Plant communities of the western part of the Bloemfontein district: the Ca land type

An analysis of the plant communities of the Ca land type of the Bloemfontein West District is presented. The Braun-Blanquet technique, supplemented by TWINSPAN, was used for phytosociological classification of the vegetation of the study area. Eleven distinct vegetation units were recognized and described. An hierarchical classification is suggested and each vegetation unit is related to its particular environmental characteristics. Relevés were compiled in 76 sample plots.‘n Ontieding van die plantgemeenskappe van die Ca-landtipe van die Bloemfontein-Wes-distrik word aangebied. Die Braun-Blanquet-tegniek, ondersteun deur TWINSPAN, is gebruik vir die fitososiologiese klassrfikasie van die plantegroei van die studiegebied. Elf plantegroei-eenhede is geïdentifiseer en beskryf. ‘n Hiërargiese klassifikasie word voorgestel en elke plantegroei-eenheid word aan die hand van toepaslike omgewingsfaktore verklaar. Reievés is in 76 monsterpersele saamgestel

Heat stress in dairy cattle under southern African conditions. II. Identification of areas of potential heat stress during summer by means of observed true and predicted temperature-humidity index values

November-March are the hottest months of the year with the highest monthly mean "temperature-humidity index" (THI) in South Africa and Namibia. These 5 months are associated with severe heat stress in dairy cattle, are of critical importance for their performance and may have great economic implications for the owner as well as for the dairy industry. Firstly, compared with the existing Livestock Weather Safety Index (LWSI), more relevant meteorological data can be generated when mapping South Africa and Namibia according to the LWSI modified for lactating dairy cattle (LDC). Secondly, compared with the observed true THI values alone, more relevant data on heat stress and its deleterious effects on dairy cattle performance, become available when mapping South Africa and Namibia according to the combined observed true and predicted THI values. Minimum precautions against heat stress in dairy cattle are recommended depending on THI values as classified by the LWSI for LDC.The articles have been scanned in colour with a HP Scanjet 5590; 600dpi. Adobe Acrobat XI Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format.mn201

Heat stress in dairy cattle and other livestock under southern African conditions. III. Monthly temperature-humidity index· mean values and their significance in the performance of dairy cattle

Temperature-humidity index (THI) values applicable to South Africa and Namibia have been established during this investigation for each month of the year by means of computerized modelling and mapping techniques. The data indicate that each year heat stress risk areas (HSRA's) expand from August to January and retract from February to July. The THI values classified according to the Livestock Weather Safety Index (LWSI) for lactating dairy cattle (LDC), suggest that, especially during November to March there is the risk of moderate to advanced heat stress in most South African dairy cows. This has important implications for their general health, udder health, production and reproduction. Careful planning of facilities and highly adaptable herd management are required to protect dairy cattle from heat stress.The articles have been scanned in colour with a HP Scanjet 5590; 600dpi. Adobe Acrobat XI Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format.mn201

Modelling nitrogen leaching : are we getting the right answer for the right reason?

The complexities and challenges in quantifying N leaching have led to development of a range of measurement and modelling techniques, but none are widely applied. Observations that N moves more slowly than water through the soil profile has resulted in different approaches being used to simulate impeded N movement in crop models: (i) by accounting for nitrate NO−3 adsorption to the soil, (ii) by considering incomplete mixing between resident and draining soil water fractions or (iii) a combination of both.We compare and discuss strengths and weaknesses of these approaches. Our inability to directly measure model parameters (especially with regards to simulating N dynamics), and the risk of compensating errors during model testing and calibration, often results in low confidence in simulated N leaching. We caution that our current ability to simulate N leaching is in most cases not yet well enough developed for reliable and accurate predictions. We recommend a more strategic approach involving better linking measurement and modelling to improve understanding of the critical soil processes that control N leaching as one way of further improving our understanding and quantification of N leaching.http://www.elsevier.com/locate/agwathb201