Final Report for LNC11-330
Our research investigated the impact of strip tillage (ST) and cover crops on weeds, insects, crop yield and profitability in sweet corn, snap beans, and cucurbit crops. In most cases, ST maintained yields and reduced costs relative to full-width tillage, resulting in economic benefits. Contrary to expectations, use of rye cover cropping provided relatively few measurable benefits, and in some cases resulted in losses in yield and profitability. Publications and presentations from our work have reached over 1000 growers, who are now better equipped to decide whether and how to adopt ST on their farms.
Strip-tillage in vegetable crops has the potential to provide multiple direct benefits relative to conventional tillage systems, including: 1) improvements in soil physical, chemical and biological properties for optimal crop growth; 2) reductions in energy- and labor- use due to fewer tractor passes; 3) protection of vulnerable vegetable seedlings from intense wind and rain events; 4) reductions in disease and physical damage to plants through reduced rain-splash and crop-soil contact; 5) more timely planting under wet field conditions; 6) enhancement of beneficial organisms such as predaceous insects and earthworms; and 7) improvement in nutrient and pesticide use-efficiency through reduced run-off and leaching.
In recent years, vegetable growers have observed an increase in extreme rain and wind events, and have expressed interest in reduced tillage systems to help protect their vulnerable soils and crops. Given predicted increases in climate variability, the need for resilient cropping systems has never been more important. Innovative vegetable growers have begun experimenting with the use of cover crops grown in combination with reduced tillage for wind protection. For example, in Oceana and Mason counties in W. Michigan, strip tillage in combination with winter wheat cover crops has gained popularity as a means to protect stand losses of vulnerable carrot seedlings.
Increases in the cost of diesel fuel and energy-intensive agrichemicals like N fertilizers provide increasing incentives for growers to reduce tractor passes in their fields. Strip-tillage typically involves 2 tractor passes for crop establishment, where 5 or more passes are common under conventional tillage systems. Strip-tillage also facilitates placement of fertilizer in the strip at depths where the plant needs it most, thus improving fertilizer-use efficiency.
In winter squash and pumpkin production, fruit scarring and staining is a problem that often results in reductions in marketable yield. Growers have attempted no-till to address this problem, but have observed poor stand establishment and costly delays in emergence and growth of crops under no-till systems. Strip-tillage facilitates improved seed-bed preparation and soil warming, thus addressing stand-establishment problems while maintaining benefits of surface residue for reducing fruit scarring. Surface residues present under strip-tillage systems may also reduce the dispersal of soil borne propagules of plant pathogens onto developing fruit and leaves. In recent years, diseases such as Phytophthora blight have become a major problem for vegetable growers. If reduced tillage systems can suppress these diseases, they would provide a big boost to farm profits.
Although strip-tillage has the important potential benefits outlined above, additional information is needed to 1) understand the effects of reduced tillage and cover crops on pests of vegetables, and 2) develop complementary management practices to optimize strip-tillage systems for crop productivity. When asked about strip-tillage, many growers express concern that this practice may make weed, insect or disease management more challenging. These are legitimate concerns that must be addressed before growers will invest in equipment and take the risk associated with changing their current practices. Successful adoption of strip-tillage depends on understanding pest responses, and adjusting pest management practices including rates, types, and timings of pesticides, as well as complementary practices such as cover crops and stale seed beds to reduce the risk of crop yield losses in these systems.
Weed management is particularly challenging in reduced tillage vegetable production systems and is often cited as the major constraint to adoption. When tillage is reduced, many weed species that were previously controlled through soil disturbance become more problematic. Weed populations in the undisturbed between-row environments may shift over time towards more winter annual and perennial weeds. On the other hand, summer annual weeds may be less problematic in undisturbed areas, since weed seeds will not experience germination stimuli associated with tillage (e.g. light, nitrates), and new seeds will not be readily brought to the soil surface. Strip tillage also makes it possible to take greater advantage of surface residues for inhibiting weed seed germination through reductions in light penetration, physical obstruction, or release of allelochemicals.
By definition, sustainability of alternative management practices can only be adequately assessed through long-term studies. While such studies exist for many agronomic cropping systems, relatively few have examined long-term impacts of management practices in vegetable cropping systems. Results from existing studies demonstrate the potential value of reduced tillage for reducing energy costs, improving vegetable quality, and improving soils. However, these studies have generally concluded that more work needs to be done to develop longer-term reduced tillage systems for vegetable crops, adopt research to different agro-ecological zones, and improve complementary management practices, including weed management.
Strip-tillage effects on crop yields and input costs. The practical potential benefits of strip-tillage for selected field and vegetable crops have been well summarized in several extension bulletins (e.g. Al-Kaisi and Hannah 2008; Luna and Staben 2003; Myers et al. 2008). For field crops like corn and soybean, strip tillage has been observed to produce equivalent yields to moldboard plowing and higher yields than no-till under many soil conditions (Al-Kaisi and Hannah 2008). Yield improvements relative to no-till in these systems are often attributed to improved pre-plant soil warming and drying. Strip-tillage also allows deep banding of fertilizers during tillage operations and hence improvements in fertilizer use efficiency relative to no-till, and reductions in tillage costs relative to conventional tillage. Overall, the number of tractor passes in strip-till systems is typically reduced to 2, where 2-3 passes are required in no-till systems, and 5 or more required for conventional tillage (broadcast P and K; chisel plow; knife in N; field cultivate; plant).
