Cultivated surface soil

In a review of the mercury content of virgin and cultivated surface soils from a number of countries, it was found that the average concentrations ranged from 20 to 625 ng/g (0.020 to 0.625 ppm) (Andersson 1979). The highest concentrations were generally found in soils from urban locations and in organic, versus mineral, soils. The mercury content of most soils varies with depth, with the highest mercury... 

Much of the surface soil erosion and hence nutrient loss occurs when deforestation and biomass burning removes and/or consumes the organic materials that protect the soil surface. Significant losses may occur by dry ravel or overland water erosion associated with precipitation events. Under a shifting cultivation system in a tropical deciduous forest ecosystem in Mexico, Maass et al. 61) reported first year losses of N, P, K, and Ca were 187, 27, 31, and 378 kg ha" respectively. In contrast, losses in adjacent undisturbed forests were less than 0.1 kg ha for all nutrients except Ca (losses were 0.1-0.5 kg ha for Ca). 

Cultivation of soil has and will continue to be an important means of controlling weeds (1). However, extensive soil cultivation leads to various problems such as losses of soil, soil moisture and nutrients. This results in water pollution by both the soil itself and pesticides and nutrients associated with it (2, 3, 4). Minimum or no-till cropping systems can reduce these problems because various crop residues (i.e., mulch) are left on the soil surface with a minimum of soil disturbance in planting the crop. 

Internalization of E. coli 0157 H7 within lettuce seedlings cultivated in soil or hydroponically No surface sterilization Confocal microscopy to detect gfp label Wachtel et al. (2002)... 

Soil samples were taken from the experimental field in which spinach is cultivated at the National Institute for Agro-environmental Sciences, Tsukuba, Japan. The top 10 cm of soil was collected from 15 points and then mixed, air-dried, and passed through a 2-mm sieve. For comparison, surface soil was also taken from the adjacent non-cultivated land. The soil classification based on the world reference base for soil resources is Andosols. Relevant soil properties are shown in Table 1. A distinctive feature of this soil is a high amount of organic matter and a higher capacity for phosphate adsorption due to the presence of non-crystalline minerals. 

You may also want to till or cultivate the soil in garden beds that are cleared out in the faU to help reduce pest problems. Tilling exposes soil pests to the surface, where they may be killed by cold temperatures or spotted and eaten by predators. 

Drainage, liming, fertilization, and cultivation of peatlands all enhance decomposition and humification. Since humus is more compact than plant debris, cultivated organic soils subside (lose surface elevation typically by... 

The humification and resultant subsidence of cultivated organic soils, typically 2.5 cm/yr, not only threaten the existence of these soils but also necessitate periodic intensification of the drainage systems, and protection of the fields against flooding from surrounding higher groundwater or surface water bodies. Therefore, development of methods to control subsidence is an important area of research and requires the application of what is known about the process of humification and chemical properties of humic substances. 

Algae are found in nearly aU cultivated soils but they are found also in hot deserts as dry as the Negev desert (see also Section 8.1.3) and cold deserts of Antarctica. They are there represented by the coccoid Chlorophyta. The soil floras have been shown to be extensive and the algal biomass on surface soil must be considerable since it is frequently visible to the naked eye. 

Fig.7.2. Effect of cultivation on nitrogen content of surface soils of Hays, Colby, and Garden City,...

In the early years of the present century much emphasis was placed on the maintenance of a dust mulch by frequent hoeing or cultivation. Aside from the killing of weeds, such a dust mulch was considered as a water conservation measure. It was reasoned that moisture continually rises by capillarity from the subsoil or water table to the surface, and much of it is lost to the air by evaporation from an undisturbed soil surface. By frequent shallow cultivation it was hypothesized that the dry, loose surface soil would break the capillarity and thus hold the moisture in the root zone. 

Wind erosion is most obvious, and often most serious, in semiarid or arid regions, where vegetative cover is scarce or absent, but winds can also do much damage in humid regions. Wet soils are not subject to wind transport, but even in humid regions the surface soil can become air-dry in a very short time. The more the soil surface is disturbed by cultivation in the absence of crops, usually the greater is the opportunity for wind to transport it. 

Soils are highly used and abused natural resources. For example, farmers who employ conventional crop production methods cultivate the soils each year, and if they routinely apply more than the recommended amounts of nutrient fertilizers, this could lead to overfertilization. In rainy areas, the excess nutrients leach down to the aquifer and run off horizontally, polluting the surface water and groundwater. In arid regions, the excess nutrients facilitate the development of saline soils. Annual cultivation of soil... 

Mulching films make it possible to cultivate alkaline soils or use water for irrigation that is too alkaline for the regular growing of crops. By preventing evaporation, salts will not be deposited on the surface and the continuous drip irrigation will keep the salts in solution and wash them down into the lower layers of the soil. Within the limitations of this chapter it not possible to go into more detail on this subject, but examples of results are given in Tables 10.3-10.7. They show that the initial cost of the plastic films is repaid many times by the direct increase of the cash value of the crops. 

Wastes spread on the surface should he disked or plowed into the soil soon after apphcation (1 to 7 days). To promote aerobic conditions and rapid hioconversion of the wastes the soil-waste mixture should he cultivated periodically. 

Plot maintenance B Expertise must be available to maintain the test site and, if cropped, to take care of the crop For bare-soil studies, the soil surface must be carefully prepared prior to test substance application and kept weed-free without disturbing the test areas. If the test is cropped, the crop should be treated according to Good Agricultural Practice. In case of a soil accumulation study, the field may be cultivated and cropped each season for up to 6 years... 

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