• Energy Research

Little is understood on the interaction between irrigated agriculture and surface water quality in South African catchments. A case study was conducted on the Middle Olifants Catchment, which contains the second largest irrigation scheme in South Africa. Dams, rivers, irrigation canals, and drainage canals were sampled between the Loskop and Flag Boshielo Dams. Results were compared to historical water quality monitoring data from the Department of Water and Sanitation (DWS). While DWS data indicate that phosphate-phosphorus (PO4-P) does not pose a eutrophication risk, our monitored data were above the eutrophication threshold for the majority of the sampling period. In general, phosphorus (P) pollution is a bigger issue than nitrogen (N), and concentrations of these nutrients tend to be higher during the summer rainfall months, potentially indicating a link to agriculture and fertilization events. We estimated that waste water treatment works (WWTW), which are currently systematically failing in South Africa, have the potential to pollute as much P as irrigated agriculture. Electrical conductivity levels increased downstream, moving from the acceptable towards the tolerable category, while the sodium adsorption ratio (SAR) presents a moderate risk of infiltrability problems. The pH values were generally in the ideal range. This study has highlighted existing and looming water quality issues for irrigation and the environment in the Middle Olifants. Similar scoping studies are recommended for other intensively-irrigated catchments in the region to identify issues and allow timely intervention.

Using the current state of life cycle assessment (LCA), carbon and water footprinting, and EPDs in South Africa, this work explores the challenges and opportunities for scholarly development in these areas in the country. Being a relatively small LCA community in South Africa, academics, consultants, and other stakeholders were approached to provide lists of known studies, with further reports, that may have been missed, obtained through internet searches. Information was collated on database development, capacity building, and other aspects and presented here in a single paper. While the authors are aware of companies working on LCA and related studies, hidden in confidential reports, we were able to find 27 LCA, 17 water and 12 carbon footprinting, and 10 EPD studies. Although these studies have potential advantages for policymaking and business, their number, implementation, and impact remain limited. While previously seen as an academic exercise, life cycle thinking has been adopted by industry, private consultants, and the South African National Cleaner Production Centre (NCPC-SA), among others. Growing interest has led to the creation of several training courses available at academic institutes, the NCPC-SA, and consulting firms, ranging from the basic understanding to advanced use of software packages and modeling techniques. The development of a national LCI database and further exposure and opportunity for LCA studies are important steps to hopefully spur LCA in Southern Africa in the future.

AbstractSmallholder farmers in sub‐Saharan Africa (SSA) currently grow rainfed maize with limited inputs including fertilizer. Climate change may exacerbate current production constraints. Crop models can help quantify the potential impact of climate change on maize yields, but a comprehensive multimodel assessment of simulation accuracy and uncertainty in these low‐input systems is currently lacking. We evaluated the impact of varying [CO2], temperature and rainfall conditions on maize yield, for different nitrogen (N) inputs (0, 80, 160 kg N/ha) for five environments in SSA, including cool subhumid Ethiopia, cool semi‐arid Rwanda, hot subhumid Ghana and hot semi‐arid Mali and Benin using an ensemble of 25 maize models. Models were calibrated with measured grain yield, plant biomass, plant N, leaf area index, harvest index and in‐season soil water content from 2‐year experiments in each country to assess their ability to simulate observed yield. Simulated responses to climate change factors were explored and compared between models. Calibrated models reproduced measured grain yield variations well with average relative root mean square error of 26%, although uncertainty in model prediction was substantial (CV = 28%). Model ensembles gave greater accuracy than any model taken at random. Nitrogen fertilization controlled the response to variations in [CO2], temperature and rainfall. Without N fertilizer input, maize (a) benefited less from an increase in atmospheric [CO2]; (b) was less affected by higher temperature or decreasing rainfall; and (c) was more affected by increased rainfall because N leaching was more critical. The model intercomparison revealed that simulation of daily soil N supply and N leaching plays a crucial role in simulating climate change impacts for low‐input systems. Climate change and N input interactions have strong implications for the design of robust adaptation approaches across SSA, because the impact of climate change in low input systems will be modified if farmers intensify maize production with balanced nutrient management.

