Olam compost, were used on processing tomatoes.
Meanwhile, GO Compost has slowly been ramping up production and diversifying its product line. Bagley connected with a local mushroom grower and began composting its spent bedding. They also began working with a major marketer of bagged compost to move their products into the horticulture industry. They have an organic input registered with the California Department of Food and Agriculture.
“We don’t push our particular brand of compost, because, one, we don’t have that high a volume and we would run out quickly if they all used it, and two, there’s a lot of options out there,” he said. “As a contractor for their tomatoes, we want them to make that choice. Our product has been in fields for two or three years, and we’ve done trials and we think we‘ve done a good job on those. But the major message is, you’ve got to increase the organic matter in your soil. Whether that’s the traditional—the chicken or turkey manure—or something else does not matter. The idea at the end of the day is to increase that OM (organic matter) so your soil can build on itself and you’ll have the amount of nutrients you need.”
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For more information contact: Compost Use in Agriculture, organics@calrecycle.ca.gov