Research comparing strip-tillage and conventional tillage in vegetable crops is limited, but promising results have been demonstrated in several regions and cropping systems. Studies with strip-tillage systems in sweet corn have generally reported equivalent yields with reduced costs and hence increased profitability. For example, in Oregon, strip-tillage yields have generally been equivalent to conventional tillage, with approximately $15/A savings in tillage costs (Luna and Staben 2003). Similarly, in NY, strip-tilled sweet corn has been reported to produce equivalent yields with reduced input-costs compared to conventional tillage (Rangarajan et al. 2006).
Strip-tillage effects on beneficials and crop pests. Several studies have documented increases in beneficial organisms associated with strip-tillage systems. Untilled strips with residue or live cover crops provide alternative resources and microhabitat for beneficial insects such as predators and parasitoids (Letourneau, 1990; Landis et al., 2000; Wilkinson & Landis, 2005; Schellhorn & Sork, 1997). In North Carolina, a long-term study comparing conventional and strip tillage treatments in tomato production systems, reported a 31-fold increase in earthworm populations under strip-tillage (Overstreet et al. 2010). In Oregon, Luna and Staben (2003) report increases in beneficial earthworm and carabid beetle populations in strip-tilled sweet corn relative to conventional tillage.
Strip-tillage effects on insect and nematode pests depend on the specific crop, pest and climate. In some cases, reductions in insect pests have been observed under reduced tillage. For example, a recent study in strip-tilled versus conventionally tilled cotton production showed significant reductions in thrips under strip tillage (Tubbs et al. 2010). On the other hand, populations of plant pests including slugs (Luna and Staben 2003) and plant-parasitic nematodes (Overstreet et al. 2010) have been reported to increase in strip-tillage systems.
Reduced tillage systems can have both positive and negative effects on diseases. Since the survival of many important plant pathogens (e.g., Exserohilum turcicum, northern corn leaf blight) is reduced with incorporation of crop residue, reduced tillage systems may result in greater inoculum levels for successive crops. On the other hand, the presence of crop or cover crop residue on the soil surface can reduce propagule dispersal by minimizing run-off and soil splashing. For example, Ristaino et al. (1997) showed that planting bell pepper into wheat stubble reduced propagule dispersal and incidence of Phytophthora blight. Similarly, rots of pumpkin caused by Plectosporium tabacinum and/or Didymella bryoniae were less in no-tillage plots compared to conventional tillage plots (Everts 2002).
Weeds in strip-tillage systems. The most commonly cited constraint to adoption of reduced tillage systems is weed management. Weeds have been acknowledged as an important impediment to adoption of strip-tillage systems in vegetables (Luna and Staben 2003; Morse 1999; Walters and Kindhart 2002). In strip-tilled pumpkin trials conducted in Long Island, pumpkin yields were reduced, and weed pressure higher in two of three on-farm trials reported (Rangarajan et al. 2006). Since many vegetable growers rely heavily on soil disturbance to uproot and bury weeds, reduced tillage systems often present a weed management challenge for vegetable growers.
In field crops, reduced tillage systems were not widely adopted until low-cost herbicides became available to compensate for lack of tillage. However, in many vegetable crops, herbicide options are limited. This lack of effective herbicides has been cited as an obstacle to adoption of reduced tillage cucurbit production, and likely contributes to limited adoption in other crops as well (Ne-Smith et al. 1994; Walters and Kindhart 2002).
As with insects, the impact of tillage on weeds depends critically on complementary management practices. In particular, strip-tillage in combination with winter cover crops may result in comparable weed suppression relative to conventional tillage without the need for additional herbicides. However, the long term effects of tillage and cover crop practices on weeds are unclear, as are the interactive effects of tillage and cover crops on weeds, insects, diseases and crop health in multiple crops in a vegetable rotation.
The central objectives of our proposed work were 1) to evaluate the interactive effects of strip-tillage, cover crops, and weed management intensity within vegetable cropping systems on soil health, pest population dynamics, and crop quality and yield; and 2) to work with growers and extension educators to disseminate useful information and identify and address constraints to adoption of reduced tillage production systems.
General approach. A combination of long-term research farm trials, short-term on-farm trials, and grower interviews and surveys were conducted to evaluate the interactive effects of strip-tillage, cover crops and weed management intensity within vegetable cropping systems on weed community density and composition; predaceous and herbivorous insect activity; crop quality and yield; and profitability. Research trials were complemented with outreach activities designed to engage grower cooperators, extension agents and industry representatives.
Long-term tillage experiment, South West Michigan Research and Extension Center (SWMREC). Long-term field trials were conducted to evaluate the effects of tillage, cover crops, and weed management practices on soils, pests and profitability in a three year sweet corn-snap bean-cucurbit rotation. This experiment was initiated in 2009 with short-term competitive funding from the C.S. Mott Group, MSU’s Project GREEEN, and the Michigan Vegetable Council. NCR-SARE funding allowed continuation of the study through two full cycles of the vegetable rotation in two adjacent fields, referred to hereafter as Field 1 and Field 2 (see Fig. 1). Field 1 and Field 2 were managed identically, but crops were offset by 1 year, in order to better understand the impact of year (weather) on responses.
Experimental factors included tillage (strip tillage [ST] vs conventional full-width tillage [FWT]) cover crops (none, rye or rye-vetch) and weed management intensity (low vs high). Plots were arranged in a split-split plot design with tillage as the main plot factor, cover crop as the sub-plot factor, and weed management intensity as the sub-subplot factor. Tillage main plots measured 60’ x 37.5’, with 60’ x 12.5’ cover crop subplots and 12.5’ x 30’ weed management sub-sub plots. Cover crop, tillage and weed management treatments were maintained in the same plots through the entire rotation sequence in order to assess cumulative effects.
