Adoption of supplemental irrigation as a practice in Puerto Rico will be slow, Because irrigation is thought to be needed only occasionally, farmers look at it as an uneconomical operation. Even in the agricultural policy, supplemental irrigation is treated lightly, with limited funds allocated for research in this area.

With a growing world population, estimated to 9.6 billion in 2050, the world food demand is estimated to increase with 45-50 %. One way to meet the demand is to increase the areal yield from the agricultural sector, where rain-fed agriculture has the highest potential. 95 % of the agriculture in Sub-Saharan Africa is rain-fed and the same region is predicted to holds the largest share of poor people in 2015. Since 40-70 % of the rural households highly depend of on-farm sources, investments to increase the agriculture productivity target both the poverty alleviation in the region as well as the world’s food security. By a tripartite methodology, this study analyzed the use of small-scale rain water harvesting (RWH) ponds for supplemental irrigation (SI) of cereals to reduce the inter-annual variability and to increase the areal yield in semi-arid areas in Ethiopia. A physically based simulation model (CoupModel) considering the plant-soil-atmosphere system was used to study how a C4-plant responded to different irrigation scenarios with 30 years climate data (1980-2009) from six regions in Ethiopia. Moreover, two years field data with maize yield from Triple Green project’s experimental fields in Ethiopia was used to analyze the correlation between SI and yield. Finally, ten farmers that used RWH ponds for SI of cereals within Triple Green project were interviewed to find out their perception of the RWH and SI. The model results showed that irrigation almost eliminated the inter-annual variability and increased the areal yield for all the climates. SI was most efficiently used in areas with more than 900 mm precipitation/year were the two annual rain periods could be bridged to create a prolonged growth season (>180 days). The mean annual irrigation water demand was estimated to 224 mm distributed over 7 irrigation events. The field results showed a moderate but significant 10 % increase of the areal yield with SI. None of the farmers wanted to use the RWH for SI of cereals, instead they wanted to use it to water their livestock, grow cash crop seedlings and fruit trees. If the future world food demand is to be targeted, the study suggests societal investments to build infrastructure to collect, store and distribute water for irrigation.

<p>Drainage water recycling (DWR) is the practice of capturing, storing, and reusing subsurface drained agricultural water to support supplemental irrigation and has recently been proposed as a practice for improving the crop production and water quality performance in the tile-drained landscape of the U.S. Midwest. This study describes the development of a modeling framework to quantify the potential irrigation and water quality benefits of DWR systems in tile-drained landscapes and the application of the model using ten years of measured weather, tile drain flow and nutrient concentrations, water table, and soil data from two sites in the U.S. Midwest. From this modeling framework, the development and testing of an open-source online tool is also presented.</p><p></p><p>A spreadsheet model was developed to track water flows between a reservoir and drained and irrigated field area at each site. The amount of tile drain flow and associated nutrient loads that could be captured from the field and stored in the reservoir was estimated to calculate the potential water quality benefits of the system. Irrigation benefits were quantified based on the amount of applied irrigation annually. A reservoir size representing 6% to 8% of the field area with an average depth of 3.05 m was sufficient in meeting the annual irrigation requirements during the 10-year period at each site. At this reservoir size, average annual nitrate-N loads were reduced by 20% to 40% and soluble reactive phosphorus loads by 17% to 41%. Variability in precipitation within and across years, and differences in soil water characteristics, resulted in a wide range of potential benefits at the two sites.</p><p>An online tool was developed from the model, and a variance-based global sensitivity analysis was conducted to determine influential and low-sensitivity input parameters. The input parameter, depth of root zone, was the most influential input parameter suggesting that the estimation of total available water for the field water balance is a critical component of the model. Input settings describing the irrigation management and crop coefficients for the initial establishment and mid-season crop growth periods were also influential in impacting the field water balance. Reservoir seepage rate was influential in regard to the reservoir water balance, particularly at larger reservoir sizes. Sensitivity analysis results were used to develop a user-interface for the tool, Evaluating Drainage Water Recycling Decisions (EDWRD).</p><p>This study shows that DWR is capable of providing both irrigation and water quality benefits in the tile-drained landscape of the U.S. Midwest. The developed modeling framework supports future research on the development of strategies to implement and manage DWR systems, and the online tool serves as a resource for users to increase their awareness and understanding of the potential benefits of this novel practice.</p><p></p>