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Fall 2004 - Vol. 5/No. 1
Cover/cash crops in tillage systems
by Steven R. Temple, Kaden B. Koffler, Johan Six, and Francisco Reis
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Fall planting of lupin/chickpea into corn residue (photo by Steve Temple) |
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The first and second seasons of experience with tomato and corn in the SAFS Conservation Tillage (CT) treatments at
Russell Ranch have produced mixed results, especially in management of water, weeds, and timely nitrogen (N) supply to
high-demand summer cash crops. Treatments whose management combines cover cropping with CT present the greatest
challenges. Organic and conventional growers at the June 24 SAFS field day panel stressed the value of multiple and
diverse cash and cover crop rotation options in responding to the complex problems of reduced till, cover crop
production systems, and particularly organic systems.
During the 2003 summer cropping season, several “companion” experiments were initiated at the Russell
Ranch as a part of the SAFS effort to improve the performance of the corn-tomato rotation. Efforts are being made to
identify cash and cover crop species that perform particularly well in one or more of the SAFS CT systems. An experiment
studying the effects of continuous soil food web enrichment under both CT and Standard Tillage (ST) was described by
Louise Jackson et al. in the SAFS Spring 2004 newsletter
(http://safs.ucdavis.edu.newsletter/v4n2-3-spring2004.pdf).
Two other experiments were initiated to evaluate the utility of alternative cover and cash crops under CT management.
One concluded in July, and featured the planting of grain lupin line RS 2034 (Lupinus albus), and the chickpea variety
Sierra, following the fall 2003 harvest of field corn. The other concluded in late September comparing summer and/or
winter cover crops grown between the processing tomato harvest in 2003 and field corn planting in 2004.
Cash crop alternatives: Post-corn grain legumes
After flail mowing and two passes with a Buffalo rolling stalk chopper, two winter legumes (lupin and chickpea) were
planted into corn residues on Nov. 18, 2003 and Mar. 17, 2004 using a John Deere 1750 No-till planter. Spacing was 30”
between rows on the 60” bed, which placed the legume seed in the same location as the maize root residues. No
fertilizers were applied. Lupin seed was inoculated with rhizobial inoculant, and chickpea with a granular implant.
Fall-planted chickpea was not inoculated and an herbicide mixture of 1.0 lbs/A of Prowl and 0.125 lbs/A of Goal was applied
Dec. 3, 2004 over the fall- and spring-plant treatments to reduce weed pressure.
Germination was good for both species at both planting dates, and little predation by seed corn maggot was observed.
Fall-planted garbs were retarded in early growth by 0.125 lbs/A of Goal 2XL, but plants recovered in February. Rainfall
was good during the 2003-04 December-February winter season, but sharply reduced (with unusually high temperatures) in
March. Spring-planted treatments were sown with no additional tillage or weed management. Because of the early cutoff of
spring moisture, the fall-planted crops received two supplemental spring irrigations, while the spring-planted crops
received three irrigations. Spodnam was applied to lupin during pod-fill to reduce shattering losses. Fall plantings
were harvested on June 23, and spring plantings on July 22. Samples of plant dry weight biomass were taken for all
treatments on Mar. 30 (mid-flower for fall plant) and May 27 (mid-flower for spring plant). Data for biomass dry weight
and grain yield are shown in Table 1.
The same chickpea variety, planted Dec. 3 under ST at the UC West Side Research and Extension Center (WSREC) 200 miles
to the southwest of Davis, yielded 3,913 lbs/A. And the same lupin line, planted at WSREC under ST, yielded 1,997 lbs/A.
Perhaps the most interesting result was at UC Davis’ Field Station, where 2003-crop common bean beds received a single
pass of the Sundance bed disc, were ring-rolled, and planted with Rhizobia-inoculated grain lupin. That two-acre block,
planted the same day as the “post-corn” experiment six miles west of Davis, averaged 2,287 lbs/A.
Biomass accumulation data (Table 1) show that spring-planted legumes accelerated crop growth rapidly between March 30
and May 27. With the extra irrigation provided to the spring-plant crop, the chickpea continued to produce flowers and
fill pods well into June. The result was a respectable 1,873 lbs/A on a plant that was visibly much smaller than those
harvested at WSREC. The gross crop value for this 2004 harvest would be nearly $550/A, with very limited cash investment.
The late July harvest would nonetheless preclude reasonable chances of harvesting a late-summer crop.
There is an opportunity to select for genotypes of both crops that are better adapted to planting date(s), location,
and CT system. Adjusting seed rows (perhaps 3/bed) offset from corn rows appears desirable. In this study, fall-planted
chickpea showed more virus than spring-plant, and spring-planted lupin was attacked more by insects and soil diseases.
