Practical Experience and On-Farm Research with Weed Management in an Iowa Ridge Tillage-Based System

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Abstract
The weed management system of most producers is complex and represents the summation of years of experience and informal observation. The ridge tillage, row crop system described here is especially complex because it seeks to use cultural and mechanical weed controls in preference to herbicides. Both experience and formal experimentation have contributed to the development of the system. Fundamental are two working hypotheses that may appear counterintuitive: (i) that tillage can stimulate weeds and (ii) that weeds can be used to control other weeds. Results of on-farm trials on the Thompson farm have supported these hypotheses. Additional on-farm trials have pointed toward conditions in which rotary hoe tillage can be used to best effect to eliminate weeds. Results of 51 replicated on-farm trials by Practical Farmers of Iowa (PFI), an organization that generates and shares information about profitable, environmentally sound farming methods, showed that ridge tillage without herbicides is an effective and economical system for weed management and row crop production. Experience gained developing this alternative weed management system can be summarized in guidelines applying, respectively, to the overall system, the planter, the rotary hoe, first cultivation, and second (lay-by) cultivation. Research Question Can weeds be effectively managed in a row crop system that relies primarily on cultural and mechanical techniques? Moreover, would such a weed management system be economical and could it be compatible with cover crops and residue management practices that reduce soil erosion? Literature Summary Observation: Farmers who do not use primary tillage frequently see a great increase in weeds where endrows are disked. Research has shown that ridge tillage avoids this kind of soil disruption and the stimulatory effect it has on some weeds. Ridge-till also mechanically displaces weed seeds from the row at planting. Observation: Highway widening exposed soil along several fields; the ditches taken out of fields where herbicides had been used and only row crops were raised grew a solid stand of velvetleaf. The ditches from fields in a corn-soybean-corn-oatkay-hay rotation, where herbicides had not been used for the previous 18 yr did not have velvetleaf. While the crop rotation difference may have affected the weed seed bank in the two kinds of fields, crop history showed a seed reserve in both. Research has shown that plants can have chemically mediated suppressive effects on other plants, the phenomenon termed allelopathy. Could allelopathy be responsible for the observed difference in velvetleaf along the road cut? Study Description Observation and experimentation have led to an alternative weed management system in which herbicides have not been used for 18 yr. Important elements of the system are: ridge tillage, the rotary hoe, a weed suppressive and allelopathic cover crop of rye drilled just on the ridge, and a diverse crop rotation to break weed cycles. Replicated on-farm experiments have contributed to the evolution of this system. Applied Questions How can tillage best be used to control weeds? Tillage can have a stimulatory effect on weeds that is not always desirable. Primary tillage stimulates weeds that can cause problems later in the season. Preplant row cultivation increased weed numbers in on-farm trials. However, the high-residue rotary hoe can be an effective tool for in-row weed control, especially under the right circumstances. High-residue row cultivators can effectively eliminate weeds in spring, when conditions favor weed growth. Does allelopathy have any practical application? How can competition best be used to control weeds? Allelopathy refers to a direct or indirect, antagonistic effect of one plant species on another, mediated by chemicals in the soil. Competition is a direct antagonistic effect, as different plants contend for limited resources. Preplant weed control can be “too successful” if it eliminates weeds that could allelopathically suppress later weeds. Our present solution is to avoid preplant tillage or herbicides and to use a cover crop rather than rely only on early weeds to control later weeds. A fall cover crop of rye, drilled just over the row, competes with weeds, may allelopathically suppress later weeds, contributes other benefits such as erosion control and nitrogen sequestering, and is easy to remove mechanically at planting. Is it practical to manage weeds primarily through mechanical and cultural methods? When herbicides are not used, differences are apparent in the ability of tillage systems to control various weeds. Ridge tillage offers the best overall weed control under these conditions. There are several specific pointers and modifications that augment the effectiveness of ridge-till planters, the rotary hoe, and ridge-till cultivator. This is a system that substitutes for purchased inputs some additional management and labor. It is not beyond the capabilities of a wide range of producers. In 7 yr of replicated on-farm trials (21 corn trials and 30 soybean trials), there was an average of less than 1 bdacre difference between the mechanical treatment and the herbicide treatment (Fig. I). In these 51 trials by producers from the Practical Farmers of Iowa (PFI), the mechanical-only treatments saved an average $5.82 and $5.95/ac1-e in corn and soybeans compared with herbicide-based management. Figure 1 Open in figure viewer PowerPoint Herbicide compared with mechanicaVcultural controls in 1987 to 1993 ridge tillage trials by Practical Farmers of Iowa. Economics reflect Iowa State University estimated machinery costs, labor at %6h, herbicide costs, and, where significant yield differences occurred, crop value of treatments.