Cover Cropping and Residue Management for Weed Suppression, Soil Fertility and Organic Crop Production

Final Report for LS02-132

Project Type: Research and Education
Funds awarded in 2002: $99,117.00
Projected End Date: 12/31/2006
Region: Southern
State: North Carolina
Principal Investigator:
Keith Baldwin
NC A&T State University
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Project Information

Abstract:

The goal of this project was to investigate the growth of cover crops and manage residues to manage weed pressure in organic farming systems and supply nutrients for subsequent cash crops. Cash crops in the first, second, and third years were edamame soybean, corn, and corn, respectively. Although weed competition in the cover crop was minimal, in all crop years cover crop residues failed to control weeds in the cash crops. No meaningful yield was achieved in any crop year. None of the cover cropping and residue management strategies was successful enough to demonstrate in outreach activities.

Project Objectives:

The focus of this proposal is the design of organic farming systems that integrate essential aspects of crop management in order to increase the crop’s competitiveness with weeds, build soil fertility, and produce high-value organic crops. These integrated systems are also expected to benefit conventional growers who see them as more sustainable alternatives to traditional rotations. Moreover, with current USDA guidelines strongly encouraging surface residue on highly erodible soils, development of mulch systems for use with mechanical weed management can simultaneously improve weed control and soil conservation in organic and other low herbicide cropping systems.
Objectives
1. Investigate the weed suppression of crimson clover, rye, and crimson clover/rye biculture cover crops prior to the establishment of principal crops and in the subsequent vegetable soybean and corn crops.
2. Evaluate techniques for mechanically killing cover crops as alternatives to use of herbicides.
3. Investigate the reseeding capacity of crimson clover left to mature in a strip crop tillage system.
4. Investigate the N contribution of a cover crop biculture (crimson clover/rye) in a cereal rye-edamame-crimson clover/rye biculture-corn rotation.
5. Characterize N cycling in a cereal rye-vegetable soybean-crimson clover/rye biculture-corn rotation.
6. Publish results, demonstrate successful production practices to growers, produce written production guidelines, and discuss results at professional and county meetings, conferences, and field days.

Introduction:

Intensive cropping systems, cover crop residues, and no-till can reduce weed pressure without reducing yields in organic production systems. Weed management systems that reduce herbicide usage without significantly reducing yields (or even enhancing yields), not only enhance the economic sustainability of farmers and farm communities, but reductions in herbicide use also contribute to the environmental sustainability of agroecosystems. Moreover, with current USDA guidelines strongly encouraging surface residue on highly erodible soils, development of mulch systems for use with mechanical weed management can simultaneously improve weed control and soil conservation in organic and other low herbicide cropping systems. In the event that yields are impacted in no-till systems, high-value organic crops such as edamame (vegetable soybean) may provide returns to growers to offset any increased costs.
With the aforementioned factors in mind, the focus of this proposal is the design of organic farming systems that integrate essential aspects of crop management in order to increase the crop’s competitiveness with weeds, build soil fertility, and produce high-value organic crops. These integrated systems are also expected to benefit conventional growers who see them as more sustainable alternatives to traditional rotations. The specific objectives are to: 1) investigate the weed suppression of crimson clover (Trifolium incarnatum L.), subterranean clover (Trifolium subterraneum L.), cereal rye (Secale cereal L.), and crimson clover/cereal rye biculture cover crops prior to the establishment of principal crops and in the subsequent vegetable soybean (Glycine max L.) and corn (Zea mays L.) crops; 2) evaluate techniques for mechanically killing cover crops as alternatives to use of herbicides; 3) investigate the reseeding capacity of crimson clover and subterranean clover left to mature in a strip crop tillage system; 4) investigate the N contribution of a cover crop biculture (crimson clover/cereal rye) in a cereal rye-vegetable soybean-crimson clover/rye biculture-corn rotation; 5) characterize N cycling in a cereal rye-vegetable soybean-crimson clover/rye biculture-corn rotation; and 6) publish results, demonstrate successful production practices to growers, produce written production guidelines, and discuss results at professional and county meetings, conferences, and field days.
In years 1 and 2, the research will be conducted at the Upper Piedmont Research Station in Reidsville, NC. Treatments that show promise for effectively controlling weeds in vegetable soybean/corn rotations will be demonstrated in the third year at the Clemson University Farm, the Center for Environmental Farming Systems (CEFS) in Goldsboro, and the Mountain Horticultural Crops Research and Extension Center in Fletcher, NC. Growers will observe the weed suppression provided by residues at field days held 6 to 8 weeks after planting both crops into respective residues. Research results will be published in popular farm media and appropriate scientific journals. Joint comprehensive annual reports and “fact sheets” will provide information to a wider audience. Farmers will be recruited for on-farm projects that investigate the research results locally and demonstrate successful practices.

