Water loss from soil

Sparks DL (ed) (1986) Soil physical chemistry. CRC Press, Boca Raton, Florida Sparks DL (1989) Kinetics of soil processes. Academic Press, San Diego Sparks DL, Huang PM (1985) Physical chemistry of soil potassium. In Munson RE (ed) Potassium in agriculture, ASA, Madison, Wisconsin, pp 201-276 Sparks DL, Jardine PM (1984) Comparison of kinetic equations to describe K-Ca exchange in pure and mixed systems. Soil Sci 138 115-122 Spencer WF, Cliath MM (1969) Vapor densities of dieldrin. Environ Sd Technol 3 670-674 Spencer WF, Chath MM (1973) Pesticide volatilization as related to water loss from soil. J Environ Qual 2 284-289... 

Soil water. The water loss from soil on drying to a constant mass at 105°C expressed as the mass of water per unit mass of dry soil or as the volume of water per unit bulk volume of soil. 

If water losses from the surrounding area are a major component of the total evaporative losses of the pond, then soil moisture conditions will be expected to be high. Under non-limiting soil moisture conditions vegetative moisture losses are often defined as "potential" losses. Evaporative losses in this case would not be expected to differ greatly from free water evaporation. The literature recommends... 

Water losses from the soil represent the sum of downward movement of gravitational water and surface losses by evaporation. Man s activities, other than drainage procedures or long-term water use from pumps in industrial areas, do not usually influence the downward movement of water. On the other hand, agricultural practices have a great effect on surface evaporation losses. 

For advection, it is necessary to select flow rates. This is conveniently done in the form of advective residence times, t in hour (h) thus the advection rate G is V/t m3/h for each medium. For air, a residence time of 100 hours is used (approximately 4 days), which is probably too long for the geographic area considered, but shorter residence times tend to cause air advective loss to be a dominant mechanism. For water, a figure of 1000 hours (42 days) is used, reflecting a mixture of rivers and lakes. For sediment burial (which is treated as an advective loss), a time of 50,000 hours or 5.7 years is used. Only for very persistent, hydrophobic chemicals is this process important. No advective loss from soil is included. The D value for loss by advection DAi is G,Z and the rates are DAif mol/h. 

A simple environmental chamber is quite useful for obtaining volatilization data for model soil and water disposal systems. It was found that volatilization of low solubility pesticides occurred to a greater extent from water than from soil, and could be a major route of loss of some pesticides from evaporation ponds. Henry s law constants in the range studied gave good estimations of relative volatilization rates from water. Absolute volatilization rates from water could be predicted from measured water loss rates or from simple wind speed measurements. The EXAMS computer code was able to estimate volatilization from water, water-soil, and wet soil systems. Because of its ability to calculate volatilization from wind speed measurements, it has the potential of being applied to full-scale evaporation ponds and soil pits. 

As the soil dries, roots often shrink in the radial direction, leading to the development of a root-soil air gap (Fig. 9-19). Hence less contact occurs between a root and the water adjacent to soil particles, leading to a hydraulic resistance at the root-soil interface. Such a resistance can decrease water movement from a root to a drying soil and thereby help prevent excessive water loss from plants during the initial phases of drought (Fig. 9-20). 

Barrows, H.L. and Kilmer, V.J., 1963. Plant nutrient losses from soils by water erosion. Adv. Agron., 15 303—316. 

Avermectins and the breakdown products are nearly insoluble in water and bind strongly to soil. Thus they have little mobility and are unlikely to leach into groundwater. Avermectins are rapidly degraded in soil, sensitive to rapid photodegradation. When applied to the soil surface, its soil half-life was about 1 week. Under dark, aerobic conditions, the soil half-life is somewhat extended (2 weeks to 2 months). Microbial degradation also contributes to rapid loss from soils. Avermectins are also rapidly degraded in water (half-life 12-24 h), principally due to photodegradation. 

G. Morgan, Q. Xie and M. Devins, (2000) Small catchments -NMP Dripsey - water quality aspects. In Tuimey, H. (ed.) Quantification of Phosphorus Loss from Soil to Water, EPA, Wexford, pp. 24-37. 

G. Morgan (2000), Quantification of phosphorus loss from soil to water, EPA, Wexford. 

It is also a known fact that leaching of saline soils making about 60% of the cultivated lands requires 4,000-5,000 m of water, on the average. Assuming transit water losses from irrigation sources to the field being 30% of the withdrawn water, then the actual water use exceeds twice the needed quantity of water. The result of such practices was a drastic distortion of the environmental equilibrium on irrigated lands. 

Jury et al. (1984) also classified nitrobenzene as intermediately mobile, but noted that its loss from soil would be enhanced by evaporation of water. Moreover, because nitrobenzene has relatively poor diffusive flux, the material would tend to move as a bolus within soil. Jury et al. (1984) hypothesized that a deposit 10 cm deep in soil would have a half-life of about 19 days. 

