- Authors:
- Smith, J. L.
- Johnstone, D. L.
- Geyer, D. J.
- Keller, C. K.
- Source: Journal of Contaminant Hydrology
- Volume: 11
- Issue: 1-2
- Year: 1992
- Summary: Increased nitrate concentrations in groundwater associated with the application of nitrogen fertilizers have led to inquiries concerning the fate of nitrate beneath agricultural fields. This study was conducted to identify the processes affecting the distribution of nitrate in the unsaturated and saturated zones beneath an agricultural field and to assess how each process is influenced by factors associated with slope position. Nested piezometers were installed at two slope positions at the study site in southeastern Washington, U.S.A. Unsaturated- and saturated-zone sediment cores were analyzed for water content, pH, total and soluble organic carbon, ammonium, nitrate, and denitrification potential. Waters from the piezometers showed decreasing nitrate concentrations with depth below the water table. Trends in measured parameters indicated depth intervals where the distribution of nitrate could be attributed either solely to transport or to a combination of transport and biological denitrification. Denitrification explained the distribution of nitrate in the root zone while transport explained the interval between the root zone and the water table. There was a higher potential for denitrification below the water table at the bottom slope than at the top slope. Factors associated with slope position, such as a shallow water table and impeding stratigraphic layers, may explain this higher potential. Regardless of slope position, comparing nitrous oxide and carbon dioxide production from nitrate- and carbon-amended or -unamended samples indicated that denitrifier populations present in high-potential zones arc nitrate-limited. Results from spherical microsite modelling suggest that anoxic conditions are possible in the bulk sediment despite the presence of oxygenated groundwaters beneath both slope positions. Advective-dispersive transport will continue to transport nitrate through the unsaturated and saturated zones. The data from this study suggest that there is greater potential for nitrate attenuation by denitrification beneath the bottom slope than the top slope. The data also show that large masses of nitrate reside in deep subsoil vadose zones. These regions must therefore be monitored to detect threats to future groundwater quality.
- Authors:
- Source: Journal of Soil and Water Conservation
- Volume: 47
- Issue: 4
- Year: 1992
- Summary: Rapid expansion of the Virginia poultry industry has resulted in poultry litter production that in certain areas exceeds the potential for use in crop agriculture. If land application exceeds crop requirements, litter production may result in environmental damage. In this study, potential litter surpluses in intensive poultry-producing Virginia counties were quantified. The costs of transferring such surpluses to litter-deficient areas were compared with the economic value of litter as fertilizer. Estimates of potential cropland and pasture for spreading litter took dairy manure production into account. Use of litter surpluses by transfer was found to be economically viable. Public policy actions are needed, however, to promote such transfer.
- Authors:
- Shennan, C.
- Stivers, L. J.
- Source: Journal of Production Agriculture
- Volume: 4
- Issue: 3
- Year: 1991
- Summary: Results from the first 2 years of the experiment are used to compare the productivity of several legume green manures and to determine if they can provide adequate available soil N to support yields of a subsequent crop of processing tomatoes (Lycopersicon lycopersicum L. Karsten var. lycopersicum) typical for this area. Lana woolly-pod vetch (Vicia dasycarpa Ten.), bell beans (Vicia faba L.), berseem clover (Trifolium alexandrinum L.), Austrian winter peas (Pisum arvense L.), oats (Avena sativa L.), and an oats and vetch mixture, planted in October and disked under in April, were compared with various levels of ammonium sulfate fertilizer.
- Authors:
- Source: Communications in Soil Science and Plant Analysis
- Volume: 21
- Issue: 1-2
- Year: 1990
- Summary: Crop response to fertilizer nitrogen (N) is dependent upon tillage management. This study was conducted to determine how tillage rotation influences non‐irrigated crop growth, N uptake and yield. The effects of tillage rotation, N rate and N timing schedule on early season dry matter production and N uptake, ear leaf N concentration at silking, and yield of corn [Zea mays (L.) Pioneer 3378] were investigated at Painter, VA, on an Altavista loam (fine‐loamy, mixed, thermic Aquic Hapludult). In 1986, maximum yields achieved in the 6‐year continuous no till (NT) [5.82 Mg/ha] and first year no till (AT) [5.64 Mg/ha] were significantly greater than that of the 6‐year continuous conventional till (CT) [3.67 Mg/ha], but no yield differences were obtained in the drier 1987 season. A higher rate of N fertilizer was required to obtain maximum yield in the first year no till (168 kg N/ha) than in the NT (112 kg N/ha) during 1986. Early 1986 N uptake and growth response with and without N at planting increased in the order CT < AT = NT and AT < CT < NT, respectively, indicating greatest immobilization of soil N occurred in the newly established no till soil. Lack of differences in critical ear leaf N values developed for NT and CT in each year imply that plant norms developed for one tillage system may accurately assess N status of corn grown under different tillage practices.