Rye (2 bu/A) and rye-vetch (1 bu rye 20 lbs vetch/A) were drilled in early September each year. The following spring, all cover crops were sprayed with glyphosate approximately 3 weeks before the anticipated planting date for each crop. One to two weeks after glyphosate application, cover crops were flail-mowed and then either incorporated with a moldboard plow or strip-tilled. For snap bean, sweet corn and pickling cucumbers, ST was accomplished with a two-row (30” spacing) Hiniker-6000 equipped with row-cleaners, offset disks and a rolling basket for seed bed preparation. ST in winter squash was accomplished with a single-row modified Unverferth-120 Zone Builder equipped with row-cleaners, offset burming disks and a rolling basket. The Unverferth unit was used to accommodate wider row-spacing of winter squash. The two units differed primarily in their depth of soil disturbance (shank depth), with the Hiniker tilling to 10-12”, and the Unverferth tilling from 14-16”.
In weed management sub-sub plots, two levels of weed management intensity were examined: low and high. In the high intensity treatment, typical pre and post-emergence herbicides (varying by crop) were applied at standard rates, and supplemental hand-weeding was used as necessary to maintain minimal competition and weed seed production. In low-intensity weed management treatments, post-emergence herbicides and hand weeding were used only as a last resort when it appeared that crop failure would otherwise occur in all treatments. Diseases and soil fertility for each crop in the rotational sequence were managed in accordance with MSU recommendations in combination with scouting and soil test results. In order to investigate the effects of treatments on insects, insecticides were used sparingly as a last resort.
Soil monitoring. Soil samples were taken for nutrient evaluation and weed seedbank analysis (see below) each spring. Soil volumetric water content (VWC) was monitored in tillage x cover crop (rye vs none) subplots in high weed management subplots, in both the in-row and between-row environment, using the Diviner 2000 soil probe. The Diviner 2000 provided estimates of VWC in 10 cm depth increments to a depth of 60 to 100 cm depending on crop and year. Soil splash on vegetable crops was evaluated following heavy rains by obtaining the dry weight of soil that had adhered to crop leaves; soil was collected from the leaves of 5-10 plants from each tillage x cover crop sub-plot.
Weed assessment. Weed assessments included: 1) winter annual weed counts and biomass prior to tillage in early spring; 2) emergence counts of both ambient and sown weeds; 3) visual ratings and biomass samples of summer annuals at harvest; and 4) weed seedbank assessment. Weed biomass and emergence counts were generally taken from two 0.25m2 quadrats in each plot in both the in-row and between-row environments. Weed seedbank density and composition was assessed through a greenhouse germination method (Gross 1990; Brainard 2006), in which 500 mL of soil was mixed with 500 mL of soil-less potting mix (50:50 Peat:Vermiculite with nutrients); spread thinly (
Insect assessment. In each tillage x cover crop sub-plot in each crop, 10 focal plants were visually surveyed for the presence of herbivores and natural enemies at least 2 times during the growing season; in addition, yellow sticky traps were hung 15 cm above the canopy of the plants to capture flying insects, such as predators and parasitoids. Sticky traps were replaced as needed throughout the growing season. Insect pests of particular interest for each crop were: the European corn borer and the corn earworm (in sweet corn); leafhoppers (in snap beans) and striped cucumber beetle (in winter squash). Herbivore, parasitoid and predator numbers were compared among the treatments to determine the effect of tillage and cover crops on arthropods.
Crop yield. Crops were harvested from 20-40’ (depending on crop) sections from two central rows. At harvest, the marketable portion of crops was weighed and separated into size and quality categories appropriate for the specific crop (e.g. corn tip-fill; insect and disease damage; squash fruit staining). Yields were determined for each class/quality category. In addition, five whole plant sub-samples were taken for each crop at the end of the season for dry weight in order to assess total productivity and harvest index.
Statistical analysis. The effects of tillage and cover crops on soil moisture, weed responses; crop quality and yield; were evaluated using Proc MIXED in SAS, with tillage, cover crop, and weed management intensity as fixed effects, and replication as a random effect. For insect and volumetric water content assessments, the effect of weed management intensity was not evaluated, and only tillage and cover cropping were evaluated as fixed effects. Log or square root transformations of weed and insect density data were performed as necessary to satisfy assumptions of normality and homogeneity of variance.
On-farm and MSU SOF experimental methods. On-farm trials and demonstrations were conducted annually at 1-2 grower locations and at MSU’s student organic farm (SOF). In the on-farm trials, the effects of tillage (ST vs FWT) and cover crop (none or oats) on sweet corn yield and weeds were evaluated in a randomized complete block design with four replicates. Nitrogen fertilizer was split evenly between three applications—prior to or at tillage (broadcast and incorporated in FWT while banded 6” deep in ST), with the planter, and side dressed when the sweet corn was 6-8” tall. Standard grower practices were used to manage pests and weeds, including herbicides. In the SOF trial, ST was demonstrated with various complementary cover cropping methods, including cereal rye and hairy vetch mixtures that were grown either in full-width mixtures, or in segregated strips in which rye was targeted to the in-row zone, and rye to the between row zone. Sweet corn in all trials was planted in early or mid-June and harvested in early or late August.
Partial budget for adoption of ST in sweet corn. To better understand the potential economic impact of adoption of ST on sweet corn production, nine growers, representing eight different operations, were queried about their production practices. Information from these interviews was combined with cost estimates from various sources and yield data from 9 sweet corn field trials (summarized in Table 1) to create a partial budget analysis of changes in profitability expected under adoption of ST. This was part of the PhD research conducted by Erin Haramoto in consultation with MSU economist Scott Swinton. Details of the methodology are provided in her thesis (Haramoto 2014). In brief, we conducted one focus group with four growers (representing three different operations) in the Macomb County, Michigan area and individual interviews with five additional growers in Monroe, Berrien, and Kent counties. These counties are the top four fresh market sweet corn producing counties in Michigan (NASS 2007) and, at the time of the 2007 Census of Agriculture, represented 32% of the sweet corn acreage in the state.
