Effects of an agropastoral system on the production of soybean and wheat were investigated by comparing, from 2003 to 2007, agropastoral plots that had been converted from 7-year pasture (guinea grass: Panicum maximum; 1996 to 2003) to crop cultivation, with control plots that had been continuously cropped over 10 years with soybean at the Japan International Cooperation Agency's Paraguay Agricultural Technology Center (CETAPAR-JICA). Soybean productivity in this area increased from 1979 until 1993, when yield peaked at 3.39 t/ha and then declined. In this study, soybean yields ranged from 1.48 to 3.56 t/ha in agropastoral plots and from 0.63 to 2.47 t/ha in control plots. In each year, the yield in the agropastoral plots was 1.1 to 2.4 times more than in the control plots. Wheat yields were also higher in agropastoral plots (1.59 to 3.17 t/ha) than in control plots (1.18 to 2.31 t/ha). In each year, yield in the agropastoral plots was 1.2 to 1.8 times more than in the control plots. Thus, soybean and wheat yields were sustained by introducing an agropastoral system. We also examined the chemical and physical properties of the soil under initial conditions in both plot types. The concentrations of phosphate, potassium and magnesium in surface soil in agropastoral plots were significantly lower than in control plots. The content of organic matter at soil depths of 0 to 60 cm in the agropastoral plots was significantly higher than in the control plots, and the physical properties of the agropastoral plot soil (gaseous phase, bulk density, and soil aggregates) were improved. We conclude that the agropastoral system positively affected all these properties.

The effects of an agropastoral system on the production of soybean and wheat were investigated by comparing (from 2007 to 2009) agropastoral plots that had been reconverted from 4-year pasture (Guinea grass: Panicum maximum; 2003 to crop cultivation, with control plots that had been continuously cropped over 13 years with soybean and wheat at CETAPAR-JICA. In 2003, Guinea grass pastures were converted from 10-year continuous cultivated soybean and wheat fields, and then grazed intensively from 2004 to 2007, while the control plots continued to be cultivated with soybean and wheat. Animal production in converted pastures was very high and the weight gain per hectare was 1,113 to 1,500 kg/ha over 3 years after introducing an intensive grazing system with supplemental feeding in dry season. The average daily gain was maintained at 0.554 to 0.621 kg/head/day despite a high stocking rate (4.5-6.0 UA/ha). However, after the reconversion in 2007, the soybean yields from 2008 to 2009 were 3.71 and 1.24 ton/ha, which were 1.02 and 1.43 times higher than those in the control plots, respectively. In 2008, the wheat yield was 2.72 ton/ha, the same as that in the control plots. Thus, we concluded that the agropastoral effects on the soybean and wheat yield were small after reconversion to intensive grazing. The reason for the small effect is likely to be the low supply of Guinea grass litter under high grazing pressure, which did not result in any accumulation of the organic matter in the soil.