Combining Rainwater Harvesting and Grass Reseeding to Revegetate Denuded African Semi-arid Landscapes

In African drylands, perennial grasses preferred by grazing livestock are disappearing at an alarming rate. This has led to recurrent livestock feed shortages threatening pastoralist’s livelihoods. Combining native grass reseeding and rainwater harvesting offers a viable and innovative solution to reverse this trend. However, studies to determine how biomass yields are affected by soil moisture availability attributed to in situ rainwater harvesting in African drylands are limited. We investigated how biomass yields of three grasses native to Africa, i.e., Enteropogon macrostachyus (Bush rye grass), Cenchrus ciliaris (African foxtail grass), and Eragrostis superba (Maasai love grass), are affected by soil moisture content in a typical semi-arid landscape. Rainwater harvesting structures included trenches, micro-catchments and furrows. Additionally, rain runoff was diverted from an adjacent road used as a catchment area. Soil moisture was measured between November 2018 and August 2019 using PlantCare Mini-Logger sensors installed at 40 and 50 cm depths and 0, 1, 5 and 15 m away from the trench. Quadrat method was used to determine biomass yields in August 2019. Peaks in soil moisture were observed after rainfall events. Soil moisture content gradually decreased after the rainy season, but was higher closer to the trench. This is attributed to the prolonged rainwater retention in the trenches. Biomass yields were in the order Eragrostis superba > Cenchrus ciliaris > Enteropogon macrostachyus. Biomass production was higher near the trenches for all the studied species. Sensitivity to soil moisture demonstrated by the magnitude to yield reduction during the growing season was in the order Eragrostis superba > Cenchrus ciliaris > Enteropogon macrostachyus. These results suggest that Eragrostis superba is more sensitive to drought stress than Enteropogon macrostachyus that is adapted to a wide range of soil moisture conditions. We demonstrated that in situ rainwater harvesting structures enhanced soil moisture availability and displayed great potential for revegetating denuded natural rangelands in semi-arid African landscapes. Thus, combining rainwater harvesting and reseeding techniques can produce measurable improvements in pastoral livelihoods and should be incorporated in dryland development policies in the region. Ultimately, incorporating such innovative strategies can strengthen the effectiveness of ecological restoration in African drylands to meet the objectives of the UN Decade on Ecosystem Restoration and achieving the UN Sustainable Development Goals. Graphical abstract

Effect of Soil Moisture Regimes on the Glyphosate Sensitivity and Morpho-Physiological Traits of Windmill Grass (Chloris truncata R.Br.), Common Sowthistle (Sonchus oleraceus L.), and Flaxleaf Fleabane [Conyza bonariensis (L.) Cronq.]

The glasshouse study was conducted with the objectives of (i) investigating the effect of soil moisture variations on the control efficiency of glyphosate on windmill grass (Chloris truncata R.Br.), common sowthistle (Sonchus oleraceus L.), and flaxleaf fleabane [Conyza bonariensis (L.) Cronq.], (ii) evaluating the tolerance of tested weed species under soil moisture variations, and (iii) determining the morphological and physiological characteristics of these species to partially explain herbicide tolerance under periods of reduced soil moisture availability (RSM). The species’ tolerance to glyphosate increased significantly under reduced soil moisture availability (p < 0.001). The lethal dose to cause herbicide injury or biomass reduction by 50% (LD50) and 80% (LD80) in relation to untreated control for water-stressed plants [i.e., moderate soil moisture availability (MSM) and RSM] was significantly higher than that of plants grown under high soil moisture availability (HSM). The tolerance factor (TF) for C. truncata, S. oleraceus, and C. bonariensis, in terms of biomass reduction under RSM, was 2.6, 2.4, and 2.6, respectively, as compared to HSM. The results showed that the glyphosate sensitivity, especially at the sub-lethal rates, of the three weed species under study decreased as soil moisture availability reduced (p < 0.01). Overall glyphosate efficacy, in relation to the recommended rate, was unaffected, except for C. truncata; the weed survived the highest tested glyphosate rate [750 g active ingredient (a.i.) ha−1] under RSM. There was significant interaction between weed species and soil moisture regimes for weed morpho-physiological traits (p < 0.001), with reduced soil moisture having a more influential impact on the growth of C. bonariensis and S. oleraceus compared to C. truncata. Changes in the leaf characteristics, such as increased leaf thickness, higher leaf chlorophyll content, reduced leaf area, and limited stomatal activity for all the tested weed species under MSM and RSM in relation to HSM, partially explain the tolerance of species to glyphosate at sublethal rates.