In both the focus group and individual interviews, growers were asked to outline the timeline of a typical sweet corn production season. Each operation, and the number of times it was performed, was recorded. This information was used to compile practices used and the frequency of use during a “typical” production season for fresh market sweet corn.
Tillage costs were estimated using the Farm Machinery Economic Cost Estimation Spreadsheet (Machdata.XLSM; Lazarus 2014), a spreadsheet that determines ownership and operating costs for equipment using an economic engineering approach. Local dealers provided cost estimates for different types of new ST equipment, while websites selling used farm equipment were surveyed for these prices. Six-row equipment with 30” row spacing was priced out; this size is flexible enough to be used by both larger and smaller Michigan sweet corn growers and is the equipment size of some of the growers we interviewed. Power requirements for these strip tillers were based on equipment specifications and dealer recommendations (25-35 HP per shank), while those provided by Lazarus (2014) were used for the conventional tillage options analyzed. Tillage was assumed to use 20% of the hours operated by the power unit; other potential uses include spraying, fertilizing, mowing, etc. An operational speed of 5.5 mph and field efficiency of 85% was assumed. We assumed growers would use the ST equipment on 200 acres, with one pass per year. This acreage was chosen by considering the average farm size of interviewed growers and the crops for which this equipment could be used (those not grown on raised beds or with different row spacing).
Cost per acre for ST was determined for three scenarios: 1) a high cost scenario with a new 6 row pull-type strip tiller with attached fertilizer cart and capability to band fertilizers (STH); 2) a medium cost scenario with six new row units mounted on a toolbar (STM); and 3) low cost scenario with the least expensive used strip tiller (STL). Each row unit on the high and medium cost strip tillers is equipped with trash cleaners, cutting disks, a shank, berming disks, and a rolling basket. Given the wide range of available used ST equipment, the low cost option may have all of these components. To add fertilizer banding capability to the two lower cost scenarios, $2000 for a fertilizer tank or hopper, tubes, and metering unit was added to the purchase price. All scenarios assumed an eight-year-old 200 HP tractor for the associated power unit. For comparison, we also priced new and used conventional tillage equipment with appropriate used power units—a 15’ chisel plow (CP) with a 130 HP tractor and 18’ field cultivator (FC) with a 105 HP tractor.
Costs expected to change upon adoption of ST were selected from the sweet corn cost of production budget for use in the partial budget analysis. These included costs related to soil preparation, fertilization passes, herbicide products and applications, and cultivation. Because all of our ST scenarios included the capability to band fertilizers, the additional broadcast fertilization pass used with conventional tillage was eliminated. The cultivation pass was also eliminated in the ST partial budget. Changes in revenue expected under ST, were estimated based on data from 9 separate trials in which ST and FWT were compared in sweet corn, including the SWMREC trial, 3 on-farm trials (“Z7” and “Z8”), and three additional trials conducted at the KBS research station (“KBS 2011” KBS 2012” and “KBS 2013), as part of Erin Haramoto’s PhD project. The partial budgets included four parts—additional revenue, additional costs, reduced revenue, and reduced costs. These were summed together for each scenario in the partial budget to produce changes in profit. These changes were compared to the total production costs.
Economics of ST and cover crop adoption in snap beans. Additional economic analyses were conducted to evaluate the impact of ST and rye cover cropping on profitability taking into consideration observed effects on insect and weed pests in snap beans from the long term SWMREC trial. Estimates of changes in pesticide costs associated with a change from the standard grower practice control treatment (FWT-no rye) to three alternative treatments (FWT-rye, ST-no rye and ST-rye) were calculated by comparing the density of pests in the alternative treatment to that in the control treatment. For pests whose densities were influenced by treatment, published threshold densities were used to evaluate whether changes in pesticide use would occur. Because considerable uncertainty surrounds threshold values for particular pests, as well as the density of pests across different years, we calculated the expected value of changes in pesticide use under “Baseline”, “Optimistic” and “Pessimistic” scenarios for each of the three alternative treatments. Assumptions for the Baseline scenario represented our best guess of pesticide applications that a typical grower would use given the level of pests observed in each treatment relative to published threshold densities. Under the Optimistic scenario we assumed that observed increases in pest density under alternative treatments would not require additional pesticide applications, while observed decreases in pests under the alternative treatment would allow pesticide savings. Finally, under the Pessimistic scenario we assumed that increases in pest density under the alternative treatments would require additional pesticide applications, while observed decreases in pest densities would not result in pesticide savings. These net changes in pesticide cost were then combined with information on the costs associated with tillage and cover cropping practices (similar to method outlined for sweet corn) to estimate the net effect of each alternative practice on total input costs. Details of the methodology used will be provided in a forthcoming publication (Brainard et al. unpublished).
SWMREC long-term trial.
The long-term trial evaluated the effects of tillage (strip tillage [ST] vs full width tillage [FWT]) cover crops (none, rye or rye-vetch) and weed management intensity (low vs high) in a sweet corn/snap bean/cucurbit rotation initiated in 2009 and 2010 in two adjacent fields (Fig. 1). During the reporting period for this grant (2012-2014), 6 site-years of data were collected. Tillage (alone or in interactions with other factors) influenced yields in 3 out of 6 site-years, while cover crops influenced yields in 2 of 6 site-years (Table 2). Specific results are discussed by crop below, followed by information regarding tillage and cover crop effects on weeds and insects. Results of economic analysis using data from the SWMREC trial are presented in a separate section below.
