In-field Rainwater Harvesting Research Articles

Investigating the Synergistic Effect of Tillage System and Manure Application Rates on Selected Properties of Two Soil Types in Limpopo Province, South Africa

Sustainable agricultural practices are needed to find a solution to the problem of soil erosion and decreased soil quality. A study was conducted during the 2021/2022 and 2022/2023 cropping seasons to evaluate the synergistic effect of the tillage system (TS) and manure rates (MR) on selected soil properties at the University of Limpopo Experimental Farm (Syferkuil) and University of Venda Experimental Farm (UNIVEN). The experiment had a split plot design with three replications. The main plots used conventional (CON) and in-field rainwater harvesting (IRWH) tillage systems, while subplots used poultry and cattle manure at rates of 0, 20, and 35 t ha−1. Bulk density (BD), aggregate stability (AS), pH, total N, organic carbon (OC), available P, and exchangeable cations (Ca, Mg, and K) were determined. IRWH significantly increased AS in the 0–20 cm soil layer at Syferkuil. TS × MR interaction significantly influenced AS and total N in the 20–40 cm soil layer during the 2022/2023 season at Syferkuil. IRWH significantly increased Mg content in the 2021/2022 season and total N, OC, and Mg content in the 2022/2023 season at Syferkuil over CON. At UNIVEN, CON significantly increased total N, whereas IRWH increased available P in the 2022/2023 season. MR significantly increased AS, exchangeable Ca, Mg, and K at both sites. At Syferkuil, MR significantly increased total N, OC, and available P during both seasons, whereas at UNIVEN the significant increase was observed on OC and available P during both seasons and total N in the 2021/2022 season. It was found that IRWH and poultry manure (35 t ha−1) improved most soil properties at both sites; however, this study recommends long-term experiments to investigate the combined effect of IRWH and manure rate on soil properties to validate the findings observed in this study.

Effect of intercropping maize and sunn hemp at different times and stand densities on soil properties and crop yield under in-field rainwater harvesting (IRWH) tillage in semi-arid South Africa

Abstract Background Evidence suggests that manipulating intercropping timing and stand density within intercropping systems could enhance crop yields. However, our current understanding of the effects of intercropping a cover crop on soil chemical properties and moisture still needs to be improved. This study investigates the effects of intercropping sunn hemp with maize at different timings and stand densities on selected soil properties and crop yield. Materials and methods A split-plot experiment was conducted under the in-field rainwater harvesting (IRWH) tillage. The trial had three intercropping times (simultaneously with maize planting, at V15 maize growth stage, and R1 maize growth stage) as the main plot factors and three stand densities (16, 32, and 48 plants m−2) as the subplot factors, with three replicates for both the 2019/20 and 2020/21 seasons. Changes in soil properties were assessed within the uppermost layer (0-30 cm). Soil moisture content was continuously monitored throughout the growing season and specific soil chemical properties were analyzed at harvest. Results The results showed that the interaction of sunn hemp intercropping period and stand densities did not significantly influence most of the measured soil properties. The early planting of sunn hemp had significantly 32.4% higher soil organic matter (SOM) than the last planting date at low stand density. After two growing seasons SOM, nitrogen, potassium, and manganese were significantly enhanced by 39.7%, 19.0%, 21% and 60.6% respectively. However, during the same period calcium, sodium and iron were significantly reduced by 13.4%, 46.1% and 78.0% respectively. The management of sunn hemp crop had significant effect on maize grain yield across the two seasons. The maize yields in the medium and high stand densities in the first season were significantly 15.3% and 34.3% higher than in the second season, respectively. Conclusion Due to the intercropping treatments, the retention of sunn hemp residues with varying quantities and qualities may have influenced the soil nutrient dynamics in the short-term. Significant changes in soil chemical properties and yield may need more time, and future research should be conducted out in agricultural regions with different soil mineral matrices.