Abstract Food production comes at an ecological cost, and the lack of sustainability of South Africa’s crop production systems is becoming increasingly worrisome. While small scale emerging and homestead subsistence farming are significant in the agricultural sector, food production is dominated by large scale commercial agriculture. In this paper we analyse the ecological impact of South African commercial crop production and what can be done about it. Impact categories considered are divided into what we consider ‘better-researched’ problems: fresh water depletion, salinisation, soil degradation, eutrophication and land use change; and into what we consider ‘emerging’ problems for agriculture: greenhouse gas emissions, soil profile acidification, ecotoxicity and non-renewable resource consumption. While there is a paucity of quantitative information, it is clear that after decades of cultivation many of our agroecosystems are degraded or degrading. Sustainable crop production and food security are ‘wicked’ problems – containing dynamic social, economic and biophysical complexities. Increased stakeholder engagement to better understand these problems, the tradeoffs linked to finding solutions and to involve those with the resources to turn knowledge into action is required. Collecting key data, turning it into information within local contexts (involving the ecology, agronomy, sociology, psychology, economics and other disciplines simultaneously) and communicating it effectively to allow learning and adaptive management at various spatial and temporal scales is essential. An example is the display of river flows on a website in real-time to help farmers manage and adapt irrigation practices better, and to connect them with other stakeholders to improve understanding of the responsibilities of managing water at local and catchment scales.

Une estimation précise du rendement des cultures dans les scénarios de changement climatique est essentielle pour quantifier notre capacité à nourrir une population croissante et à développer des adaptations agronomiques pour répondre à la demande alimentaire future. Une évaluation coordonnée des simulations de rendement à partir de modèles écophysiologiques basés sur les processus pour l'évaluation de l'impact du changement climatique fait toujours défaut pour le soja, la légumineuse à grains la plus cultivée et la principale source de protéines dans notre chaîne alimentaire. Dans cette première étude multimodèle sur le soja, nous avons utilisé dix modèles de premier plan capables de simuler le rendement du soja sous différentes températures et concentrations atmosphériques de CO2 [CO2] pour quantifier l'incertitude dans les simulations de rendement du soja en réponse à ces facteurs. Les modèles ont d'abord été paramétrés avec des données mesurées de haute qualité provenant de cinq environnements contrastés. Nous avons trouvé une variabilité considérable entre les modèles dans les réponses de rendement simulées à l'augmentation de la température et du [CO2]. Par exemple, en cas d'augmentation de la température de + 3 °C dans notre endroit le plus frais en Argentine, certains modèles ont simulé que le rendement diminuerait jusqu'à 24 %, tandis que d'autres simulaient une augmentation du rendement allant jusqu'à 29 %. Dans notre emplacement le plus chaud au Brésil, les modèles ont simulé une réduction du rendement allant d'une diminution de 38 % sous + 3 °C à une augmentation de la température sans effet sur le rendement. De même, en augmentant le [CO2] de 360 à 540 ppm, les modèles ont simulé une augmentation du rendement allant de 6% à 31%. L'étalonnage du modèle n'a pas réduit la variabilité entre les modèles, mais a eu un effet inattendu sur la modification des réponses du rendement à la température pour certains des modèles. La forte incertitude dans les réponses des modèles indique l'applicabilité limitée des modèles individuels pour les projections alimentaires