Sweet corn. ST had no effect on sweet corn yields compared to FWT in 2012, but in 2013, a marginally significant (P=0.078) increase in yield was observed under ST when weeds were well managed (Table 2; Fig. 2). In 2013, ST treatments had higher early growth rates and earlier maturation then FWT treatments, with FWT treatments exhibiting symptoms consistent with sulfur deficiency prior to side-dress fertilization (Fig. 3). Following side-dressing of ammonium sulfate, these symptoms dissipated. Weeds in low-weed management intensity treatments—especially common lambsquarters—grew vigorously and suppressed crop yields regardless of tillage or cover crop treatment (Table 2; Fig. 2). Cover crops had no detectable effect on sweet corn yield in either year (Table 2).
Snap beans. ST had no effect on yields of snap beans in either year (Table 2), although large variability in yields—particularly in 2014—limited our ability to detect yield differences of less than 10%. The impact of cover crops on snap beans varied with tillage system and year. In 2013, the rye-vetch cover crop improved yields compared to no cover crop by 18% in FWT treatments, but had no effect in ST treatments. In 2014, cover crops had no detectable effect on snap bean yield, but both rye and rye-vetch treatments resulted in reductions in snap bean stands of 12%. We attribute this stand reduction to interference with the planter as well as N-immobilization due to heavy rye residue in that year. A similar effect was seen in cucumbers in 2014 (see below).
Butternut squash. The effect of tillage on cucurbit yields, differed by year and crop (Table 2). In butternut squash in 2012, ST resulted in yield loss compared to FWT, especially under low weed management intensity (Fig. 4). Reduced yields under ST in butternut squash were largely the result of increased survival and growth of large crabgrass in the ST system. Large crabgrass was poorly controlled by the pre-emergence herbicide (s-metolachlor), and higher densities in ST treatments resulted in greater than twice the biomass at the time of post-emergence herbicides and cultivation (Fig. 5). Moreover, these differences in early crabgrass growth were magnified because cultivation was used in the FWT-high weed management treatments, whereas only clethodim herbicide was used in ST treatments, and the application was delayed until 7 days after cultivation, due to high winds and equipment constraints. This delayed clethodim application, combined with its slow mode of action, allowed large crabgrass in ST plots to grow substantially prior to cessation of growth (Fig. 5).
Pickling cucumbers. In pickling cucumbers in 2014, ST resulted in a 34% increase in yield compared to FWT treatments, when cover crops were not used (Fig. 6). This yield improvement in ST may have been due in part to improved soil moisture retention in ST compared to FWT (Fig. 7). Although irrigation was used, soil moisture late in the season was lower in FWT compared to ST treatments and low volumetric water content in FWT may have resulted in drought stress. In addition, heavy rainstorms resulted in soil erosion and crop damage in FWT plots, but not ST plots (Fig. 8); similar benefits of erosion protection were evident under heavy rainfall in snap bean and winter squash fields, resulting in reduced soil splash on crop leaves (Fig. 9). Within the ST treatments, both rye and rye-vetch resulted in reductions in cucumber yield relative to ST without cover crops (Fig. 6). This yield reduction was due in part to poor cucumber establishment and reduced stands in treatments with rye; ST treatments with rye and rye-vetch had 6-19% reduction in cucumber densities (data not shown), and were noticeably stunted and chlorotic relative to non-cover crop treatments early in the season. Cool wet temperatures following glyphosate application resulted in incomplete decomposition of rye which impeded strip-tillage in some plots. This was particularly problematic when the strip-tiller shank aligned with the rye planting row, where root-balls were concentrated.
Summer annual weed seedbank density and composition. The cumulative effects of tillage and cover cropping on weed communities were evaluated through seedbank analysis. Dominant summer annual species in the seedbank in both fields were common lambsquarters, Powell amaranth and large crabgrass (Fig. 10). In Field 1—following 5 years of the study—ST did not influence the total size of the summer annual seedbank relative to FWT, but resulted in a shift in weed community composition towards large crabgrass and away from broadleaf weeds (Fig. 10A). In Field 2—following 4 years of the study—ST resulted in higher weed seedbank densities relative to FWT, but only under low weed management (Fig. 10B). In Field 2, the large crabgrass seedbank density was increased in ST relative to FWT following snap beans (data not shown), but following squash in 2012, this difference had dissipated, and common lambsquarters became the dominant weed in ST (Fig. 10B). A seed burial study conducted in Field 1, demonstrated that large crabgrass has relatively short longevity (<10% survival per year) regardless of tillage system (data not shown), which may help explain more ephemeral differences in large crabgrass densities.
Winter annual weeds. In the absence of cover crops, the emergence of winter annual weeds—including henbit, purple deadnettle and chickweed—was greater in ST than FWT (Fig. 11); however, with either winter rye or rye-vetch mixtures, winter annual densities under ST were equivalent to FWT. FWT treatments likely had lower winter annual weed density than ST because tillage prevented seed production and buried freshly produced seeds below the germination zone. Winter cover crops appear to have reduced winter annual emergence in the fall because they suppressed seed production through competition. Winter cover crops suppressed winter annual biomass production in the spring by between 75-100% depending on year and field (data not shown). Although weed seed production was not measured, it is likely that it was also majorly suppressed by cover crops, resulting in lower seedbank and emergence.
Perennial weeds. Under ST, the abundance of the perennial weed horsenettle (Solanum carolinense) has gradually increased (Fig. 12). Following 6 years in Field 1, horsnettle was absent from FWT treatments, but averaged 1-3 ramets per m2 in ST treatments (data not shown). Contrary to expectations, the presence of winter cover crops has not resulted in significant reductions in horsenettle. Individuals of other perennial weed species (e.g. dandelion) have also appeared in ST treatments, but not at economically significant levels. The presence of horsenettle may necessitate an extra herbicide application (or other changes in management) in ST treatments in coming years to avoid yield losses.
