- Agronomic: rye, grass (misc. perennial), hay
- Animal Production: feed/forage
- Crop Production: agroforestry, application rate management, conservation tillage, continuous cropping, cover crops, no-till, nutrient cycling, organic fertilizers
- Education and Training: demonstration
- Natural Resources/Environment: hedgerows
- Pest Management: chemical control, mulching - vegetative
- Production Systems: holistic management, permaculture
- Soil Management: nutrient mineralization, organic matter, soil analysis, soil quality/health
A comparison of various organic mulches in conjunction with winter and summer high biomass cover crops during herbicide-free no-till collard production found that mulches applied in the fall were effective in altering weed species composition away from broadleaves and sedges, although forage soybean as a summer cover crop was not, due to rapid decomposition. Persistence and nutrient release rates from organic residues result in slowly released nitrogen that may be available to subsequent crops. This study shows that it is possible to increase soil organic matter and nitrogen content while simultaneously keeping land productive.
Organic agriculture is one of the fastest growing sectors in the US agricultural industry. The sale of organic foods in the United States had an average annual growth rate of 19.5% from 1998-2003, representing $10.38 billion in consumer sales in 2003 (OTA, 2004). Certified organic cropland in the US increased 103% between 1997 and 2005, while total acreage increase 201% (USDA, 2009). Although organic producers make efforts to adopt a sustainable approach on their farms, they often use conventional tillage because they cannot use herbicides to kill weeds and cover crops. Conventional tillage destroys organic matter, increases erosion risk, damages soil structure, reduces aggregate stability, promotes crusting and decreases soil moisture compared to no-till (Raczkowski et al., 2002; Bessam and Mrabet, 2003). Research conducted by Dr. Ron Morse has demonstrated the feasibility of organic no-till in Virginia (Rodale, 2005).
The key to organic no-till is the production of high biomass cover crops. High biomass cover crops are desirable because they contribute substantial amounts soil organic matter (SOM) and cover a large percentage of the soil surface. However, high biomass cover crops with low C/N ratios such as sunn hemp (Crotalaria juncea L.) require additional weed control as residues decompose (Ron Morse, personal commmunication, May 17, 2005), necessitating some form of weed control later in the season. On the organic farm, further weed control is often accomplished by hoeing, cultivating or purchasing off-farm inputs, which can be costly in terms of labor, transportation and input costs. Alternatively, mulching materials can be provided in situ by the production of high biomass perennial legumes grown as hedgerows in the field border or within the field itself, such as in alley cropping systems (Jordan, 2004). High biomass perennial legumes are desirable because they can provide a high quality mulch, rich in nitrogen (N) as well as other nutrients that become available to the crop as it decomposes, reducing the need to supply nutrients from other sources. Nutrients not used by the concurrent crop become potentially available to subsequent crops upon mineralization. Perennial legumes do not require re-seeding and often are more productive than annual species. By growing the legume mulch in the field, the costs of purchasing and transporting mulch are eliminated and the cost of providing nutrients to the crop is also reduced.
The rate at which plant residues and mulches decompose is dependent upon several factors. Mulches with a lower C/N ratio tend to decompose faster than those with a low N content, while presence of lignin and polyphenols slows decomposition rates (Fox et al., 1990). A balance must therefore be achieved between nutrient release and mulch persistence. Mimosa (Albizia julibrissin), a leguminous tree, and lespedeza (Lespedeza sericea) may be appropriate perennial leguminous species for mulch production because they can tolerate heavy pruning and have been shown to produce up to 4.0 U.S. tons of dry matter per acre in Alabama (Mosjidis, 1996; Kang et al., 2008). Although both species have a low C/N ratio, lespedeza is likely to decompose more slowly due to higher tannin concentrations, and thus persist longer as mulch (Kalburtji et al., 1999). Straw, a common organic mulch having a high C/N ratio, is likely to have slower nutrient release rates than mimosa prunings or lespedeza cuttings, and therefore may be more effective for weed suppression later in the growing season.
Summer cover crops have the capacity to improve soil quality, recycle or contribute nutrients, reduce weed growth, minimize soil erosion and produce large amounts of biomass in a short period of time (Creamer and Baldwin, 2000). After termination, nutrients released from residues are available for subsequent crops upon mineralization. Forage soybean (Glycine max) is an annual legume that may be a useful in the Southeast for its utility as a high biomass, low C/N summer cover crop.
Timing of cover crop termination is important in organic no-till systems. Crimping and rolling cereal cover crops may not be sufficient to produce an adequate kill if the crop is not mature. At the soft-dough stage of cereal growth, roller-crimping was as effective as herbicide in achieving an adequate kill (Ashford and Reeves, 2003). This period is identified as the 11.1 to 11.2 stage according to the Feekes Growth Stages (Large, 1954). This stage of growth is achieved around April 15-20 for rye (Donald Ball, personal communication May 23, 2005) in central Alabama. Alternatively, adequate termination of cover crops has been achieved by flail-mowing (Morse, 1999).
The objectives of our experiment were:
1. To compare mimosa prunings, lespedeza cuttings and straw as organic mulches in a high residue no-till system; and
2. To evaluate forage soybean as high-residue summer cover crop for no-till production of collards and the interaction of cover crop and mulch type on assessment parameters.
Mulches and cover crops were evaluated in terms of weed control over three years, decomposition and nutrient release rates, and crop yields.