Conservation tillage

Fertilizer Use. The worldwide use of fertilizers has an important, positive effect on the environment. Conservative estimates (112) iadicate that about 30% of world food production is direcdy attributable to fertilizer use. Without fertilizer, therefore, at least 30% mote virgin land would have to be devoted to agriculture, and 30% more labor and other resources would have to be expended. Even more serious would be the effects of land tillage and cropping without nutrient replenishment. Past experience has shown that, under such a condition, crop yields progressively decrease, the land eventually becomes barren, and forces of wiad and water erosion prevail. 

Conservation tillage increased atra2ine and metolachlor surface mnoff by 42% and decreased tile discharge by 15% compared with conventional tillage, but total field mnoff was the same from all treatments (53). Runoff events shordy after herbicide appHcation produced the greatest herbicide concentrations and losses in both surface mnoff and subsurface drainage. 

The interaction of all these factors makes it difficult to predict an overall effect of conservation tillage on the potential leaching of a pesticide compared to that in a conventionally tilled field. However, it was found that a prolonged rain immediately after appHcation resulted in short-term levels of pesticide in groundwater to be greater under no-tiU than under conventional till plots, which suggested that preferential transport in no-tiU had occurred... 

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. 

Various forms of soil cultivation, or non-cultivation, exist ranging from mouldboard ploughing to no-tillage, as listed below (from CTIC and Conservation Technology Information 1998) ... 

In those cases that conservation tillage, particularly no tillage, can be adopted, advantages can be appreciable under diverse aspects ... 

CHC, Conservation Technology Information Center (1998). Available at http //www.ctic.purdue.edu Diaz-Zorita M, Duarte G, Grove J (2002) A review of no-till systems and soil management for sustainable crop production in the subhumid and semiarid Pampas of Argentina. Soil Tillage Res 65 1-18... 

Uri ND (1998) Conservation tillage and the use of energy and other inputs in US agriculture. Energy Econ 20 389—410... 

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... 

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. 

In the direct drilling (no-till seeding) practice in the united Kingdom/ straw residues from the preceding crop are usually burnt because poor crop establishment and yields can result/ particularly on heavy soils in wet years (10). Similar problems can occur in the conservation tillage systems oF the Pacific Northwest (L.F. Elliott and H.-H. Cheng/ this volume). 

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). 

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. 

Allelopathic problems have been especially troublesome with conservation tillage systems (6.7.9). An example is the reduced growth of winter wheat when it is direct-drilled into stubble (Figure 1). In the heavy residues (left), the plants grew poorly. 

---