Insects. In general, the effects of tillage and cover cropping on insect pests and natural enemy abundance were inconsistent and relatively small compared to weed effects. In sweet corn, neither tillage nor cover crops affected major pests including corn ear worm or European corn borer. In snap beans, ST reduced potato leafhoppers by 31% in 2011, but had no detectable effect on other insect pests including tarnished plant bug, aphids or thrips in either year (Table 3). Contrary to expectations, ST in combination with rye surface residue resulted in reductions in beneficial ladybeetles and parasitoids in one of two years in snap beans (Table 3). Rye cover cropping also resulted in a 4-fold increase in tarnished plant bug and a 2.5-fold increase in aphids in one year, although densities of these pests were below damage thresholds. In butternut squash, ST and rye cover cropping resulted in increases in the prevalence of squash bug in 2012 (Fig. 13A), and cucumber beetles in 2011 (Fig. 13B). Effects on beneficial insects in squash were variable: In 2012, rye resulted in an increase in lacewings under FWT, but a decrease in lacewings under ST (Fig. 13C); ladybeetles appear to have been suppressed somewhat in rye compared to bare soil treatments (Fig. 13D). On the other hand, bees—especially honeybees—were more abundant in ST rye compared to all other treatments in 2012 (Fig. 14).
On-farm sweet corn trials. No differences in sweet corn yield were detected between tillage treatments in on-farm trials (Fig. 14). Final weed density in sweet corn was low at all sites (approximately 1 weed per meter of row) and neither weed density nor biomass was affected by treatment at any site, suggesting that the herbicide program used was equally effective in all treatments. Information from these trials was used for the economic analysis described below.
Short-term outcomes (changes in knowledge, skills, awareness, and attitudes)
1) Increased understanding of the potential benefits of ST systems for improving soil health and reducing energy and labor costs: We have observed improvements in soil moisture retention under strip tillage, reductions in input costs, and equivalent or higher yields in snap beans, sweet corn and pickling cucumber. Growers have also commented specifically on new awareness of moisture retention benefits, as well as reduced soil splash on vegetables.
2) Identification of complementary weed management practices to optimize strip-tillage systems: We have identified the need for greater attention to weed management practices to address potential problems from build-up of large crabgrass and horsenettle under ST.
3) Increased understanding of optimal cover crop practices for strip-tillage systems: The effects of rye and rye-vetch cover cropping have been highly variable by crop and year. On the one hand, cover crops have in some cases improved soil moisture retention, reduced soil erosion, and helped suppress winter annual and summer annual broadleaf weeds. On the other hand, cover crop residues have sometimes interfered with crop establishment and early growth, and also occasionally exacerbated insect pest problems.
4) Increased awareness of the circumstances under which reduced tillage systems are most/least likely to be beneficial due to changes in insect, disease and weed dynamics: We have observed no consistent impacts of tillage or cover crops on insect or disease pests. However, our results suggest that growers should be wary of attempting strip-tillage in fields where perennial weeds and crabgrass are abundant.
5) Greater grower understanding and interest in reduced tillage systems for vegetable crops: Our grower surveys and focus groups suggest that grower interest in strip-tillage and cover crop use is strong. However, grower concerns about potential negative effects of reduced tillage on weeds and insects remain obstacles to successful adoption.
Anticipated intermediate-term outcomes (changes in behavior or practices)
1) Increased adoption of strip-tillage systems by vegetable growers.
2) Increased use of complementary cover crops resulting in greater soil coverage and moisture retention.
3) Implementation of optimal, complementary weed management practices.
4) Reductions in tractor use and diesel fuel purchases.
5) Reductions in insecticide and fungicide applications.
Anticipated long-term outcomes (systemic changes)
1) Improvements in human health and environmental quality
2) Strengthening of rural communities through improvements in farm profits
3) Improved resilience of soils and crops to environmental stresses
Partial budget for ST adoption in sweet corn. In sweet corn, we estimated that a shift from FWT to ST would result in increased profits of approximately $25 to $34/acre (Table 4). This estimate was based on savings in tillage costs of $7 to $16/acre, combined with savings of $19/acre associated with elimination of a broadcast fertilizer application and one cultivation pass (Table 4). Because yields were affected by ST in only 1 of 9 site-years in sweet corn trials (Fig. 15), we assumed there would be no change in revenue, so estimated savings represented increased profit. In conventional sweet corn production systems, we observed no economically significant impact of ST on weed or insect pests, so no changes in the costs of insecticides or herbicides were included in our analysis. However, it should be noted that the buildup of large crabgrass and horsenettle observed in our long term tillage trial, suggest that continued use of ST may necessitate increased use of herbicides or other weed management practices that could reduce or eliminate gains in profit. On the other hand, cumulative improvements in soil characteristics anticipated under ST systems might ultimately result in increased yields, or reductions in costs (e.g. sulfur application in SWMREC 2013 trial) and hence further improvements in revenues under ST. Such tradeoffs will require continued investigation to determine the long-term implications of reduced tillage on the economics of vegetable cropping systems.
