The role of dung beetle species in nitrous oxide emission, ammonia volatilization, and nutrient cycling.

This study evaluated the role of dung beetle species alone or associated under different species on nitrous oxide (N2O) emission, ammonia volatilization, and the performance of pearl millet [Pennisetum glaucum (L.)]. There were seven treatments, including two controls (soil and soil + dung without beetles), single species of Onthophagus taurus [Shreber, 1759] (1), Digitonthophagus gazella [Fabricius, 1787] (2), or Phanaeus vindex [MacLeay, 1819] (3); and their assemblages (1 + 2 and 1 + 2 + 3). Nitrous oxide emission was estimated for 24 days, when pearl millet was planted in sequence to assess growth, nitrogen yield (NY), and dung beetle activity. Dung beetle species presented greater N2O flow of dung on the 6th day (80 g N2O-N ha-1 day-1) compared to soil and dung (2.6 g N2O-N ha-1 day-1). Ammonia emissions varied with the presence of dung beetles (P < 0.05), and D. gazella had less NH3-N on days 1, 6, and 12 with averages of 2061, 1526, and 1048 g ha-1 day-1, respectively. The soil N content increased with dung + beetle application. Dung application affected pearl millet herbage accumulation (HA) regardless of dung beetle presence, and averages ranged from 5 to 8 g DM bucket-1. A PCA analysis was applied to analyze variation and correlation to each variable, but it indicated a low principal component explanation (less than 80%), not enough to explain the variation in findings. Despite the greater dung removal, the largest species, P. vindex and their species combination, need to be more studied to get a better understanding about their contribution on greenhouse gases. The presence of dung beetles prior to planting improved pearl millet production by enhancing N cycling, although assemblages with the three beetle species enhanced N losses to the environment via denitrification.

Effects of grazing management in brachiaria grass-forage peanut pastures on canopy structure and forage intake1.

Maintenance of mixed grass-legume pastures for stand longevity and improved animal utilization is a challenge in warm-season climates. The goal of this study was to assess grazing management on stand persistence, forage intake, and N balance of beef heifers grazing mixed pastures of Brachiaria brizantha and Arachis pintoi. A 2-yr experiment was carried out in Brazil, where four grazing management were assessed: rest period interrupted at 90%, 95%, and 100% of light interception (LI) and a fixed rest period of 42 d (90LI, 95LI, 100LI, and 42D, respectively). The LI were taken at 50 points at ground level and at 5 points above the canopy for each paddock using a canopy analyzer. For all treatments, the postgrazing stubble height was 15 cm. Botanical composition and canopy structure characteristics such as canopy height, forage mass, and vertical distribution of the morphological composition were evaluated pre- and post-grazing. Forage chemical composition, intake, and microbial synthesis were also determined. A randomized complete block design was used, considering the season of the year as a repeated measure over time. Grazing management and season were considered fixed, while block and year were considered random effects. In the summer, legume mass accounted for 19% of the canopy at 100LI, which was less than other treatments (a mean of 30%). The 100LI treatment had a greater grass stem mass compared with other treatments. In terms of vertical distribution for 100LI, 38.6% of the stem mass was above the stubble height, greater than the 5.7% for other treatments. The canopy structure limited NDF intake (P = 0.007) at 100LI (1.02% of BW/d), whereas 42D, 90LI, and 95LI treatments had NDF intake close to 1.2% of BW/d. The intake of digestible OM (P = 0.007) and the ratio of CP/digestible OM (P < 0.001) were less at 100LI in relation to the other treatments. The production of microbial N (P < 0.001) and efficiency of microbial synthesis (P = 0.023) were greater at 95LI and 90LI, followed by 42D and less at 100LI. Overall, the range from 90% to 95% of LI is the recommendation to interrupt the rest period, since this strategy enhanced community stability, forage intake, and nutritional value of the diet. Under on-farm conditions, brachiaria grass and forage peanut pastures should be managed at a range height of 24 to 30 cm.