Transcriptome Analysis Revealed Plant Hormone Biosynthesis and Response Pathway Modification by Epichloë gansuensis in Achnatherum inebrians under Different Soil Moisture Availability

The present study was designed to explore the effects of the endophyte Epichloë gansuensis on gene expression related to plant hormone biosynthesis and response pathways and the content of salicylic acid (SA) and jasmonic acid (JA) hormones of Achnatherum inebrians, under different moisture conditions. Through a pot experiment and transcriptome analysis, we found a total of 51 differentially expressed genes (DEGs) related to hormone biosynthesis and response pathways, including 12 auxin related genes, 8 cytokinin (CTK) related genes, 3 gibberellin (GA) related genes, 7 abscisic acid (ABA) related genes, 7 ethylene (ET) related genes, 12 JA related genes and 4 SA related genes. Furthermore, key genes of JA and SA biosynthesis and response pathways, such as LOX2S, AOS, OPR, ACX, JMT, JAZ, PAL, NPR1, TGA and PR-1, showed different degrees of upregulation or downregulation. Under 60% soil moisture content, the JA content of endophyte-free (EF) A. inebrians was significantly (p < 0.05) higher than that of endophyte-infected (EI) A. inebrians. Under 30% and 60% soil moisture content, the SA content of EF A. inebrians was significantly (p < 0.05) higher than that of EI A. inebrians. SA content of EI A. inebrians under 30% and 60% soil moisture content was significantly (p < 0.05) higher than that under 15% soil moisture content. With both EI and EF plants, the SA and JA levels, respectively, are very similar at 15% soil moisture content. This study has revealed that E. gansuensis differentially activated plant hormone synthesis and signal transduction pathways of A. inebrians plants under different soil moisture availability.

Impact of Soil Moisture on Crop Yields in Major Rainfed Growing Regions of Peninsular India

Assessment of soil moisture availability and timely declaration of drought are keys for exemplary relief assistance in water stressed regions. Percent available soil moisture (PASM) is one among several drought declaration indices, needs evaluation with respect to individual crop and cropping system, as the amount of water requirement varies with respect to crop and its growth stage. Analysis of yield variability due to PASM was carried out by employing correlation and linear regression analyses based on long term observations in experiments conducted at different dry farming locations of the peninsular India. The range of available soil moisture in order to obtain at least 50 per cent of optimum yield in cereals (maize: 26 and finger millet: 52.9 PASM), pulses (pigeonpea: 37.2 PASM), oilseeds (soybean: 26.8 to 30.5, groundnut: 53.8 to 61.7 PASM) and commercial crops (cotton: 26.3 PASM) was 26 to 61 per cent. Establishment of these regression models helped in timely drought declaration / precise identification of drought hit areas and assuring feasible relief assistance. The outcomes of the study may be used for amending the existing drought norms (0–50; severe, 50–75; mild and 75–100; no drought) for provision of proportionate compensations to the farmers.

Managing Water Stress by Potassium Fertilizer in Legumes for Sustainable Agricultural Intensification: A Review

Water stress has become the most uncontrolled and unpredictable factor, which is continuously limiting production in crops. Legumes are the major source of protein and are well-recognized for their nutritional benefits as well as their impact on the sustainability of agricultural systems are well known. Leguminous crops are severely affected by water stress causing alterations in various development processes. Proper nutrient management helps in attaining economical legume yields from drought-prone lands. The protective role of potassium in plants suffering from water stress has been documented and it positively influences plant capacity to adjust water stress conditions. This review compromises the information on the water stress-induced harmful effects on legumes growth, nitrogen fixation, gaseous exchange and mineral uptake parameters and proposes appropriate management by potassium application to alleviate the severity of water stres on above mentioned parameters. Application of potassium proved to meet higher yield from legume on cultivation under low/residual soil moisture availability conditions.

Splitting the Difference: Heterogeneous Soil Moisture Availability Affects Aboveground and Belowground Reserve and Mass Allocation in Trembling Aspen

