Unintended consequences of water management in agroecosystems

Abstract:

Wise use of water is critical when we seek to intensify agriculture yet still target sustainability. Whether we are looking at water quality or quantity, water management plays a role in effective design of sustainable management practices. However, as we manipulate the amount of time water spends in the landscape or the flow pathways within a farm field, there can be unintended environmental impacts on carbon and nutrient cycling. In this talk, we look at two ends of the development spectrum in relation to water management in agroecosystems. First, we consider water management targeting irrigation efficiency to reduce overall water use across a gradient of agricultural intensification. We use the case of Tanzania’s Kilombero Valley wetland, which is being targeted for multi-stakeholder initiatives that aim at developing agricultural potential through combinations of large-scale and small-scale irrigation schemes. We assessed the effect of irrigation and fertilization in agricultural systems going from low intensity smallholder to high intensity commercial production. Irrigation had a positive effect on soil organic carbon concentrations and stocks while fertilization had a negative effect. There was less clear impact on soil nutrients; however, we did see a decrease in water quality downstream from irrigation schemes across the Kilombero Valley. Second, we consider water management targeting controlled drainage to reduce nutrient loads leaving farm fields. We report on some initial results for an automated tile drainage water management system located in a corn-soy experimental field at the Ohio Agricultural Research and Development Center. While drainage water management systems reduce nutrient loads to streams by holding water in the farm field and can even promote increased yield in some cases, there can be unintended impacts on soil health and nutrient cycling due to elevated water levels in the subsurface – particularly at the edge of field where water enters into the local stream network. Taken together, these examples highlight that we need to adopt a whole systems approach to ensure we manage water across agroecosystems such that we do not unintentionally sacrifice environmental health to secure social and economic benefits.

Wise use of water is critical when we seek to intensify agriculture yet still target sustainability. Whether we are looking at water quality or quantity, water management plays a role in effective design of sustainable management practices. However, as we manipulate the amount of time water spends in the landscape or the flow pathways within a farm field, there can be unintended environmental impacts on carbon and nutrient cycling. In this talk, we look at two ends of the development spectrum in relation to water management in agroecosystems. First, we consider water management targeting irrigation efficiency to reduce overall water use across a gradient of agricultural intensification. We use the case of Tanzania’s Kilombero Valley wetland, which is being targeted for multi-stakeholder initiatives that aim at developing agricultural potential through combinations of large-scale and small-scale irrigation schemes. We assessed the effect of irrigation and fertilization in agricultural systems going from low intensity smallholder to high intensity commercial production. Irrigation had a positive effect on soil organic carbon concentrations and stocks while fertilization had a negative effect. There was less clear impact on soil nutrients; however, we did see a decrease in water quality downstream from irrigation schemes across the Kilombero Valley. Second, we consider water management targeting controlled drainage to reduce nutrient loads leaving farm fields. We report on some initial results for an automated tile drainage water management system located in a corn-soy experimental field at the Ohio Agricultural Research and Development Center. While drainage water management systems reduce nutrient loads to streams by holding water in the farm field and can even promote increased yield in some cases, there can be unintended impacts on soil health and nutrient cycling due to elevated water levels in the subsurface – particularly at the edge of field where water enters into the local stream network. Taken together, these examples highlight that we need to adopt a whole systems approach to ensure we manage water across agroecosystems such that we do not unintentionally sacrifice environmental health to secure social and economic benefits.