• Energy Research

<p>Water scarcity is a major limiting factor for crop production by irrigation in sub-Saharan countries. Improved irrigation scheduling that can ensure the optimal use of the allocated water and enhance water productivity (WP) is required to address future water scarcity in the region. Maximizing WP by exposing the crop to a certain level of water stress using deficit irrigation (DI) is considered a promising strategy. To adopt DI strategies, a shred of comprehensive evidence concerning DI for different crops is required. This review aims to provide adequate information about the effect of DI on WP. We reviewed 90 research papers from Ethiopia and summarize the effect of DI on WP and yield. It is shown that DI considerably increased WP compared to full irrigation. Despite higher WP, reduced biomass yield was obtained in some of the studied DI practices compared to full irrigation. It was also found that yield reduction may be low compared to the benefits gained by diverting the saved water to irrigate extra arable land. From this review, we understood that growers must recognize specific soil management and crops before applying DI strategies. Maize revealed the highest (2.65 kg m<sup>-3</sup>) and lowest (0.50 kg m<sup>-3</sup>) WP when irrigated at only the initial stage compared with being fully irrigated in all growth stages, respectively. Also, onion showed a decreasing WP with increased irrigation water from 60% crop water requirement (ETc) (1.84 kg m<sup>-3</sup>) to 100% ETc (1.34 kg m<sup>-3</sup>). Increasing water deficit from 100 to 30% ETc led to an increase of wheat WP by 72.2%. For tomato, the highest WP (7.02 kg m<sup>-3</sup>) was found at 70% ETc followed by 50% ETc (6.98 kg m<sup>-3</sup>) and 85% ETc (6.92 kg m<sup>-3</sup>), while the water application of 100% ETc (or full irrigation) showed the least WP (6.79 kg m<sup>-3</sup>). Teff showed the lowest WP (1.72 kg m<sup>-3</sup>) under optimal irrigation, while it was highest (2.96 kg m<sup>-3</sup>) under 75% ETc throughout the growing season. The regression analysis (R<sup>2</sup>) for WP increment and yield reduction versus saved water showed higher values, indicating that DI could be an option for WP increment and increasing overall yield by expanding irrigated area and applying the saved water in water-scarce regions. In conclusion, in areas where drought stress is the limiting factor for crop production, the application of DI is feasible.</p><p> </p><p> </p><p> </p><p>Keywords: Overall yield increase, water productivity, water saved, yield reduction</p>

<p>Water scarcity is a major limiting factor for crop production by irrigation in sub-Saharan countries. Improved irrigation scheduling that can ensure the optimal use of the allocated water and enhance water productivity (WP) is required to address future water scarcity in the region. Maximizing WP by exposing the crop to a certain level of water stress using deficit irrigation (DI) is considered a promising strategy. To adopt DI strategies, a shred of comprehensive evidence concerning DI for different crops is required. This review aims to provide adequate information about the effect of DI on WP. We reviewed 90 research papers from Ethiopia and summarize the effect of DI on WP and yield. It is shown that DI considerably increased WP compared to full irrigation. Despite higher WP, reduced biomass yield was obtained in some of the studied DI practices compared to full irrigation. It was also found that yield reduction may be low compared to the benefits gained by diverting the saved water to irrigate extra arable land. From this review, we understood that growers must recognize specific soil management and crops before applying DI strategies. Maize revealed the highest (2.65 kg m<sup>-3</sup>) and lowest (0.50 kg m<sup>-3</sup>) WP when irrigated at only the initial stage compared with being fully irrigated in all growth stages, respectively. Also, onion showed a decreasing WP with increased irrigation water from 60% crop water requirement (ETc) (1.84 kg m<sup>-3</sup>) to 100% ETc (1.34 kg m<sup>-3</sup>). Increasing water deficit from 100 to 30% ETc led to an increase of wheat WP by 72.2%. For tomato, the highest WP (7.02 kg m<sup>-3</sup>) was found at 70% ETc followed by 50% ETc (6.98 kg m<sup>-3</sup>) and 85% ETc (6.92 kg m<sup>-3</sup>), while the water application of 100% ETc (or full irrigation) showed the least WP (6.79 kg m<sup>-3</sup>). Teff showed the lowest WP (1.72 kg m<sup>-3</sup>) under optimal irrigation, while it was highest (2.96 kg m<sup>-3</sup>) under 75% ETc throughout the growing season. The regression analysis (R<sup>2</sup>) for WP increment and yield reduction versus saved water showed higher values, indicating that DI could be an option for WP increment and increasing overall yield by expanding irrigated area and applying the saved water in water-scarce regions. In conclusion, in areas where drought stress is the limiting factor for crop production, the application of DI is feasible.</p><p> </p><p> </p><p> </p><p>Keywords: Overall yield increase, water productivity, water saved, yield reduction</p>

