Soil compaction

Strictly speaking, Soil Compaction is a REDUCTION IN SOIL PORE SPACE. When pore space is reduced the bulk density (weight of a given volume of dry soil) increases. Soil Compaction is often recognized and even defined (although improperly) as an increase in the "hardness" of soil. An increase in soil strength is only one of a number of changes that occur in soil when pore space is reduced. Ordinary soil is usually about half solid material and half pore space. At optimal field wetness, about half the pore space is filled with water. So, the soil as it rests in your field, is about half solid material, one fourth water, and one fourth soil-air. Some soils have more organic matter than others. In "typical" Pacific Northwest Soils not more than one or two percent of the solid material is composed of stable organic matter

Research contribution to the understanding and management of irrigation-induced erosion

Preventing irrigation-induced erosion takes on a special importance because of the indispensable role irrigated agriculture plays in feeding and clothing humanity. Irrigation is one of humanity's most potent weapons in the war against starvation and one of the best strategies for preserving earth's remaining undisturbed environments while meeting human food and fiber needs

Irrigation

Recent inventories suggest that about 15-17% of the world's cultivated cropland is irrigated. About 40% of these acres were developed after 1960 to meet the food and fiber needs of the world's population, which grew rapidly after World War II in response to medical and hygienic advances. The lack of significant new water resources and the cost of developing present ones have caused irrigated acreage to plateau at around 6 x 10^8 acres (2.4 x 10^8 hectares) since the late 1980s. Recent advances in irrigation include the further development of sprinkler technolog

Stomatal closure in oxygen-stressed plants

Stomatal closure of plants in flooded soil, as determined by leaf gas exchange, has been recognized since 1973, and for simple hypoxia since 1975. At least 58 species have been shown to close stomata with hypoxic or flooded conditions. Various factors interact to affect the relationship between rhizosphere oxygen availability, as measured by soil oxygen diffusion rate (ODR), and degree of stomatal closure. These factors include root temperature, species, plant growth stage, plant mineral nutrition, and duration and nature of hypoxia. Soil water content, bulk density, and temperature also influence ODR. Abscisic acid accumulation in leaves appears to induce stomatal closure, as a stress response to root hypoxia, through its effect on potassium ion regulation of guard cell turgor. Stomatal closure generally persists well beyond actual soil hypoxia. Photosynthesis is reduced by root hypoxia, both by reduction of leaf gas exchange and by a lowering of the photosynthetic rate at a given leaf gas exchange rate. This phenomenon deserves greater attention in evaluating and modelling of crop response to soil hypoxia and as a sensitive indicator of severity of soil hypoxic stress

Management options for control of irrigation-induced erosion

Irrigation-induced erosion is a threat both to the sustainability of irrigated agriculture and to global food security. Arid zone soils are usually low in organic matter and poorly aggregated, with thin, easily eroded A horizons. Carter (1993) demonstrated that, once eroded, yield potentials of PNW soils are severely reduced (Table 1). Furthermore, furrow irrigation, used on much of the world's irrigated land, is an inherently erosive process

Physical aspects of soils of disturbed ground (Chapter 21)

Humanity's presence on earth has forced the selective adoption of both anthropocentric and naturalistic perspectives of soil as an ecosystem component. From the anthropocentric perspective, soil is an ecosystem component used by humans for specific purposes (e.g., to grow forests and crops; support structures or roadways; and as a filtration medium). The naturalistic perspective sees soil primarily as the natural foundation or backdrop for other ecological systems and processes, and philosophically excludes many soil-management technologies and scenarios, favoring only soil uses and management practices that derive from natural ecosystem processes. The naturalistic perspective is more willing to concede that soil, like other ecosystem elements, may at times respond to perturbations counter to human needs and aesthetics. The role of environmental managers and scientists is to know when and how firmly to embrace the validity of either or both outlooks. That requires an appreciation of the properties of ecosystem components, and how those properties affect a given management objective. Familiarity with fundamental soil properties is essential to understanding the physical aspects of soils of disturbed ground, regardless of the interpreter's perspectiv