du changement climatique. Cependant, la moyenne d'ensemble des simulations à travers les modèles était un outil efficace pour réduire la forte incertitude dans les simulations de rendement du soja associées aux modèles individuels et à leur paramétrage. Les réponses du rendement moyen de l'ensemble à la température et au [CO2] étaient similaires à celles rapportées dans la littérature. Notre étude est la première démonstration des avantages obtenus en utilisant un ensemble de modèles de légumineuses à grains pour les projections alimentaires du changement climatique, et souligne qu'un développement plus poussé du modèle du soja avec des expériences sous des [CO2] et des températures élevées est nécessaire pour réduire l'incertitude des modèles individuels. Una estimación precisa del rendimiento de los cultivos en escenarios de cambio climático es esencial para cuantificar nuestra capacidad para alimentar a una población en crecimiento y desarrollar adaptaciones agronómicas para satisfacer la demanda futura de alimentos. Todavía falta una evaluación coordinada de las simulaciones de rendimiento a partir de modelos ecofisiológicos basados en procesos para la evaluación del impacto del cambio climático para la soja, la leguminosa de grano más cultivada y la principal fuente de proteínas en nuestra cadena alimentaria. En este primer estudio multimodelo de soja, utilizamos diez modelos prominentes capaces de simular el rendimiento de la soja a diferentes temperaturas y concentraciones de CO2 atmosférico [CO2] para cuantificar la incertidumbre en las simulaciones de rendimiento de soja en respuesta a estos factores. Los modelos se parametrizaron por primera vez con datos medidos de alta calidad de cinco entornos contrastantes. Encontramos una variabilidad considerable entre los modelos en las respuestas de rendimiento simuladas al aumento de la temperatura y [CO2]. Por ejemplo, bajo un aumento de temperatura de + 3 ° C en nuestra ubicación más fresca en Argentina, algunos modelos simularon que el rendimiento se reduciría hasta un 24%, mientras que otros simularon aumentos de rendimiento de hasta un 29%. En nuestra ubicación más cálida en Brasil, los modelos simularon una reducción del rendimiento que va desde una disminución del 38% con un aumento de temperatura de + 3 ° C hasta ningún efecto en el rendimiento. Del mismo modo, al aumentar [CO2] de 360 a 540 ppm, los modelos simularon un aumento del rendimiento que osciló entre el 6% y el 31%. La calibración del modelo no redujo la variabilidad entre los modelos, pero tuvo un efecto inesperado en la modificación de las respuestas de rendimiento a la temperatura para algunos de los modelos. La alta incertidumbre en las respuestas de los modelos indica la aplicabilidad limitada de los modelos individuales para las proyecciones alimentarias del cambio climático. Sin embargo, la media del conjunto de simulaciones entre modelos fue una herramienta efectiva para reducir la alta incertidumbre en las simulaciones de rendimiento de soja asociadas con modelos individuales y su parametrización. Las respuestas de rendimiento medio del conjunto a la temperatura y [CO2] fueron similares a las informadas en la literatura. Nuestro estudio es la primera demostración de los beneficios logrados al utilizar un conjunto de modelos de leguminosas de grano para las proyecciones de alimentos del cambio climático, y destaca que se necesita un mayor desarrollo del modelo de soja con experimentos bajo [CO2] y temperatura elevadas para reducir la incertidumbre de los modelos individuales. An accurate estimation of crop yield under climate change scenarios is essential to quantify our ability to feed a growing population and develop agronomic adaptations to meet future food demand. A coordinated evaluation of yield simulations from process-based eco-physiological models for climate change impact assessment is still missing for soybean, the most widely grown grain legume and the