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Growing Tomatoes With Less Tillage

The Tomato Magazine
October 2005

By Jeff Mitchell
University of California, Davis

Since 1999, we have evaluated conservation tillage (CT) and cover cropping (CC) practices for tomato production in an eight-acre field in Five Points, Calif. The objective of this work has been to compare standard till (ST) with and without (NO) winter cover crops and conservation tillage with and without cover crops in terms of economics, productivity, soil properties and dust emissions through a tomato – cotton rotation. The study field is divided in half to allow both crops to be grown in each year. A summary of the first five years of this work is presented here.

Tillage management
The standard tillage systems have been managed as is customarily done in the West Side San Joaquin Valley region. Beds are disked and reformed following harvest of each crop. Prior to tomatoes, the beds are also shaped with a power incorporator. The standard till cover crop system uses a triticale/rye/vetch “green manure” approach with the cover crop disked in each spring before establishing the summer crops.

The CT systems use about 50 percent of the overall tillage, or soil disturbance operations, as the ST systems. Tomatoes are “no-till” transplanted, and cotton is no-till seeded into beds that haven’t been worked or moved since the beginning of the study—except for a shallow cotton root undercutting following harvest for Pink Bollworm management compliance. Tomato beds have been quite “rough” following the one-pass fall cotton stalk management operation and are “re-readied” using furrow sweeps at the time of transplanting and during in-season cultivations. In the CT cover crop systems, the cover crop is sprayed with glyphosate, chopped and left on the soil surface as a mulch before transplanting tomatoes or planting cotton. A summary of pre-tomato tillage operations used in each system is shown in Table 1.

CT Equipment
A few equipment modifications have been made in the CT system. A three-row transplanter sled was used. It was fitted with 20-inch diameter coulters ahead of each transplanter shoe, residue-slicing disks in front of each sled and additional press wheels behind the transplanter drive wheels to seal seedlings into the soil.

A Sukup high residue corn cultivator (Sheffield, IA) was converted to a three-row, 60-inch configuration, and bed-top L-sweep blades were added for tomato bed cultivation.
Sidedress fertilizer was applied using Yetter Mfg. (Colchester, IL) high residue liquid or dry fertilizer applicators that had coulters fitted in front of the shanks.

Processing tomato yields (cv Heinz ‘8892’) are shown in Table 2 for 2000 - 2004. Letters following each yield number indicate whether there were statistically significant differences between treatments within a given year; if the letters in a particular column are different, this indicates that the systems likely had significant yield differences. CTNO yields matched or exceeded those of either ST systems in all five years of this work while using considerably less tillage. Yields of the CTCC system were lower than the other systems in 2000 and were lower than the CTNO in each of the next two years of the project as well. We observed that tomato plants often grow more slowly early in the season over the heavy CT cover crop mulches, and this is perhaps due to lower above and below mulch temperatures that we have measured. We also observed more surface “trash” entering the harvester in the CT systems, however, virtually all of this was typically removed by the harvester’s suction cleaning mechanism before entering transport trailers.

These results indicate at least the short-term potential to produce tomatoes following cotton with considerably less tillage than is currently done in most production fields. The tillage management approach that has been pursued in this study seeks to reduce primary, intercrop tillage and depends on subsequent, early-season bed “reconditioning” with the transplanter and cultivator operations. By doing this, beds have been left quite rough during the winter and into the spring, and this may be a management strategy that today’s growers may not be comfortable with because early-season beds are rather degraded and may not be well shaped. In this study, however, we have found that it is possible to establish tomato transplants into these beds, to rebuild beds using the transplanter and cultivator that are both fitted with “ridging wings” or furrowing tools and to successfully harvest fruit with this management system. With this approach, early cultivation is needed to recreate furrows and to clean residues out of furrows to enable surface irrigation.

Within this CT tomato system, the largest challenge has been to consistently manage weeds during the entire production season. The strategy we have pursued involves cultivation—generally two to three times per season—and hand weeding. However, because herbicides have not been incorporated into the soil, the CT systems have consistently had many late-season weeds grow in the furrow, and they have not been effectively managed because the tomato plants are, by then, too big to allow herbicide spraying or cultivation. Thus, there is a need to improve the CT systems, particularly late in the season.

CT Production at San Joaquin Valley Tomato Farms
Two commercial variations of the general CT and cover crop systems that are described here were recently featured as part of the San Joaquin Valley Conservation Tillage 2005 conference farm tours held in June. One farm was Sano Farms, a processing tomato and cotton farm in Firebaugh, Calif., and the other was Sun Pacific’s fresh market tomato farm, also in Firebaugh. Each of the farms that were visited uses winter cover crops and a spring strip tillage operation to mix cover crops and incorporate herbicide in the transplant line. Cultivation has not been used in either of these commercial fields. In one case, subsurface drip irrigation is carefully managed to avoid wetting the soil surface, thereby controlling weeds to a great extent.

At the other CT tomato farm, over-the-top herbicide was used. More details about these systems may be obtained by emailing Jeff Mitchell at mitchell@uckac.edu and requesting the DVD video distributed to participants of CT2005 and that describes these CT tomato systems.

Future CT Tomato Systems
There may be long-term economic and resource conservation benefits from substantially reducing tillage in production systems relative to what is done today. To develop sustained no-till rotations that include tomatoes, a number of changes will be required with respect to optimizing management of the overall production system. Current systems—including the approach we pursued in this study—rely primarily on surface, or gravity irrigation systems that necessitate clean, or clear furrows for efficient and uniform water application. If the irrigation water delivery system is changed to either subsurface drip or low pressure overhead delivery, we hypothesize that production costs might be lower, surface residue might be left in place, soil disturbance could be avoided and weeds might be better controlled without cultivation. These management systems, as well as other production system alternatives, are now being evaluated.

Jeff Mitchell is a Cropping Systems Specialist with the University of California, Davis, at the Kearney Agricultural Center in Parlier, Calif. Contact information: 9240 South Riverbend Avenue, Parlier, CA 93648; phone (559) 646-6565; fax (559) 646-6593;
e-mail: mitchell@uckac.edu.

© 2006 Columbia Publishing

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