Crop Diversity A Pillar Of Sustainable Production

Including more than three crops in a cash crop system may not only help increase yield, but significantly enhance the long-term sustainability of a farm. Dr Johann Strauss of the Western Cape Department of Agriculture spoke to Glenneis Kriel about the benefits of crop diversity.

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Around the world, a growing number of farmers are switching to crop rotation due to its capacity to improve farm earnings through higher yield and reduced fertiliser, pesticide and herbicide usage, while boosting sustainability.

Long-term rotation trials by the Western Cape Department of Agriculture at the Langgewens Research Farm in the Swartland and Tygerhoek in the Southern Cape confirm this.

In crop rotation evaluations that started at Langgewens in 1996, wheat monoculture has always been the poorest performer of all the combinations under trial. But in rotations that included at least one type of legume, such as lupines or medics, the average wheat yield was 30% higher than when wheat was produced in a monoculture. The yields of rotations containing no legumes were on average 12% higher.

BEST ROTATION

A medic-canola-medic- wheat rotation consistently performed the best, producing an average yield 37% better than a system where wheat was produced on its own (see table).

Water- and nitrogen-use efficiency also improved. Wateruse efficiency of rotations that included canola was 11% higher, and rotations that included one or more years of legume crops or pastures were between 26% and 31,6% higher than when wheat was planted on its own.

Nitrogen-use efficiency was on average 89% better in rotations that included legumes than when wheat was produced alone, and 35% better when the rotation included only one year of legumes. The use of canola in the rotation, without any legumes, increased nitrogen-use efficiency by 9%.

During the past two seasons, of which 2017 was dry and 2018 had below-average rainfall, the researchers set out to establish how low the nitrogen level could be reduced in a medic and wheat rotation.