Livestock in the Amazon is mainly limited by the lack of forage biomass production in the dry season. The sensitivity of pasture to drought depends on pasture management and on certain natural factors that enable the grass cover to stay green for longer under low rainfall. The sustainability of livestock production systems depends on identifying these natural factors to make better use of their forage production potential without consuming additional water resources or resorting to deforestation. We built an index of pasture dependence on rainfall at the beginning of the dry season by calculating the slope of the linear regression between the MODIS enhanced vegetation index and monthly cumulative rainfall obtained from the Tropical Rainfall Measuring Mission. The index was calculated in Paragominas municipality. A 15-year time series (2000 to 2014) was used to assess the sensitivity of pasture to drought. A map of geomorphological units was overlaid on the index map to check whether the soil and the landform influence drought sensitivity at a large scale. Drought resistance was shown to be higher in lowland areas with loamy sand with a shallow groundwater table and on plateaus covered by fertile sedimentary clay. The escarpments with a ferruginous duricrust and mottled clay were shown to be the most sensitive to drought. These results underline the importance of natural factors in pasture productivity in tropical humid areas.

中文翻译：

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东部亚马逊地区与土壤和地貌有关的牧场对干旱的敏感性

亚马逊地区的牲畜主要受到干旱季节缺乏牧草生物质生产的限制。牧场对干旱的敏感性取决于牧场管理和某些自然因素，这些因素可使草皮在低雨量下保持绿色更长的时间。畜牧生产系统的可持续性取决于确定这些自然因素，以便更好地利用其草料生产潜力，而不会消耗额外的水资源或诉诸砍伐森林。通过计算MODIS增强植被指数与从热带雨量测量团获得的月累积雨量之间的线性回归斜率，我们建立了干旱季节开始时牧场对降雨的依赖性指数。该指数是在帕拉戈米纳斯市计算的。使用15年时间序列（2000年至2014年）评估牧场对干旱的敏感性。在索引图上叠加了地貌单位图，以检查土壤和地形是否对干旱敏感性产生了较大的影响。结果表明，在低壤土地区，壤土多，地下水位浅的高原地区和肥沃的沉积粘土覆盖的高原地区，其抗旱性较高。带有铁质榴ric和斑驳的粘土的悬崖被证明对干旱最敏感。这些结果强调了自然因素对热带潮湿地区牧场生产力的重要性。结果表明，在低壤土地区，壤土多，地下水位浅的高原地区和肥沃的沉积粘土覆盖的高原地区，其抗旱性较高。带有铁质硬质灰泥和斑驳的粘土的悬崖被证明对干旱最敏感。这些结果强调了自然因素对热带潮湿地区牧场生产力的重要性。结果表明，在低壤土地区，壤土多，地下水位浅的高原地区和肥沃的沉积粘土覆盖的高原地区，其抗旱性较高。带有铁质硬质灰泥和斑驳的粘土的悬崖被证明对干旱最敏感。这些结果强调了自然因素对热带潮湿地区牧场生产力的重要性。