Nitrogen in soils, plants, surface water and shallow groundwater in a bahiagrass pasture of Southern Florida, USA

被引:0
作者
Gilbert C. Sigua
Robert K. Hubbard
Samuel W. Coleman
Mimi Williams
机构
[1] Subtropical Agricultural Research Station,United States Department of Agriculture, Agricultural Research Service
[2] Southeast Watershed Research Laboratory,United States Department of Agriculture, Agricultural Research Service
[3] Natural Resources and Conservation Service,United States Department of Agriculture
来源
Nutrient Cycling in Agroecosystems | 2010年 / 86卷
关键词
Bahiagrass; cow–calf; Groundwater; Inorganic nitrogen; Nutrient cycling; Plant uptake; Water quality;
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摘要
Despite substantial measurements using both laboratory and field techniques, little is known about the spatial and temporal variability of nitrogen (N) dynamics across the landscapes, especially in agricultural landscapes with cow–calf operations. This study was conducted to assess the comparative levels of total inorganic nitrogen, TIN (NO3–N + NH4–N) among soils, forage, surface water and shallow groundwater (SGW) in bahiagrass (Paspalum notatum, Flueggé) pastures. Soil samples were collected at 0–20, 20–40, 40–60, and 60–100 cm across the pasture’s landscape (top slope, TS; middle slope, MS; and bottom slope, BS) in the spring and fall of 2004, 2005 and 2006, respectively. Bi-weekly (2004–2006) groundwater and surface water samples were taken from wells located at TS, MS, and BS and from the run-off/seepage area (SA). Concentrations of NH4–N, NO3–N, and TIN in SGW did not vary with landscape position (LP). However, concentrations of NH4–N, NO3–N, and TIN in water samples collected from the seep area were significantly (P ≤ 0.05) higher when compared to their average concentrations in water samples collected from the different LP. Average concentrations of NO3–N (0.4–0.9 mg l−1) among the different LP were well below the maximum, of 10 mg l−1, set for drinking water. The maximum NO3–N concentrations (averaged across LP) in SGW for 2004, 2005 and 2006 were also below the drinking water standards for NO3–N. Concentration of TIN in soils varied significantly (P ≤ 0.05) with LP and soil depth. Top slope and surface soil (0–20 cm) had the greatest concentrations of TIN. The greatest forage availability of 2,963 ± 798 kg ha−1 and the highest N uptake of 56 ± 12 kg N ha−1 were observed from the TS in 2005. Both forage availability and N uptake of bahiagrass at the BS were consistently the lowest when averaged across LP and years. These results can be attributed to the grazing activities as animals tend to graze more at the BS. The average low soil test value of TN (across LP and soil depth) in our soils of 10.9 mg kg−1 (5.5 kg N ha−1) would indicate that current pasture management including cattle rotation in terms of grazing days and current fertilizer application (inorganic + feces + urine) for bahiagrass pastures may not have negative impact on the environment.
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页码:175 / 187
页数:12
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