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Low rainfall could lead to poor Western Cape wheat harvests

21 Jul 2017

According to Johan van den Berg, agricultural meteorologist at Santam Agriculture, rain fell at the right time over the last few years, resulting in good wheat production over the majority of the Western Cape. There is, however, a real possibility that poorer rainfall may occur over the next few years during the active growing season, especially the southern Cape, which could lead to poorer harvest.

Couleur via pixabay

“During the past few years, average to above-average rainfall fell during the growing season in the Western Cape wheat district, although in 2015 the Swartland area of the Western Cape had below-average rainfall,” said Van den Berg.

Low rainfall, berg winds and drought-induced stress

The Swartland’s wheat harvest fell to 368,000 tonnes in 2015, in comparison to harvests of 593,000 tonnes in 2014 and 558,893 tonnes in 2013. Although the Swartland district had average rainfall in 2016, Van den Berg explained that very good rain fell in September, which contributed to a leap to 644,000 tonnes in the area’s harvest for the year.

September is a critical rainfall month for Western Cape wheat, as the plants are then in their reproduction phase and drought-induced stress can inflict great damage.

Neel Rust, chief operating officer of Laeveld Agrochem, explained that berg winds, which normally come in August, can also have a negative effect on the wheat harvest. The effects of cold fronts which move across the country, together with the start of the warmer summer temperatures, often cause the dry land/berg winds.

Wheat is predominantly cultivated in the Western Cape’s Swartland and Rûens growing areas, but also in the Southern Cape, as far as Mossel Bay.

According to Van den Berg, the climatic cyclical effect over the long-term has the greatest effect on the average rainfall variance and, up until now, climate change has played a lesser role.

Low rainfall could lead to poor Western Cape wheat harvests

The attached graphs show the rainfall variance of the long-term, average rainfall (expressed as a percentage of the long-term rainfall average) for the critical times of the wheat growing season, from June to September, for the Rûens and Swartland areas.

Van den Berg is of the opinion that the expected weaker rainfall situation over the next few years will be more concentrated in the Southern Cape than the Swartland production areas.

Western Cape the biggest contributor to the SA's wheat harvest

The Western Cape is the biggest contributor to the country’s wheat harvest. The National Crop Estimates Committee’s latest figures show that the Western Cape harvested 1,098,200 tonnes of wheat in 2016. The country’s total harvest estimate for 2016 stood at 1,910,000 tonnes.

According to Rust, South Africa is a net importer of wheat, which means that the country must import wheat to fulfill the market’s demand. At the moment, the yearly demand stands at more than three million tonnes.

Background information

• The sowing of wheat in the Western Cape occurs until the end of May, and it is imperative that rain falls before mid-June, but preferably before the end of May, so that the new plants can emerge and establish.

• Rain must also fall in the vegetative part of the growth season, from June to August, but it is not as critical as in September.

• Just before and during harvesting, from October until the first part of November, rain must preferably not fall, as even a little rain, together with overcast skies, can cause much damage to the quality of the crop.