SA Graan April 2018

April 2018

POTENTIAL BENEFIT

DESCRIPTION

Sustainable intensification

Cool season cover crops expand and intensify summer cropping systems and keep production

at a high level over a long period. It allows us to use resources (sunlight, residual moisture and

-nutrients) optimally. Spatial and temporal intensification making use of intercropping systems is

made possible.

Starting with CA can be a daunting experience for first timers. Cool season cover crops allow

ample time to correct soil nutrients, uplift compaction, get rid of problem weeds (e.g. kweek) and

build a soil mulch. CA without diversity and soil mulch is doomed to be a failure.

Integration of livestock

Cool season cover crops’ nutritional content is high and productive animals (lactating cows,

weaners and growing sheep) can benefit from utilising them.

General

Cover crops scavenge soil nutrients as they grow and ultimately release them for following crops

to use. This reduces the potential of nutrient losses, especially N.

Cover crops reduce crusting, runoff, and protect soil against wind and water erosion.

Cover crops biomass contributes to soil organic matter, which helps to improve soil structure,

water infiltration, and water-holding and nutrient-supply capacity.

Cover crop roots can act as ‘living ploughs’ breaking up compacted soil layers.

Cover crop residues increase water infiltration and limit evaporation. This helps to reduce mois-

ture stress during drought conditions.

Leguminous cover crops fix N as they grow. This N mineralises after the cover crop is terminated

and becomes available for use by future crops.

Cover crops shade the soil, which can reduce high surface temperatures, weed germination and

growth. Some cover crops also have an allelopathic effect on weeds.

TABLE 1: POTENTIAL BENEFITS OF COOL SEASON COVER CROPS.

0,5 kg/ha fodder radish

0,5 kg/ha tiller radish

0,5 kg/ha rape

Total seeding density of 24,5 kg/ha.

Terminating the cover crop

The use of a roller-crimper is a handy tool to terminate cover crops.

Small grains are very sensitive during the soft dough stage and will

terminate through crimping. If left too late viable seed can create

problems as weeds during planting of cash crops. Often producers

will use glyphosate after rolling small grain to get rid of other weeds.

Brassicas and legumes are not killed successfully by using a roller

crimper. A good herbicide programme to terminate legumes and

brassicas is a mix of glyphosate and 2,4-D or dicamba. Glyphosate

alone is not a recommended programme to kill a legume such as

hairy vetch since its performance is variable.

Plant growth regulators such as 2,4-D and dicamba are effective, but

also require some delay (one to two weeks) between application and

maize planting to avoid herbicide injury. Faster desiccation by using

paraquat and 2,4-D or paraquat and atrazine is also a possibility.

Grazing of cover crops

Cool season cover crops are preferably utilised or managed by live-

stock through mob grazing, also called short duration grazing and

ultra-high-density grazing. The main purpose of this grazing prac-

tice is to increase competition among livestock, concentrate urine

and manure and trampling more plant material onto the soil surface.

The amount of biomass utilised and trampled by grazers should be

managed, for example through different camp sizes (using electrical

fences) (

Photo 8

Mob grazing (e.g. grazing intervals) still needs more research in

South Africa. A temporary recommendation is to move livestock

daily if shorter intervals are impractical. Creating an inclusion zone

where livestock can be ‘parked’ during periods of bad weather, or

when you have to work with the animals, will make implementation

more manageable.

Conclusion

Cool season cover crops use substantial volumes of water and it

is imperative that response farming principles are adhered to. The

recharge of the soil profile with soil moisture before planting grain

crops is necessary and grain crops should only be planted after suf-

ficient rain (20 mm in 24 hours). As organic matter in the soil increas-

es, more water will infiltrate and more plant available water will be

stored in the soil. Pest problems might occur due to the availability

of more food.

For more information contact Gerrie Trytsman at

gtrytsman@arc.agric.za

5: Intercropping winter and summer cover crop mixture with maize.

6: Delayed intercropping with winter cover crops in soybeans.

7: Winter cover crops planted after soybean, Vrede area.

8: Mob grazing on winter cover crops.