Dual cropping – it can work!

Dual cropping can dramatically improve the profitability of maize and livestock production units.

Dual cropping – it can work!
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Sheer disbelief. That’s the response of most maize farmers when I suggest it’s possible to improve profits by dual cropping maize with annual winter forage legumes. It appears to them to be just another too-good-to-be-true scheme. Part of the problem is, I suspect, that they think dual cropping will involve a radical change in the maize industry. But this is not what I have in mind. What I’m advocating is the adoption of dual cropping on a limited scale in specific situations.

I’m confident this can result in a significant improvement in the profitability of maize and livestock production. Moreover, it has the potential to restore biological fertility to run-down soils, which means higher yields at lower input costs with reduced risk in the long run.

A trial conducted in the Harrismith region this past season yielded data that supports the concept of dual cropping. Let’s look at it in more detail. I was asked by a company that markets carbon-based fertilisers to conduct a maize trial to test their products. A randomised block trial with three replications was used. There were seven treatments and the plot size was 3,68m (4 rows x 0,92m) x 6m. In other words, each plot was 22,08m².

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The outside rows are greener and will remain so for longer than the inside rows. This is due to the fact that the outside rows have greater access to soil and moisture.

The goal was to achieve a plant population of 36 000 plants/ha. To ensure that every plot had the identical number of plants at the same spacing between plants, the planter – a conventional four-row maize planter – was set to 72 000 plants/ha. After germination, plants were thinned out to 36 000 using a marked rope to indicate the desired spacing. Only the two inner rows of each plot were thinned – the plant population in the outside rows stayed at 72 000.

This is because only the two inner rows were reaped for yield determination in this trial. The outside rows were effectively ‘guard rows’. Another important fact about the trial layout is that the three blocks were separated by a full planter’s width to create 3,68m pathways.

In March this year, the inner rows started ripening before the outside rows. The latter were noticeably greener for about three weeks after the inner rows started turning brown. As the cobs on the outside rows seemed as good as those on the inner rows, I decided to reap the outer rows and compare the yield with that of the inner rows.

The results were better than expected. The average grain yield for all the treatments was 5,5t/ ha for the inside rows and 11,6t/ ha for the outside ones. The outside rows had double the yield of the inside rows.In tramline maize, both rows are outside rows. The trial therefore sheds some light on what can be expected from tramline maize. The yield from maize planted in the tramline configuration must be twice the yield per unit area of conventional four-row maize, because tramlines occupy only half the area of conventionally planted maize.

As I see it, tramline maize must be planted at the same population as that of conventional four-row maize. In other words, the number of plants/ha must be the same and the spacing between plants in tramlines must be half that of conventional maize.
The same amount of fertiliser should be applied per plant. This means that fertiliser applied to tramline rows must be double that applied to conventionally spaced rows. I’m sure that readers will have questions about tramline/dual cropping. Next time, I’ll do my best to cover the most important ones.

John Fair is a pasture consultant who heads up Fair’s Biofarm Assist. He can be contacted on 058 622 3585 or
[email protected].