Sunflower Growth and Grain Yield under Different Tillage Systems and Sources of Organic Manure on Contrasting Soil Types in Limpopo Province of South Africa

A field study was conducted to assess the effect of tillage systems (TSs) and manure rates (MRs) on sunflower growth and yield at the University of Limpopo Experimental Farm (Syferkuil) which is on sandy loam soils and University of Venda Experimental Farm (UNIVEN) clayey soils, both located in Limpopo Province of South Africa for 2021/2022 and 2022/2023 cropping seasons. The experimental design was a split plot with three replications. The main plot was the tillage treatments: conventional (CON) and in-field rainwater harvesting (IRWH), while the subplots were the manure treatments: viz. poultry and cattle manures at rates of 20 and 35 t ha−10, plus a control (no manure application). The IRWH is a tillage technique that collects rainwater on a 2 m wide runoff strip into the 1 m wide basin where it infiltrates deep into the soil beyond the evaporation zone but is available for crop use. The results revealed that at Syferkuil IRWH had a significant increase (p < 0.05) on grain yield, head diameter, head dry matter and aboveground dry matter yield in both cropping seasons, whereas at UNIVEN, the significant increase was obtained on grain yield, head diameter, aboveground dry matter, plant height and stem girth during both cropping seasons. The effect of manure rate significantly increased with the application rate, with poultry manure at the highest rate of 35 t ha−1 significantly recording high mean values of grain yield, head diameter, head dry matter, aboveground dry matter, plant height and stem girth at both sites during the two cropping seasons. The increase in leaf area index and 100 seed weight by IRWH and manure rate application varied across the growing stages and cropping seasons with no consistent trend. At Syferkuil, TS and MR interaction was significant on head diameter and on aboveground dry matter at flowering stage in the first cropping season, whereas at UNIVEN, it was significant on head diameter in the first cropping season. Therefore, these results suggest that IRWH combined with poultry manure (35 t ha−1) can be adopted to improve sunflower crop yield under similar management and environmental conditions. In the absence of poultry manure, farmers may opt to use cattle manure at a rate of 35 t ha−1 for better improved yield.

Optimizing the planting time and stand density of sunn hemp intercropping for biomass productivity and competitiveness in a maize-based system

ContextOptimizing cover crop intercropping should aim to be sustainable, economically feasible and environmentally benign. Significant consideration must be given to cover crop plant timing and stand density adjustments to complement the resource demands of the dominant crop, while ensuring optimal biomass yields. ObjectiveThe study assessed a range of intercropping indices to evaluate the influence of different planting times and stand densities of sunn hemp (Crotalaria juncea L.) when intercropped with maize (Zea mays L.). The evaluation focused on interspecies interactions in relation to aboveground biomass production. MethodsA split-plot experiment was conducted using the in-field rainwater harvesting (IRWH) technique. The main plot factors included three intercropping times: simultaneous with maize planting, at the V15 and the R1 maize growth stages. The subplot factors consisted of three stand densities (16, 32 and 48 plants m−2), with three replicates for both the 2019/20 and 2020/21 seasons. Intercropping indices, including land equivalent ratio and coefficient, area time equivalent ratio, land use efficiency, system productivity index, percentage yield difference, relative crowding coefficient, aggressivity, competitive ratio and actual yield loss were employed to assess interspecific interactions and their impact on biomass productivity. ResultsResults show that intercropping sunn hemp at maize planting or the V15 maize growth stage can reduce stand density to 32 plants m−2 without reducing sunn hemp biomass yield. The land equivalent ratio was highest (2.20), with intercropping at the V15 maize growth stage and lowest (2.09) with simultaneous intercropping at maize planting. The relative crowding coefficient was highest (34.4) at the V15 maize growth stage at 32 plants m−2 stand density and lowest (−45.9) with simultaneous intercropping at planting at the same stand density. Intercropping during the R1 maize growth stage influenced competition on sunn hemp with the highest actual yield loss of − 0.07. Competitive ratios were significantly higher for maize (26.19) and sunn hemp (0.16) with R1 and V15 maize growth stage intercropping, respectively. However, sunn hemp's actual yield loss was higher (0.25) with intercropping during the V15 maize growth stage than in sole cropping. ConclusionsIntercropping sunn hemp both simultaneously with maize planting and during the V15 maize growth stage with a stand density of 32 plants m−2 demonstrated enhanced biomass productivity, thereby offering viable intensification choices. The utilization of multiple intercropping indices can contribute to a more comprehensive and precise evaluation of interspecies interactions, consequently leading to improved decision-making.

