ISSN:0038-075X    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Water soluble polyacrylamides (PAMs) have been proposed as soil amendments for various agricultural purposes. Recent interest has centered on very high molecular weight (10–20 g mol−1), low to moderate charge (10–20 mol %) anionic materials, added to irrigation water to prevent silt loss from irrigated fields. These PAMs are within a broad spectrum of commercially available compounds employed for a variety of applications in other industries. These include solid-liquid separations in clarification of potable and waste waters, dewatering of sludges, mining separations, food processing and paper making, as well as petroleum recovery, textile additives, friction reduction, personal care products, and cosmetics. This paper reviews PAM characteristics (chemistry, synthesis, molecular weight, product form), residual monomer concentrations, toxicology, regulations, and fate and effects in soil and plant systems. Anionic PAMs for soil systems have residual acrylamide (AMD) concentrations of50> 5 mg Kg−1) and fish (LC50> 100 mg L−1)

ISSN:0038-075X    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Polymer impacts on soil physical properties are thought to be a function of its adsorption and desorption by the soil material. This chapter reviews published results of polymer sorption studies with emphasis on synthetic polymer application to soil rather than biologically synthesized polymer in situ. The following statements summarize the main findings of polymer adsorption studies. Adsorption of polymers on pure clays is strongly influenced by electrostatic attraction whereby the order of adsorption of polymers is cationic > nonionic > anionic. Polymer adsorption occurs on the external surface of clay packages. Therefore, the effects of factors such as clay type and electrolyte composition on adsorption are manifested by their effects on microstructure of clay packages. High molecular weight polymers do not penetrate soil aggregates so that adsorption on soil materials is related to soil aggregate size and molecular conformation of the polymer rather than total soil surface area and electrostatic charge interactions. Very little polymer desorption occurs when the system is kept wet, and most of the polymer in solution becomes irreversibly bonded to the soil by drying the soil

ISSN:0038-075X    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

High application rates (50–200 mg Kg−1soil) and strong adsorption to soil aggregates severely limit polyacrylamide (PAM) application as a soil conditioner below the top soil. Limited penetration, 0 to 20 cm, was obtained upon introducing tritium-labeled PAM-2J into a clayey and sandy loam, respectively. This low penetration rate is related to the adsorption of the polymer to the surface of soil particles. This study tested the potential effect of modifying PAM application management by lowering the viscosity of the applied PAM solution, thus increasing the efficiency of polymer subsurface penetration under reduced application rates. One way of enhancing PAM penetrability may be a temporary reduction in adsorption. A significant reduction (up to five fold) in the viscosity of polymer solution flowing through narrow capillaries, caused by the addition of NaCl or CaCl2to the solution, was observed in the laboratory. The application of PAM affected soil structure by redistributing soil pore sizes, as indicated by changes in water content under different pressures

ISSN:0038-075X    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

The ability to understand and/or predict the physical properties of polymers is important in efforts to help reduce erosion in irrigated land by treating irrigation water with minute amounts of certain polymers. The key properties of polymers for this application (water solubility and water absorption capability, dilute solution properties, and stability) are discussed. Methods used to predict the properties of polymers include quantitative structure-property relationships, statistical mechanical theories, atomistic simulations, and quantum mechanical calculations. Each general method is best applied to different types of problems. For example, combination of quantum mechanical calculations and atomistic simulations may shed light on the solution conformation of a polymer and hence on its soil activity. On the other hand, a new method, based mainly on topological descriptors calledconnectivity indices, predicts key polymer physical properties very rapidly from the structures of polymeric repeat units via empirical and semi-empirical quantitative structure-property relationships. This new method can be used for the overall evaluation of the potential of candidate polymers for erosion reduction. Applications of this method to polyacrylamide and structural variants and copolymers are discussed. An outlook is provided for the future of applications of computational chemistry to water-soluble polymers. It is suggested that significant future advances can be expected from further developments of each of the different types of theoretical methods, as well as from their more synergistic and interdisciplinary utilization

ISSN:0038-075X    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

The beating action of rain or sprinkler drops causes the breakdown of aggregates and clay dispersion, which subsequently leads to seal formation. Seal formation reduces infiltration rate and generates high levels of runoff. Chemical soil amendments (e.g., phosphogypsum, organic polymers) can improve aggregate stability and limit clay dispersion and thus prevent seal formation. This review discusses the effects of organic polymers on controlling seal formation as characterized by changes in soil infiltration rate and dependence on soil properties. Soil susceptibility to sealing depends on a number of soil properties, including soil texture and mineralogy, composition of the exchangeable cations, and water quality. Addition of small amounts of polymers (10–20 kg ha−1), either sprayed directly onto the soil surface or added to the applied water, stabilizes and cements together aggregates at the soil surface, thereby increasing their resistance to seal formation. The infiltration rate of a polymer-treated soil subjected to distilled water rain is two to three times that of a non-treated soil. The efficacy of anionic polymers in preventing seal formation is enhanced when the soil clay is maintained in a flocculated state. The latter is achieved by addition of electrolytes (either in the “rain” water or phosphogypsum addition) in the soil solution at the soil surface. Combined application of anionic polymers with electrolytes results in final infiltration values of ∼25 mm h−1, which are 10 times higher than the control. Polymer effectiveness in controlling seal formation depends also on charge type and density and on the molecular weight of the polymer. The effect of polymers and water quality on seal formation is in good agreement with the effect of the polymers on the flocculation patterns of soil clays. Of the polymers currently available and under study, anionic polyacrylamide has been found to be the most effective in controlling seal formation, and soil erosion and has the longest residual effect

