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the volume of a liquid (water or oil) or gas discharged from a natural or artificial source (a well or borehole) per unit time. It is measured in liters per second or in cubic meters per second, hour, or day. Yield characterizes a steady inflow of a liquid or a gas over a prolonged period of time. The volume of water per unit time that flows through the cross section of a river or water-bearing horizon is called the water flow rate, a term that is often used to designate the volume of water obtained by forced pumping from wells and boreholes. In this case the quantity of liquid depends on the method and intensity of pumping and on the lowering of the liquid level. Specific yield, which is the yield obtained by lowering the water level by 1 m through pumping, is used to characterize the productivity of water-supply wells.
The yield of a borehole or well depends on the permeability and thickness of the water-bearing layer, the way in which the layer is fed, the layer’s extent and connection with other layers, and the presence of a pressure head, as well as the conditions of use of the layer, the extent to which it has been stripped, the lowering of water level caused by pumping, and the type of filter.
A distinction must be made between steady and unsteady yield. During the initial operation of a well or borehole, excessively high yield values are often obtained, particularly in cases where a newly stripped water or oil layer contains a large amount of gas. The yield of water is determined with the aid of measuring vessels, spillways, various types of water meters, and recording discharge meters; the yield value is sometimes calculated using formulas of the dynamics of subterranean waters.
Water flow gauges of the Venturi type (see Figure 1) are frequently used in measuring the yield of liquids. These gauges utilize the pressure differential created by a change in the cross section of a pipe. By observing the pressure differential (p1 - p2) on a scale or transmitting it to a recorder, it is possible to determine the quantity of water flow from the formula where k is constant. If the overflow of water at a fixed location forms a steady stream (with a yield of no less than I //sec), the discharge can be measured with the aid of spillways (see Figure 2). Depending on the shape of the cross section of the spillway, the yield is calculated according to various formulas, using values for the height of the head (h) and the width of the spillway (b).
Curves that show the changes in yield that occur during the operation of oil wells can be constructed based on observations of the yield of the wells. The industrial categories of petroleum reserves are determined from an analysis of yield curves. This method of curves is based on the statistical computation of petroleum production collected over a certain period of time. The drop-off coefficient for the yield, which is the basis for an estimate of oil reserves, for a group of boreholes, and for the entire oil-bearing stratum, is determined through mathematical calculations from a curve showing the relationship between time and yield.
The yield from boreholes and wells is one of the most important indexes used in hydrogeologic research (the determination of the productive capacity of a water intake, the estimation of subterranean water reserves, and research on the flow of water into drains). If experiments on the yield from boreholes or wells are not performed, an estimate is made based on the transmission coefficient of the layer, its thickness, and the pressure head or by means of a comparison with other boreholes and wells in hydrogeologically similar locations. Experimental pumping is used for highly accurate determinations of yield in service installations.
Gas yield is usually measured in cubic meters per day. Measurements of gas yield are made with the aid of anemometers and float-type flowmeters. The simplest method for taking a sample of gas emanating from the bottom of a body of water is shown in Figure 3. During measurements the gas must be completely contained in the funnel. The yield value is determined from the time required to fill a vessel of known volume. If the water is gassy, gas separators are usually installed, and the gas factor is determined.
REFERENCESMetodika polevogo oprobovaniia prirodnykh gazov. General editor, A. L. Kozlov. Leningrad-Moscow, 1940.
Bindeman, N. J. Uskorennye vychisleniia debita burovykh skvazhin, kolodtsev i rodnikov. Moscow, 1945.
I. S. ZEKTSER
in plant-growing, the amount produced per unit area. Yield is calculated in quintals per hectare (ha) or, in hothousehotbed culture, in kg per sq m. Several indicators of yield are used in crop planning, accounting, and economic analysis.
The potential yield is the maximum amount of produce that can be obtained from 1 ha when there is complete realization of the reproductive potentiality of an agricultural crop. It is calculated at agricultural research and experimental institutions for both ideal and real conditions. This index is used to determine rational structures for crop areas and crop rotation and to determine suitable varieties and agricultural crops for a specific farm, oblast, or zone.
The planning yield is the amount of produce it is possible to obtain from 1 ha under specific farming conditions. Determined before planting, it takes into account the potential yield of the variety, previous yields, soil fertility, and the availability of farming machinery and mineral fertilizers. The planning yield is an item in the production-financial plan used in the management of agricultural production at a particular farming enterprise.
The expected yield is calculated in quintals per ha or conditionally (high, average, low, at last year’s level) at certain periods of crop growth and development. The figure is obtained by evaluating the stand density and the general condition of the plants. The expected yield is used for planning agronomic and crop-managing field work.
The standing, or biological, yield is the quantity of cultivated produce. It is determined selectively by visual estimation, by taking samples before gathering the harvest, or by averaging calculations after harvesting (according to data of actual thrashed yield and losses during harvesting). The index is used in economic analysis to find ways of decreasing losses during harvesting.
The factual yield per ha is the harvested and stocked yield. It is determined by calculating the freshly stocked or net (after cleaaing) weight per ha of sown, spring vegetating, or actually harvested area (depending on the crop). It is calculated twice by agricultural enterprises and organs of the Central Statistical Board: a preliminary calculation is based on progress reports obtained during harvesting, and a final calculation is based on registered accounts. (The index is published in statistical manuals to show the development of various agricultural branches.)
The yield depends on climatic, geographic, soil, microbiological, biological, technological, organizational-economic, and other conditions. With intensive systems of land-crop production, yield is increased mainly as a result of factors of intensification of agriculture.
For yields of principal agricultural crops of the USSR and other countries, seeAGRICULTURE.
E. B. KHLEBUTIN
yield(1) In semiconductor manufacturing, the percentage of chips in a finished wafer that pass all tests and function properly.
(2) To yield something is to produce a result.