Effects of tillage, fertilization, and stocking rate on stargrass pasture performance in the humid tropics of Costa Rica

Dairy farms in the San Carlos region of Costa Rica commonly utilize stargrass (Cynodon nlemfuensis) with a stocking rate averaging 2.6 animals/ha/year. The research site was located in Aguas Zarcas, Costa Rica, and received an average annual precipitation of 432 cm. This location is characterized as a humid tropical biome. Serious soil compaction due to cattle traffic was evident through redoximorphic features beginning at 7.5 cm below the soil surface in the stargrass dairy pastures; therefore, we hypothesized that compaction may be impeding forage production by diminished root growth and nutrient uptake. The objectives of this one year study were to characterize existing pasture conditions with regard to soil physical properties, and to determine the effect of stocking density, deep tillage, and fertilizer rate on soil bulk density, forage yield, and forage quality. Nine stargrass pastures with three different stocking densities were studied to assess the effect of tillage and fertilizer rate on forage yield and quality. The experimental design was such that the whole plot treatments where high (385 head/ha), medium (192 head/ha), and low (128 head/ha) stocking density. Stocking density treatments were not randomized due to limitations of management practices; however for experimental design purposes we treated them as randomized. The sub plot treatment was tillage, where each pasture was divided in half with deep tillage (35 cm) applied to one subplot and no tillage treatment on the other subplots. The sub-sub plot treatments were three fertilizer treatments; no fertilizer, 50% of the recommended fertilizer rate, and the recommended fertilizer rate. Soil bulk density was measured at three depths before tillage, one month after tillage, and one year after tillage. Bulk density samples were taken at the soil surface, 7.5 cm, 18 cm, and measured 0.8 Mg/m3, 0.9 Mg/m 3, and 0.9 Mg/m3 for the three depths respectively, before treatments were in place. There were no statistical differences between tillage treatments for soil bulk density. Bulk density was not consistently measured in the tillage furrow, and so it might not have accurately measured tillage results. There were no statistically significant differences between treatments for forage yield. Additionally, stocking density was the only treatment with statistically significant differences for forage quality. The highest stocking density plots had the best forage quality (p≤0.05). Seasonal differences in forage production were consistent with weather patterns. Rainy season forage production yielded more, with poorer quality than the semi-dry season. Pasture yield averaged 4225 kg/ha for rainy months, 3582 kg/ha for semi-dry months, and ranged from 3056 to 5691 kg/ha each month