Cooperators

Click linked name(s) to expand
  • Michael Wagger

Research

Materials and methods:

The 2-year experiment will consist of seven main plot treatments (outlined at the end of this section), with each treatment a combination of cover crop, tillage system, and method of residue management. Main plot treatments will be split into two subplot treatments that reflect different N management strategies for the corn crop in the rotation. This approach will allow broader interpretations and applications that reflect system rather than single component influences. The split treatments are 1) zero additional N, or 2) additional N (based on cover crop biomass N) to provide 120 kg N ha-1.
The experiment will be conducted at the North Carolina Department of Agriculture and Consumer Services (NCDACS) research station in Reidsville, NC. All inputs and production practices will comply with the 2000 USDA National Organic Program Final Rule (USDA, 2000). The experiment will be a randomized complete block with four replications. Plots will be 4.6-m wide by 15-m long. Edamame plant and row spacing will be based on trials conducted in 2001 at the Center for Environmental Farming Systems (CEFS) in Goldsboro, NC.
Following soil sampling for inorganic N determinations in all treatments, cover crops will be seeded in September, 2002, at seeding rates of 20, 12, and 80 kg ha-1 for ‘Tibbee’ crimson clover, ‘Mount Barker’ subterranean clover, and ‘Wheeler’ rye, respectively. Lime and supplemental nutrients will be applied on the basis of the soil test report. To determine how well the establishing cover crops compete with weeds, plots will be evaluated after planting at monthly intervals until full canopy closure. Treatments will be evaluated for percent surface cover by cover crop and weeds using the beaded string method (Sloneker and Moldenhauer, 1977). The cover crops will be allowed to grow until approximately mid-May, at which time, tillage and residue management practices will be initiated. Cover crop biomass in all treatment plots will be harvested from 0.5-m2 quadrats and separated into crop/weed components just prior to planting edamame. The weed component will be subdivided into grasses and broadleaves, and principle species noted. All components will be dried and weighed. Carbon and N concentrations of the aboveground cover crop biomass will be determined, as well as soil inorganic N to a depth of 45 cm in 15-cm increments.
In early May, the crimson clover and subterranean clover cover crops (treatments 1 & 2) will be strip-tilled on 75 cm row centers and edamame will precision seeded with 7.5 cm in-row spacing. The crimson and subterranean clover cover crops between the tilled strips will be left standing and allowed to produce mature seed. The mature seed remain in treatment plots to produce a stand for the following season’s winter cover crop. The rye crop in the five remaining treatments (treatments 3, 4, 5, 6, and 7) will be disked and harrowed, flail mowed, undercut, rolled, or chemically desiccated, respectively. Edamame will be no-till planted into these treatment plots at 50 kg ha-1 (268,000 plants ha-1) in rows 75 cm apart into all treatments. Weed pressure in the edamame crop six weeks after planting will be based on a visual rating system. A zero to 100 rating system will be used to assess weed pressure. The standard basis for comparison will be treatment 3. Three evaluators will rate weed pressure in all plots, and their ratings will be averaged to give one value per plot. Weed biomass in the edamame crop six weeks after planting will be harvested from two 0.5 m2 frames per plot. Samples will be dried and weighed, weeds will be sorted on the basis of grasses or broadleaves, species noted and enumerated, and comparisons among treatments statistically evaluated. Weed biomass and species characterization will provide information about the relative competitiveness of individual cover crop species with specific weeds. In particular, presence or absence of particular weed species will help to discern allelopathic relationships between cover crops and weeds.
Immediately prior to harvest, aboveground edamame biomass will be collected from a 1-m2 frame. Biomass will be dried, weighed, and C and N concentrations determined. Edamame will be harvested using a butterbean picker, graded, and yields of number one quality fruit recorded. Total C and N in the harvested edamame will be determined. Following harvest, the experimental plots will be mowed, and soil mineral N determined to a depth of 45 cm in 15-cm increments.
In the fall (September) following the edamame crop, treatments 3 to 7 will be drilled with a biculture of crimson clover and cereal rye (15 kg crimson clover and 45 kg of rye ha-1). Treatments 1 and 2 will be left alone to allow crimson and subterranean clover seed from the previous winter cover crop to germinate and produce a new stand.
Weed suppression by the respective cover crops in the second (revised: and third) year of the experiment will be evaluated in the same manner as previously described for year 1. Likewise, all aspects of cover crop management and sampling (cover crop and soil) will be identical to that described in the first year of the experiment.
The crop following the winter cover crop in the second year will be organic corn grown for corn meal. We foresee a market for organic corn for meal and animal feed. Corn is included as the main crop in the second year because it is typically grown in rotation with soybeans. Organic egg producers in NC pay a premium (2X market price for conventional corn) as well as a $0.50 bu-1 transportation charge for organic feed corn imported into the state (Pike, 2002).
Weeds will be evaluated in the corn crop with the same methods used to evaluate weed pressure in the edamame crop. At corn harvest, yield, corn N concentration, biomass, and biomass N will be determined, as will soil mineral N to a depth of 45 cm in 15-cm increments. Corn plots will be split and one half of each plot will receive either feather meal or composted manure to supply additional N for the corn crop.
To further evaluate N dynamics within the systems, above-ground plant samples will be collected just prior to cover crop growth termination and analyzed for total C and N. Decomposition and nutrient release will be determined from the respective cover crop residues by placing representative samples of air dried, above-ground plant material in 1-mm mesh nylon bags at a residue rate representative of field conditions. Bags will be placed on the soil surface after spring planting and retrieved at 1, 2, 4, 8, and 16 weeks after placement. After retrieval, the bag contents will be dried, weighed, ground, and analyzed for C and N. One and two pool non-linear regression equations will be fit to data for percent original dry matter and N remaining at each retrieval date. At the end of the second year of the experiment, an N budget will be determined using biomass and biomass-N data from cover and cash crops and soil mineral N data.
(Revised: The crop following the winter cover crop in the third year will be organic corn grown for corn meal. All treatment plots will be moldboard plowed to bury weed seed accumulated on the soil surface and just below it. Corn will be fertilized with feather meal as per recommended rates to supply adequate N for the corn crop. Weeds will be evaluated in the corn crop with the same methods used to evaluate weed pressure in the edamame crop. At corn harvest, yield, corn N concentration, biomass, and biomass N will be determined, as will soil mineral N to a depth of 45 cm in 15-cm increments. To further evaluate N dynamics within the systems, above-ground plant samples will be collected just prior to cover crop growth termination and analyzed for total C and N. Decomposition and nutrient release will be determined from the respective cover crop residues by placing representative samples of air dried, above-ground plant material in 1-mm mesh nylon bags at a residue rate representative of field conditions. Bags will be placed on the soil surface after spring planting and retrieved at 1, 2, 4, 8, and 16 weeks after placement. After retrieval, the bag contents will be dried, weighed, ground, and analyzed for C and N. One and two pool non-linear regression equations will be fit to data for percent original dry matter and N remaining at each retrieval date. At the end of the second year of the experiment, an N budget will be determined using biomass and biomass-N data from cover and cash crops and soil mineral N data.

