Written by: Niels Harmuth (Agronomist)
How can cover crops alleviate some of the many challenges that farmers are faced with?
In many areas of our country this past summer, above average rainfall was a welcome bonus particularly in the maize producing areas of the North West and Free State provinces.
It was however sad to see that numerous producers lost substantial amounts of topsoil caused by excessive runoff of water due to heavy downpours. This can be attributed to various tillage techniques which have been practiced for many years. Other aspects like lack of contours are also a contributing factor. These techniques are not necessarily wrong, however in many cases changes need to be made to prevent the loss of our precious topsoil.
This past season excess water was the culprit. During other seasons high winds in spring lead to substantial topsoil loss. Bear in mind that 1mm of topsoil lost per hectare equates to 10 ton loss/ha.
We need to take into consideration that many of these soils particularly in major maize producing regions, the pantry of SA maize production are sandy with often low clay percentages. Over many years of cultivation these soils have lost structure and in essence have low organic matter percentages which indicate low levels of carbon. This coupled with low clay percentages leads to low cation exchange capacity, which in turn is normally indicative of soils that have a low nutrient supply base. To sum up, this means that many of the nutrients plants require, both macro and micro, need to be added through the judicious use of chemical fertilizers, which in turn over time have their own associated consequences. These include the decline of essential fungi and bacterial populations in the soil. In fertile soils the latter assist in plant health and nutrition.
So the big question is what can be done to alleviate to some extent the dilemma we are faced with? The following are some options at our disposal:
Move away from conventional tillage where possible to a system of no or minimum tillage.
Keep soils covered 24/7, 365. Bare soils in spring or early summer that have surface temperatures varying from 45°C-75°c and higher do not lend themselves to successful germination or early seedling development.
Improving the organic matter percentage of the soil. Living plants and their roots are carbon pumps that improve soil organic matter percentages.
Increase biodiversity by introducing cover crops. Seldom in nature do we have single plant species domination. Mother nature is biodiverse. Every species contributes to the other’s wellbeing by a process of give and take, and therefore benefits the whole process. Bacteria, fungi, and many other forms of life in the soil in turn provides much needed nutrients for plants. The whole process is therefore symbiotic.
Legumes should form part of the amelioration process of our soils.
The whole aspect of improving our soils has to be looked at holistically and requires a total mindset change.
Often many of our decisions regarding cropping are entirely profit driven. Achieving maximum yields should not be the only ultimate goal as this comes at a cost. Somewhere along the line we need to find a balance between the short-term profit motive and the long-term sustainability of our soils.
Moving towards reconstructive agriculture through the introduction of cover crops is multi-dimensional, has many aspects to it and is also challenging to say the least. To put this into perspective lets have a look at the numerous questions we need to ask ourselves regarding the topic:
What type of crop should I plant?
When and how should I plant the crop?
When should the crop be desiccated or incorporated into the soil?
When a cover crop is selected, consider soil conditions, climate and what is to be accomplished.
Is the main purpose to add available N to the soil, or to scavenge nutrients and prevent loss to the system? Legumes add N, other cover crops take up available N.
Is the cover crop to provide organic matter?
Is the cover crop to be used as a surface mulch or to be incorporated into the soil?
Is erosion control in spring, summer or autumn your primary objective?
Is the soil very acidic, not fertile and has low nutrient availability?
Is the soil compacted? Some crops like Sudan grass, sweet clover and forage radish are good at alleviating compaction.
Is weed suppression your main goal? Certain cover crops establish vigorously and quickly.
Which species are best for your climate?
Will the climate and water holding capacity of your soil cause a cover crop to affect the availability of moisture for the following crop?
Are root diseases or plant parasitic nematodes a problem, that requires attention?
The above are but a few of the many questions that need to be taken into consideration.
Remember cover cropping is a universal concept with individual needs based on your farming set up and goals that need to be achieved.