ISSN:0038-075X    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Furrow irrigation-induced soil erosion is a serious threat to sustainable irrigated agriculture globally. Recent field studies have demonstrated that small concentrations of polymers dissolved in irrigation water appreciably reduce soil loss from irrigated furrows and increase net infiltration (total inflow - total outflow). This paper summarizes polymer-related field studies conducted in Idaho on highly erodible silt loam soils (Durixerollic Calciorthids, Xerollic Haplargids, Haploxerollic Durargids). A range of furrow lengths (163–264 m), slopes (0.5–7%), and inflows (15–38 L min−1) were included in the studies. A moderate-charge-density anionic polyacrylamide (PAM), highly effective for controlling furrow sediment losses, was employed in the field trials. Treatment efficacy depended primarily on application rate, PAM concentration in irrigation water, duration of furrow exposure, and inflow rate. Nontreated furrow soil loss in 75% of the irrigations exceeded soil loss tolerance (T) for these soils, whereas only 13% of the PAM-treated irrigations exceeded T. Those treatments that applied at least 0.7 kg ha−1PAM (mean, 1.3 kg ha−1) reduced furrow sediment loss by 94% (range: 80–99%) and increased not infiltration by 15% (range: −8–57%). One of the most effective treatments applied PAM at 10 g m3in irrigation inflows during the furrow advance period. This initial high-load treatment was nearly twice as effective as a continuous 0.25 g m−3PAM application on these soils when slopes were 1–2%. The initial high-load treatment protected furrows with slopes ranging from 0.5 to 3.5%. PAM reduced total phosphorus (84% of control value), nitrate (83%), biochemical oxygen demand (72%), and sediment (57%) in treated runoff water

ISSN:0038-075X    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Irrigation strategies must be designed to maximize or optimize production while conserving water, minimizing irrigation cost, and avoiding pollution of the environment. Self-propelled moving sprinkler irrigation systems (MSIS) have become increasingly popular in recent years. Runoff and erosion during irrigation with MSIS can be high under some conditions. The objective of this review was to address three aspects related to runoff and erosion with irrigation by MSIS: (i) factors that lead to an increase in runoff and erosion during irrigation, (ii) effect of runoff on crop production, and (iii) evaluation of the beneficial effect of polymer application by reducing runoff and erosion and increasing crop yield. Surface runoff from 3-m2fallow plots in a silt loam loess and a clay vertisol under irrigation with linear MSIS at an average application rate of 100 mm h−1was 53% and 39%, respectively. The high runoff levels were caused mainly by seal formation at the soil surface. Prevention of surface runoff movement along the slope in a field increased the available water distribution uniformity in the soil and increased the average pod peanut yield by 882 kg ha−1. Application of 20 kg ha−1polyacrylamide (PAM) and 40 kg ha−1polysaccharide (PS) on the soil surface prior to the irrigation season reduced runoff and erosion levels significantly, and increased the cotton and potato yield under irrigation with MSIS. The application of PS in the field was more convenient than PAM application because of the higher dissolution rate in water and lower viscosity of PS

ISSN:0038-075X    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Polyacrylamides (PAMs) are xenobiotic polymers consisting of covalently linked carbon atoms (-CH2-CH2), unlike the an-hydro bonds of many biological polymers. Although the carbon chains are resistant to microbial breakdown, field observations by people in the oil industry support the notion that polyacrylamides can somehow stimulate the growth of microorganisms. This paper presents data indicating that PAMs can provide nitrogen (as ammonia) for several species ofPseudomonasisolated from soil. Growth in a defined medium can be sustained over several transfers in a chemically defined medium with no added NH4Cl. The level of growth attained was less (∼25–50%) than that with NH4Cl. No change in the viscoelastic property (screen factor) of the PAM occurred. Growth of sulfate-reducing bacteria is also stimulated by polyacrylamides, with a loss of screen factor of the polymer solution accompanying the growth. To some extent this is because the polymer serves as a nitrogen source, but another factor, in the case of SRBs, is the ability of the polymer to serve as an incomplete substrate (mixotrophic growth)

ISSN:0038-075X    

出版商:OVID    

年代:1994

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1994

数据来源: OVID