Irrigation water, chemical

Evaluation of Chemical Characteristics of Irrigation Water Under Water Scarcity... 

The following chemical characteristics determine the quality of irrigation water under scarcity of water. 

A record of any irrigation schemes (type of system used and amount of water) used during the conduct of the trial must be recorded. Often, fertilizers and maintenance chemicals may be mixed into and delivered with the irrigation water, and, hence, details must be recorded. In the case of long-term studies such as soil dissipation or accumulation studies, additional information about the water being used for irrigation (pH, major ion constituents, etc.) must be recorded. 

It is desirable to determine the chemical properties of irrigation water, paddy water in the field, and adjacent streams and rivers. Since especially the pH of the paddy water fluctuates diurnally (high in daytime and low at night), this may affect the water solubility of certain chemicals, e.g., sulfonylureas, which have dissociation constants (p/fa) in an environmentally relevant range. 

The harmful liquid that collects at the bottom of a landfill is known as leachate. The generation of leachate is a result of uncontrolled runoff, and percolation of precipitation and irrigation water into the landfill. Leachate can also include the moisture content initially contained in the waste, as well as infiltrating groundwater. Leachate contains a variety of chemical constituents derived from the solubilization of the materials deposited in the landfill and from the products of the chemical and biochemical reactions occurring within the landfill under the anaerobic conditions. 

The volume of solution in the subsurface, under partially saturated conditions, varies with the physical properties of the medium. In the soil layer, the composition of the aqueous solution fluctuates as a result of evapotranspiration or addition by rain or irrigation water to the system. Changes in the solution concentration and composition, as well as the rate of change, are controlled by the buffer properties of the sohd phase. Because of the diversity in the physicochemical properties of the sohd phase, as well as changes in the amount of water in the subsurface as result of natural and human influences, it is difficult to make generalizations concerning the chemical composition of the subsurface aqueous solution. 

Chemicals were leached from the soil column by applying water, twice daily, at a rate of 55.8 mL per day, per column, for 30 days. The irrigation water (27.9 mL per application) was applied at 8 a.m. and 2 p.m., each day, for 30 days. Leachates from the small columns were captured daily and stored in the dark at 4°C until analyzed (column I leachates were analyzed within 3 days after collection column II and III leachates were stored for almost 30 days prior to extraction). After the 30-day experiment, each column was cross sectioned into nine discrete segments (5 cm in depth). Prior to segmenting, the soil columns were frozen at -10°C for 8 hours to facilitate sectioning. All soil samples were kept frozen at -10°C until analysis was performed. 

Whenever complete chemical analyses are provided for soil extracts or irrigation waters, the sum of major cations (mmol(+) L-1) should approximately equal the sum of all major anions (mmol(—) L-1). Repeated exact agreement, however, indicates that one ion is being determined by difference. This is usually sulfate for recent analyses, or sodium for older analyses. Also, reported concentrations of carbonate should be negligible at solution pH >9. In the water-supply literature, Ca plus Mg concentrations are reported as hardness, the chemically equivalent quantity of CaC03 in milligrams per liter. Concentrations of bicarbonate plus carbonate may be reported -as alkalinity, the equivalent acid-neutralizing capacity of the water. 

A review paper covering forms of boron in soils, interactions between soil solution boron and adsorbed boron, adsorption-desorption processes, and relationships to plant nutrition is presented. Diagnostic criteria are given for chemical analysis of soils and irrigation waters in terms of boron status, i.e., deficient, adequate, or excessive, and specified according to crop species group. The potential boron hazard of municipal sewage effluents to water supplies is discussed. 

J. D., Vaughn, R. B., and Welsch, E. P. (1992). Results of Chemical Analysis for Sediments from Department of the Interior National Irrigation Water Quality Program Studies, 1988-1990. U.S. Geological Survey open-file report 92-443. 

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