Crop productivity

Chemical, cultural, and mechanical weed control practices have been relatively successful ia reducing yield losses from weeds (448). However, herbicide-resistant weed populations, soil erosion, pesticide persistence ia the environment, and other problems associated with technologies used (ca 1993) to control weeds have raised concerns for the long-term efficacy and sustainability of herbicide-dependent crop production practices (449). These concerns, coupled with ever-increasing demands for food and fiber, contribute to the need for innovative weed management strategies (450). 

In addition to these uses related to crop production, hydrocarbons are used extensively in packaging, particularly in plastic films and to coat boxes with plastic and (to a much lesser extent) wax. Polymeric resins derived from hydrocarbons are also used to make trays and cases for deflvery of packaged foodstuffs (see Eilmand sheeting materials Packaging Paper). 

Soil Nutrient. Molybdenum has been widely used to increase crop productivity in many soils woddwide (see Fertilizers). It is the heaviest element needed for plant productivity and stimulates both nitrogen fixation and nitrate reduction (51,52). The effects are particularly significant in leguminous crops, where symbiotic bacteria responsible for nitrogen fixation provide the principal nitrogen input to the plant. Molybdenum deficiency is usually more prominent in acidic soils, where Mo(VI) is less soluble and more easily reduced to insoluble, and hence unavailable, forms. Above pH 7, the soluble anionic, and hence available, molybdate ion is the principal species. 

E-C. Oerke, H-W. Dehne, F. Schunheck, and A. Weber, Crop Production and Crop Protection—Estimated Tosses in MajorFood and Cash Crops, Elsevier Science B. 

Table 2. Quantities of Pesticides Most Commonly Used in U.S. Agricultural Crop Production in 1995 ...

Extensive use of two more recendy developed classes of herbicides will further dramatically reduce the amount of appHed to control weeds. The sulfonylurea herbicides are extremely active compounds first discovered in the mid-1970s at DuPont they have been discussed extensively (78). Sulfonjiurea herbicides have experienced a rapid and widespread success since thek commercial introduction in 1982 with chlorsulfuron (Table 5). The sulfonylureas are appHed at rates of 2—75 g/ha. The chemistry of the sulfonylurea molecule permits the synthesis of a very large number of useful analogues, consequentiy many new herbicides are anticipated for crop production. As of this writing (1996), over 350 patents have been issued to about 27 agricultural companies covering tens of millions of stmctures known or expected to be herbicidaHy active. 

On the positive side, the three-dimensional nature of the resource provides it with a distinct advantage compared to other solar technologies. Specifically, because siting usually involves placing the individual turbines as high as possible, typically spacing turbines about 2 to 3 blade diameters apart crosswind and 10 diameters apart downwind, only a small fraction of a wind farm area is actually occupied. The rest of the land remains available for other appHcations, such as crop production or Hvestock grazing. 

Plant nutrient sulfur has been growing in importance worldwide as food production trends increase while overall incidental sulfur inputs diminish. Increasing crop production, reduced sulfur dioxide emissions, and shifts in fertilizer sources have led to a global increase of crop nutritional sulfur deficiencies. Despite the vital role of sulfur in crop nutrition, most of the growth in world fertilizer consumption has been in sulfiir-free nitrogen and phosphoms fertilizers (see Fertilizers). 

Between 1935 and 1960 outputs per man-hour of labor increased about 4.5 times, and crop production per hectare of crop-land almost doubled. Inputs of labor were decreased by 50 percent, inputs of land remained relatively stable, but inputs of non-real-estate capital inputs were nearly tripled. Among these capital inputs, those of seed, feed, and livestock purchased increased by about four times, and those of mechanical power and machinery by more than 2.5 times. 

The role of water in the life of plants is well known. In terms of its major effects this role consists in transporting the mineral nutrition, maintenance of intracellular pressure responsible for the vertical growth of plants and, finally, participation in photosynthesis which provide the biomass growth, or plainly speaking, the crop production. 

Despite the use of 2.5 million tons of pesticide worldwide, approximately 35% of potential crop production is lost to pests. An additional 20% is lost to pests that attack the food post-harvest. Thus, nearly one-half of all potential world food supply is lost to pests despite human efforts to prevent this loss. Pesticides, in addition to saving about 10% of world food supply, cause serious environmental and public health problems. These problems include human pesticide poisonings fish and bird kills destruction of beneficial natural enemies pesticide resistance contamination of food and water with pesticide residues and inadvertent destruction of some crops. 

Table 5-2. Methyl Parathion Use in Crop Production in 1992 (continued)...

Gianessi LP, Anderson JE. 1995. Pesticide use in U S. crop production National data report, ed. Washington, DC National center for food and agriculture policy,... 

Monteith, J.L. (1977). Climate and the efficiency of crop production in Britain. Philosophical Transactions of the Royal Society of London B, 281, 277-94. 

Takeda, T., Sugimoto, H. Agata, W. (1978). Water and crop production. I. The relationship between photosynthesis and transpiration in corn leaf. Japanese Journal of Crop Science, 47, 82-9. 

Hanks, R.J. (1983). Yield and water-use relationships an overview. In Limitations to Efficient Water Use in Crop Production, ed. H.M. Taylor, W.R. Jordan and T.R. Sinclair, pp. 393-412. Madison, Wisconsin American Society of Agronomy. 

On die other hand, the measure of the afforestation is also classified into no-regrettable one from the viewpoint of environment. Furthermore, most of desert area is said to be formed by partly somewhat human activities. The activities of afforestation of arid land without crop production are also a no-regrettable measure [14-17]. 

Crop yields can rise dramatically with the use of commercial fertilizers. For example, in 1800 an acre of land in the United States produced about 25 bushels of com. In the 1980s the same acre of land produced 110 bushels. Worldwide, approximately 4 billion acres of land are used to grow food crops. This would probably be enough land to feed the world s population if the entire acreage could be fertilized commercially. It has been estimated that world crop production would increase by about 50% if about 40 per acre were spent to apply modem chemical fertilizers. However, it would cost about 160 trillion to produce this additional food. Furthermore, the use of chemical fertilizers can lead to the contamination of streams, lakes, and bays with phosphates and nitrates. 

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