Increasing crop yields

To determine the feasibiUty of, or need for, fertilization requires knowing (/) which of the required elements, if any, are deficient in the soil (2) what chemical forms of the deficient elements are assimilable by the plants and thus suitable as fertilizers (5) what quantity of fertilizer material is required to meet the needs of the crop and (4) whether the crop yield increase resulting from fertilizer appHcation would warrant the cost of the fertilizer production and appHcation. 

We know that brassinolide and the other brassinosteroids are novel plant growth regulators that contribute either to crop yield increases or to promotion of crop quality. How do we successfully exploit them for their use in commercial applications to agricultural productivity ... 

Peterson (1964) also points out that soil and water losses from sloping lands decrease as soil fertility and crop yields increase. This is attributable to more rapid early growth, more lush canopy, larger root systems, more organic residues, more active soil flora and fauna, higher organic matter content, and better tilth. Essentially the same ideas were expressed earlier by Truog (1950). 

Decreased crop yields. Increased skin cancer rates. Increased biological mutations in oi anisms. 

Prolonged systematic fertilizer application with rates of phosphorus, which exceed carry-over of the element by crop yields increases mobile phosphorus content in soils of agroecosystem in the beginning of intensive fertilizer application only. In the further due to phosphorus transition in sedimentary forms mobile phosphorus content in soils increases very slightly or even has a tendency to decrease. Intensity of mobile phosphoms transition in slow-moving forms laigely depends on soil type, also depends on the duration of the interaction of mobile phosphates with soil and on the value of positive phosphoms balance. 

In the United States, DDT was used extensively in homes as well as on crops, such as cotton and soybeans. Because of its stable chemical structure, DDT did not break down quickly in the environment, which meant that it did not have to be applied as often. At first, everyone was pleased with DDT as crop yields increased and diseases such as malaria and typhus were controlled. 

The flush of a tea shoot is defined as the apical bud and two new leaves below it (Pig. 2). This is the ideal target for harvesting fresh tea of optimum quahty. Commonly, three or even four leaves are plucked in an attempt to increase crop yield. 

Such titanium sulfinates are reported to increase crop yields (407—409). Isocyanides insert to yield imines as follows (410,411) ... 

Plant and Animal Nutrient. Copper is one of seven micronutrients that has been identified as essential to the proper growth of plants (87). Cereal crops are by far the most affected by copper deficiency (see Wheat and other cereal grains). Greenhouse studies have shown yield increases from 38% to over 500% for wheat, barley, and oats (88) using copper supplementation. A tenfold increase in the yield of oats was reported in France (89). Symptoms of copper deficiency vary depending on species, but often it is accompanied by withering or chlorosis in the leaves that is not ammenable to iron supplementation. In high concentrations, particularly in low pH sods, copper can be toxic to plants. 

It has been estimated that of the total U.S. increase in farm output between 1940 and 1955, 43 percent is attributable to increased crop yields per hectare, 27 percent to increases in value added by livestock production, 23 percent to reduction in farm-produced power, and 7 percent to changes in the amount of capital used. While it is not possible to isolate the effect of a single input, it is estimated that increased use of fertilizer accounted for more... 

High concentrations of SO, can produce tempo-rai y breathing difficulties in asthmatic children and in adults who are active outdoors. Sulfur dioxide also can directly damage plants and has been shown to decrease crop yields. In addition, sulfur oxides can be converted to sulfuric acid and lead to acid rain. Acid rain can harm ecosystems by increasing the acidity of soils as well as surface waters such as rivers, lakes, and streams. Sulfur dioxide levels fell, on average, by 39 percent between 1989 and 1998. 

Furthermore, the share cf crops lost to Insects has nearly doubled during the last 40 years (Table 1), despite a more than 10-fold increase in both the amount and toxicity of synthetic insecticide used (17-19). Up to the present time the increased insect losses, in terms of yields per hectare, have been offset by increased crop yields obtained through the use of higher yielding varieties and greater use of fertilizers and other energy-based inputs (20, 21). 

This analysis has demonstrated that pesticide use in the world could be reduced by approximately 50% without any reduction in crop yields (in some cases increased yields) or the food supply. This effort would require applying pesticides only-when-necessary plus using various combinations of the nonchemical control alternatives currently available (34). Although food production costs might Increase slightly (0.5% to 1%), the added costs would be more than offset by the positive benefits to public health and the environment (15). 

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. 

Weeds are an enormous problem affecting field crops in the Mid-South. They reduce yields, increase the cost of production, reduce the quality of the harvested produce, and decrease the value of the marketed product. These effects of weeds are present wherever crops are grown however, they seem to be more devastating... 

It was emphasized in the two conference reports (36, 37) that proper understanding and application of allelochemicals could lead to potentially increasing the crop productivity by protecting the crop plants from natural toxins and by increasing the crop yields by the action of natural stimulants. 

The presence of crop residues has been reported to both increase (5, 6) and decrease crop yields ( 7) and not tilling to increase certain difficult to control weeds (8). However, other reports indicate that the presence of certain mulches can reduce the biomass of certain weeds (9-15) and allow for higher crop yields ( 5, 6). Thus, under certain conditions, mulches can suppress certain weed species, but determining the reason(s) presents many logistical problems, especially under field conditions. To determine the cause(s), the physical and chemical (i.e., allelopathy) effects of the mulch and the role of soil disturbance (or the lack of, as would be the case in a no-till system) must be separated. 

Although arsenic is not an essential plant nutrient, small yield increases have sometimes been observed at low soil arsenic levels, especially for tolerant crops such as potatoes, com, rye, and wheat (Woolson 1975). Arsenic phytotoxicity of soils is reduced with increasing lime, organic matter, iron, zinc, and phosphates (NRCC 1978). In most soil systems, the chemistry of As becomes the chemistry of arsenate the estimated half-time of arsenic in soils is about 6.5 years, although losses of 60% in 3 years and 67% in 7 years have been reported (Woolson 1975). Additional research is warranted on the role of arsenic in crop production, and in nutrition, with special reference to essentiality for aquatic and terrestrial wildlife. 

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