Planting time and stand density effect on radiation interception and use efficiency of maize and sunn hemp intercropping in semi-arid South Africa

Solar radiation must be efficiently utilised to enhance dry matter accumulation and carbon sequestration capacity within dryland agroecosystems. The study evaluated the effects of sunn hemp (Crotalaria juncea L.) intercropping time and stand density on radiation interception and radiation use efficiency (RUE) in a maize-based system. Field experiments were conducted under the in-field rainwater harvesting (IRWH) technique for two consecutive growing seasons, 2019/20 and 2020/21. Radiation interception and productivity were measured and calculated for maize and sunn hemp, sole and intercrops. The intercrops were identified by the sunn hemp intercropping times [simultaneous with maize planting (P1), at V15 maize growth stage (P2), at R1 maize growth stage (P3)] and stand densities [16 plants m–2 (D1-low), 32 plants m–2 (D2-medium), 48 plants m–2 (D3-high)]. Total radiation interception was calculated using a row-crop radiation transmission (RCRT) model from strip width of component crops, extinction coefficient (k), plant height, and leaf area index (LAI) measurements taken throughout the growing season. The results showed that the LAI of sunn hemp was high when intercrop was planted simultaneous with maize planting and at 48 plants m–2. The overall k for the sole sunn hemp (SSH) cropping system was 0.37. The correlations (r2) between the modelled and measured fractions of photosynthetic active radiation (PAR) in simultaneous maize planting, V15 maize growth stage, and R1 maize growth stage intercropping treatments were 0.87, 0.97 and 0.93, respectively. Simultaneous planting of sunn hemp intercrop with maize captured the most growing season PAR of 798.70 MJ m–2 and had the highest RUE of 1.42 g MJ−1. These results suggest that intercropped sunn hemp planted simultaneously with maize would help to increase production through the more efficient use of solar radiation. Optimising planting time and density can help plan the planting time to increase radiation utilisation in maize/sunn hemp intercropping systems.

In-Field Rainwater Harvesting Tillage in Semi-Arid Ecosystems: I Maize-Bean Intercrop Performance and Productivity.

The purpose of this study was to monitor and compare the growth and productivity of maize/beans sole and inter-cropping systems under conventional (CON) and in-field rainwater harvesting (IRWH) tillage practices. During the typical drought conditions of the 2018/19 growing season, seven homestead gardens of smallholder farmers (four in Paradys and three in Morago villages) in the Thaba Nchu rural communities of South Africa were selected for on-farm demonstration trials. Two tillage systems CON and IRWH as the main plot and three cropping systems as sub-treatment (sole maize and beans and intercropping) were used to measure crop growth and productivity parameters. The results showed that IRWH tillage had significantly higher above-ground dry matter for both sole maize (29%) and intercropped maize (27%) compared to CON treatments. The grain yield under both tillage systems showed that IRWH-Sole >> IRWH-Ic >> CON-Sole >> CON-Ic, with values ranging from 878.2 kg ha-1 to 618 kg ha-1 (p ≤ 0.05). The low harvest index values (0.21-0.38) could have been due to the effect of the drought during the growing season. The results of precipitation use efficiency (PUE) showed that the IRWH tillage was more effective at converting rainwater into maize biomass and grain yield compared to CON tillage. However, the different cropping systems did not show a consistent trend in PUE. During the growing season, the PUE for AGDM varied for different tillage and cropping system treatments in Morago and Paradys. For maize, it ranged between 10.01-6.07 and 9.93-7.67 kg ha-1, while for beans, it ranged between 7.36-3.95 and 7.07-3.89 kg ha-1 mm-1. The PUE for grain yield showed similar trends with the significantly highest values of PUE under IRWH tillage systems for the Morago sites, but there were no significant differences at the Paradys site in both tillage and cropping systems. There is a critical need, therefore, to devise alternative techniques to promote an increase in smallholders' productivity based on an improved ability to capture and use resources more efficiently.

In-Field Rainwater Harvesting Tillage in Semi-Arid Ecosystems: II Maize-Bean Intercrop Water and Radiation Use Efficiency.