When exploring the impact of resource availability on perennial plants, artificial treatments often apply conditions homogeneously across space and time, even though this rarely reflects conditions in natural systems. To investigate the effects of spatially heterogeneous soil moisture on morphological and physiological responses, trembling aspen (Populus tremuloides) saplings were used in a split-pot experiment. Following the division of the root systems, saplings were established for a full year and then subjected to either heterogeneous (portion of the root system exposed to non-lethal drought) or homogeneous (whole root system exposed to non-lethal drought or well-watered) treatments. Above- and belowground growth and non-structural carbohydrate (NSC) reserves (soluble sugars and starch) were measured to determine how allocation of reserves and mass between and within organs changed in response to variation in soil moisture availability. In contrast to saplings in the homogeneous drought treatment, which experienced reduced shoot growth, leaf abscission and fine root loss, saplings exposed to the heterogeneous conditions maintained similar aboveground growth and increased root system allocation compared to well-watered saplings. Interestingly under heterogeneous soil moisture conditions, the portion of the root system that was resource limited had no root dieback and increased carbon reserve concentrations, while the portion of the root system that was not resource limited added new roots (30% increase). Overall, saplings subjected to the heterogeneous soil moisture regime over-compensated belowground, both in mass and NSC reserves. These results indicate that the differential allocation of mass or reserves between above- and belowground organs, but also within the root system can occur. While the mechanisms and processes involved in these patterns are not clear, these responses could be interpreted as adaptations and acclimations to preserve the integrity of the entire sapling and suggests that different portions of plant organs might respond autonomously to local conditions. This study provides further appreciation of the complexity of the mechanisms by which plants manage heterogeneous conditions and offers evidence that spatial and temporal variability of resource availability, particularly belowground, needs to be accounted for when extrapolating and modeling stress responses at larger temporal and spatial scales.

Integrated Effect of Deficit Irrigation and Sowing Methods on Weed Dynamics and System Productivity of Maize–Cowpea Sequence on Vertisols

The aim of this study was to explore the effect of sowing methods and deficit irrigation on weed dynamics, yield and water-use efficiency (WUE) of the maize–cowpea system during the summer and monsoon seasons, respectively. The field experiment was carried out for two years (2015 and 2016) using a split design with three replicates under irrigated (maize) and rainfed (cowpea) conditions on vertisols of a semi-arid region. Treatments included three sowing methods [i.e., broad bed and furrow (BBF), corrugated furrow (CF) and ridges and furrow (RF)] and four irrigation levels [i.e., irrigation once in 10 days (I10D), irrigation at 40% (I40), at 50% (I50) and at 60% (I60) depletion]. The results indicated that, regardless of weed flora (monocots, dicots and sedges), the RF method produced higher weed density (2.09–2.98 No. m−2) compared to CF (2.00–2.80 No. m−2) and BBF (1.85–2.64 No. m−2) in maize at 30 and 60 days after sowing (DAS). The RF method with irrigation at I40 and I50 recorded significantly higher weed density, followed by the CF and BBF method. A similar trend was also observed with dry weight of weeds (monocot; 24.19%, dicot; 25.52%, and sedges; 29.80%) in maize at 30 and 60 DAS. Higher weed density and dry weight of weeds in the RF method with I40 was due to higher soil moisture availability and higher nutrient uptake due to larger lateral wetting of the soil and greater water use (29.27%). However, the BBF method favoured the growth of weeds (9.33–16.60%) in cowpea at 55 DAS and coped under rain-fed situation over CF and RF. The CF with moderate depletion (I50) method produced significantly higher maize equivalent yield (MEY) of cowpea (10,000 kg ha−1) with considerable reduction in the total water usage (19.33%). Therefore, under a water scarcity situation, growers can practice CF and I50 for higher yield and WUE of maize–cowpea sequence cropping.

Evaluation of Multiple Methods for the Production of Continuous Evapotranspiration Estimates from TIR Remote Sensing

Continuous daily estimates of evapotranspiration (ET) spatially distributed at plot scale are required to monitor the water loss and manage crop irrigation needs. Remote sensing approaches in the thermal infrared (TIR) domain are relevant to assess actual ET and soil moisture status but due to lengthy return intervals and cloud cover, data acquisition is not continuous over time. This study aims to assess the performances of 6 commonly used as well as two new reference quantities including rainfall as an index of soil moisture availability to reconstruct seasonal ET from sparse estimates and as a function of the revisit frequency. In a first step, instantaneous in situ eddy-covariance flux tower data collected over multiple ecosystems and climatic areas were used as a proxy for perfect retrievals on satellite overpass dates. In a second step, instantaneous estimations at the time of satellite overpass were produced using the Soil Plant Atmosphere and Remote Sensing Evapotranspiration (SPARSE) energy balance model in order to evaluate the errors concurrent to the use of an energy balance model simulating the instantaneous IRT products from the local surface temperature. Significant variability in the performances from site to site was observed particularly for long revisit frequencies over 8 days, suggesting that the revisit frequency necessary to achieve accurate estimates of ET via temporal upscaling needs to be fewer than 8 days whatever the reference quantity used. For shorter return interval, small differences among the interpolation techniques and reference quantities were found. At the seasonal scale, very simple methods using reference quantities such as the global radiation or clear sky radiation appeared relevant and robust against long revisit frequencies. For infra-seasonal studies targeting stress detection and irrigation management, taking the amount of precipitation into account seemed necessary, especially to avoid the underestimation of ET over cloudy days during a long period without data acquisitions.