A Review. Measurement of root porosity (volume of root air space)

Root research can benefit under many circumstances from determination of the % fraction of root volume occupied by air (root porosity). Root porosity provides an indication of root reaction or adaptability to environments with insufficient oxygen availability. Three primary approaches have been used for root porosity determinations: cross-sectional ratios, pycnometry, and dynamic gas displacement. These three methods are explained and their relative advantages and disadvantages discussed

Winter rapeseed performance in the southeastern Coastal Plain

Fifty-five rapeseed (Brassica napus L.) cultivars were evaluated between 1982 and 1987 on a Norfolk loamy sand (fine, loamy, siliceous, thermic Typic Paleudult) near Florence, South Carolina. The average seed yield (1,590 kg/ha or 1,420 pounds/acre) was comparable to that at other southern locations where rapeseed is grown as a winter annual, but it was lower than in the Pacific Northwest, where the crop is grown as a true biennial. Assuming a contract price of $0.2011cg ($0.09/pound), estimated gross returns for rapeseed would be about $320/ha 0130/acre). For conservation purposes, the crop may be more valuable because of its potential to reduce soil erosion; rapeseed provides soil surface cover at an earlier date than winter wheat (Triticum aestivum L.). Results of this evaluation suggest that additional research is needed to evaluate rapeseed as a winter forage and/or cover crop for soil erosion control

Mineral nutrition of oxygen-stressed crops and its relationship to some physiological responses (Chapter 35)

Historically nutritional studies of anoxic plants have simply catalogued concentration and uptake changes of treated plants, frequently on a non-partitioned whole-plant basis. Major reviews of soil aeration and flooding generally agree that N, P, and K concentrations in plants are reduced by anoxia (Kozlowski, 1984; Glinski and Stepniewski, 1985). Sodium concentration increases and other major elements either remain unaffected or react irregularly. Until recent years explanations of nutritional changes have focused chiefly on alterations in the poorly aerated soil physicochemical environment. Factors such as: increased mineral solubilization, leaching, and dilution in high water content soils, increased water film coverage of roots, altered ion diffusion, solubility changes at altered valence states, altered pH resulting from redox reactions or increased CO2 concentrations, etc. have been used to explain nutritional responses to oxygen-limiting soil environments

Long-term polyacrylamide formulation effects on soil erosion, water infiltration, and yields of furrow-irrigated crops

Two formulations of water-soluble anionic polyacrylamide (WSPAM) are used in agriculture to reduce erosion and manage infiltration in furrow irrigations, although few if any reports have compared their effectiveness. A control and two WSPAMs, a granular form and the inverse emulsion, or oil-based liquid form, were applied to irrigation water supplied to furrows formed in a silt loam soil with 1.5% slope during each irrigation from 1993 to 1999. Stock solutions prepared from the two WSPAMs in tap water were injected into furrow inflows to attain a concentration of 10 mg L?1 only during furrow advance. During irrigations, furrow inflow and runoff rates, and runoff sediment concentrations were measured. Crop yields were measured in five of the 7 yr. Relative to controls, both WSPAM treatments reduced runoff sediment loss equally well, decreasing soil losses by 84% per irrigation, and prevented the loss of 47.8 Mg soil ha?1 over the 7-yr period. The yearly soil loss reductions produced by WSPAMs ranged from 66 to 99%, and may reflect changes in the electrical conductivity (EC) of the irrigation water. Both WSPAM treatments increased the proportion of applied irrigation water that infiltrated into newly formed furrows, but the emulsion produced the greatest overall increase in water infiltration fraction. As a class, WSPAM treatments increased yields by 14.3% for bean (‘Viva Pink’ Phaseolus vulgaris L.) and 4.5% for silage corn (Zea mays L.), suggesting that the cost of WSPAM applications may be recoverable. While the two WSPAM formulations provide equivalent erosion protection, differences in infiltration effects, product costs, and potential environmental impacts should be considered when selecting the formulation