The purpose of this study was to evaluate alternative management practices such as in-field rainwater harvesting (IRWH) and intercropping techniques through conducting on-farm demonstrations. Seven homestead gardens in Thaba Nchu rural communities in the central part of South Africa were selected as demonstration trials. Two tillage systems, conventional (CON) and IRWH, as the main plot, and three cropping systems as sub-plot (sole maize and beans and intercropping) were used to measure water use and radiation use parameters. The water productivity (WP) of various treatments was positively related to the radiation use efficiency (RUE), and the degree of associations varied for different tillage systems. The water use in IRWH was higher by 15.1%, 8.3%, and 10.1% over the CON for sole maize and beans and intercropping, respectively. Similarly, the intercropping system showed water use advantages over the solely growing crops by 5% and 8% for maize and by 16% and 12% for beans under IRWH and CON tillage, respectively. Maximum RUE was found for sole maize and beans under IRWH, higher by 13% and 55% compared to the CON tillage, respectively. The RUE under IRWH tillage was estimated to be 0.65 and 0.39 g DM MJ-1 in sole maize and intercropping, respectively. However, in sole and intercropped beans, the RUE showed higher values of 1.02 g DM MJ-1 and 0.73 g DM MJ-1, respectively. WP and RUE were associated with water deficits and proportional to lower radiation use. This relationship indicates that the intercepted radiation by plants for photosynthesis is directly related to the transpiration rate until radiation saturation occurs. Therefore, the higher water deficit and lesser efficiency in using the radiation available during the season can be improved by practicing IRWH techniques. Furthermore, in semi-arid areas, to enhance the efficiency of water and radiation usage in intercropping management, it is crucial to adjust plant population and sowing dates based on water availability and the onset of rainfall.

Selected Farming Systems for Improving Crop Production and RainWater Productivity in Semi-Arid Zone, Sudan

The problem of water shortages for rainfed agricultural production is due to low rainfall and uneven distribution throughout the rainy season makes rainfed agriculture a highly risk enterprise. Appropriate farming systems and soil conservation measures are the only opportunity to reduce the high risk of crops yield losses. The aim of this study was to evaluate the effect of three farming systems; Conventional Farming (CF), Conservation Agriculture (CA), and in-field rain Water Harvesting (WH); on the yield and water productivity of sorghum, sesame and cowpea crops. Field experiments were conducted in semi-arid area of Sennar State, Sudan for two consecutive seasons (2015 and 2016). Three different planting machines were used. The CA recorded higher crop yield for sorghum (2594 kg/ha) followed by in-field rainwater Harvesting (WH) which gave 2362 kg/ha, while CF has the lowest crop yield (2072 kg/ha). For the sesame crop the WH gave the highest crop yield (740kg/ ha) followed by CA (718 kg/ha) and the lowest crop yield was obtained by CF (602 kg/ha). The highest cowpea crop yield was obtained by WH (927.kg/ha) followed by CA farming system (847 kg/ha) and the lowest crop yield was obtained by CF (785kg/ha). The CA farming system recorded the highest water productivity for sorghum (1.081 kg/m3) compared to the WH and CF, while the WH farming system recorded the highest water productivity (0.32 and 0.366 kg/m3) for sesame and cowpea respectively compared to the CA and CF. WH is best recommended farming system in semi-arid areas and CA the best recommended practice where annual rainfall is relatively high.

The Effect of Agronomic Management on Micronutrients of Vegetables Grown by Smallholders in Free State and KwaZulu-Natal Provinces of South Africa

The production of nutritious food amongst rural farmers has been a challenge for m Cany years. Challenges can be attributed to many factors, including poor access to water, use of old planting methods, financial challenges, etc. Therefore, new climate-smart technologies (CSTs) were introduced to the farmers. The CSTs implemented in the study were in-field rainwater harvesting (IRWH) techniques compared with conventional production (CON). These technologies were applied in combination with sound agronomic management practices, such as mulching and fertilizer application, to produce cabbage, beetroot, spinach and orange-fleshed sweet potato. The vegetables produced were harvested and their nutritional composition analysed to assess whether or not agronomic treatments, water-use technology and season affected their micronutrient levels, with a particular focus on provitamin A and mineral levels. The main finding of the study was that the nutrient levels of the vegetables can be enhanced by adopting IRWH technology combined with different agronomic treatments, especially including mulching as one of the treatment combinations. Limitations: Farmer research participants did not always adhere to research agreements, particularly regarding reserving vegetable samples for analyses. As a result, some experiment replicates are missing. Value: The study findings are of socio-economic significance as they demonstrate that rural, small-scale farmers can apply local, accessible and appropriate agronomic treatments and water-use technologies to achieve economically viable yields of nutritive vegetables to enhance food and nutrition security and household livelihoods of the farmers.

