Developing environmental principles, criteria, indicators and norms for potato production in South Africa through field surveys and modelling

Abstract

a b s t r a c tThe sustainability of agricultural production is linked to the environment from which it draws its resources. Potato production in the Sandveld in the South African Western Cape occurs in the Cape Floral Kingdom: a vulnerable and globally significant biodiversity hotspot. A scientific approach defining and monitoring sustainability criteria and indicators is required to improve the sustainability of potato production in such a sensitive area. In this paper we propose principles related to the ecological impact of potato production (nature preservation, water preservation and the minimization of chemical and carbon-dioxide emissions) and their derived criteria related to land clearing, irrigation, emissions, and others. Next we defined calculable and measurable indicators of the efficiency with which resources are used, such as proportion of land cleared, water use by the crop, amount of biocides used, the embodied energy of biocides, and the energy needed for farming operations versus the potato yields obtained. Indepth interviews were held with 14 farmers representing 20% of the total potato production area to obtain the current values of these indicators. These were compared to model outcomes of two main sustainability indicators: land and water use efficiency. The land use efficiency varied least between growers, from (36 to 58 Mg (tonnes) ha À1 ), water use efficiency returned values between 3 and 9 g potato l À1 water, while chemical fertilizer phosphorus use efficiency varied most at 98 and 995 g potato g À1 P applied. Model outcomes confirmed some of the trends revealed by the survey, e.g. growing potatoes in winter and growing them with less than optimal water offers possibilities to double water use efficiency. Ways to derive indicator threshold norms are proposed based on the knowledge of physical and biological processes determining resource availability, the observed variation among farmers and the model outcomes. Knowing indicator values, their range and the means to improve resource use efficiency will aid in establishing sustainability norms by providing a quantitative approach to any environmental certification scheme that wishes to licence the delivery of potatoes from the Sandveld.

Climate Change and Potato Production in Contrasting South African Agro-ecosystems 1. Effects on Land and Water Use Efficiencies

“…The discrepancy between calculated and actual WUE is even greater, as actual yields are lower than potential yields. If farmers achieve 65% of the potential yields, WUEs are expected to equal between 35% and 45% of the calculated values, as was observed by Franke et al (2011) for the Sandveld region. Still, the improved WUE as a result of enhanced CO 2 levels may mitigate the impact of an expected reduction in future water availability in the Sandveld due to current overuse (Archer et al 2009) and possible declining rainfall.…”

“…The LINTUL crop growth model used in the present study-similar to the one used by Franke et al (2011) to calculate current potential potato yields and water use efficiencies in the Sandveld region-simulates potato dry matter production based on the amount of intercepted radiation by its green foliage and a conversion factor for RUE (Spitters 1990), following the approach of Kooman and Haverkort (1994) by calculating the temperature-dependent phenological development of a potato crop. Higher temperatures lead to earlier crop emergence and a more rapid initial leaf growth, resulting in increased interception of solar radiation at early stages of crop growth, a more rapid maturation of the crop, and a reduced length of the growing cycle from planting to harvest.…”

Where eagles soar: Fine‐resolution tracking reveals the spatiotemporal use of differential soaring modes in a large raptor

“…Nests in this region are mostly located on isolated rocky outcrops interspersed through relatively flat plains. There is little formal conservation in the Sandveld, which is consequently highly fragmented by agriculture (Franke, Steyn, Ranger, & Haverkort, 2011; Heydenrych, 1993). Nevertheless, this region maintains an important population of Verreaux’s eagles characterized by high annual breeding productivity (Murgatroyd, Underhill, Rodrigues et al., 2016).…”

A Robust Potato Model: LINTUL-POTATO-DSS

“…To simulate water-limited yield using LINTUL-POTATO, Stol et al (1991), Franke et al (2011), andVerhagen et al (1998) calculated the daily crop evaporation from Penman-Monteith grass reference transpiration (ETo) and a crop-specific coefficient (using the daily maximum and minimum temperatures, relative humidity, wind speed, solar radiation as input parameters), crop canopy cover, rainfall, and soil evaporation (calculated according to Ritchie, 1972). Water availability was calculated from soil water-holding capacity and precipitation and a water balance dependent on precipitation, drainage, and evapotranspiration.…”