Jeff Mitchell Final Report R96.49

Evaluation of Cover Crop Mulches in No-Till Processing Tomato Production Systems

Final Report - January 1999

Principal Investigator:
Jeff Mitchell, Department of Vegetable Crops, UCD
Kearney Agricultureal Center
9240 S. Riverbend Avenue,
Parlier, CA 93648
(559)646-6565, mitchell@uckac.edu

Other Investigators:
Tom Lanini, Department of Vegetable Crops
Steve Temple, Department of Agronomy
Gene Miyao, Cooperative Extension
Fred Thomas, Cerus Consulting

Location of project: Fresno County

Commodities: tomatoes

Funding:
FY 1997-98: $8,400
FY 1996-97: $8,400

A two-year field study was conducted in Five Points, CA to evaluate and refine the potential of using surface organic mulches in no-till transplanted processing tomato production systems. The winter cover crops rye/vetch, triticale/vetch, Sava and Sephi medic were grown and converted to surface mulches and compared with conventional fallow production systems. Preliminary findings of this work include: 1) transplanting and harvesting processing tomatoes in surface cover crop mulches is feasible, 2) cover crop mulches may actually contribute more favorably to annual water balances than previously thought, 3) earthworm populations tended to be higher under cover crop mulch surfaces than under fallow surfaces at the beginning of the second year of the study and 4) soil carbon content was increased by mulch surfaces relative to fallows. Economic analyses comparing production costs between conservation tillage and conventional tillage systems are needed as may be in-season, post-transplant weed control by appropriate bed shoulder cultivation or chemical materials to make conservation tillage production more farm-ready. These modifications are the focus of our ongoing 1999 studies at a number of sites.

Objective

The objective of this research has been:

to evaluate the effectiveness of surface organic mulches in reduced-tillage processing tomato production systems for:

suppressing weeds

improving production efficiencies in terms of nutrient inputs

providing optimal soil temperature regimes for crop growth and

conserving soil moisture

Introduction

Currently, preplant tillage operations account for about 18 - 24% of overall production costs for annual crops grown in the West Side region of the San Joaquin Valley (SJV) (Biologically Integrated Farming Systems (BIFS) Project Farmer Survey, 1998). An average of about 9 to 11 tillage-related passes are routinely done during the fall-spring period to prepare the soil for summer cropping. These tillage operations represent not only considerable energy, equipment and labor costs, but recent research indicates that tillage reduces soil organic matter (SOM) as well. Because SOM is widely regarded as an important attribute of good soil quality and long-term productivity, interest has been growing over the last several years, in developing alternative production systems that reduce costs while at the same time improve the soil resource through greater carbon sequestration. Conservation tillage (CT) systems may serve to maintain and increase SOM levels. A variety of CT systems have been established for a number of crops including cotton, corn and wheat in the Midwest and throughout the world over the last several decades.

Recently, growing interest in growing vegetables using conservation tillage approaches has also surfaced in a number of places (American Vegetable Grower Magazine, February 1997). The winter annual legume hairy vetch for example, has been used successfully as both a cover crop and as a mulch in fresh market tomato production systems on the east coast (Abdul-Baki and Teasdale, 1993; Abdul-Baki, Stommel and Teasdale, 1995). As a cover crop, the vetch fixes N, recycles nutrients, reduces soil erosion and recycles nutrients and adds organic matter to the soil. When mowed and converted to a mulch, the vetch reduces weed emergence, lowers soil temperature during the hot summer months, reduces water loss from the soil and acts as a slow-release fertilizer (Abdul-Baki and Teasdale, 1994). This system that Abdul-Baki and Teasdale have developed eliminates tillage, reduces the need for applying synthetic fertilizers and herbicides, and is, according to these workers, adaptable to both large and small-scale production in a low-input, reduced tillage system (Abdul-Baki and Teasdale, 1993). Personal communications with Drs. A. Abdul-Baki and R. Morse, who have worked with organic mulches in no-tillage vegetable systems for over ten years, indicate that such approaches could definitely be adapted to Central Valley conditions provided innovative modifications are made. Recent work in Australiz by Stirzaker (1992), with subterranean clover has shown similar benefits in lettuce and tomato production systems (Stirzaker, Sutton and Collis-George, 1992; Stirzaker, Passioura, Sutton and Collis-George, 1993). There may be however, problems associated with using cover crops in this way: land is put out of production, soil moisture may be depleted during the cover crop growing season relative to a winter fallow, and early summer season soil temperatures may be cooler under a surface mulch than bare soil. There may also be problems related to the management of cover crop residues that can be phytotoxic to certain crops that follow a green manure mulch (Lovett and Jessop, 1982).