- Authors:
- Ojima, D. S.
- Cole, C. V.
- Schimel, D. S.
- Parton, W. J.
- Source: Soil Science Society of America Journal
- Volume: 51
- Issue: 5
- Year: 1987
- Summary: We analyzed climatic and textural controls of soil organic C and N for soils of the U.S. Great Plains. We used a model of soil organic matter (SOM) quantity and composition to simulate steady-state organic matter levels for 24 grassland locations in the Great Plains. The model was able to simulate the effects of climatic gradients on SOM and productivity. Soil texture was also a major control over organic matter dynamics. The model adequately predicted aboveground plant production and soil C and N levels across soil textures (sandy, medium, and fine); however, the model tended to overestimate soil C and N levels for fine textured soil by 10 to 15%. The impact of grazing on the system was simulated and showed that steady-state soil C and N levels were sensitive to the grazing intensity, with soil C and N levels decreasing with increased grazing rates. Regional trends in SOM can be predicted using four site-specific variables, temperature, moisture, soil texture, and plant lignin content. Nitrogen inputs must also be known. Grazing intensity during soil development is also a significant control over steady-state levels of SOM, and since few data are available on presettlement grazing, some uncertainty is inherent in the model predictions.
- Authors:
- Source: Ibis
- Volume: 128
- Issue: 1
- Year: 1986
- Summary: Field experiments were carried out to test the effects of cereal pesticides (herbicides, fungicides and insecticides) on chick survival of Grey Partridge Perdix perdix, Red-legged Partridge Alectoris rufa and Pheasant Phasianus colchicus. On fields in experimental plots the outer 6 m of cereal (the headland) were not sprayed with pesticides from 1 January 1984, whereas control plots were fully sprayed. Gamebird brood counts were carried out after the cereal harvest. In addition, nine Grey Partridge broods were radio-tracked for 21 days after hatching (four in sprayed plots and five in unsprayed plots) to determine their movements, home range size and survival in relation to pesticide spraying. The mean brood size of Grey Partridge and Pheasant was significantly higher on plots where field edges were unsprayed than on fully sprayed control plots. Data for Red-legged Partridge were inconclusive. The survival of individually marked Grey Partridge broods was negatively related to the distance moved between successive nocturnal roost sites. Survival was significantly higher, the distance moved between roost sites significantly shorter and the proportion of home range including headland significantly greater for broods feeding in spring barley fields with unsprayed field edges compared with broods feeding in fully sprayed fields.
- Authors:
- Seastedt, T. R.
- Knapp, A. K.
- Source: BioScience
- Volume: 36
- Issue: 10
- Year: 1986
- Summary: Focuses on the reduction in the amount of tallgrass prairie in North America. Study conducted by the International Biological Program; The three dominant warm-grasses which tallgrass prairie is divided into; Reasons why tallgrass prairie flourished; Effects of prairie fires on nitrogen levels; Efforts to remove detritus.
- Authors:
- Source: Soil Science Society of America Journal
- Volume: 48
- Issue: 4
- Year: 1984
- Summary: Surface soils from long-term tillage comparison experiments at six U.S. locations were characterized for aerobic and anaerobic microbial populations and denitrification potential using an in situ acetylene blockage technique. Measurements of soil water content, bulk density, and relative differences in pH, NO-3-N, water-soluble C, and total C and N contents between tillage treatments were also determined at the time of sampling. Numbers of aerobic and anaerobic microorganisms in surface (0-75 mm) no-till soils averaged 1.35 to 1.41 and 1.27 to 1.31 times greater, respectively, than in surface-plowed soils. Bulk density, volumetric water content, water-filled pore space, and water-soluble C and organic C and N values were similarly greater for surface no-till soils compared to conventionally tilled soils. Deeper in the soil (75-300 mm), however, aerobic microbial populations were significantly greater in conventionally tilled soils. In contrast, below 150 mm, the numbers of anaerobic microorganisms differed little between tillage treatments. In no-till soils, however, these organisms were found to comprise a greater proportion of the total bacterial population than in conventionally tilled soils. Measurements of the denitrification potential from soils at three locations generally followed the observed differences in anaerobic microbial populations. Denitrifying activity, after irrigation with 15 mm of water, was substantially greater in surface 0- to 75-mm no-till soils than in conventionally tilled soils at all locations. At the 75- to 150-mm soil depth, however, the denitrification potential in conventionally tilled soils was the same or higher than that of no-till soils. In surface no-till soils, increased numbers of anaerobic microorganisms and a substantially greater denitrification potential, following irrigation, indicate the presence of less-aerobic conditions in comparison to conventionally tilled soils. This condition appears to result from greater soil bulk densities and/or water contents of no-till soils, which act to increase water-filled porosity and the potential for water to act as a barrier to the diffusion of oxygen through the soil profile.
