Irrigation scheduling to manage crop quality

Irrigation scheduling at one of South Africa’s largest irrigation farming enterprises has led to a saving of up to 34% in water use and possible enhanced crop performance. Robyn Joubert reports.

Settling dams are used to recycle the flush water from the sand filters of the irrigation systems. Clay and silt settles in the small rectangular compartments on the side and the clean water flows back into the dam.
Photo: Courtesy of Willem van Aarde

Karsten, one of South Africa’s largest irrigation farming enterprises, with 11 farms in the Orange River region and nearly 2 000ha under irrigation in this area, has made considerable progress in optimising the use of its precious water allocation. At its Keboes Fruit Farm in the Upington area, accurate irrigation scheduling has resulted in water savings of up to 34%.

Founded by Piet and Babsie Karsten in 1968, Karsten produces mainly export table grapes on nine farms covering 1 082ha on the banks of the Lower Orange River between Upington and Klein Pella. It also produces wine and raisin grapes, citrus, dates, watermelons, sweet melons, maize, wheat, potatoes and pomegranates on nearly 900ha.

In Ceres, Kartsen produces deciduous fruit on 187ha, as well as nuts, maize, wheat and vegetable seeds on 1 000ha in Prieska, in the Northern Cape. In the Hex River Valley and Piketberg, it produces table grapes on 90ha and 30ha respectively.
The enterprise also owns packing facilities, export and logistics companies, an import and distribution business in the UK, as well as production and packhouse facilities in Egypt. 


Willem van Aarde

The problems

Karsten agronomist Willem van Aarde says there were a number of motivations for water saving techniques. One of these was pressure from supermarkets. “We get increasing pressure from both local and overseas supermarkets to protect the environment and conserve our natural water sources. Added to this, the cost of electricity has increased severely over the last few years. Irrigation pumps use a lot of electricity, so the less we irrigate and the more accurately we irrigate, the less electricity we use,” says Willem.

Karsten has introduced a number of water optimising measures. These include using maize and wheat straw as mulch in the vineyards to reduce evaporation from the soil and to improve its water holding capacity over time, and the automation of irrigation systems to make it easier to manage irrigation scheduling.

All Karsten’s dams are lined with 2mm high-density polyethylene to prevent water loss. On some of the bigger farms, flush water from the irrigation systems is pumped into settling dams where the clay and silt in the water sinks to the bottom, and the water can be re-used for irrigating a few more hectares.

The solutions
But the introduction of a new irrigation scheduling system has had the most significant impact on water use. Until February 2008, Karsten relied on neutron moisture meters for irrigation scheduling. “These meters are very accurate but the process was time consuming. The readings gave information about a single moment in the soil, and we had no idea what happened in the soil between measurements. We wanted a system that could do continuous logging and give a clear picture of what goes on in the soil at different depths,” says Willem.

In 2008, Karsten began installing the first of 500 DFM soil moisture probes, bought from DFM Software Solutions at a cost of around R3000 each, and a software programme called Irricheck, developed by Bertus van der Westhuizen from Farmsecure Agri Science Irrigation (FASI). Irricheck automatically draws the weather forecast from the internet and actual weather data from an automatic weather station, and calculates the actual evaporative demand and the expected evaporative demand.


Straw mulch is used in vineyards in combination with a cover crop such as fescue to prevent evaporation from the soil and improve water holding capacity.Watermelon and sweet melon lands are covered with plastic to prevent water loss and control weeds.

One person on each farm is responsible for downloading data from the probes onto a wireless logger every Monday and Thursday, which is then plugged into a computer and the data is downloaded onto Irricheck. A team of four Karsten agronomists visit each farm on a weekly basis, making any necessary adjustments to the software and providing each farm manager with an accurate weekly irrigation schedule.

“They dig a few soil profile holes every week to double-check the system and to make sure the recommended irrigation schedule correlates with the current soil moisture level,” says Willem.

How it works
The system enables Karsten to determine the maximum safe moisture depletion level, to maximise the irrigation intervals and to minimise evaporation losses. “We over-irrigated a lot in the past. The more accurate irrigation spells help to create favourable soil conditions with more oxygen for root and microbial life.”

Keboes Fruit Farms executive manager Jacey Fölscher introduced the system at the 560ha Raap en Skraap farm and five production units in Blouputs in 2008. Water use on Raap en Skraap was reduced by about 34%, from 43 116 pumping hours in 2007 to 28 248 pumping hours during 2009 and 2010. For the January to December 2011 period, Raap en Skraap saved on average 24% pumping hours compared to 2007.


All Karsten’s dams are lined with 2mm high-density polyethylene to prevent water loss.

The company has installed mechanical flow meters on most of the newer farms to record the amount of water that is used for irrigation. However, the high amount of silt in the irrigation water erodes the working parts of the mechanical flow meters, which then calls the reliability of the readings into question, Willem points out. “The tendency nowadays is to use electronic flow meters that are clamped on the outside of the irrigation pipes and do not have any moving parts.”

Water savings potentially means the group can increase land under irrigation. “It is very difficult to secure additional water rights, so it would have a huge positive impact on our farming business if we could measure the water savings and use this water to increase land under irrigation. This will also motivate farmers to save even more water. Expansion is very important to us and it will enable us to make full use of our infrastructure and to create more jobs,” he says.

The purpose of irrigation scheduling is not confined to saving water, but also to optimise water use. “Crops are over-irrigated most of the time and occasionally under-irrigated for shorter periods. In cases like these, the scheduling system can improve water use efficiencies without necessarily making any water savings. “The grapevine and all other plants perform much better when they receive well-timed irrigation. We also try to limit drainage from the soils which means less leaching of nutrients and savings on fertiliser.”

Willem is also experimenting with tweaking irrigation scheduling to influence the crops’ performance. “We have had good results with enhancing grape colour by applying a certain amount of water stress during the season. This is, however, not standard practice in our company, and should be done with extreme care. We also manage soil moisture a little below the optimal level before and during bud break and in the first few weeks of the season, to increase soil temperature and the amount of oxygen in the soil.

We believe that bud break is more even and that the initial growth at the onset of the season is quicker if this is done correctly.” Karsten feels its investment in irrigation scheduling has been worth the expense. “We have a big responsibility towards our workers and their families to make sure our company performs well in a very challenging industry.

We want our children to have the privilege of farming one day. I have more peace of mind about irrigation than in the past. If an orchard doesn’t perform well, I can look at the irrigation history and see if there were times when the soil was too wet or too dry,” concludes Willem.

Contact Willem van Aarde on 082 826 1409 or email [email protected]