Over the last three years, we have evaluated and refined conservation tillage approaches for processing and fresh market tomato production in the Central Valley. Conservation tillage work has also been initiated in other regions throughout the State including the Coachella Valley within a mixed vegetable rotation study at the University of California Desert Research and Extension Center in Indio and the Central Coast regions of San Luis Obispo and Santa Barbara counties. Though these production practices are new for the State, steady progress is being made in evaluating their potential and in refining practices that have been successful in other areas. Progress on our recent work with tomatoes is reported here.

Accomplishments / Procedures

Field studies were conducted in 1997 and 1998 at the UC West Side Research and Extension Center (WSREC) and the Sustainable Agriculture Farming Systems (SAFS) Project’s "playground" area on the UC Davis campus. In the WSREC experiment, six winter cover crop mixtures were planted in October 1997 on preshaped 60" tomato beds and killed in late February to provide a surface mulch into which processing tomatoes were machine transplanted. Cover crops were only planted on the bed tops, not in the furrows. These cover crop treatments were compared with a winter fallow to which preplant herbicide is applied and a fallow control to which no herbicide is applied. Each treatment plot was 2250 ft²which permitted normal tractor operations. The cover crop mixtures were 1) Medicago scutellata "Sava", 2) Medicago truncatula "Sephi", 3) Triticale / Lana vetch and 4) Ryegrain / Lana vetch / Magnus pea. These treatments permitted a testing of mulches with different growth and cover attributes and cover crop mixtures of different seed costs. Each mulch/fallow plot was split into 3 subplots. One subplot was fertilized at 100 lbs N / acre, one at 200 lbs N / acre and one was not fertilized to evaluate the potential for reducing fertilizer inputs in this system. The mulch/fertilizer treatments were replicated four times in a split plot design with fertilizer applications as main plots and mulch treatments as subplots. A common processing tomato variety, 3155, was transplanted using a single-row machine transplanter that has been modified by B & B No-Till of Laurel Fork, VA. The modifications are based on a successfully-used no-till transplanter that has been developed by R. Morse at Virgina Polytechnic Institute (Morse, 1995). Tomato crop growth was determined during the growing season using a Decagon Accupar Ceptometer, Pullman, WA. Fifty tomato petioles of the first fully expanded leaf were sampled four times during the tomato growing season and analyzed for tissue N at the UC DANR Lab in Davis using a LECO FP428 Nitrogen Gas Analyzer (St. Joseph, MI). Soil temperature at 10 cm depth was monitored continuously during the tomato growth season using a microprocessor controlled temperature data logger (Campbell Scientific). Changes in soil water content during the tomato season were monitored by neutron hydroprobe (Campbell Pacific Nuclear) readings in access tubes installed in the planted row of beds before and after irrigations. Fruit yield determinations were accomplished by machine harvest using field weighing gondolas. Tomato quality was assessed by measurement of soluble solids and color at a State grading station and pH by Mitchell at the WSREC lab.

At four weeks after tomato transplanting, and twice again thereafter, weed cover and species composition were assessed from 3 randomly placed 50 X 50 cm quadrats per subplot.

The trial conducted at the SAFS plots in Davis was primarily for demonstration and observation purposes. Tomatoes were transplanted into a variety of cover crop mulched plots and compared with + herbicide and - herbicide fallow plots. Tomato growth was monitored using a Ceptometer and yields were determined by hand harvesting 20 ft sections of each plot.

Results

In general, the following preliminary findings surface from this work.