Economics of ST and cover crop adoption in snap beans. In snap beans, the overall impact of ST and rye cover cropping treatments on input costs are summarized in Figure 16. Under our Baseline assumptions, ST resulted in increased costs for weed management (due to increased prevalence of large crabgrass), but reductions in tillage and insecticide costs (due to reductions in potato leafhoppers). Yields under ST were comparable to those under FWT, while savings in input costs under our Baseline scenario, were estimated to be $24/ha ($10/acre) due to reductions in tillage and insecticide costs which outweighed increased herbicide costs. Under the Optimistic scenario for ST—in which it was assumed that negative weed effects were minimal and beneficial insect effects were maximal —the estimated savings in input costs was $89/ha ($36/acre). In contrast, the net impact of ST under the Pessimistic scenario—in which it was assumed that negative weed effects were maximal and insect benefits minimal– was an increase of input costs of only $7/ha ($3/acre). Therefore, the potential risks associated with weeds under ST appear to be low for commercial snap bean producers, while potential short-term benefits appear to be substantial under some circumstances.
In contrast, our economic estimates of the impact of rye cover cropping in snap beans suggest—at least in the short-term—economic benefits associated with rye were insufficient to cover the costs associated with its establishment and maintenance. Although snap bean yields under ST-R and FWT-R treatments were equivalent to those under FWT-NR, increased input costs associated with rye management, were estimated at $172-202/ha ($70-82/acre), with weed and insect management cost savings of only $91-128/ha ($37-52/acre) even under the Optimistic scenario (Fig. 16). Under the Pessimistic scenario—in which negative effects of rye on tarnished plant bug and large crabgrass were assumed to be maximal, and positive effects of rye on winter annuals were assumed to be minimal—rye resulted in an estimated net increase in input costs of $216 to 265/ha ($87-107/acre). However, it should be noted that several commonly cited potential long-term benefits of rye that may ultimately improve yields and profits were not fully evaluated in this study, including potential improvements in soil characteristics, nutrient cycling and moisture retention.
Number of farmers reached by the project. We estimate that results from our project have been presented directly to over 500 growers at grower conferences and field days (see listings above), including 50-150 attendees at each session of the Great Lakes Fruit and Vegetable Expo. We do not have reliable information on the number of growers reading publications related to our work, but based on readership of media in which we have published, we estimate that the number is likely to be at least an additional 500 growers. Our work has also been presented through oral presentations at scientific meetings (see listings above) to over 400 scientists and extension educators who work closely with growers, and whose advice to growers may have been influenced by our work. Many of these scientists have also downloaded and read our scientific publications. For example, we know that our article “Hairy vetch varieties and bi-cultures influence ecosystem services in strip-tilled sweet corn” has been downloaded over 600 times according to the Agronomy Journal website.
Extent of grower interest and adoption of new technologies. We do not have reliable information on the extent to which farmers have adopted ST practices as a result of our work. However, our discussions with sweet corn growers, and evaluations from extension presentations suggest that although growers have strong interest in these practices, relatively few have actually adopted ST on a large scale. Grower interest is reflected in evaluations of our presentations at grower meetings. For example, the 2013 presentation at the GLEXPO “Protecting soils and boosting profits with strip tillage and cover crops” was attended by approximately 150 growers, who were asked to turn in written evaluations. Among respondents, 46% reported that the information was “very helpful”, 56% reported it as “somewhat helpful”, and 0% reported it as unhelpful (compared to ratings of 30%, 56%, and 14% for other speakers in the same session). When asked to list “one thing you learned during the session that you can use in your business”, 64% of respondents mentioned strip tillage, including specific interest in benefits for reducing soil splash on crop leaves, and retaining soil moisture to reduce drought stress.
Specific recommendations for farmers.
• Growers should consider adoption of strip-tillage as a means of reducing input costs and protecting soils particularly in the following crops and situations:
• Growers should be cautious in attempting strip tillage in the following situations:
• Growers should consider the following guidelines and cautions when using winter rye as a cover crop in combination with strip-tillage:
- Broadcasting rather than drilling rye. This approach minimizes the risk of creating a “seam” of rye roots which may interfere with effective strip tillage.
- Planting rye only in the between row zone of fields that will be strip-tilled. For crops with 30” row spacing, this can be accomplished using a typical grain drill (with 7.5” between row spacing), either by blocking every fourth drop tube (creating 3 rows of rye in the between row zone and a 15” gap for strip tillage) or by alternating two un-blocked and two blocked drop tubes (creating 2 rows of rye in the between row zone and a 22.5” gap for strip tillage).
- Increasing initial N fertilization rates to reduce risk of N immobilization.
- Allowing at least 2 weeks following termination with glyphosate, or 3 weeks following termination with mowing or roller crimping before attempting strip-tillage. These intervals can be shortened by at least one week if rye has been excluded from the in-row zone (via blocked drop tubes as described above).
• Growers should consider the following guidelines and cautions when using hairy vetch as a cover crop in combination with strip-tillage:
Educational & Outreach Activities
• Hayden, Z.D., M. Ngouajio and D.C. Brainard. 2014. Rye-vetch mixture proportion tradeoffs: Cover crop productivity, nitrogen accumulation, and weed suppression. Agronomy Journal 106: 904-914.
• Brainard, D.C., E. Haramoto, M.M. Williams and S.B. Mirsky. 2013. Towards a no-till no-spray future? Introduction to the symposium on non-chemical weed management in reduced tillage cropping systems. Weed Technology 27: 190-192.
• Brainard, D.C., E. Peachey, E. Haramoto, J. Luna and A. Rangarajan. 2013. Weed ecology and management under strip-tillage: Implications for Northern U.S. vegetable cropping systems. Weed Technology 27: 218-230.
• Hayden, Z.D., D.C. Brainard, B. Henshaw, and M. Ngouajio. 2012. Winter annual weed suppression in rye-vetch cover crop mixtures. Weed Technology 26: 818-825.
• Brainard, D.C., B. Henshaw and S. Snapp. 2012. Hairy vetch varieties and bi-cultures influence cover crop services in strip-tilled sweet corn. Agronomy Journal 104:629-638.
