ALBERT

Description: The tank cascade system (TCS) has been used for over 2000 years for water management in Sri Lanka. Since surface water is limited in the dry zone of Sri Lanka, agricultural production, especially of upland crops, relies on groundwater for irrigation. We sampled 29 wells in the Ulagalla cascade, a prominent TCS near Anuradhapura city in the dry zone of Sri Lanka, in Yala (dry) and Maha (wet) seasons, the two main cropping seasons in Sri Lanka. We evaluated the suitability of groundwater for irrigation using the analytic hierarchy process and geographical information system. Water quality did not vary notably between seasons. However, it deteriorated with the onset of high intensity heavy rain, especially during the Maha season. A water quality zoning map indicated that groundwater in 4% and 96% of the study area is suitable and moderately suitable for irrigation, respectively. Irrigation water quality in tank cascade landscapes and similar environments can be assessed using this methodology and our results.

Description: Rainfed agriculture constitutes around 80% of the world’s agricultural land, achieving the lowest on-farm crop yields and greatest on-farm water losses. Much of this land is in developing countries, including sub-Saharan Africa (SSA), where hunger is chronic. The primary constraint of rainfed agriculture—frequently experienced in SSA—is water scarcity, heightened by the unpredictability of season onset, erratic rainfall, as well as the inability of farmers to provide adequate soil and crop management. Farmers react differently to constraints, making a variety of choices—including the timing of planting, type of land cultivation, fertilization, and scattered fields, among many others. Limited information is available on the combined effects of these strategies for improving crop yield and water use efficiency (WUE). An experiment was co-conducted with farmers over four consecutive rainy seasons (2014–2018) in Tanzania, to evaluate these strategies for single and joint effects in improving yield and WUE on rainfed pearl millet (Pennisetum glaucum (L.) R.Br.). The treatments used were flat cultivation both without and with microdosing, as well as tied ridging without and with microdose interaction, with different planting dates depending on farmers’ decisions. Results show that farmers react differently to the early, normal, or late onset of the rainy season, and cumulative rainfall during its onset, which affects their decisions regarding planting dates, yield, and WUE. Microdose fertilization increases both the yield and WUE of pearl millet significantly, with greater effects obtained using tied ridging compared to flat cultivation. For low-income smallholder farmers in a semi-arid agroclimate, using tied ridging with microdosing during early planting is an effective response to spatiotemporal rainfall variability and poor soils.

Description: Nitrogen (N) in soybean (Glycine max L.) plants derived from biological nitrogen fixation was shown to be a sustainable N resource to substitute for N fertilizer. However, the limited water supply in sandy soil is a critical factor for soybean nodulation and crop growth. This study investigated the potential mechanism of the effect of biochar and irrigation on the soybean-Rhizobium symbiotic performance and soil biological activity in a field trial. In the absence of N fertilizer, 10 t ha−1 of black cherry wood-derived biochar were applied under irrigated and rainfed conditions on an experimental, sandy field site. The plant biomass, plant nutrient concentrations, nodule number, nodule leghemoglobin content, soil enzyme activities, and soil-available nutrients were examined. Our results show that biochar application caused a significant increase in the nodule number by 35% in the irrigated condition. Shoot biomass and soil fluorescein diacetate hydrolytic activity were significantly increased by irrigation in comparison to the rainfed condition. The activity of soil protease reduced significantly, by 8%, with the biochar application in the irrigated condition. Further, a linear correlation analysis and redundancy analysis performed on the plant, nodule, and soil variables suggested that the biochar application may affect soybean N uptake in the sandy field. Nodulation was enhanced with biochar addition, however, the plant N concentration and nodule Lb content remained unaffected.

Description: Weed suppression is a potential benefit of cover crop mixtures, as species diversity may allow for combining early and late-season competition with weeds. Here, we studied if this is possible for only-legume mixtures containing species with different growth rates, by testing two legumes, alsike clover (AC; Trifolium hybridum L.) and black medic (BM; Medicago lupulina L.) in two field trials sown in 2016 and 2017. Five AC:BM ratios (100:0, 67:33, 50:50, 33:67, and 0:100) were grown at three densities (50%, 100%, and 150% of recommended seed density). Cover crop and weed aboveground biomass (CCB and WB, respectively) were harvested three times, after establishment in spring (H1), in summer (H2), and in autumn after mulching (H3). Compared to fallow plots, all monocultures and mixtures showed early-season weed suppression in terms of biomass production and more efficiency over time with an average reduction of 42%, 52%, and 96% in 2016, and 39%, 55%, and 89% in 2017 at H1, H2, and H3, respectively. Out of 54 mixture treatments, only eight mixtures showed stronger weed suppression than monocultures. Mixtures reduced WB by 28%, as an average value, in 2017 compared to the respective monocultures, but not significantly in 2016, indicating that the crop diversity effect on weeds was dependent on the growing environment. Weed suppression was significantly higher at 100% and 150% seed density than 50%, but no significant differences were determined between 100% and 150% seed density. After mulching, no density effect was observed on CCB and WB. In conclusion, AC and BM can be used as a keystone species on weed suppression for sustainable agriculture as they possess plasticity to suppress weeds when higher biomass productivity is limited by environmental conditions. However, their diversity effects are time and condition dependent. Appropriate seed density and mulching can successfully be employed in weed management, but seed density may not have an effect after mulching.