Estimating soil water evaporation as influenced by “dry-and green-mulch” cover beneath maize canopy

Soil evaporation reduction can improve rainfed crop production in semi-arid climates. The purpose of this study was to develop empirical models to estimate cumulative soil evaporation (∑Es) from a maize field across the basin and runoff area (BA and RA) of the in-field rainwater harvesting (IRWH) technique as influenced by different levels of stover mulch ("dry-mulch") and canopy shading ("green-mulch"). Soil water evaporation (Es) was measured with micro-lysimeters 300 mm deep and 71 mm in diameter in the BA and RA sections for three consecutive drying cycles. Four different runoff strip lengths, RSL (RSL-1, 1.5, 2 and 3m) and three mulching levels (ML) of bare, 39%, and 96% were used to estimate the Es. The coefficient crop cover (Kcover) values for full and partial canopy shade (FC and PC) on the RA were in the range of 0.46–0.97 and 0.43–0.94, respectively, while in the BA the Kcover values ranged between 0.33 and 0.92. Under IRWH, the ∑Es values from a basin area beneath a maize canopy averaged 42% of the seasonal rainfall. ∑Es proportion of seasonal rainfall is about 62, 64, and 66 percent for bare soil, but as low as 28, 30 and 32 percent for FC, PC, and unshaded canopy (UC), respectively. In conclusion, the microclimate of the cropping system changes according to surface treatments, which greatly affect the Es losses for the IRWH technique and contributes to ET partitioning. Hence, reducing unproductive water losses in dryland crop production improves water use efficiency by storing more water in the root zone for transpiration.

Soil microbial activity as influenced by crusted runoff strip length and mulch cover under in-field rainwater harvesting (IRWH)

A field experiment was designed to provide insight into the system of in-field rainwater harvesting (IRWH) in determining the effect of microbial activities. The treatments that were evaluated include narrow bare (NB) narrow mulch (NM), wide bare (WB) and wide mulch (WM) runoff strips. Soil samples were collected at depths of 5 and 15 cm from the center section of the runoff area and directly from the rhizosphere of the maize roots around basins. From fresh soil samples, Colony Forming Unit (cfu) readings were taken by using a colony counter and total microbial activity was estimated using the fluorescein diacetate (FDA) hydrolysis method. Community-level diversity physiological profiles of the soil samples were assessed by using Biolog EcoPlates™. Results revealed that the mean values of microbial activity indicated the greatest was found under NM rhizosphere (1.611 ± 0.038) and lowest under WB (0.079 ± 0.005) at 5cm depth. Microbial activity under NM at 5 cm was higher (63% increase) than at the rhizosphere (8% increase). However, there was a decrease in the microbial activity of 17% at 15 cm for WM compared to WB. FDA values were positively correlated with measured soil water content across both 5 and 15 cm depths (r = 0.61 and 0.67) and highly significant (r = 90 at P-value ≤ 0.01) for rhizosphere. Some interesting positive correlations between yield and microbial activity were also found however further investigation on microclimatic aspects in association with microbial diversity and activity on soil surface treatments are important for non-uniform canopy structures of IRWH.

Effects of intercropping sunn hemp into maize at different times and densities on productivity under rainwater harvesting technique

Maize is a major food crop in Sub-Saharan Africa (SSA), and its productivity is affected by climate change-adaptive sustainable management practices. A 2-year field study (2019/20 and 2020/21 growing seasons) was carried out to evaluate the effect of sunn hemp (Crotalaria junceaL.) living mulch management on maize (Zea maysL.) production. Three sunn hemp planting periods were simultaneous with maize planting (P1), V15 maize growth stage (P2), and R1 maize growth stage (P3) and three densities 16.1 plants m−2(D1-low), 32.1 plants m−2(D2-medium), and 48.1 plants m−2(D3-high). The intercrop components were planted in a split-plot treatment arrangement as an additive series with three replications and laid out in a randomized complete block design under the in-field rainwater harvesting (IRWH) technique. The growing season conditions revealed significant differences in rainfall distribution. Therefore, the planting period had highly significant (p< 0.001) effects on sunn hemp biomass, with an LSD value of 610.2 kg ha−1, showing that the highest was obtained in P2 (2636.7 kg ha−1) compared to P3 (811.3 kg ha−1). However, the P3 treatment resulted in maize grain yield penalty, with yields as follows: P3 (2775.2 kg ha−1), sole maize (3263.8 kg ha−1), P2 (3281.9 kg ha−1), and P1 (3287.8 kg ha−1). P2 yielded a significantly (p< 0.05) high-income equivalent ratio of 2.09, indicating a 109% advantage for increasing farmers' income by integrating sunn hemp under the no-till area of IRWH. P1 and P2 sunn hemp planting periods are viable options for smallholder farmers in summer rainfall regions to improve economic benefits.