• Erin R. Haramoto. 2014. Strip tillage and cover crop effects on soils, weed-crop competition, and profitability in sweet corn and cabbage. PhD Thesis. Department of Horticulture, Michigan State University.
• Zachary D. Hayden. 2014. Optimizing cereal-legume cover crop mixtures in vegetable cropping systems through replacement series analysis and investigation of staggered seeding. PhD Thesis. Dept of Horticulture, Michigan State University.
Presentations at Grower Conferences
• Brainard, D.C. 2013. Protecting soils and boosting profits with strip tillage and cover crops. Soil Health Session. Great Lakes Fruit, Vegetable, and Farm Market Expo, Grand Rapids, MI, December.
• Brainard, D.C. 2013. Cover crop research and your bottom line. Making Sense with Cover Crops Workshop. Midwest Cover Crop Council Annual Meeting. London, Ontario, Canada. Feb 28.
• Brainard, D.C. 2013. Reduced tillage and cover crops in vegetables. Midwest Cover Crop Council Annual Meeting. London, Ontario, Canada. Feb 28.
• Brainard, D.C. 2013. Benefits and limitations of cover crops in vegetable production. Illinois Specialty Crops, Agritourism, and Organics Conference. St. Louis, MO. Jan 9.
• Brainard, D.C. 2013. Using cover crop residues and reduced tillage to protect soil and reduce energy costs in sweet corn production. Illinois Specialty Crops, Agritourism, and Organics Conference. St. Louis, MO. Jan 9.
Presentations at scientific meetings
• Brainard, D.C., E. Haramoto, D.C. Noyes. 2014. Long-term effects of strip tillage and cover crops on weed seedbank dynamics and profitability in vegetables. Abstract no. 223. Weed Science Society of America Annual Meeting, Vancouver, Canada, Feb. (Oral)
• Lowry, C.J. and D.C. Brainard. 2014. Zone tillage and cover crop spatial arrangement effects on weed emergence and competition in organic sweet corn production. Abstract no. 334. Weed Science Society of America Annual Meeting, Vancouver, Canada, Feb. (Oral)
• Haramoto E. and D. C. Brainard. 2014. Can fungal pathogens, nitrogen, and moisture explain suppression of weed emergence in strip-tilled cabbage with cover crops? Abstract no. 225. Weed Science Society of America Annual Meeting, Vancouver, Canada, Feb. (Oral)
• Haramoto, E.R., D.C. Brainard, S. Snapp and K. Kahmark. 2013. Can strip tillage with deep fertilizer banding improve agronomic nitrogen use efficiency? Ecological Society of America Annual Meeting. Minneapolis, MN. 6 Aug.
• Haramoto, E.R., D.C. Brainard, S. Snapp, and K. Kahmark. 2012. Relative location of strips influences sweet corn yields, potentially leachable nitrate, and trace gas flux under strip tillage. ASA, CSSA, SSSA International Annual Meeting, Cincinnati, OH. Nov. (Poster)
• Bryant, A., D.C. Brainard and Z. Szendrei. 2012. Cover crop mulch and strip tillage influence biological control in cabbage (Brassica oleracea). Entomological Society of America, National Meeting. Knoxville, TN, Nov. (Oral)
• Brainard, D.C., E. Haramoto and D. Noyes. 2012. Tillage and cover crop effects on weed management in snap beans. Abstract no. 57. Weed Science Society of America Annual Meeting, Waikoloa, HA, Feb. (Poster)
Other Extension Presentations and Publications
• Hayden, Z.D., M. Ngouajio, and D.C. Brainard. 2013. The Organic Report-?Cover Crops: Managing Nitrogen. American Vegetable Grower, February, 2013. pp 29-?30.
• Brainard, D.C. 2012. Conserving soil moisture in vegetables: Effects of weed management and cover crop mulches. Vegetable Crop Advisory Team Alert Newsletter, July 18.
Other Education/Outreach events
• Hayden, Z.D. and Brainard, D.C. 2014. Overview of long-term reduced-tillage field study. MSU Vegetable Extension Group Summer Tour. South West Michigan Research and Extension Center, Benton Harbor, MI. August.
• Brainard, D.C. 2013. Overview of long-term reduced-tillage field study. MSU Vegetable Extension Group Summer Tour. South West Michigan Research and Extension Center, Benton Harbor, MI. August 5.
• Brainard, D. C. 2013. Reduced tillage strategies for sweet corn and hard squash. Ag. Consultants Breakfast. Hart, MI, June 20.
• Hayden, Z.D., Ngouajio, M., and D.C. Brainard. 2013. Cover Crops, Strip-Tillage, and Nitrogen Management. Oceana County Soil Management Extension Workshop, Shelby, MI. 20 March.
Areas needing additional study
• Development of complementary weed management practices for ST systems. Our results suggest that continued research is needed to identify methods for managing problematic weeds such as large crabgrass and horsenettle without excessive reliance on herbicides. Ideas for doing so are summarized in our recent review article (Brainard et al. 2013). In brief, promising areas of research include:
• Evaluation of alternative cover cropping practices for enhancement of strip tillage benefits. Our research efforts to date have focused primarily on integration of cereal rye and hairy vetch cover crops into strip-tillage. These cover crops have several distinct advantages, but both also create significant challenges and risks for vegetable growers. Continued work is needed to optimize use of these and other cover crops for strip tillage including efforts in the following areas:
• Improved understanding of impacts of tillage and cover crops on development and dispersal of plant diseases including Phytophthora capsici.
• Development of optimal fertilization strategies for strip-tillage systems and characterizing nitrogen losses to the environment.