Conservation tillage development

How weeds produce their effect is the subject of continuing research. As rather recently defined, the negative effect of weeds on crop plants includes both competition and allelopathy (1.) and has been termed interference. Previous weed science research considered the competition component foremost and, usually, solely (e.g. 2). Allelopathy, however, has received some attention recently, with a number of symposia and reviews devoted to allelopathic effects. Some of these cover the effects of weeds on crops (3, 4, 5). In this chapter, I review the possible role of allelopathy in weed interference in crop production in the Mid-South. A second objective of this review is to indicate where research is needed and to suggest potential lines of future research, especially with respect to the developing role of conservation tillage practices in this region. 

Conservation agroecosystems developed in the Great Plains of the U.S. to control soil erosion are characterized by the presence of varying quantities of plant residues on the soil surface. This residue mulch protects the soil from the erosive forces of wind and water, resulting in improved stream water quality and soil conservation. Conservation tillage systems also help maintain soil productivity and reduce energy requirements of crop production (15). However, crop yield reduction has been observed with conservation wheat production in some areas of the U.S. (16-18) and with rice culture in the Far East (, 20). 

Triazine herbicides have been important tools in the development and implementation of conservation tillage systems. Postemergence and residual activity, low vapor pressure, weak adsorption to surface crop residue, root uptake, broad weed control spectrum, and crop safety make these herbicides compatible with the high crop residue conditions of conservation tillage. 

The impact of herbicides on our modern agricultural technology has been phenomenal. It is almost impossible to measure or to overemphasize the importance of herbicides in their potential for overcoming famine, pestilence, poverty and crop losses due to weeds that were prevalent throughout most of the history of mankind prior to the 1950s. Herbicides have been essential, not only for their direct effects on weed control and crop yield, but also in providing more efficient use of water and fertilizers for the optimum development of improved crop varieties and hybrids. They have also been essential tools in the recent development of conservation tillage methods, which have reduced topsoil erosion and moisture losses in many areas of the world. 

The information presented in this section clearly shows an increase in pesticide sales and use globally and in individual developing countries during the last two decades. This increase is expected to continue into the next decade as more farmers adopt conservation tillage practices and genetically modified crops which allow increased applications of pesticides. 

Peters RD, Sturz AV, Carter MA, Sanderson JB (2003) Developing disease-suppressive soils through crop rotation and tillage management practices. Soil Till Res 72 181-192 Pfiffner L, Luka H (2003) Effects of low-input farming systems on carabids and epigeal spiders - a paired farm approach. Basic Appl Ecol 4 117-127 Pimentel D, Harvey C, Resosudarmo P, Sinclair K, Kurz D, McNair M, Crist S, Shpritz L, Fitton L, Saffouri R, Blair R (1995) Environmental and economic costs of soil erosion and conservation benefits. Science 267 1117-1123... 

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