Assessment of the potential adoption of infield rainwater harvesting technique in the communal farming areas of the upper and middle Modder River Basin, South Africa

Published ArticleRiver basin is a geographical unit that defines an area where various users of the basin's water interact. In a river basin there are many water-related human interventions that modify the natural systems and impact on those who live downstream. Researchers from the Agricultural Research Council's Institute for Soil, Climate and Water (ISCW) have developed an infield rainwater harvesting (IRWH) technique for small-scale farmers in the Modder River basin. This technique increased crop yield significantly compared to conventional practices. Since the start of its dissemination by the ISCW programme, adoption at a homestead level grew from six to more than 950 households. The suitable land for the IRWH in the study area is estimated to be 80 667 hectares, of which approximately 14 500 hectares are in the communal farming area. If all the suitable areas were to be put under IRWH practice, a decrease in the runoff could be expected, with consequences on downstream water users. A field survey conducted using a participatory methodology on a sample of 21 villages selected randomly, revealed that there are strong positive motivators, such as increase in crop yield and more food available for the household which explain the rapid expansion of IRWH in homestead application. However, some very strong demotivators were identified, such as high levels of poverty, limited family labour for the preparation of the plots, lack of tools, and the lack of fences around community gardens which could lead to theft and damage by animals. It appears that the demotivators identified are strong enough to prevent a significant expansion of the IRWH technique beyond homestead scale. Hence the expected impact on water availability for downstream users is expected to be minimal

Impact of climate change on irrigation water management

Paper presented at the South African Society for Agricultural Extension Conference 4 - 7 May 2010 "The Impact of Climate Change on Extension Delivery in South Africa", Langebaan, Western Cape, South Africa.This paper was transferred from the original CD Compiled and produced by Beta Products cc. The material on the CD ROM was published using Adobe Acrobat technology

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

Mathematical simulation of crop growth and water relations has become indispensable to agricultural science and practice. A critical assessment of how modelling has contributed to the development of crop science and to the management of crop production and natural resources in South Africa (SA) over the past 25 years could give new perspectives on the benefits derived from modelling, the appropriateness of approaches employed and the best way forward. The initial objectives of the major SA modelling initiatives (ACRU, BEWAB, CANEGRO, CERES, PUTU, SAPWAT, SWB) dictated the approaches that were followed and determined their impacts. Significant advances were made with regard to improved understanding of crop growth and water use and adapting models for local conditions such as dryland grain crop production under very low rainfall. Modelling provided invaluable support for strategic investigations into the impacts of climate change, land use and water use. Many of the models succeeded in providing much-needed information to improve tactical and operational management of irrigated and dryland agriculture. Some models have been (and are being) used operationally to forecast crop production (maize, wheat and sugar) and to monitor droughts in natural vegetation, adding value to the respective industries. Modelling has formed, in some cases, an integral part of tertiary education in crop science and hydrology. This should be strengthened to build more capacity to address the ever-increasing complexity of challenges in agriculture. The review identified factors that are crucial for modelling to maintain effective impacts on the science and practice of crop production and natural resource use. These were excellent scientific leadership, long term funding, effective collaboration between local and with international groups, expertise on local agronomy and high quality experimental data for model testing and adaptation. Future modelling efforts should explore opportunities to integrate information obtained from technologies such as remote sensing and genomics.Articl

Full orbital solution for the binary system in the northern Galactic disc microlensing event Gaia16aye

Gaia16aye was a binary microlensing event discovered in the direction towards the northern Galactic disc and was one of the first microlensing events detected and alerted to by the Gaia space mission. Its light curve exhibited five distinct brightening episodes, reaching up to I = 12 mag, and it was covered in great detail with almost 25 000 data points gathered by a network of telescopes. We present the photometric and spectroscopic follow-up covering 500 days of the event evolution. We employed a full Keplerian binary orbit microlensing model combined with the motion of Earth and Gaia around the Sun to reproduce the complex light curve. The photometric data allowed us to solve the microlensing event entirely and to derive the complete and unique set of orbital parameters of the binary lensing system. We also report on the detection of the first-ever microlensing space-parallax between the Earth and Gaia located at L2. The properties of the binary system were derived from microlensing parameters, and we found that the system is composed of two main-sequence stars with masses 0.57 ± 0.05 M⊙ and 0.36 ± 0.03 M⊙ at 780 pc, with an orbital period of 2.88 years and an eccentricity of 0.30. We also predict the astrometric microlensing signal for this binary lens as it will be seen by Gaia as well as the radial velocity curve for the binary system. Events such as Gaia16aye indicate the potential for the microlensing method of probing the mass function of dark objects, including black holes, in directions other than that of the Galactic bulge. This case also emphasises the importance of long-term time-domain coordinated observations that can be made with a network of heterogeneous telescopes