main source of protein in our food chain. In this first soybean multi-model study, we used ten prominent models capable of simulating soybean yield under varying temperature and atmospheric CO2 concentration [CO2] to quantify the uncertainty in soybean yield simulations in response to these factors. Models were first parametrized with high quality measured data from five contrasting environments. We found considerable variability among models in simulated yield responses to increasing temperature and [CO2]. For example, under a + 3 °C temperature rise in our coolest location in Argentina, some models simulated that yield would reduce as much as 24%, while others simulated yield increases up to 29%. In our warmest location in Brazil, the models simulated a yield reduction ranging from a 38% decrease under + 3 °C temperature rise to no effect on yield. Similarly, when increasing [CO2] from 360 to 540 ppm, the models simulated a yield increase that ranged from 6% to 31%. Model calibration did not reduce variability across models but had an unexpected effect on modifying yield responses to temperature for some of the models. The high uncertainty in model responses indicates the limited applicability of individual models for climate change food projections. However, the ensemble mean of simulations across models was an effective tool to reduce the high uncertainty in soybean yield simulations associated with individual models and their parametrization. Ensemble mean yield responses to temperature and [CO2] were similar to those reported from the literature. Our study is the first demonstration of the benefits achieved from using an ensemble of grain legume models for climate change food projections, and highlights that further soybean model development with experiments under elevated [CO2] and temperature is needed to reduce the uncertainty from the individual models. يعد التقدير الدقيق لمحصول المحاصيل في ظل سيناريوهات تغير المناخ أمرًا ضروريًا لتحديد قدرتنا على إطعام عدد متزايد من السكان وتطوير التكيفات الزراعية لتلبية الطلب على الغذاء في المستقبل. لا يزال التقييم المنسق لمحاكاة الغلة من النماذج الفسيولوجية البيئية القائمة على العمليات لتقييم تأثير تغير المناخ مفقودًا بالنسبة لفول الصويا، وهو بقول الحبوب الأكثر زراعة على نطاق واسع والمصدر الرئيسي للبروتين في سلسلتنا الغذائية. في هذه الدراسة الأولى متعددة النماذج لفول الصويا، استخدمنا عشرة نماذج بارزة قادرة على محاكاة محصول فول الصويا تحت درجات حرارة متفاوتة وتركيز ثاني أكسيد الكربون في الغلاف الجوي [CO2] لقياس عدم اليقين في محاكاة محصول فول الصويا استجابة لهذه العوامل. تم قياس النماذج أولاً ببيانات مقاسة عالية الجودة من خمس بيئات متباينة. وجدنا تباينًا كبيرًا بين النماذج في استجابات العائد المحاكاة لزيادة درجة الحرارة و [CO2]. على سبيل المثال، في ظل ارتفاع درجة الحرارة بمقدار + 3 درجات مئوية في أروع موقع لنا في الأرجنتين، قامت بعض النماذج بمحاكاة أن العائد سيقلل بنسبة تصل إلى 24 ٪، بينما يزيد العائد المحاكى الآخر بنسبة تصل إلى 29 ٪. في موقعنا الأكثر دفئًا في البرازيل، قامت النماذج بمحاكاة انخفاض العائد الذي يتراوح بين انخفاض بنسبة 38 ٪ تحت + ارتفاع درجة حرارة 3 درجات مئوية إلى عدم التأثير على العائد. وبالمثل، عند زيادة [ثاني أكسيد الكربون] من 360 إلى 540 جزء في المليون، قامت النماذج بمحاكاة زيادة العائد التي تراوحت من 6 ٪ إلى 31 ٪. لم تقلل معايرة النموذج من التباين عبر النماذج ولكن كان لها تأثير غير متوقع على تعديل استجابات الخضوع لدرجة الحرارة لبعض النماذج. يشير عدم اليقين الشديد في الاستجابات النموذجية إلى التطبيق المحدود للنماذج الفردية للتوقعات الغذائية لتغير المناخ. ومع ذلك، كان المتوسط الجماعي للمحاكاة عبر النماذج أداة فعالة للحد من عدم اليقين العالي في محاكاة غلة فول الصويا المرتبطة بالنماذج الفردية ومعلماتها. كانت استجابات متوسط العائد على درجة الحرارة و [CO2] متشابهة مع تلك الواردة في الأدبيات. دراستنا هي أول عرض توضيحي للفوائد التي تحققت من استخدام مجموعة من نماذج البقوليات لتوقعات تغير المناخ الغذائية، وتسلط الضوء على الحاجة إلى مزيد من تطوير نموذج فول الصويا مع التجارب تحت [CO2] ودرجة الحرارة المرتفعة لتقليل عدم اليقين من النماذج الفردية.