The unpredictability of South Africa’s regional climate has a profound influence on feed provision for domestic livestock, game animals and people. The recent extended drought has affected feed, food and livestock prices and caused damage to farms in many areas. Possible causes of this damage include higher intensity, and more frequent occurrence of extreme weather conditions.
The paradoxical effect of GHGs
Many researchers attribute this to a measurable increase in greenhouse gases (GHGs). The primary GHGs are CO2 (carbon dioxide), CH4 (methane) and N2O (nitrous oxide). In the last 200 years, from the beginning of the industrial revolution, atmospheric CO2 concentration has doubled, and in the last 40 years GHG emissions have increased by 40%. The average global temperature has risen, by an average increase of 0,12°C per decade during the past 60 years.
A rise in atmospheric CO2, and sunlight on crops, leads to an increase in production. While more carbohydrates (starches or sugars) are manufactured in plants when photosynthesis increases, the concentration of other nutrients, crude protein, zinc and iron, per kg of plant yield, is reduced. However, with higher temperatures and drier conditions the rate of photosynthesis will reduce. Thus, despite the increased CO2, crop yield will be lower when temperatures rise during droughts.
Research conducted on the nutrient content of crops found that minerals, such as calcium, phosphorous, potassium, zinc and iron, as well as nitrogen (crude protein), were reduced by up to 8% under conditions of increased atmospheric GHGs.
Scientists predict that by the year 2050, 150 million people will not have access to sufficient protein in their diets. Reduction in zinc content will put the health of 138 million people at risk. Researchers estimate that a billion mothers and 350 million children will suffer an increased risk of anaemia. GHGs will exert a negative effect on food security. There is an acceptance that the increase in GHG concentration will decrease the nutrient content per kg of crop produced. The impact of this for the farmer is that there will be a reduction in rangeland nutrient provision and that maize used in feeding will have a lower nutrient content per kg offered.
Future planning for farmers
Knowing this, the farmer can plan to ensure the right amount of quality nutrients are provided for profitable farming. To achieve this the farmer needs to know the veld quality and the nutrients it provides and cannot assume that historical data is valid. Historical data are based on lower average temperatures and GHG concentrations and different plant species composition.
There are cultivar differences and this information can be used to plant crops or grasses that have better nutrient composition for beef production. Nutrient availability (digestibility) must also be determined to improve choice of crop or pasture species. This will help determine the amount (kg) of crop protein produced per hectare, which can be connected to the amount of beef produced per hectare. – Dr Klaas-Jan Leeuw, ARC