Submitted to: Weed Technology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/27/2003
Publication Date: 1/1/2004
Citation: Anderson, R.L. 2004. A paradox with herbicide resistance, tillage and semiarid crop production. Weed Technology 18: 186-192. Interpretive Summary: Crop production is changing in the Central Great Plains because of no-till systems. No-till maintains crop residues on the soil surface, thus improving soil water storage and crop yields. Herbicides enabled producers to eliminate tillage, but resistant weeds are disrupting their effectiveness. Producers are considering tillage again to reduce the selection pressure exerted by intensive herbicide use in no-till. We reviewed the literature to assess the impact of tillage on weed dynamics. With all aspects of weed populations, tillage favors weeds. Crop residues enabled producers to grow more crops, suppress weed establishment, and improve crop competitiveness. Tillage eliminates all of these benefits. A further concern is that tillage minimizes the beneficial effect of no-till on increasing soil organic matter levels and soil health. Producers are struggling with this paradox; tools (herbicides) needed for crop residue management are being rendered ineffective by resistant weeds, yet residue management and intensive corpping are less feasible in tilled systems. A key issue facing producers and scientists is devising cropping systems that do not favor herbicide-resistant weeds. Otherwise, producers may return to tillage-based systems that are not as effective as no-till from an economic, agronomic, or environmental perspective.
Technical Abstract: Maintaining crop residues on the soil surface has changed cropping practices in the Central Great Plains. Where previously winter wheat-fallow was the prevalent rotation, producers now grow warm season crops in sequence with winter wheat and fallow. Controlling weeds during fallow with herbicides eliminates the need for tillage, thus conserving more crop residues. But, producers are considering tillage again because of herbicide-resistant weeds. We are concerned that tillage may be detrimental to both weed management and long-term sustainability of semiarid crop production. Therefore, we reviewed the impact of tillage on weed dynamics and crop growth compared to no-till systems. Long-term cropping systems studies show that rotations can be designed to reduce weed community density several fold; tillage minimizes this rotational effect by burying weed seeds and prolonging their survival in soil. Crop residues on the soil surface reduce weed seedling establishment in no-till systems, but tillage eliminates this effect. Proso millet is less competitive with redroot pigweed if tillage occurs before planting; redroot pigweed produces 34 percent less seeds per plant if proso millet is grown without tillage. Also, crops yield less after tillage compared to no-till in this semiarid climate. Tillage may help in managing herbicide resistance, but it favors weed populations as well as hinders crop growth. An additional concern is that tillage minimizes the beneficial effect of no-till on increasing soil organic matter levels and soil health.