Society calls for protection of agricultural soils in order to sustain the production of foods for a growing population. Compaction of subsoil layers is an increasing problem in modern agriculture and a cause of serious concern because of the poor resilience in natural amelioration. The concept of soil precompression stress has been adapted from civil engineering, although in soil science it is applied to unsaturated soils that have developed a secondary structure from the action of weather, biota and tillage. It assumes strain is elastic at loads up to the precompression stress, while plastic deformation is expected at higher stresses. To determine this threshold we performed uniaxial, confined compression tests for a total of 584 minimally disturbed soil cores sampled at three subsoil layers on nine Danish soils ranging in clay content from 0.02 to 0.38 kg kg−1. The cores were drained to either of three matric potentials (−50, −100 or − 300 hPa) prior to loading. Stress was applied by a constant-strain rate method. We estimated the point of maximum curvature of the strain-log10(normal stress) relation by a numerical procedure. This point is considered here as a compactive stress threshold, typically labeled the soil precompression stress, σpc. The preload suction stress (PSS) was calculated as the product of initial (i.e., before loading) water suction and initial degree of pore water saturation. Multiple regressions were performed to evaluate the effect of soil properties (textural classes, volumetric water content, bulk density (BD), soil organic matter (SOM), and PSS) on σpc. The best model explained 39% of the variation in σpc, and indicated that σpc increases with increasing PSS, BD and SOM. For a given combination of clay, BD and SOM, PSS affected σpc negatively. We recommend our regression model for use in risk assessment tools for estimating sustainable traffic on agricultural soils. The model was validated by five independent data sets from the literature. Our study shows that caution should be applied when regarding σpc as a fixed threshold for compressive strength. We hypothesize that plastic deformation is initiated over a range of stress rather than at a distinctive single value. Further studies are needed to better understand—and potentially quantify—to what extent the predicted σpc can be regarded a central estimate of allowable stress for a given soil.

Society calls for protection of agricultural soils in order to sustain the production of foods for a growing population. Compaction of subsoil layers is an increasing problem in modern agriculture and a cause of serious concern because of the poor resilience in natural amelioration. The concept of soil precompression stress has been adapted from civil engineering, although in soil science it is applied to unsaturated soils that have developed a secondary structure from the action of weather, biota and tillage. It assumes strain is elastic at loads up to the precompression stress, while plastic deformation is expected at higher stresses. To determine this threshold we performed uniaxial, confined compression tests for a total of 584 minimally disturbed soil cores sampled at three subsoil layers on nine Danish soils ranging in clay content from 0.02 to 0.38 kg kg−1. The cores were drained to either of three matric potentials (−50, −100 or − 300 hPa) prior to loading. Stress was applied by a constant-strain rate method. We estimated the point of maximum curvature of the strain-log10(normal stress) relation by a numerical procedure. This point is considered here as a compactive stress threshold, typically labeled the soil precompression stress, σpc. The preload suction stress (PSS) was calculated as the product of initial (i.e., before loading) water suction and initial degree of pore water saturation. Multiple regressions were performed to evaluate the effect of soil properties (textural classes, volumetric water content, bulk density (BD), soil organic matter (SOM), and PSS) on σpc. The best model explained 39% of the variation in σpc, and indicated that σpc increases with increasing PSS, BD and SOM. For a given combination of clay, BD and SOM, PSS affected σpc negatively. We recommend our regression model for use in risk assessment tools for estimating sustainable traffic on agricultural soils. The model was validated by five independent data sets from the literature. Our study shows that caution should be applied when regarding σpc as a fixed threshold for compressive strength. We hypothesize that plastic deformation is initiated over a range of stress rather than at a distinctive single value. Further studies are needed to better understand—and potentially quantify—to what extent the predicted σpc can be regarded a central estimate of allowable stress for a given soil.