Farmers’ knowledge, attitudes, and perceptions for the adoption of in-field rainwater harvesting (IRWH) technique in Thaba Nchu, South Africa

A systematic engagement strategy was used to identify contextual factors that prevent farmers from accepting the in-field rainwater harvesting (IRWH) technique. The purpose of the qualitative study is to assess farmers’ knowledge and attitudes about the technique, as well as their adoption and perceptions thereof. A total of 48 knowledge, attitude, perception, and adoption questionnaires were used to gather information. The gathered data was used to determine whether farmers had made an informed choice. The results show that less than a third (27%) made an informed choice while 89.6% had a positive attitude. The overall reflection of excellent knowledge (75%) about the technique was high among farmers aged 41 and over and amounted to 55.6%. According to the survey results, farmers over the age of 45 years (75%), women (56.2%), farmers with a high school certificate (62.5%), and those who are unemployed, continue to adopt the technique (56.2%). According to the binary logistic regression model, increasing household family size had a significant negative impact on adoption (p < 0.05), whereas farmers with high school certificates and crop-livestock households had a significant positive impact (p < 0.01). Most farmers (56.3%) agreed that there was a lack of training, and that more attention is needed on issues such as lack of rainfall (63.3%) and technology taking up more land, which reduce farmers’ crop population and yield (52%). Farmers’ narratives about anticipated interventions, such as intercropping training and timely drought warning services, should increase their adoption. This study focuses on farmers’ specific technology adoption needs, offering another perspective on how achieving the sustainable development goals (SDGs) of zero hunger and climate action necessitates a decentralized approach.

Modelling Rainfed Pearl Millet Yield Sensitivity to Abiotic Stresses in Semi-Arid Central Tanzania, Eastern Africa

Drought and heat-tolerant crops, such as Pearl millet (Pennisetum glaucum), are priority crops for fighting hunger in semi-arid regions. Assessing its performance under future climate scenarios is critical for determining its resilience and sustainability. Field experiments were conducted over two consecutive seasons (2015/2016 and 2016/2017) to determine the yield responses of the crop (pearl millet variety “Okoa”) to microdose fertilizer application in a semi-arid region of Tanzania. Data from the experiment were used to calibrate and validate the DSSAT model (CERES Millet). Subsequently, the model evaluated synthetic climate change scenarios for temperature increments and precipitation changes based on historic observations (2010–2018). Temperature increases of +0.5 to +3.0 °C (from baseline), under non-fertilized (NF) and fertilizer microdose (MD) conditions were used to evaluate nine planting dates of pearl millet from early (5 December) to late planting (25 February), based on increments of 10 days. The planting date with the highest yields was subjected to 49 synthetic scenarios of climate change for temperature increments and precipitation changes (of −30% up to +30% from baseline) to simulate yield responses. Results show that the model reproduced the phenology and yield, indicating a very good performance. Model simulations indicate that temperature increases negatively affected yields for all planting dates under NF and MD. Early and late planting windows were more negatively affected than the normal planting window, implying that temperature increases reduced the length of effective planting window for achieving high yields in both NF and MD. Farmers must adjust their planting timing, while the timely availability of seeds and fertilizer is critical. Precipitation increases had a positive effect on yields under all tested temperature increments, but Okoa cultivar only has steady yield increases up to a maximum of 1.5 °C, beyond which yields decline. This informs the need for further breeding or testing of other cultivars that are more heat tolerant. However, under MD, the temperature increments and precipitation change scenarios are higher than under NF, indicating a high potential of yield improvement under MD, especially with precipitation increases. Further investigation should focus on other cropping strategies such as the use of in-field rainwater harvesting and heat-tolerant cultivars to mitigate the effects of temperature increase and change in precipitation on pearl millet yield.

