Organic Vegetable Production in Alabama

Tillage Trials

May 2008

Tillage trials

This summer we will be conducting tillage trials at E.V. Smith, Cullman, and Alabama A & M research centers as part of our CSREES Integrated Organic Program Grant on mid-summer tomato and pepper production. We will be comparing no-till (NT) with 3 different tillage types; each research station will do a slightly different tillage treatment. At E.V. Smith, where the soils are sandy and droughty, we will use strip till; the surface residues are chopped up and mixed in the top surface layers. At Cullman, where the soil has a higher clay content, but still sandy, we will do conventional tillage. The tilled areas are still in strips, but they are first deep plowed, and then tilled so that the soil surface is inverted or completely turned over. The surface residues will be buried deeper than at E.V. Smith. At A&M, where the soil has the highest clay content of the three locations, the tillage method will be raised beds. The soil will be plowed and then what remains in the aisles will be removed and placed on the beds. At all three locations we will plow/till strips for planting and mow between them. We will compare these three types of tillage treatments to NT with respect to crop yield, soil health, and weed populations.

NT is sustainable

NT production is compatible with the concept of sustainable agriculture; it protects natural resources and the resource base that farming depends on. Plant residues left on the soil surface act as mulch that protects the soil from erosion, which in turn, protects water quality. Surface residues also decompose more slowly than when incorporated into the soil by tillage. The slower decomposition rates allow more time for soil organic matter to accumulate. Increasing soil organic matter content enhances soil fertility and sequesters carbon, which reduces the release of CO2 into the atmosphere. Plant residue mulches also decrease water evaporation from the soil surface which increases water use efficiency. Omitting tillage operations requires fewer field passes with machinery which reduces energy usage. Some of the benefits to the farmer include increased profits by building soil organic matter content and improving soil fertility using on-farm inputs. Cover crop residues aid in weed control. Additionally, no-till can produce higher crop yields than conventional tillage.

Challenges of NT

Despite the many benefits of NT, it can be challenging for organic farmers who don’t have herbicides at their disposal. Conventional NT production practices rely on herbicides to terminate the cover crop before planting the cash crop. In organic NT, the cover crop must be terminated by other means, such as mowing or rolling and crimping. Mowing works well if the subsequent crop is to be hand-planted. The best method of mowing is with a flail mower, which spreads the cut residue evenly and does not chop it too finely, leaving a coarse surface mulch that will decompose slowly and provide weed control for a longer period of time. If the subsequent crop is to be mechanically transplanted or seeded, the mowed residues may interfere with the machinery. In this case, it is better to roll and crimp the cover crop so that the residues are held in place and do not bunch up in front of the machinery. Rolling will kill some cover crops better than others. Rye is more easily killed than some others, such as clover and vetch, if it is rolled after flowering, but before fruit maturation. If allowed to set seed, it may re-sprout to compete with the crop. If mowed before flowering, it may spring back up. Crimping helps to crush the residues enough to aid in killing them. You can view pictures of roller-crimpers on the Rodale website: http://www.rodaleinstitute.org/no-till_revolution. You may also be able to knock back the cover crop with a tiller with the tines unengaged.

Key to Success

The key to success with organic NT is to grow enough cover crop biomass so that the residues remain on the soil surface long enough to provide some control of summer weeds. The cover crop may need to be fertilized in order to obtain optimum growth. Cover crop residue must also have a high C:N ratio to prevent it from decomposing too rapidly. Grasses have a high C:N ratio compared to legumes. Rye is the fall cover crop that has been found to produce the greatest amount of biomass and provide the greatest amount of weed control. The disadvantage of having a cover crop that produces abundant biomass, has a high C:N ratio, and decomposes slowly is that plant nutrients are tied up in this biomass and are not available immediately for the subsequent cash crop. To remedy this problem, we will be trying various levels of pre-plant fertilizer applications to the cash crop. We will also be experimenting with some cover crop combinations of rye and legumes, such as Austrian winter pea, crimson clover, or hairy vetch.

NT systems may take 5-7 years before the soil fertility improvements become noticeable. It takes time to build soil organic matter and for soil organism populations to increase substantially. Equilibrium should be reached where nutrients are being released continuously from stored soil organic matter, and at that point, it may not be necessary to apply any more pre-plant fertilizer for the cash crop. We hope to be able to continue our tillage research long enough to observe the beneficial effects of NT.

If any of you have had experiences with NT in your garden, please let us know how it went for you. If you would like more information on NT production, see the references below or contact Jan Garrett at garrecj@auburn.edu.

Online resources on organic no-till methods:

Kuepper, G. 2001. Organic Matters: Pursuing Conservation Tillage Systems for Organic Crop Production. NCAT/ATTRA. Online publication: http://attra.ncat.org/attra-pub/organicmatters/conservationtillage.html#tillage

Rodale Institute. No-till Revolution. Online. http://www.rodaleinstitute.org/no-till_revolution

Wilson, D. and C.Z. Ulsh. 2007. Researchers roll out the details of 2006 no-till organic corn numbers. Rodale Institute. Online publication. www.rodaleinstitute.org/node/207.