New irrigation guidelines for pasture production developed under the auspices of the Water Research Commission (WRC) are proving to farmers that with the efficient application of water and fertiliser the grass can be greener on their side of the fence.

According to the Milk Producers’ Association, South Africa’s dairy farmers are expected to produce 2 460 million litres of milk by December. As the human population increases and diets become more affluent, so the demand for animal protein (such as milk) increases. At the same time, farmers are under pressure to decrease their share of water and fertiliser usage.

Despite the latest fertiliser and irrigation application equipment and scientifically-based guidelines, knowledge gaps have been identified between research and farming practices. A number of experiments have been carried out throughout the country on the effect of nitrogen on yield and quality of grass pastures; however, there is a lack of reliable information and data pertaining to ryegrass water requirements to facilitate efficient irrigation management.

To fill some of these knowledge gaps the WRC funded a five-year solicited project to study the irrigation management of ryegrass and kikuyu pastures under different management conditions. The research was undertaken by the universities of KwaZulu-Natal (UKZN) and Pretoria (UP) along with the CSIR. The main objective was to study water use of these pastures, with field experiments undertaken over a period of two years at two agricultural research sites (in Pretoria and KwaZulu-Natal). This has led to the recent publication of water use and irrigation guidelines for the major pasture growing areas of South Africa.

At UP’s Hatfield experimental farm and KZN’s Cedara research station experiments were conducted to determine the effects of different water levels in combination with different nitrogen fertiliser applications on the growth rate and dry matter production, quality, water use and water use efficiency of annual ryegrass for two seasons.

The experiments showed that irrigation and nitrogen fertiliser affected yield and leaf area significantly. Higher frequency of irrigation coupled with high fertiliser application significantly improved dry matter yield. The study concluded that by irrigating once a week and fertilising with high nitrogen application rate after each harvest, optimum yield can be achieved with better quality pasture and a better water use efficiency.

Dr Andrew Sanewe, Research Manager at WRC says, “As a result of South Africa’s variable climate, general water scarcity, and often marginal soils, it is not unusual for dairy farmers to supplement their herds’ feed with irrigated pastures. It is estimated that the total area utilised for irrigated pasture production is about 16% of the total area under irrigation in South Africa”.

Irrigated annual ryegrass (Lolium multiflorum) is the primary sources of feed in the pasture-based dairy industry, and is mostly grown in the relatively higher rainfall areas, particularly the KwaZulu-Natal Midlands, Eastern Highveld, Eastern Cape and in the winter rainfall areas of South Africa. Annual ryegrass has high nutritional qualities, palatability, digestible energy, protein and mineral contents, playing an essential role in supplying good quality grazing between the winter and summer seasons. On the other hand, kikuyu (Pennisetum clandestinum) is the predominant summer grass pasture used for milk production along the east coast of South Africa.

Irrigation water and nutrients are resources that can be optimised by selecting an appropriate irrigation type, scheduling technique and pasture type. For sustainable pasture production, the best possible fertiliser and water regimes are required in order to attain high biomass yield with minimum inputs, which maximises profit while minimising the impact on the environment. The most appropriate and cost-effective management strategy would therefore be to integrate irrigation and nutrient (especially nitrogen) inputs, since nitrogen and water cannot be managed independently.