The no-tillage cropping system, a combination of ancient and modern agricultural practices, has been rapidly increasing in use. By the year 2000, as much as 65 percent of the acreage of crops grown in the United States may be grown by the no-tillage practice. Soil erosion, the major source of pollutants in rural streams, is virtually eliminated when no-tillage agriculture is practiced. The no-tillage system reduces the energy input into corn and soybean production by 7 and 18 percent, respectively, when compared to the conventional tillage system of moldboard plowing followed by disking. In addition, crop yields are as high as or higher than those obtained with traditional tillage practices on large areas of agricultural land.
Current views of infiltration of water into soils are based on nearly complete displacement of soil water by incoming water. In general, rapid flow down macropores and its effect on water and solute distribution have not been considered very important by the majority of researchers. We present evidence to show that flow of water through macropores is important in soil and ground water recharge and in salt movement through soils.
Field studies were conducted to compare the effect of no‐tillage versus conventional tillage corn (Zea mays L.) production on soil moisture. The studies were made on a Donerail silt loam in 1968 and 1969 and on a Maury silt loam in 1970. Soil moisture was measured periodically at various depths in the soil profile during the growing seasons. No tillage treatments had higher volumetric moisture contents to a depth of 60 cm during most of the growing season. The greatest differences occurred in the upper 0 to 8‐cm depth. Beyond a depth of 60 cm, systems of tillage had little influence on soil moisture during the growing seasons. Soil moisture curves indicate different water withdrawal patterns under the two contrasting methods of tillage. The decrease in evaporation and the greater ability to store moisture under no‐tillage produces a greater water reserve. This can often carry the crop through periods of short‐term drought and avoid the development of detrimental moisture stresses in the plant. The more efficient use of soil moisture by no‐tillage is reflected in higher corn yields. This study further substantiates the effectiveness of no‐tillage systems of corn production on well to moderately well‐drained silt loam soils in Kentucky and other regions with similar climatic regimes.
The growth of an individual soybean [Glycine max (L.) Merr.] seed is an important part of the yield production process. An understanding of the effect of environmental factors on the growth of individual seeds is needed to enhance our understanding of the effect of the environment on yield. Soybeans were grown in the field on a Maury silt loam soil (fine, mixed, mesic Typic Paleudalfs) for 3 years (1979 to 1981) and subjected to varying levels of moisture stress to investigate the effect of moisture stress on seed growth. Irrigated controls were compared with moisture stress treatments from planting to beginning seed fill (growth stage RS), during seed filling (growth stage R5 to R7) or from planting to maturity (severe stress). Fruits were tagged at beginning seed fill and sampled at weekly intervals to estimate the seed growth rate and the effective filling period (EFP). Although the stress treatments reduced yield and vegetative growth, the rate of seed growth (mg seed−1 day−1) was not affected. The seed‐filling period (estimated as days from growth stage R5 to R7 or EFP) was shortened by the severe stress treatment in 1979 and 1981 (statistically significant only in 1979), and there was a trend for the period of R5 to R7 to be shortened by late stress in 1980 and 1981. The data suggest that the rate of individual seed growth is less sensitive to moisture stress than other plant processes. The seed filling period was more sensitive to moisture stress than seed growth rate and the effect of moisture stress on the duration of seed fill may be one way that stress reduces soybean yield.
Although a substantial amount of information is available on pulmonary alveolar macrophages (PAMs), little is known about pulmonary intravascular macrophages (PIMs), a separate population of lung macrophages found apposed to the endothelium of pulmonary capillaries. We compared these two populations of lung immunocytes to determine their relative immunological activity. Our results suggest that PAMs are more phagocytic than PIMs; however, PIMs may be more efficient at lysing ingested bacteria than PAMs. Although similar in antibody-dependent cellular cytotoxicity, PIMs are more spontaneously cytolytic than PAMs. Depending upon the effector:target cell ratio studied, the tumoricidal activity of PIMs was less than or equal to that of PAMs. Both cell populations produced the cytokines interleukin-1 and tumor necrosis factor-alpha at similar concentrations. These data suggest that PIMs are immunologically active, although the degree of activity may differ between PIMs and PAMs.
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