J. M. Steyn

Climate Change and Potato Production in Contrasting South African Agro-Ecosystems 3. Effects on Relative Development Rates of Selected Pathogens and Pests

A set of daily weather data simulations for 1961 to 2050 were used to calculate past and future trends in pest and disease pressure in potato cropping systems at three agro-ecologically distinct sites in South Africa: the Sandveld, the Eastern Free State and Limpopo. The diseases and pests modelled were late blight, early blight and brown spot, blackleg and soft rot, root-knot nematodes and the peach-potato aphid Myzus persicae (as indicator of Potato virus Y and Potato leaf roll virus). The effects of climate on trends in relative development rates of these pathogens and pests were modelled for each pathogen and pest using a set of quantitative parameters, which included specific temperature and moisture requirements for population growth, compiled from literature. Results showed that the cumulative relative development rate (cRDR) of soft rot and blackleg, root-knot nematodes and M. persicae will increase over the 90-year period in the areas under consideration. The cRDR of early blight and brown spot is likely to increase in the wet winter and wet summer crops of the Sandveld and Eastern Free State, respectively, but remains unchanged in the dry summer and dry winter crops of the Sandveld and Limpopo, respectively. Climate change will decrease the cRDR of late blight in all of the cropping systems modelled, except in the wet winter crop of the Sandveld. These results help to set priorities in research and breeding, specifically in relation to management strategies for diseases and pests.

Yield response of potato genotypes to different soil water regimes in contrasting seasons of a subtropical climate

SummaryPotato crops in subtropical climates are often subjected to water stress, resulting in low yields and poor tuber quality. The yield response of potato genotypes to water supply was investigated in six trials, three each in spring and autumn plantings. Trials were conducted under automated rain shelters, using an irrigation boom to impose five soil water regimes.The negative effect of water stress on tuber yield was more detrimental in spring than in autumn, because of higher atmospheric evaporative demand and higher temperatures in spring. An average yield reduction of 68% was recorded for the most severely stressed regime in spring plantings, while the mean reduction for the same treatment in autumn was only 42%. Genotypic differences in yield response to drought were clearly illustrated in spring, but not in autumn. This suggests that the choice of genotypes is only influenced by the availability of water in spring, when more drought tolerant genotypes should be used.

A robust potato model : LINTUL-POTATO-DSS

In 1994, LINTUL-POTATO was published, a comprehensive model of potato development and growth. The mechanistic model simulated early crop processes (emergence and leaf expansion) and light interception until extinction, through leaf layers. Photosynthesis and respiration in a previous crop growth model—SUCROS—were substituted by a temperature-dependent light use efficiency. Leaf senescence at initial crop stages was simulated by allowing a longevity per daily leaf class formed, and crop senescence started when all daily dry matter production was allocated to the tubers, leaving none for the foliage. The model performed well in, e.g., ideotyping studies. For other studies such as benchmarking production environments, agro-ecological zoning, climatic hazards, climate change, and yield gap analysis, the need was felt to develop from the original LINTUL-POTATO, a derivative LINTUL-POTATO-DSS with fewer equations—reducing the potential sources of error in calculations—and fewer parameters. This reduces the number of input parameters as well as the amount of data required that for many reasons are not available or not reliable. In LINTUL-POTATO-DSS calculating potential yields, initial crop development depends on a fixed temperature sum for ground cover development from 0% at emergence to 100%. Light use efficiency is temperature dependent. Dry matter distribution to the tubers starts at tuber initiation and linearly increases up to a fixed harvest index which is reached at crop end. Crop end is input of the model: it is assumed that the crop cycle determined by maturity matches the length of the available frost-free and or heat-free cropping season. LINTUL-POTATO-DSS includes novel calculations to explore tuber quality characteristics such as tuber size distribution and dry matter concentration depending on crop environment and management.