The role of water conservation strategies and benchmark ecotopes for increasing yields in South Africa’s semi-arid croplands

Recently published results regarding South Africa’s cropping potential show that about one third of the arable land is of low potential, located mainly in semi-arid areas, with the main problem being water shortage. This is therefore an appropriate time to review priorities and procedures, for selecting benchmark ecotopes to represent marginal areas, and for research needs with regard to water conservation strategies to mitigate the problems of low yields. Relevant international principles encapsulated in the words agro-ecology, sustainability and socio-economic conditions, are discussed. Relevant new technologies are described, namely: digital soil mapping that will facilitate the identification of benchmark ecotopes; a stochastic procedure to predict rainfall intensity data from daily rainfall that will facilitate runoff predictions; a crop yield cumulative probability procedure that enables sustainability to be described quantitatively. As a case study, results from a successful field experiment using the infield rainwater harvesting production technique on benchmark ecotopes in a semi-arid area, inhabited by subsistence farmers, are presented. The objectives of the study, procedures used and the method of expressing the results are recommended as guidelines for contributing towards mitigating the problem of low crop productivity across a large portion of the arable area in South Africa.

Analysis of infield rainwater harvesting and land use change impacts on the hydrologic cycle in the Wami River basin

The management of water resources in a river basin experiencing the expansion of agricultural activities requires a proper understanding of impacts on its hydrologic cycle. This study focused on the analysis of impacts of infield rainwater harvesting (IRWH) and future agricultural expansion as land and water uses change (LWUC) on the hydrologic cycle in the Wami River basin (Tanzania) using the Soil and Water Assessment Tool (SWAT). In the SWAT model, IRWH was implemented by fragmenting rainwater harvesting hydrological response units (HRUs) from cropland HRUs and assigning them as potholes for rainwater impoundment. LWUC was implemented by customizing land cover types and their corresponding model parameters in all original HRUs, and introducing projected water uses in the model. The study thus demonstrated the successful modelling of IRWH and land use change in the SWAT model using HRU fragmentation and customization approaches, respectively. The results indicated that IRWH applications in croplands led to a large increase in evapotranspiration (ET) and the soil water content, and a decrease in percolation, especially in the dry years. However, the average annual streamflow showed negligible changes when IRWH was implemented, even in 50% of current low-coverage croplands in the river basin. Thus, IRWH applications in the river basin are recommended. The results also indicated that LWUC caused huge changes in ET, the soil water content, percolation and the streamflow from the river basin. The average annual streamflow was predicted to decrease by 26% due to LWUC. However, land use change alone without projected water uses was predicted to cause a minor decrease of about 1% in the average annual streamflow. Therefore, further studies on the eco-hydrology of the river basin under various water use scenarios are recommended prior to the expansion of agricultural areas.

The Effect of In-Field Rain Water Harvesting on Orange-Fleshed Sweet Potato Biomass and Yield

Water scarcity affects both food security and human nutrition. In-field rain water harvesting (IRWH) combines the advantages of rainwater harvesting, no-till, basin tillage and mulching on high drought risk clay soils. In this study, the IRWH system was customized to fit the cropping system of orange-fleshed sweet potato (OFSP). Field trials were conducted over two seasons to compare cultivation of OFSP using IRWH versus conventional tillage (CON). Data collection included plant survival, root initiation, marketable root yield, unmarketable root yield classes and biomass. Planting OFSP using the IRWH system resulted in significantly higher total biomass, higher marketable and total root yield per plant, as well as larger number of roots per plant compared to CON. Despite the relatively higher yield, total production (t/ha) was only significantly higher in season two at 4.6 t/ha vs 2.7 t/ha for CON. Subsistence farmers and households in semi-arid areas may grow small plots of orange-fleshed sweet potato in IRWH opposed to only growing maize and in that way add vitamin A to the diet. This is the first study on the application of IRWH to produce OFSP under rainfed conditions, and more research can be conducted to expand the knowledge on application and benefits of IRWH for OFSP production.

Micrometeorological measurements and vapour pressure deficit relations under in-field rainwater harvesting