Abstract Windbreaks are key structural elements in the rural environment and affect the functionality of landscapes in multiple ways. A broad interdisciplinary view on these functions lacks in scientific literature and common knowledge. This led to under informed management decisions, a decrease in the number of windbreaks in wide areas, and a subsequent loss of landscape functionality. Therefore, the knowledge on windbreaks and associated ecosystem services (ES) was systematically reviewed to guide the way for a holistic comprehension of such structural landscape elements. We defined eight bundles of ES on the basis of the Common International Classification of ES scheme. Search terms that allowed to include only vegetative windbreaks consisting of at least one tree row were combined with appropriate search terms for the eight ES bundles in individual searches resulting in a total of 6094 hits. We considered only publications that provided quantitative data and allowed to derive a clear effect of windbreaks on ES so that 222 publications from all over the world were quantitatively and qualitatively analyzed. The outcomes provide information about the dimension of effort, scientific consensus or dissensus, and knowledge gaps in the different research disciplines involved. It was shown that windbreaks bring predominantly positive effects to landscapes in the course of all investigated ES bundles. Apparent positive effects were found for soil protection, biodiversity and pest control, whereas for biomass production, nutrient and water balance, also adverse or indifferent effects were reported. The present review reveals an intense need for further interdisciplinary research using indicators, ES approaches or similar instruments that enable quantitative and comparable statements about the functionality of windbreaks in rural landscapes.

Abstract Windbreaks are key structural elements in the rural environment and affect the functionality of landscapes in multiple ways. A broad interdisciplinary view on these functions lacks in scientific literature and common knowledge. This led to under informed management decisions, a decrease in the number of windbreaks in wide areas, and a subsequent loss of landscape functionality. Therefore, the knowledge on windbreaks and associated ecosystem services (ES) was systematically reviewed to guide the way for a holistic comprehension of such structural landscape elements. We defined eight bundles of ES on the basis of the Common International Classification of ES scheme. Search terms that allowed to include only vegetative windbreaks consisting of at least one tree row were combined with appropriate search terms for the eight ES bundles in individual searches resulting in a total of 6094 hits. We considered only publications that provided quantitative data and allowed to derive a clear effect of windbreaks on ES so that 222 publications from all over the world were quantitatively and qualitatively analyzed. The outcomes provide information about the dimension of effort, scientific consensus or dissensus, and knowledge gaps in the different research disciplines involved. It was shown that windbreaks bring predominantly positive effects to landscapes in the course of all investigated ES bundles. Apparent positive effects were found for soil protection, biodiversity and pest control, whereas for biomass production, nutrient and water balance, also adverse or indifferent effects were reported. The present review reveals an intense need for further interdisciplinary research using indicators, ES approaches or similar instruments that enable quantitative and comparable statements about the functionality of windbreaks in rural landscapes.

In the Ethiopian Upper Blue Nile Basin, like in other regions in the world, agricultural productivity is declining due to water scarcity owing to longer dry seasons coupled with soil acidity-induced fertility problems. Wheat is one of the major food security crops in Ethiopia but its productivity is reduced due to water scarcity, especially during the irrigation season. Addressing these problems might be essential to increase productivity. This study explores the effect of deficit irrigation (DI) combined with lime, manure and inorganic fertilizer on wheat production and water productivity (WP) in the Koga irrigation scheme, Ethiopia. Four levels of DI strategies (100% ETc or 0% deficit as a control, 80%, 60% and 50% ETc) were applied for two irrigated seasons. Five levels of soil fertility management were applied for four consecutive cropping seasons: (i) 0.86 t ha- 1 lime combined with 3 t ha- 1 manure and full dose urea and NPS-B (hereafter referred to as inorganic fertilizer) (L3); (ii) 1.15 t ha- 1 lime combined with 3 t ha- 1 manure and full-dose inorganic fertilizer (L2); (iii) 1.43 t ha- 1 lime combined with 3 t ha- 1 manure and full dose inorganic fertilizer (L1); (iv) 3 t ha- 1 manure combined with full dose inorganic fertilizer (M); and (v) full dose inorganic fertilizer alone (C). The grain yield and biomass data were collected at harvest from a sample area of 2 m x 3 m from each plot with three replicates. The effect of DI and liming, as well as manuring on average grain yield and biomass, were highly significant. Under all irrigation scenarios, higher grain yield and biomass were found at L1, L2, L3 and M (in that order), compared with C. The highest WP was obtained at 50% ETc irrigation dose, compared with 60%, 80% and 100% ETc (in that order). Yet, the lowest WP was found at C under all irrigation scenarios compared with L1, L2, L3 and M. The WP increased when the amount of water supply decreased and liming doses increased. The application of full dose lime and manure combined with 50% ETc DI resulted in comparable grain yield, biomass and WP as 100% ETc full irrigation at L3 and M. It could be concluded that liming and manuring could be used to mitigate the yield penalty effect of DI in the study area. In scenarios where farmers have to pay for water, profitability rises as the irrigation water supply reduces. Thus, under such conditions, a 50% ETc irrigation scenario is more profitable than scenarios with 60%, 80% and 100% ETc irrigation.