A field screening technique for drought tolerance studies in potatoes

SummaryA major objective of plant breeding programmes in semi-arid conditions is the selection of more drought-tolerant plant material. An irrigation system has been developed to assist in water use and drought tolerance screening studies of potato genotypes in the confined space of a rain shelter. The line-source principle was used as a departure point for the design of an irrigation boom, attached to the roof structure of a rain shelter. Five water regimes were achieved by using nozzles that differed in discharge rate and three genotypes per rain shelter were evaluated simultaneously.Crop production functions could be established for the different genotypes. The system shares some disadvantages of the typical line-source, such as the simultaneous irrigation of all plots and water treatments are not randomised. The main advantage above traditional plot systems, which would use drip or micro irrigation under rain shelters, is the ease of management.

Carbon footprinting of potato (Solanum tuberosum L.) production systems in Zimbabwe

Agriculture contributes significantly to the global greenhouse gas (GHG) emissions. Farmers need to fine-tune agricultural practices to balance the trade-offs between increasing productivity in order to feed a growing population and lowering GHG emissions to mitigate climate change and its impact on agriculture. We conducted a survey on the major cultural practices in four potato production systems in Zimbabwe, namely large-scale commercial, communal area, A1 and A2 resettlement production systems. The resettlement production systems were formed from the radical Fast Track Land Reform Programme initiated in 2000, which changed the landscape of commercial agriculture in Zimbabwe. We used survey data as an input into the ‘Cool Farm Tool – Potato’ model. The model calculates the contributions of various production operations to total GHG emission. Experienced growers were targeted. The average carbon footprint calculated was 251 kg CO2 eq./t potato harvested, ranging from 216 kg CO2 eq./t to 286 kg CO2 eq./t in the communal area and A2 resettlement production systems, respectively. The major drivers of the GHG emissions were fertilizer production and soil-related field emissions, which together accounted for on average 56% of the total emissions across all production systems. Although mitigation options were not assessed, the model outputs the factors/farm operations and their respective emission estimates allowing growers to choose the inputs and operations to reduce their carbon footprint. Opportunities for benchmarking as an incentive to improve performance exist given the large variation in GHG emission between individual growers.

Analysis of the potato (Solanum tuberosum L.) value chain in Zimbabwe

The performance of the Irish potato sector in Zimbabwe is not well understood. Using value chain analysis, this article evaluated the potato industry using quantitative data gathered from stakeholders using structured questionnaires, field observations, local knowledge and expert consultation. About 65% of potato production is processed as French fries and less than 35% for household fresh consumption. Average fresh potato household per capita consumption was 34 kg per year, while the total per capita consumption was 9 kg per year. Gross profit estimated at each linkage was at least 13%. Major factors impacting on the value chain performance relate to high production costs, low yields and a lack of farmer training. Potato marketing is also hampered by the poor road network in the country. The research recommends a lowering of production costs, supplying high yielding cultivars, providing credit facilities, guaranteed land ownership and improving the country’s road network.

A Quantitative Framework for Evaluating the Sustainability of Irish Potato Cropping Systems after the Landmark Agrarian Reform in Zimbabwe

Frameworks to evaluate the sustainability of cropping systems in developing countries are scarce. This study proposes a framework to select easily quantifiable indicators that can be used to assess and communicate the sustainability of cropping systems in developing countries. The widely accepted social, economic and environmental dimensions of sustainability were covered using predefined criteria from which the indicators were then drawn. An initial list of indicators was established based on literature review and expert opinion, and through filtering reduced to 16 core indicators. Using the case of Irish potato-based cropping systems, a grower survey was conducted to collect data on production practices in four different cropping systems. The survey data were then used to calculate the sustainability indicators expressed as resource use efficiencies based on actual potato yields. The survey data also served as input into the Cool Farm Tool – Potato model to estimate greenhouse gas emissions from farm operations involved in potato production. With the help of local agricultural extension officers, focus group discussions were held with farmers of each production system to decide on sustainable and unsustainable indicator threshold levels. The participatory nature of the framework involving farmers and local extension officers secured buy-in from key stakeholders important for operationalization, monitoring and evaluation.