As expected, the more immature peanuts lost moisture sooner in the 29°C soil than in the 25°C soil. Generally, it took about a week longer for kernels in the cooler treatment to reach moistures attained in the warmer treatment. The data clearly showed a direct relationship between soil temperature and the rate of water loss from peanut kernels under late-season drought stress. 

Pure phospholipid bilayers are essentially impermeable to water, but most cellular membranes contain water-channel proteins that facilitate the rapid movement of water in and out of cells. Such movement of water across the epithelial layer lining the kidney tubules of vertebrates is responsible for concentrating the urine. If this did not happen, one would excrete several liters of urine a day In higher plants, water and minerals are absorbed from the soil by the roots and move up the plant through conducting tubes (the xylem) water loss from the plant, mainly by evaporation... 

In the subsoils of arid and semiarid soils, Ca commonly precipitates as cakite (CaCC>3) rather than being leached away. It is found as indurated layers (caliche and other local names) in many arid soils and as more diffuse CaC03 in Aridisols and Mollisols. Precipitation of CaCCTj in soils is affected by the rates of soil water movement, CO2 production by roots and microbes, CO2 diffusion to the atmosphere, and water loss by soil evaporation and plant transpiration. CaCC>3 layers are also derived from upward movement and evaporation of Ca-rich waters. Calcium carbonate accumulations can amount to as much as 90% of the mass of affected soil horizons. Gypsum precipitates in some arid soils, despite being about 10 x as water soluble as Ca carbonate. 

The phosphate concentrations of waters draining from soils usually are about 10-7 M. Worldwide, this amounts to a phosphate loss of 17 x 1010 moles yr-1 (10 mol ha-1 yr-1 or 1 kg ha-1 yr-1). Phosphate in eroded soil particles reaching the sea is estimated to be an additional 13 x 1010 mol yr-1. Fertilization affects the phosphate content of sediments eroded from surface soils, and increases the phosphate concentrations of drainage waters and groundwaters. Preventing erosion has the added benefit of reducing phosphate inputs to streams and lakes. 

Potassium losses from soils comprise crop removal, leaching, and erosion. The large potassium output by harvesting in agriculture must be balanced by potash fertilization in the form of potassium chloride or potassium sulfate. Compared with the amount of potassium absorbed by crops, the potassium content of soil solution is small. The potassium content in soil solution is dependent upon the water content of the soil, and can be raised by liming. Plants may remove potassium selectively from the soil solution indeed, during erosion the clay fraction with its high potassium content is selectively removed. 

Vapor-phase sorption onto the same dry Woodbum soil is illustrated in Figure 3.16 where soil uptake is expressed as a function of the relative pressure-equilibrium partial pressure/saturated vapor pressure. The data indicate a BET adsorption process. Increasing relative humidity decreases the adsorption (Fig. 3.17) of dichlorobenzene ultimately resulting in a linear isotherm. It is concluded that at low humidities adsorption on the mineral surfaces is involved. Increasing availability of water reduces the availability of these sites until sorption is due to partitioning into the SOM. It will be demonstrated that the converse of this relation is important in assessing the potential for evaporative loss from soils. 

From the standpoint of water conservation, the main aim should be to minimize evaporation losses from the soil surface, thus leaving as much as possible of the soil moisture for the use of the crop. In recent years much research (see Pierre etal., 1965) has been conducted in attempts to reduce evaporation from soils and lakes by means of chemicals. Hexadecanol, for example, suppresses the evaporation of water from either a free-water surface or from soil. Olsen et al. (1964) observed that this chemical decreased water loss from a loam soil 43% during a 10-day period. A portion of the data is shown in Fig. 17.3. A surface placement was most effective, remaining unchanged during a... 

In practice, root length and degree of branching are also major factors in water loss because most of the water loss from cropped soils is via transpiration. Root length often determines how much water reaches the leaves. A radish plant may be able to draw on the water supply in only the upper foot of soil, whereas an alfalfa or kudzu plant may remove water from a depth of 10—15 ft. Obviously with increase in root length and branching the crop is less and less dependent upon surface soil moisture. 

The above statements are illustrated in part by the studies of Greb (1966). He observed that wheat straw applied to the soil surface at rates of 1,120, 2,240 and 3,360 kg/ha, equivalent to 30, 60 and 90% coverage, reduced water losses from a wet soil surface by evaporation 16, 33 and 49%, respectively, during a 20-day period compared with no straw. An application of 6,720 kg/ha, or 180% soil coverage, was only slightly more effective than the 3,360 kg/ha application. As the soil water was evaporated the effectiveness of the mulches diminished. 

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). 

H. Turney and O. T. Carton, Eds., Phosphorus Loss from Soil to Water, CAB Internal, Wallingford, UK, 1997. 

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