Modelling crop growth and crop water relations in South Africa: Past achievements and lessons for the future

Singels, A.; Annandale, J. G.; Jager, J. M. de; Schulze, R. E.; Inman-Bamber, N. G.; Durand, Wiltrud; Rensburg, L. D. van; Heerden, Pieter S. van; Crosby, Charles; Green, G.C.; Steyn, J. M.

doi:10.1080/02571862.2010.10639970

Cited by 25 publications

(13 citation statements)

References 95 publications

(90 reference statements)

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“…South Africa is classified as semi-arid and its water profile is rapidly moving from water scarce to water stressed [74]. The country's annual average rainfall fluctuates around 500 mm, which is far below the world's average of 860 mm per annum [1].…”

Section: Potential Of Nus In Smallholder Farming Systemsmentioning

confidence: 99%

Status of Underutilised Crops in South Africa: Opportunities for Developing Research Capacity

2017

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Underutilised crops represent an important component of agro-biodiversity with potential to contribute to climate change adaptation, food security and sovereignty in poor rural areas. However, despite emerging research interest, they continue to occupy the peripheries of mainstream agriculture. There is a need to consolidate the gains made and propose a coherent strategy for translating underutilised crops into mainstream agriculture. The status of underutilised crops in South Africa (past, present and on-going research) was reviewed with a view to identifying existing gaps, opportunities and challenges for developing future research capacity. The review confirmed that several underutilised crops are drought tolerant, adapted to low levels of water use and thus suitable for cultivation in most marginal production areas typical of semi-arid and arid cropping systems. In addition, several are nutrient dense and could be used to improve dietary diversity among poor rural people. These characteristics make them ideal for inclusion in climate change adaptation and promotion of food sovereignty. There is need for a paradigm shift away from practices that have promoted a few major crops to an agro-ecology based land use classification system that recognises diversity and strengthens food networks. There is a need to identify those underutilised crops that show the greatest potential for success and can be fitted into semi-arid and arid cropping systems and prioritise them for future research, development and innovation.

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Section: Potential Of Nus In Smallholder Farming Systemsmentioning

confidence: 99%

Status of Underutilised Crops in South Africa: Opportunities for Developing Research Capacity

2017

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“…17 In addition, the crop varieties database in SAPWAT is extensive and it has provision for tree and deciduous crops which is not common in other models. SAPWAT uses the Koppen climate system 18 for calculating crop coefficients and will therefore make it widely acceptable 14 . SAPWAT uses the basic methodology proposed in FAO-56 19 in its calculation of crop water requirements utilising the reference evapotranspiration rate (ET 0 ) and the crop coefficient (K c ).…”

Section: Sapwatmentioning

confidence: 99%

simulation study on the effect of climate change on crop water use and chill unit accumulation

Ogundeji¹,

Jordaan²

2017

S. Afr. J. Sci.

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Climate change and its impact on already scarce water resources are of global importance, but even more so for water scarce countries. Apart from the effect of climate change on water supply, the chill unit requirement of deciduous fruit crops is also expected to be affected. Although research on crop water use has been undertaken, researchers have not taken the future climate into consideration. They also have focused on increasing temperatures but failed to relate temperature to chill unit accumulation, especially in South Africa. With a view of helping farmers to adapt to climate change, in this study we provide information that will assist farmers in their decision-making process for adaptation and in the selection of appropriate cultivars of deciduous fruits. Crop water use and chill unit requirements are modelled for the present and future climate. Results show that, irrespective of the irrigation system employed, climate change has led to increases in crop water use. Water use with the drip irrigation system was lower than with sprinkler irrigation as a result of efficiency differences in the irrigation technologies. It was also confirmed that the accumulated chill units will decrease in the future as a consequence of climate change. In order to remain in production, farmers need to adapt to climate change stress by putting in place water resources and crop management plans. Thus, producers must be furnished with a variety of adaptation or management strategies to overcome the impact of climate change.

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“…However, the majority of these studies have been conducted at the global and regional scales using a Geographic Information Systems (GIS) modified version of the EPIC model, Global-EPIC (GEPIC), with few studies conducted in South Africa.In Africa, studies using EPIC have mostly been performed in West Africa [27][28][29] where soil and weather conditions differ from the semi-arid conditions in South Africa. Studies that have applied EPIC in South Africa have been at the sub-Saharan scale [11,30] where combined data from provincial statistics have been used to calibrate models due to data scarcity issues [31,32]. The application of the EPIC model at the regional scale in Africa implies that field-scale conditions, such as local heterogeneity in climate, soil, and farm management practices, are difficult to incorporate, potentially resulting in high levels of uncertainties in model results [33,34].…”

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Calibration and Validation of the EPIC Model for Maize Production in the Eastern Cape, South Africa

2019

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Crop models are useful tools to evaluate the effects of agricultural management on ecosystem services. However, before they can be applied with confidence, it is important to calibrate and validate crop models in the region of interest. In this study, the Environmental Policy Integrated Climate (EPIC) model was evaluated for its potential to simulate maize yield using limited data from field trials on two maize cultivars. Two independent fields at the Cradock Research Farm were used, one for calibration and one for validation. Before calibration, mean simulated yield was 8 t ha −1 while mean observed yield was 11.26 t ha −1 . Model calibration improved mean simulated yield to 11.23 t ha −1 with a coefficient of determination, (r 2 ) = 0.76 and a model efficiency (NSE) = 0.56. Validation with grain yield was satisfactory with r 2 = 0.85 and NSE = 0.61. Calibration of potential heat units (PHUs) and soil-carbon related parameters improved model simulations. Although the study only used grain yield to calibrate and evaluate the model, results show that the calibrated model can provide reasonably accurate simulations. It can be concluded that limited data sets from field trials on maize can be used to calibrate the EPIC model when comprehensive experimental data are not available.Agronomy 2019, 9, 494 2 of 16 used to test the effectiveness of alternative agricultural land management practices under varying climate change scenarios. However, to yield meaningful results, it is prudent to calibrate crop models in the region of intended use before their application [11].Model calibration is the procedure where model parameters are fine-tuned to increase the agreement between model simulations and real-world observations [12]. Calibration is important to increase model accurateness and decrease model prediction uncertainty [13]. Calibration is done by judiciously choosing model parameter values, adjusting them within recommended ranges, for example, from literature or expert opinions, and comparing the simulated outputs with observed data for a given set of conditions [14]. A successful calibration would be when the model reproduces observed data within a satisfactory degree of accuracy and precision for the intended model use [15,16]. Once calibrated and validated, the model can be reasonably applied in the area of interest. Calibrated crop growth models can, therefore, be useful tools to complement field experiments and support decision making for sustainable agricultural land management.The Environmental Policy Integrated Climate (EPIC) model [17], originally developed in the United States of America (USA), is a process-based, field-scale model with a daily time scale. It simulates the chemical processes occurring in the soil-water-plant interaction under different agricultural management regimes [18]. The main components of EPIC are weather simulation, crop growth, carbon and nutrient cycling, tillage, soil erosion, and hydrology [19]. Globally, the model has been applied to study crop yield responses to nutrients and...

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Modelling crop growth and crop water relations in South Africa: Past achievements and lessons for the future

Cited by 25 publications

References 95 publications

Status of Underutilised Crops in South Africa: Opportunities for Developing Research Capacity

Status of Underutilised Crops in South Africa: Opportunities for Developing Research Capacity

simulation study on the effect of climate change on crop water use and chill unit accumulation

Calibration and Validation of the EPIC Model for Maize Production in the Eastern Cape, South Africa

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