Research results and discussion:

Crimson clover and subteranean clover residues left on the surface did not control weeds in subsequent crops. While annual weeds were not particularly competitive with the following cash crops, perennial weeds curly dock and purple nutsedge were not inhibited by residues and completely overtook the cash crop (as well as other annual weed species, one assumes). No allelopathic properties were observable. Residues of both species produced viable seed which germinated in the subsequent fall period and provided adequate plant cover in all years. Biomass (dw) produced by crimson clover was 5100, 4993, and 5238 lbs/acre in 2003, 2004, and 2005, respectively. Biomass produced by subteranean clover was 3006, 3919, and 4413 in 2003, 2004, and 2005, respectively. Forty-five (45) percent of these residues were decomposed after 3 weeks. This left little residue on the surface to physically deter weed emergence and growth, while supplying sufficient N for vigorous weed growth.

Cereal rye residues left on the surface in no-till management (strip-till, flail mow, roll used to kill cover crop) did not control weed competition. No allelopathic of physical barrier effects of the cereal rye residues was observed. Biomass production of cereal rye crops was low for these three residue management systems and is the most likely explanation for very poor weed control. Mean biomass production in mowed treatments was 2384, 1688, and 5265 lbs/acre in 2003, 2004 and 2005, respectively. Biomass production in rolled treatments was 1978, 2364, and 3769 lbs/acre in 2003, 2004 and 2005, respectively. Biomass production in strip-tilled treatments was 2016, 2135, and 3800 lbs/acre in 2003, 2004 and 2005, respectively. It is not clear why biomass production was so low in these systems. While no N was applied to these plots, P and K were applied as per soil test report recommendations and other nutrients were reported to be present in adequate amounts. No N application to cereal rye cover crops is the standard of practice and normally does not limit crop vigor.