Description: Rainfed agriculture constitutes around 80% of the world’s agricultural land, achieving the lowest on-farm crop yields and greatest on-farm water losses. Much of this land is in developing countries, including sub-Saharan Africa (SSA), where hunger is chronic. The primary constraint of rainfed agriculture—frequently experienced in SSA—is water scarcity, heightened by the unpredictability of season onset, erratic rainfall, as well as the inability of farmers to provide adequate soil and crop management. Farmers react differently to constraints, making a variety of choices—including the timing of planting, type of land cultivation, fertilization, and scattered fields, among many others. Limited information is available on the combined effects of these strategies for improving crop yield and water use efficiency (WUE). An experiment was co-conducted with farmers over four consecutive rainy seasons (2014–2018) in Tanzania, to evaluate these strategies for single and joint effects in improving yield and WUE on rainfed pearl millet (Pennisetum glaucum (L.) R.Br.). The treatments used were flat cultivation both without and with microdosing, as well as tied ridging without and with microdose interaction, with different planting dates depending on farmers’ decisions. Results show that farmers react differently to the early, normal, or late onset of the rainy season, and cumulative rainfall during its onset, which affects their decisions regarding planting dates, yield, and WUE. Microdose fertilization increases both the yield and WUE of pearl millet significantly, with greater effects obtained using tied ridging compared to flat cultivation. For low-income smallholder farmers in a semi-arid agroclimate, using tied ridging with microdosing during early planting is an effective response to spatiotemporal rainfall variability and poor soils.

Description: Weed suppression is a potential benefit of cover crop mixtures, as species diversity may allow for combining early and late-season competition with weeds. Here, we studied if this is possible for only-legume mixtures containing species with different growth rates, by testing two legumes, alsike clover (AC; Trifolium hybridum L.) and black medic (BM; Medicago lupulina L.) in two field trials sown in 2016 and 2017. Five AC:BM ratios (100:0, 67:33, 50:50, 33:67, and 0:100) were grown at three densities (50%, 100%, and 150% of recommended seed density). Cover crop and weed aboveground biomass (CCB and WB, respectively) were harvested three times, after establishment in spring (H1), in summer (H2), and in autumn after mulching (H3). Compared to fallow plots, all monocultures and mixtures showed early-season weed suppression in terms of biomass production and more efficiency over time with an average reduction of 42%, 52%, and 96% in 2016, and 39%, 55%, and 89% in 2017 at H1, H2, and H3, respectively. Out of 54 mixture treatments, only eight mixtures showed stronger weed suppression than monocultures. Mixtures reduced WB by 28%, as an average value, in 2017 compared to the respective monocultures, but not significantly in 2016, indicating that the crop diversity effect on weeds was dependent on the growing environment. Weed suppression was significantly higher at 100% and 150% seed density than 50%, but no significant differences were determined between 100% and 150% seed density. After mulching, no density effect was observed on CCB and WB. In conclusion, AC and BM can be used as a keystone species on weed suppression for sustainable agriculture as they possess plasticity to suppress weeds when higher biomass productivity is limited by environmental conditions. However, their diversity effects are time and condition dependent. Appropriate seed density and mulching can successfully be employed in weed management, but seed density may not have an effect after mulching.

Description: Nitrogen (N) in soybean (Glycine max L.) plants derived from biological nitrogen fixation was shown to be a sustainable N resource to substitute for N fertilizer. However, the limited water supply in sandy soil is a critical factor for soybean nodulation and crop growth. This study investigated the potential mechanism of the effect of biochar and irrigation on the soybean-Rhizobium symbiotic performance and soil biological activity in a field trial. In the absence of N fertilizer, 10 t ha−1 of black cherry wood-derived biochar were applied under irrigated and rainfed conditions on an experimental, sandy field site. The plant biomass, plant nutrient concentrations, nodule number, nodule leghemoglobin content, soil enzyme activities, and soil-available nutrients were examined. Our results show that biochar application caused a significant increase in the nodule number by 35% in the irrigated condition. Shoot biomass and soil fluorescein diacetate hydrolytic activity were significantly increased by irrigation in comparison to the rainfed condition. The activity of soil protease reduced significantly, by 8%, with the biochar application in the irrigated condition. Further, a linear correlation analysis and redundancy analysis performed on the plant, nodule, and soil variables suggested that the biochar application may affect soybean N uptake in the sandy field. Nodulation was enhanced with biochar addition, however, the plant N concentration and nodule Lb content remained unaffected.

Description: The tank cascade system (TCS) has been used for over 2000 years for water management in Sri Lanka. Since surface water is limited in the dry zone of Sri Lanka, agricultural production, especially of upland crops, relies on groundwater for irrigation. We sampled 29 wells in the Ulagalla cascade, a prominent TCS near Anuradhapura city in the dry zone of Sri Lanka, in Yala (dry) and Maha (wet) seasons, the two main cropping seasons in Sri Lanka. We evaluated the suitability of groundwater for irrigation using the analytic hierarchy process and geographical information system. Water quality did not vary notably between seasons. However, it deteriorated with the onset of high intensity heavy rain, especially during the Maha season. A water quality zoning map indicated that groundwater in 4% and 96% of the study area is suitable and moderately suitable for irrigation, respectively. Irrigation water quality in tank cascade landscapes and similar environments can be assessed using this methodology and our results.