Print PageThe symbiotic relationship between Rhizobium bacteria and legume host plants has long been used by humans to produce forages on N-limited soils. Two experiments were conducted simultaneously to address legume establishment success, persistence under grazing, and effects on soil quality. For testing establishment, crimson clover (Trifolium incarnatum L.) and white clover (Trifolium repens L.) were chosen as model crops and either no-till drilled or broadcast seeded at two rates into a bermdudagrass (Cynodon dactylon L.) sward and grazed by cattle for 5 d either before or after establishment in a randomized complete block design with three replications. In the second experiment, crimson and white clovers and various other annual and perennial legumes were tested regarding persistence under season-long rotational grazing and effects on soil quality. Using a randomized complete block design with three replications, alfalfa (Medicago sativa L.), red clover (Trifolium pratense L.), arrowleaf clover (Trifolium vesiculosum Savi), and hairy vetch (Vicia villosa Roth) were no-till drilled into existing bermudagrass swards and rotationally grazed for 3 seasons to test persistence and effects on soil quality, including total microbial C, total microbial N, and soil-enzymatic activity.
Results/Conclusions
No-till planting resulted in higher (P<0.05) seedling counts than the broadcast method at either high or low seeding rates. Maximum counts observed were 215 seedlings m-2 for both crimson and white clover. Seedling numbers in broadcasted white clover plots that were ‘grazed after’at a high seeding rate were elevated (P<0.05) compared with ‘grazed before’ plots in the first year, but this effect did not reappear during subsequent years, making a consistent cattle hoof-action effect for providing increased soil-seed contact unlikely. Yields of above-ground biomass followed seedling count patterns. Perennial white and red clovers persisted longest, but frequency of occurrence decreased rapidly for all species during the third and final year of the study. After 3 y, the annual hairy vetch had higher (P<0.05) occurrence frequencies than other annuals but reestablishment each year may be mandatory to make long term utilization of annual legumes feasible. Alfalfa plots showed higher (P<0.05) microbial biomass, enzyme activities, and dissolved C and N with values for white and red clover being similar or lower. In contrast, microbial biomass, enzyme activities and dissolved C and N were lower (P<0.05) in hairy vetch and arrowleaf clover treatments. In summary, some tested legumes may be well suited for inclusion in pasture ecosystems, but offsetting large rates of synthetic N fertilization remains challenging.
