Discussion: Prioritize perennial grain development for sustainable food production and environmental benefits.

Perennial grains have potential to contribute to ecological intensification of food production by enabling the direct harvest of human-edible crops without requiring annual cycles of disturbance and replanting. Studies of prototype perennial grains and other herbaceous perennials point to the ability of agroecosystems including these crops to protect water quality, enhance wildlife habitat, build soil quality, and sequester soil carbon. However, genetic improvement of perennial grain candidates has been hindered by limited investment due to uncertainty about whether the approach is viable. As efforts to develop perennial grain crops have expanded in past decades, critiques of the approach have arisen. With a recent report of perennial rice producing yields equivalent to those of annual rice over eight consecutive harvests, many theoretical concerns have been alleviated. Some valid questions remain over the timeline for new crop development, but we argue these may be mitigated by implementation of recent technological advances in crop breeding and genetics such as low-cost genotyping, genomic selection, and genome editing. With aggressive research investment in the development of new perennial grain crops, they can be developed and deployed to provide atmospheric greenhouse gas reductions.

Environmental impacts on water resources from summer crops in rainfed and irrigated systems.

Irrigation is an intensification technology to increase productivity in agricultural systems, but the impacts of irrigation on the environmental performance of crops are not well understood. We evaluated impacts on water use and quality of rainfed and irrigated systems for corn and soybean production in temperate South America using nonparametric ANOVA tests for small sample sizes. We modeled blue water footprint, ecotoxicity, N and P balance, and eutrophication potential for six farms producing corn and soybean in rainfed and irrigated systems in Uruguay. Crop yields were 5948 and 7862 kg ha-1 for corn and 2482 and 3423 kg ha-1 for soybean, under rainfed and irrigation, respectively. The average blue water footprint for irrigated systems was 264 m3 ton-1 and zero for rainfed systems, with no difference between corn and soybean. The ecotoxicity was greater for soybean than for corn (1679 vs 325 CTUe kg-1) but there were no statistically significant differences in ecotoxicity between rainfed and irrigated systems. Based on Usetox methodology, insecticides had a greater ecotoxic effect (3.2 × 106 CTUe ha-1) than herbicides (7.3 × 104 CTUe ha-1), despite the lower doses applied (insecticides: 0.51 kg ha-1; herbicides: 6.83 kg ha-1). The aquatic eutrophication potential (based on Impact 2002 + methodology) among rainfed and irrigated systems presented no differences (29 vs 24 kgPO4-eq ha-1 for corn and 19 vs 27 kgPO4-eq ha-1 for soybean). The standardized environmental impacts for corn calculated per ha were similar than those per kg of grain when comparing rainfed vs irrigated systems. For soybean, however, standardized environmental impacts per ha were greater in the irrigated than in the rainfed systems, but were similar per kg of grain (except for water footprint). In summary, irrigation resulted in higher productivity and increased blue water footprint than rainfed, but in the set of farms analyzed it did not significantly increase inputs use, so no differences were detected in nutrient balance, eutrophication potential, or ecotoxicity. Soybeans had greater environmental impacts than corn in ecotoxicity and N excess per unit of area, but no statistically significant difference was found in the other indicators. These indicators may be useful as a predictive tool for resource management. Decision makers should consider the trade-offs between productivity, water use, and water quality when using irrigation for intensification of crop production.

Sustainability of meat production beyond carbon footprint: a synthesis of case studies from grazing systems in Uruguay.

Livestock production has been challenged as a large contributor to climate change, and carbon footprint has become a widely used measure of cattle environmental impact. This analysis of fifteen beef grazing systems in Uruguay quantifies the range of variation of carbon footprint, and the trade-offs with other relevant environmental variables, using a partial life cycle assessment (LCA) methodology. Using carbon footprint as the primary environmental indicator has several limitations: different metrics (GWP vs. GTP) may lead to different conclusions, carbon sequestration from soils may drastically affect the results, and systems with lower carbon footprint may have higher energy use, soil erosion, nutrient imbalance, pesticide ecotoxicity, and impact on biodiversity. A multidimensional assessment of sustainability of meat production is therefore needed to inform decision makers. There is great potential to improve grazing livestock systems productivity while reducing carbon footprint and other environmental impacts, and conserving biodiversity.