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Remote sensing helps farmers and policy makers

Remote sensing has helped the national crop estimates committee (CEC) achieve a 0.13% error margin in 2015 from 9.77% in 2002 and will allow policy makers to assess drought impact down to municipal level in the Western Cape.

When the agricultural control boards such as the Maize Board and Wheat Board were abolished in 1997 there was a need to have an independent body to provide crop estimates to guide farmers, processors, futures dealers and policy makers. This led to the establishment of the Crop Estimates Committee (CEC) within the Department of Agriculture. To prevent conflict of interest no member of the CEC could trade in the commodities being forecast.

The initial crop estimates were collected by means of a telephonic survey of industry participants, be they farmers, processers or agricultural cooperatives. As the graph below shows, there was an inherent bias to under-estimate the national maize crop in part because low supply would push up prices.


To help reduce the bias, the producer independent crop estimate system (PICES) was developed which uses remote sensing using satellite images and aerial surveys using low-flying aircraft and helicopters to estimate acreage planted to the various crops. The remote sensing is so sophisticated that it can distinguish between the various plant types and asses how well they are growing. This helps with the yield estimates, which are also compiled by on-site surveys conducted by the state-run Agricultural Research Centres (ARC) Grain Crops Institute.

From 2009 to 2015, the CEC had three underestimates and four overestimates for the size of the crop so there was no prevalent bias. In addition, the error margin has moved from 9.77% in 2002 to only 0.13% in 2015, a feat better than most national crop estimates conducted in the world, where the error margin is “satisfactory” if it is less than 5%.

In particular, the CEC was justifiably proud of its record in the last three years when despite wide fluctuation in the maize crop from 11.69 million tonnes in 2013 to 14.25 million tonnes in 2014 to 9.94 million in 2015, the error margins were respectively -.13%, +0.4% and -0.75%.

“The fact that we had less than one percent error in the past three seasons shows how robust the system is as during that time the maize crop slipped by 3.6% in 2013 from 2012, then expanded by 21.9% to the largest crop since 1981 before plunging by 30.2% as the drought cut yields,” said Eugene du Preez, director of privately-held SiQ, which provides the committee with satellite and aerial data, which helps it determine the size of the area planted.

The expertise and equipment built up to service the CEC has allowed SiQ to expand its services so that it can help individual farmers and provincial departments of agriculture. Recently they have conducted surveys to see how much arable land in the former homelands of Ciskei and Transkei could be used for maize, while also conducting census for other provincial departments.

One such census was recently completed in the Western Cape and that showed that there 97 crop types cultivated and that there was a massive 12,000 facilities in terms of agricultural infrastructure such as abattoirs. The remote sensing could answer questions such as how many pear orchards are there and what is the amount of hectares devoted to pears. What is the value of crops per municipality and how does this fluctuate in good and poor weather conditions? How many farms are there devoted to game and how much to sheep or cattle? What agri-tourism facilities are there and what do they offer?

This kind of detail means that SiQ can say that the top five districts in terms of grain production potential in the Western Cape are the Swartland at R757m, Cape Agulhas at R585m, Thewaterskloof at R547m, Hessequa at R465m and Swellendam at R463m. This will help policy makers with assessing how much revenue is likely to decrease due to drought given that Western Cape dams are at critical levels with Voelvlei dam for instance at only 19% of capacity.

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