Four-paddock rotational grazing of orchardgrass, ryegrass, or alfalfa was compared to an all-concentrate diet fed in drylot using 202 weaned lambs. Comparisons of animal performance ended in each of the 3 yr (1983, 1984, 1985) for all animals when drylot lambs reached a subjective body condition score of 12 (range 1 to 15) and estimated fat depth over the rib was 5.5 to 7.0 mm. A total of 84 representative lambs were slaughtered over the 3 yr for carcass evaluation. Mature put-and-take ewes were used to maintain forages in the vegetative stage. Average daily gain and total gain of lambs were in the order of drylot > alfalfa > grasses; performance of lambs grazing alfalfa approached performance of those fed the drylot diet. Better performance (P < .01) of lambs grazing alfalfa than of those grazing grasses is atributed to more CP (P < .01) and less NDF, ADF, and hemicellulose (P < .01) in alfalfa. Lambs grazed on grasses had smaller carcasses with less muscle, fat, and bone (P < .01) than either of the other two treatments. Although carcasses of lambs grazed on alfalfa were lighter, they had the same muscle mass as concentrate-fed lambs, indicated by leg conformation, longissimus muscle area, and by physically separated absolute muscle weight. However, these carcasses contained less fat (P < .01) and had more desirable yield grades (P < .01) than the carcasses of concentrate-fed lambs.
High levels of N fertilizer applied to pastures can result in NO3‐N concentrations in groundwater exceeding the USEPA potable water standard of 10 mg N/L. This study was conducted to determine groundwater NO3‐N levels following a change in N source from fertilizer to a legume in a grass‐pasture grazed by beef cattle. For 5 yr, 224 kg N/ha was applied annually to small watersheds with orchardgrass (Dactylis glomerata L.) pastures used for summer‐grazing and tall fescue (Festuca arundinacea Schreb.) areas used for winter‐grazing‐feeding. At the beginning of the sixth year, alfalfa (Medicago sativa L.) was interseeded into the grass pastures and N fertilizer was no longer applied. Groundwater sampies from developed springs and surface runoff samples were collected and analyzed for NH4‐N, NO3‐N, and total N for the 5‐yr fertilization period and for the following 10‐yr period without applied N fertilizer. Nitrogen in groundwater was present mainly in the NO3 form, and concentrations increased throughout the 5‐yr period of fertilizer application and reached levels that were usually in excess of 10 mg N/L. With the change from N fertilizer to legume N, the NO3‐N concentrations in groundwater dropped rapidly during a 2‐yr period. In a tall fescue‐alfalfa area, NO3‐N levels decreased from 17.7 to 9.3 mg N/L. In two orchard‐grass‐alfalfa areas, NO3‐N levels decreased from 11.2 to 2.7 and from 8.3 to 3.6 mg N/L. During the remainder of the 10‐yr period, NO3‐N concentrations declined to levels similar to those before N fertilization. Although the amount of N lost via subsurface flow decreased with decreasing concentrations, subsurface flow remained the main pathway for N loss compared with surface runoff or sediment‐attached N.
Many of the reported nutrient losses from agricultural areas, especially where artificial subsurface drainage is not present, have been from surface runoff. In unglaciated, well drained silt loams in eastcentral Ohio, a portion of the infiltrated rainfall moves through the soil returning to the surface at springs or seep areas. Such return flow often creates a constant baseflow in multi‐hectare watersheds. The purposes of this study were to compare relative water and nutrient transports via storm runoff with amounts removed in continuous baseflow and to evaluate the influence of different management practices on such transport. Baseflow and storm runoff from four watersheds with different land use practices were measured, sampled, and analyzed for these comparisons. In two watersheds, 123 and 32.1 ha in size, containing woodland, pasture, and row crops, the majority of N moved from the watersheds in the storm runoff; however, 25 to 50% of the N transport was via baseflow. Using 10‐yr averages, 5.0 and 2.8 kg/ha of mineral N were annually transported from the 123‐ha watershed via 242 and 196 mM of storm runoff and baseflow, respectively; from the 32‐ha watershed, 3.6 and 3.2 kg/ha of mineral N were annually transported via 144 and 198 mm of storm runoff and baseflow, respectively. Mineral N transport from a 28.8‐ha poor practice pasture watershed and from a 17.7‐ha wooded watershed was less than above, but the proportions in storm runoff and baseflow were similar. Although stormflow was the larger transport pathway for nutrients leaving a watershed, a sizable portion of the nutrients can be carried with the baseflow. This comparison of watersheds in an unglaciated area indicates that there is a negligible difference in the quality of water leaving an unfertilized wooded area or unfertilized pasture or a watershed that receives fertilization on 55% of its area.
This study examined the impact on groundwater quality of conventional and slow‐release N fertilizer to small, grazed watersheds in eastern Ohio. Three small watersheds (each less than 1 ha) received 56 kg N/ha annually as NH4NO3 for 5 yr. For the next 10 yr, one watershed received 168 kg N/ha annually as NH4NO3 and two others received the same amount of N as methylene urea, a slow‐release fertilizer. Shallow groundwater samples were collected from springs and analyzed. After the 5‐yr prestudy period, NO3‐N levels in the groundwater from the three watersheds were in a 3 to 5 mg/L range. Groundwater NO3‐N concentrations increased slightly during the first 3 yr at the higher N fertilizer rate, though they remained in the 3 to 5 mg/L range. Nitrate‐N levels increased more sharply during the rest of the study. Although these NO3‐N levels varied more between the growing and dormant seasons than when lower rates of fertilizer were applied, they eventually reached a slower rate of increase. During the 9th and 10th yr of the high application, seasonal NO3‐N levels in groundwater ranged from 10 to 16 and 7 to 14 mg/L from the watersheds receiving NH4NO3 and methylene urea, respectively. This study showed that 168 kg N/ha was too much for this system, regardless of whether conventional or slow‐release N was used.
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