In a cropped field, microclimate and thermal stability conditions depend on the canopy structures and the prevailing weather. The main aim of the study therefore was to characterize the vertical profiles of weather variables within and above a maize (Zea mays L.) canopy and to describe the water vapour pressure deficit (VPD) under different atmospheric and soil surface conditions for both wide and narrow runoff strips with the in-field rainwater harvesting (IRWH) system. Micrometeorological measurements of wind, temperature and relative humidity were performed at eight levels, within canopy (1.8 and 2.1 m), and just above the canopy (2.4, 2.7, 3.0, and 3.3 m) up to reference levels (3.9 and 4.5 m) when the maize reached a maximum height of 2.2 m. Under incomplete canopy cover of the IRWH system, two important factors complicated evapotranspiration estimation, namely the local advection and high temperatures of the bare soil between adjacent plant rows. Diurnal variations of water vapour related to turbulence at each locality and its position in the thermal internal boundary layers. Generally, advection was more pronounced in wide runoff strips than narrow strips. On wide runoff strips the wind was more effective in replacing the air between the rows and maintained a higher driving force for evaporation. The maximum VPD over the narrow strips was observed at reference level during a dry day, at about 2.2 kPa in the afternoon, while wet day VPD reached a maximum of 1.8 kPa. The VPD of the wide runoff strips correlated negatively with wind speed, but showed a fairly positive correlation with some scattered values on wet days after rain. Therefore, profile characteristics within and above plant canopies played a key role in determining the VPD and consequently, could help to explain transpiration rates of crops. Hence, VPD relations enhanced the understanding of the heat energy exchange processes under the heterogeneous nature of maize canopy of the IRWH tillage system.

Rainwater harvesting and conservation tillage increase maize yields in South Africa

Poverty and food insecurity are common amongst rural communities in the sub-Saharan African region. The rural population of South Africa is not excluded from poverty. With normal conventional tillage practices, crop failures are common on marginal soils in semi-arid areas with low and erratic rainfall. Therefore, selected rural communities in the Eastern Cape, Limpopo and Free State Provinces of South Africa were introduced to appropriate rainwater harvesting and conservation agricultural techniques to contribute towards the reduction of food insecurity through improved maize yields. Conventional tillage, no-till, minimum tillage, mechanized basins, in-field rainwater harvesting and the Daling plough were tested in on-station and on-farm field experiments over three to five maize growing seasons (2008/09–2011/13). The rainwater harvesting (in-field rainwater harvesting and Daling plough) and conservation (mechanized basins, no-till and minimum tillage) techniques resulted in slightly higher yields than conventional tillage due to their potential to conserve rainwater better and to harvest additional rainwater. Conventional tillage, no-till and minimum tillage had lower grain yields because they lost on average 18% of the total rainfall to ex-field runoff. The rainwater productivity of the Daling plough treatment was very similar to that of in-field rainwater harvesting, followed by mechanized basins, conventional tillage and no-till or minimum tillage.

Quantifying and predicting soil water evaporation as influenced by runoff strip lengths and mulch cover

Soil water evaporation from the cropping surface is a wasteful loss of potentially productive rainwater, thus efficient use of rainwater can help to sustain dryland production. The purpose of this study was to quantify the effect of canopy shading (CS) and mulch levels (ML) on soil water evaporation (Es) from each 1m section of in-field rainwater harvesting (IRWH) and to evaluate the Ritchie (α′) and Stroosnijder (β′) soil evaporation models on the effect of surface treatments. A microlysimetric method was used to measure Es from beneath maize (Zea mays L.) canopy for three consecutive drying cycles across the basin and runoff sections of IRWH on fine sandy loam soil of Bainsvlei Kenilworth ecotope. First, main effects of four runoff strip lengths (RSL) and three ML treatments were statistically analysed on the weighted Es values. Second, the ML treatments were allocated to the main plots and four levels of CS allocated according to lengths of the runoff sections. Third, cumulative Es (∑Es) measurements were used to evaluate empirical equations related to time (α′) and potential evaporation (β′). The two models for Es were compared by considering the effects of surface treatments. A significantly higher Es was observed from a bare (ML0%) treatment compared with either of two mulched treatments viz. mulch level 39% and 96% cover (ML39% and ML96%); no significant differences were found between the mulched treatments. The insignificant effect of RSL treatments on Es implied the dynamics of spatial distribution of soil water and energy that influenced evaporation were as a result of green mulch or shading cover (CS) on Es beneath the canopy. Less suppressive Es properties were developed from bare surface and efficient Es restriction was found under high mulch and shading cover treatments. The α′ and β′ values ranged from 2.34 to 4.26mmd−0.5 and from 1.38 to 2.06mmd−0.5, respectively. In all the treatments the simulated ∑Es was underestimated by the Ritchie model and overestimated by the Stroosnijder model. The main effect of shading was due to the dominant effect of energy limited evaporation (stage-1), while the mulched treatments were mainly driven by soil limited stage (stage-2) of evaporation. The Ritchie model performed well to estimate ∑Es from the basin area and the potential Stroosnijder model from the unshaded runoff strips. The microclimate of the cropping system changed according to surface treatments that highly influenced the Es losses in IRWH of dryland production.