Tillage practices

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. 

The time to cleanup may actually be somewhat less than 9 years if Pb migrates down in the soil profile with the addition of EDTA, or if tillage practices serve to smooth out the hot spots. Regulatory cleanup levels are usually based on a limit that cannot be exceeded, such as 400 mg/kg, and soil concentrations would need to be analyzed to ensure compliance at the end of each year. 

West TO, Marland G. A Synthesis of Carbon Sequestration, Carbon Emissions and Net Carbon Flux in Agriculture Comparing Tillage Practices in the United States. Agriculture, Ecosystems and Environment. 2002 91(l-3) 217-232. Doi 10.1016/ S0167-8809(01)00233-X... 

Tan Z, Lai R, Owens L, Izaurralde RC (2007) Distribution of light and heavy fractions of soil organic carbon as related to land use and tillage practice. Soil Till Res 92 53-59... 

Albers, P.H., G. Linder, and J.D. Nichols. 1990. Effects of tillage practices and carbofuran exposure on small mammals. Jour. Wildl. Manage. 54 135-142. 

Abou-Assaf, N., Coats, J.R., Gray, M.E., and Tollefson, J.J. Degradation of isofenphos in cornfields with conservation tillage practices,/. Environ. Sci. Health, B21(6) 425-446, 1986. 

Containers, media and seeds. Glass Petri dishes, 100 x 15 cm, were used with two sheets of 75-mm Whatman 41 filter paper as the absorptive medium. Ten seeds of TAM105 wheat were placed in a radial pattern with the micropyle end toward the center between the two sheets of filter paper. Seeds were hand-selected for normal size and absence of damage. TAM105 was selected because it is the variety used in the ongoing field research on conservation tillage practices. The bottom section of each Petri dish cover was covered with a square of kitchen-type plastic wrap to retard moisture loss before the lid was pressed on. 

Figure 16.5. SFR concentration in soil HA samples extracted from different tillage practices, cropping systems, and period of experiments (a) 5 years and (b) 9 years. NT, no tillage CT, conventional tillage O/M, oat/maize O + V/M + C, oat + vetch/maize + cowpea. Reprinted from Bayer et al. (2002a).

Conventional tillage exposes the OM, which are naturally stabilized in the soil, to the action of sunlight and oxidation conditions that favor microbial activity. Consequently, only the very stable fraction of SOM generally remains. The importance of SOM functions is well known, but structural information, chemical composition, and changes induced by anthropogenic factors, such as tillage practices, are still under research. 

Use of butylate and EPTC required mechanical incorporation into the soil. Beginning in the 1970s and 1980s, there was a steady increase in the implementation of conservation tillage practices. Although the thiocarbamates had... 

Thus, triazine movement and persistence are influenced by many factors, the interactions of which are not always easy to predict. Several models have been used as tools to estimate losses and to identify variables that will impact the rate and magnitude of loss. Considering the broad range in soil properties and climatic conditions used, some models performed well. However, modeling results and predictions are only estimates, and the fate and transport of triazines in the soil environment has been shown to be affected by many factors, including concentration, soil texture, variation in climate, and differences in tillage practices. 

Isensee, A.R. and A.M. Sadeghi (1993). Impact of tillage practice on runoff and pesticide transport. J. Soil Water Cons., 48 523-527. 

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