Contribution of Onthophagus gazella to soil fertility improvement by bovine fecal mass incorporation into the soil. 1. Greenhouse studies

The incorporation of fresh bovine fecal mass by Onthophagus gazella on a Purple Latosol from Cerrados region in Campo Grande, MS and its contribution to green matter production and nitrogen (N) and phosphorus (P) content of Brachiaria decumbens were studied, under partial lab and greenhouse controlled conditions. Sixty pots containing 10 kg of that soil were prepared for the following treatments: control (without beetle) and 3, 6 and 12 pairs of O. gazella, with 15 replicates for each treatment. After distribution of the treatments, 400 g of fresh bovine fecal mass were added to each treatment, followed by further additions of 300 g at day two and 300 g at four days after the first addition, which resulted in a total of 159 g of dry mass added. Ten days after the first addition, non incorporated feces in the soil were collected, and twenty days after seven seedlings of Brachiaria decumbens were transplanted to each pot. At 45, 65, and 85 days after planting, five replicates per treatment were harvested, and the shoot and root plant separated to determine vegetal mass production, by its dry matter weight. From the material harvest at the 85 days, the N and P contents were also determined. From the 159 g added, 75.1, 110.8, and 132.5 g were incorporated, in the treatment 3, 6, and 12 beetle pairs, respectively, which influenced plant establishment and production, as well as its N and P total content. Such a contribution was even more evident with the increase of incorporated biomass, which was proportional to the number of beetle pairs. The appearance of earthworms (non-identified) in the O. gazella treatments was observed, which did not occur in the control. These results attest the important contribution of this beetle specie to the grassland soils fertility.