Crops 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. 

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. 

Table 2. Potential Substitute Natural Gas in United States from Biomass at Different Crop Yields...

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) ... 

A goal of controlled release fertiliser research since the 1940s has been the development of a product that deUvers its nutrients at a rate matching the demand rate of the plant to which it is appHed. Such a fertiliser would represent the ultimate in use efficiency agronomic performance, ie, crop yield, quahty, and appearance agronomic safety and labor savings, ie, reduced appHcation frequency. It also would minimise potential losses to the environment. 

The nonvisual or subtle effects of air pollutants involve reduced plant growth and alteration of physiological and biochemical processes, as well as changes in the reproductive cycle. Reduction in crop yield can occur without the presence of visible symptoms. This type of injury is often related to low-level, long-term chronic exposure to air pollution. Studies have shown that field plantings exposed to filtered and unfiltered ambient air have produced different yields when no visible symptoms were present (5). Reduction in total biomass can lead to economic loss for forage crops or hay. 

Mixed fertilizers contain two or more of the elements nitrogen, phosphorus, and potassium (NPK), which are essential for good plant growth and high crop yields. This subsection briefly addresses the production of ammonium phosphates... 

Emte, /. harvest crop yield gathering, -ertrag, m. crop yield, crop, -maschine, /. harvester. 

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. 

Control laboratories in the canned food industry are usually divorced from the research organization to a lesser degree than is the case in the chemical and allied industries. For this reason, a closer relationship exists between the problems of the control laboratory and the research laboratory. Although from a research standpoint this condition is often considered undesirable, it has considerable merit in the case of the canned food industry, in which production may be seasonal and often of rather short duration. The collection of control data in many instances may also serve for research purposes—for example, in the case of soil analyses, which may be correlated with agricultural research designed to improve crop yields. Because the variables which affect the quality of canned foods must usually be investigated rather extensively, and often over a period of more than one year, the application of statistical methods to data collected for control purposes can conceivably make a substantial contribution to a research program. 

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). 

The geographic nonuniformity of climatic anomalies has important implications for agricultural productivity since some compensation is implied. That is, during a given growing season, good weather and higher crop yields in one... 

Irrigation has been practiced from the ancient time it is only in the twentieth century that the importance of the irrigation water quality was recognized [7]. The use of saline water may result in the reduction of crop yields. A high sodicity of water for irrigation may cause the deterioration in the physical properties of soils... 

Wit, C.T. de (1958). Transpiration and Crop Yields. Wageningen Centre for Agricultural Publishing and Documentation, Agriculture Research. 

Flowers, T.J. Yeo, A.R. (1989). Effects of salinity on plant growth and crop yields. In Biochemical and Physiological Mechanisms Associated with Environmental Stress Tolerance in Plants, ed. J. Cherry. Berlin Springer-Verlag, (in press). 

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