Water content (0 – 9 feet depth) was similar in fallowed and cover crop soils throughout much of the 1997 – 98 winter and at tomato transplanting in April
Earthworm populations tended to be higher under cove crop mulch surfaces than under fallow surfaces in February and March 1998 (Table 1)
Weed pressure was considerably greater in 1998 than in 1997 under both fallow and cover cropped mulches (Data still being analyzed)
Soil water content (0 – 9 feet depth) was generally higher under cover crop mulches from May through August relative to conventional tillage bare surfaces (Figures 1a – c)
As in 1997, tomato yields under certain cover crop mulches were comparable to those under bare fallows. Statistical analyses are still being made on this data however, there do not appear to be fertility benefits associated with cover crop mulches at either the 0 or 100 lb N reduced fertilizer rates. (Figure 2a – c)
Soil penetration resistance was lower under rye/vetch and triticale/vetch mulches at some 0 – 60 cm depth intervals (Figure 3)
No differences resulted from 2 year back-to-back mulching in terms of soil water holding capacity or bulk density
Soil carbon content was higher under the triticale/vetch and rye/vetch mulch surfaces than under a fallow surface at the end of the two-year study.

This project is being summarized as the MS thesis of Enrique Herrero, student in the Department of Vegetable Crops at the University of California, Davis.

Discussion and Conclusions

Considerably more work is needed to evaluate, refine and adapt conservation tillage techniques for California vegetable production systems before these approaches are ready for widespread adoption throughout the State. Steady progress is being made however, to carefully select the particular types of production contexts where they have the greatest potential opportunity of succeeding. To date, a number of preliminary conclusions can be drawn from the work reported here. These findings include the following: 1) transplanting and harvesting processing tomatoes in surface cover crop mulches is feasible, 2) cover crop mulches may actually contribute more favorably to annual water balances than previously thought, 3) economic analyses comparing production costs between conservation tillage and conventional tillage systems are needed and 4) in-season, post-transplant weed control by appropriate chemical materials or bed shoulder cultivation may make conservation tillage production more farm-ready and are the focus of ongoing 1999 studies at a number of sites.

Figures 1-6

TABLE 1

Table 1 Number of earthworms in surface 15 cm February / March 1998

Fallow + herbicide	5.17
Fallow – herbicide	1.42
Sava medic	15.25
Sephi medic	12.08
Triticale / vetch	8.08
Rye / vetch	14.08

Literature Cited

Abdul-Baki, A.A. and J.R. Teasdale. 1995. Establishment and yield of sweet corn and snap beans in a hairy vetch mulch. In Proceedings Fourth National Symposium on Stand Establishment of Horticultural Crops. Monterey, CA April 23 – 26.
Abdul-Baki, A.A., J.R. Stommel and J.R. Teasdale. 1995. Vetch mulch fetches more veggies. Agric. Res. May
Lovett, J.V. and Jessop, R.S. 1982. Effects of residues of crop plants on germination and early growth of wheat. Aust. J. Agric. Res. 33:909-916.
Morse, R.D. 1995. In-row soil loosening improves stand establishment and yield of no-till cabbage and broccoli. In Proceedings Fourth National Symposium on Stand Establishment of Horticultural Crops. Monterey, CA April 23 – 26.
Stirzaker, R.J. and I. White. 1995. Amelioration of soil compaction by a cover-crop for no-tillage lettuce production. Aust. J. Agric. Res. 46:553-568.
Stirzaker, R.J., J.B. Passioura, B.G. Sutton and N. Collis-George. 1993. Soil management for irrigated vegetable production. II. Possible causes for slow vegetative growth of lettuce associated with zero tillage. Aust. J. Agric. Res. 44:831-844.
Stirzaker, R.J. B.G. Sutton, and N. Collis-George. 1992. Soil management for irrigated vegetable production. I. The growth of processing tomatoes following soil preparation by cultivation, zero-tillage and in-situ grown mulch. Aust. J. Agric. Res. 44:817-829.

Evaluation of Cover Crop Mulches in No-Till Processing Tomato Production Systems

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