Use of fungicide-treated seed and rhizobial implant gave good nodulation for chickpeas. Supplemental spring irrigation
was complicated by corn residues in the furrow. No winter rain runoff was observed from these plots. From other herbicide
studies, it seems that Prowl alone would give adequate weed control with no chickpea stunting.
Cash crop alternatives: Summer/winter strategies
Most cover crop management practices currently used in California were developed for intensive tillage systems, and
are not transferable to CT systems. To maximize soil and water quality benefits of cover crop-driven CT systems, new
cover crop management tools need to be developed.
During the original 12-year SAFS experiment in which all treatments were under ST management, the supply of N from
vetch following spring incorporation was found to be well synchronized with the N demands of spring planted cash crops
(e.g. corn). The cover crop residues were mixed throughout the plow layer, allowing N mineralization to occur fairly
quickly. In CT systems, winter cover crops are often not incorporated to reduce spring tillage operations, but are mowed
or killed with an herbicide. This leaves the soil undisturbed and provides a surface mulch layer that enhances
winter/spring weed suppression. However, decomposition of the cover crop residues occurs at a reduced rate, and may
therefore not satisfy the demand (particularly, early season demand) of N by the cash crops.
Considering these difficulties, the SAFS group decided to lightly incorporate cover crop residues in the CT main plots
in spring 2004. Although this should increase the availability of cover crop-derived N to the corn, spring operations
add to farmer costs and disrupt the changes in soil composition and quality developed during the preceding period of
CT. Is this compromise between spring tillage and N turnover from cover crops a necessary component of cover crop-driven
CT systems? Or can we develop new cover crops and management schemes that will allow us to avoid spring cover crop
residue incorporation and tillage, while capturing cover crop benefits? We hope to address these questions by gaining a
better understanding of how the benefits of cover crops can be maximized at the interface of CT, soil
fertility/water/weed/disease management, and farming operations.
Specifically, we are exploring a cover crop component that would occupy the niche between processing tomato harvest
and corn planting the next spring. Several cover crop candidates were screened during the original SAFS experiment and
sub-tropical legume/ C4 grass mixtures were found to effectively tie up “luxury” N unused by the tomato crop
and fix significant amounts of N before being winter-killed in December. We hypothesized that this late-summer cover
crop component could benefit the SAFS CT treatments by providing N demanded by corn and surface coverage to reduce
winter/spring weeds. Since the cover crop is winter-killed the surface residue begins decomposing a full four months
earlier than a winter cover crop.
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Figure 1: Summer/winter cover crop biomass comparison among treatments (kg ha-1)
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Immediately following tomato harvest, seven rows per 60” bed (spaced 7” apart) of the summer cover crop
mixture (lablab/cover crop cowpea/sorghum-sudan hybrid) with or without lana vetch was seeded into tomato residue using
a 15’ John Deere 1560 No-till drill. On Nov. 14, vetch was seeded with the same spacing/drill into 1) beds that were
left fallow following tomato harvest and 2) beds with standing summer cover crop biomass. All treatments that had vetch
were flail mowed Mar. 31, left on the surface, and any surviving vetch in the furrows was killed in April. Field corn was
planted in all treatments on May 2 with the same John Deere 1750 No-till planter used in the “post-corn”
experiment. Corn germination and seedling survival were unacceptable, largely due to improper sealing of the seed planting
line. Moisture loss preceded the germination of many seeds, and others were plucked out by birds. Summer 2003 cover crop
biomass production was disappointing, especially when compared to the vetch biomass produced by spring (Figure 1). More
than likely, the lack of bed uniformity resulting from CT management contributed to uneven and unpredictable cover crop
seeding depth and germination, and with a late seeding date (Aug. 28), the growing season was insufficient to allow for
cover crop recovery and “fill in.” Preliminary data suggest the additional summer cover crop biomass
nonetheless may have boosted early corn growth in 2004. Corn biomass less than two months after planting was higher in
treatments that had both summer and winter cover crops than treatments with just one or the other (Figure 2). Additionally,
the summer cover crop biomass protected soil by “softening” early winter raindrops better than winter vetch,
which was in an early stage of growth.
Summary
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Figure 2: Regression of the effect of total cover crop biomass on corn biomass 54
days after planting (Each rep x treatment is represented by a data point)
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CT systems have the potential to improve soil and water quality, but only with the addition of compatible cover and cash
crops to enhance production. With appropriate genotype selection and management, it appears N-fixing winter grain-legumes
could provide an opportunity for continuous, low input cropping in CT systems. Summer cover crops can be used to cycle
forward nitrates that would otherwise contribute to a growing water pollution problem. Seeding earlier in August would
extend the growing season, allowing the cover crop to accumulate more biomass to supply crops like corn with adequate N,
suppress winter/spring weeds and protect the soil from winter runoff and erosion.
 Table of Contents
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