Biomass production in treatments where rye was incorporated by disk tillage were 1648, 1670, and 3800 lbs/acre in 2003, 2004, and 2005, respectively. Cash crops were cultivated to two times to manage weeds, but cultivation was ineffective as a weed management strategy and the subsequent crops were overgrown by weeds.

In the final treatment cereal rye with no-till management, herbicide kill and residual herbicide for weed control applied pre-plant did not control weeds. Biomass production of cereal rye cover crops in this treatment was 2098, 2076, and 4607 lbs/acre in 2003, 2004, and 2005, respectively.

Rye residues left on the surface intact did not decompose quickly. Sixty-tree percent of the residue (dw) remained after 9 weeks. Residues left on the surface after mowing had similar decomposition rates (78, 69, 71, 60, and 53 percent of residues remaining after 2,3, 5, 9, and 17 weeks, respectively).

The observation that weed pressure was sufficient to completely suppress crop growth in all systems leads to the conclusion that the weed seed bank in the research plots was high. This weed seed population pressure was exacerbated by weed seed production in experimental years. It was further exacerbated by the use of “composted” dairy manure as an organic N source in organic plots prior to planting corn in 2004. The material was, in fact, not fully composted as viable spiny amaranth seed germinated in the compost and also in treatment plots. Before the 2005 cash cropping season, the entire treatment area was moldboard plowed to bury weed seed, but this management strategy was ineffective.upplying sufficient N for vigorous weed growth.

Participation Summary

Educational & Outreach Activities

Participation Summary:

Education/outreach description:
PUBLICATIONS AND OUTREACH

No publications are planned to report results observed in this experiment. Reports will be reported to growers and other interested parties in conversation and as components of talks on cover cropping/weed management at conferences, field days, and educational meetings.

Project Outcomes

Project outcomes:

No impacts can be reported from this project except negative outcomes associated with the experiment. If results were reported in refereed journals, popular publications, at conferences, and at professional meetings, the results reported would indicate that crimson clover, subteranneum clover, and cereal rye residues left on the surface did not control weeds in subsequent crops.

Economic Analysis

Growers implementing cover crop/residue management strategies for weed control in organic farming systems that were studied in this experiment would experience crop failure and lose all monies invested in the crop.

However, growers allowing legume cover crops to produce viable seed would save approximately $20 per acre in seed costs and additional costs associated with planting those legumes in subsequent years.

Farmer Adoption

We would not recommend that farmers adopt the production practices tested in this experiment. However, we would recommend that farmers allow crimson and subterannean clover to mature seed before destroying the cover crop, whether by physically killing (rolling, mowing, strip till, incorporation) because viable seed of each species will be produced if left to mature, and growers will not need to replant the legume cover crop in the subsequent fall period.

We would also recommend that growers receive assurances from compost producers that wastes are sufficiently heated during the composting process to fully sterilize the feedstock materials, destroying any weed seed and killing plant and human pathogens. The National Organic Rule stipulates that windrow systems achieve and maintain temperatures of 130 to 170 degrees F for 15 days and 5 windrow turnings. This should adequately control weed seed viability. Growers bring in off-farm compost should demand guarantees or references from compost producers to assure high quality compost.

Recommendations:

Areas needing additional study

ADDITIONAL STUDY NEEDED

This experiment bears repeating in fields where weed seed banks are depleted and/or fields have been managed to reduce weed pressures before the experimental work is begun. The field in this experiment was in poorly managed pasture for years prior to the implementation of this experiment. Consequently, weed seed pressure was continually increased. This field should have been managed by intensive tillage or by herbicide management for one year (perhaps, two) before the experiment was started. Often, this is a recommended strategy for growers implementing a transition to organic. The alternative, going organic “cold turkey” can result in weed pressures and crop failures like those experienced in this experiment.

Additionally, a better fertility analysis/history might provide for better biomass production of cover crops and consequent better suppression of weeds. An experiment to assess possible enhancements to biomass production of N application at various rates would be helpful.

In addition, stage of growth of cover crop kill should also be studied. Information became available recently that would indicate that allelopathic properties of rye vary with stage of growth. More information about this would be valuable, as would cultivar affect of allelopathic properties.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.