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Tillage Practices

Central Valley Growers Experimenting with Cover Cropping

The Tomato Magazine
December 2005

By Lisa Lieberman

Cover cropping in California’s Central Valley has been reserved, for the more part, for permanent crops rather than annual row crops, such as tomatoes. However, over the past couple of years, a few growers on the west side of Fresno County have been experimenting with cover crops as a way to increase organic materials in their soils, reduce tillage and boost yields.

Can Reduce Tillage Up to 60 Percent
Jeff Mitchell, an extension specialist with the Department of Plant Sciences at the University of California, Davis, says that growers who use cover crops as surface mulches in conservation tillage systems can reduce tillage by as much as 60 percent.

Cover crops are more commonly associated with vineyards, almonds and orchards, Mitchell says. Their use in annual crops is not a standard practice. However, new strategies and different equipment are being developed to adapt cover crops to tomato fields.

Jesse Sanchez, farm manager for R.A. Sano Farms in Firebaugh, says that this year he planted a cover crop on about 1,000 acres of tomatoes. He planted the cover crop last year in September on 60-inch beds and let it grow for 60 days before killing it with Roundup®. Later on in March, during planting season, he tilled the ground in 12-inch wide strips in the center of the beds, putting herbicides on at the same time. Shortly after that, he transplanted the tomato plants directly into the mulch.

“ We plant right in the center of the bed, and then we try not to put any more tractors in the field until harvest time,” he explains.

On average, Sanchez says he’s been getting an extra two to 10 tons per acre in his cover-cropped fields. Fruit size and quality coming out of such fields also seems to better.
“ You see higher solids in the tomatoes. Some have brix levels as high as 6.2 to 6.4,” Sanchez says. “One cannery is paying us more for that (the higher brix), and we’re trying to get other canneries to do the same.”

The cost of planting the cover crop in the fall is relatively negligible since workers need to pre-irrigate the fields during the same time the cover crop is planted anyway, Sanchez points out.

“ We use the same water to irrigate the cover crop that we would be using to pre-irrigate the fields anyway,” he explains.

Soil Compaction Problems
Sano Farms use to rotate tomatoes with cotton, but this became increasingly difficult to do, Sanchez says. The soil was getting harder to till, and whenever heavy rains fell during the fall and they were forced to work the ground wet, it would contribute to additional soil compaction problems.

Alan Sano of Sano Farms concurs that the use of cover crops mellows the soil.

“ We used triticale and barley, and the triticale did a lot better,” he says. The reason is triticale has a deeper and more widespread root system; hence, it helps put more organic material into the soil and helps loosens it up.

In past years, Sano says he experienced problems with his soil getting so compacted and hard that it would crack and force water across the beds and into other rows. This was especially true during wet years when the workers planted cotton and needed to work the fields when they were still wet.

“ The soil would get so tight, we’d have to do three to four hour sets,” Sano recalls. Six- to eight-hour sets would cause root rot and kill the plants. Water, not absorbed quickly enough, would drown the plants.

Using cotton as a rotation crop in between tomatoes also did not seem to be helping very much, Sanchez adds. The cotton doesn’t have as many roots as crops, such as triticale, which help enrich the soil. Next year, instead of using cotton as a rotation, he plans to use cover crops on more than 3,000 acres of tomatoes.

Aside from enriching the soil, one of the goals with using cover crops in conservation tillage systems is to reduce tillage by about half, Mitchell says. But fewer passes through the field can create other challenges, such as difficulties controlling weeds.

“ Weeds are still a problem in cover crop surface mulch production systems,” Mitchell admits. “Right now, for better control, we cultivate early and then as late in the season as we possibly can.”

In his experiments with tilled and no-till cover crops in organic tomato fields in Meridian, Calif., Mitchell found that the percent weed cover in the cover crop mulches was 1.6 to 12.5 times higher in the surface mulches (no-till) systems versus the incorporated cover crop systems the first year; the second year it averaged 2.4 to 7.4 times higher.

“This indicates the inability of even quite high residue surface cover crop mulches to provide satisfactory weed control for conservation tillage production,” Mitchell says.

Reduced Weed Problem with Drip
To counter the problem with weeds, Sanchez converted several hundred acres of tomatoes to drip irrigation. This, he explains, eliminated the need to put any tractors in the field between transplanting and harvest.

“ With the drip, we noticed more nightshade control, and dodder wasn’t as much of a problem,” Sanchez observes.

But even without the drip system, Sanchez says he found himself using fewer herbicide applications to control weeds in the cover-cropped fields.

“ We were probably spending $30 less per acre on herbicides,” he says.

Considering the overall savings in herbicides, less tillage and higher tomato yields, cover cropping is likely to become a permanent part of the farm’s program, Sanchez believes.
Cover crops in tomato fields have other far reaching implications for growers, Mitchell adds. As growers face the future, many will be dealing with added government regulations limiting their tillage practices.

“ By reducing the total number of operations in the fields, we were able to reduce total dust emissions by 67 percent,” Mitchell says.

Although cover cropping and conservation tillage in row crops is not yet widely adapted in California, growers in other parts of the world, including Brazil, are taking a much closer look at the practices.

There’s a lot going on in Brazil, Mitchell points out. Processed tomato growers, in particular, are cutting back on their tillage practices considerably. And while the cost of reducing tillage practices may be only a small part of a grower’s budget, there are other benefits in addition to the cost savings.

© 2006 Columbia Publishing

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