The latest trend that is making its mark in the farming world is the planting of cover crops. Although some benefits are obvious, why would a farmer spend that extra money (between R600 - R2,000 per hectare) to plant seeds after, into or in place of a cash crop? Many farmers have some serious questions and doubts about the viability of this practice...
- Will I get my money back?
- Am I using up the little available water that I have left in my soil just for something to grow and die again?
- Will I compromise the following cash crop?
- What if it does not rain or the seeds don't germinate?
- What are the other risks?
Do these questions sound familiar? Maybe they are similar to that little voice in your head...
Let's look at what multi-species covers can or can't do for you...
They give you cover and structure
With a variety of different root systems, each with a different structure, depth and associated microbe population, they have the ability to reduce and prevent water and nutrients from leaching below the root zone. This prevention of leaching and deep soil percolation can lead to an approximate +-15kg N saving in the form of runaway Nitrates.
The cover and living roots prevent your most valuable asset, your top soil, from being eroded by wind and water. This can save an approximate >10 t/ha (around 0.8mm) of rich topsoil every year.
With the right tools and management, the cover should also allow you to save on some weed management costs.
Feed and be fed
On a microscopic level, covers will feed essential macro- and microorganisms that nourish living roots, buffer pH, break down organic matter, and unlock and process essential nutrients that were previously unavailable for living plants into a useable and highly soluble form.
Cover crops are also a great form of green forage for livestock. If grazed using the correct practices and timing, covers will give you exceptional regrowth, and you will be able to double up on the benefits of covers. If the right species are present in your cover crop mix, it will also be a low-risk standing green feed. This is in contrast to monocrop fodder, which can have a high risk of bloating and other clostridial illnesses. On average, when utilized by cattle (steers), cover crops can benefit you, conservatively measured at about R1,32 per kg of biomass or forage. And you will have tons of natural fertilizer and microorganisms added into the mix in the form of manure, urine, and saliva.
Cover crops do use up (or "feed on") existing soil nutrients throughout their life cycle. However, as long as the cover crop is not burned, harvested, baled or otherwise removed, these nutrients are merely cycled back into the system.
High-density grazing on an irrigated cover crop in KZN
They scavenge
Cover crops use their extensive root systems to tap into soil areas unreachable for cash crops, and scavenge for macro- and micronutrients and minerals that are essential for optimal plant growth, health, and quality. These essential nutrients are released in a more reachable zone for your cash crops to utilize. This in turn will give you as a farmer the ability to start considering lowering your fertilizer usage due to having access to nutrients previously unavailable, and it will prevent future overfertilization. In perspective, when managed right, this can give you a cutback on fertilizer of 5–50% (Please do soil tests and consult soil health focused professionals like SAGRIS before implementing major changes).
They are thirsty, but not greedy
Yes it's true - cover crops, like any plants, use water to grow. The amount of water used of course depends on the availability of water while the amount of water used affects the growth. Although this is obvious, the consequences are not...
What this means is that in years where not much moisture is available, the cover crop won't steal much moisture from the following cash crop. And in years where a lot of moisture is available, the fact that they steal some of that water does not impact the following crop much as there is sufficient water available anyway.
Although they are thirsty and use up some moisture, we have to be fair and acknowledge that they work hard to make life for the following crop easier in the following ways:
- By providing soil cover throughout their lifespan and afterwards, they can reduce total water loss by 28% by reducing evaporation. Critically, this cover is provided during the early stages of the following cash crop where it has not developed its own protective canopy yet. Furthermore, in the early stages, the root zone of the following cash crop is limited to the top layer which makes this the best layer to conserve moisture in as deeper soils are not yet reachable.
- The roots, heightened biological activity, improved soil structure and soil cover increases rainfall infiltration rates, meaning that each rainfall event will be more effective. This means that deeper soil moisture reserves will be replenished quicker during the rainy season.
- Increased soil organic carbon levels can improve the water holding capacity with time, allowing your soil to store an additional >150,000 litres per hectare for each 1% increase in soil organic matter.
The bottom line is that although cover crops use moisture, they ultimately provide you with a net water benefit in most years (except potentially in some low rainfall areas with the absence of a water table).
And if it works out that the cover crop actually uses too much moisture, then you will have a high-biomass cover crop which results in many soil benefits and turned into direct profits by providing high-quality feed for your livestock.
Dryland cover cropping in Mpumalanga is showing good root and fungal activity (June 2023)
They are carbon catchers
Successful farming relies on the successful energy cycling.
Cover crops act as solar panels during a part of the year when that energy is normally lost in conventional systems. The leaves (i.e. the panels) convert the sun's energy into proteins, sugars and carbohydrates. These are used primarily for crop growth but pump around 20-40% of this energy as exudates through their roots which builds soil carbon and feeds soil life.
On top of this, an annual financial payout of R300 - R1 300 in carbon credits can be expected currently for this ecosystem service.
They are inviting and easy going
Cover crops, just like any farming households, are excellent hosts. They host small predators, pollinating insects, and microorganisms, while also creating a comfortable environment for beneficial fungi. All this by means of creating a suitable microclimate that bare soil would never be able to create, and by producing beautiful-looking flowers that will put a smile on your wife's face. While not needing as much attention as a cash crop, cover crops are happy with a bit of rain, good establishment planning and grazing management to thrive.
They are investors
Any blog about cover crops would not be complete without considering their effect on cash crop yield. There are too many differences in climates, soils, management strategies and yield targets from farm to farm that it is impossible to have a true-for-all rule when it comes to the yield-effect of cover crops.
However, there is some meta-data that tells an interesting story...
AgEvidence has a great tool to discover the effect of different sustainable practices on yields, carbon and other metrics. For example, across the US, cover crops have decreased cash crop yields by 3.11% across 461 observation points.
Opposing this view is a Sustainable Agriculture Research and Education (SARE) Report that shows consistent increases in yields in a survey involving around 2,000 farms. Over 5 years, the average increase in Maize yields following cover crops was 3.6% and Soybeans was 5.3%. Interestingly, the year with the largest increase was a drought year in 2012 and the farmers who have been cover cropping longer have seen bigger yield gains than those who started recently.
And so, with much other research showing these opposing views (even in South Africa), it is not yet possible to conclude whether or not there is a consistent yield gain or loss from off-season cover cropping. However, the average effect seems to be small and the diversification of income from cover crops means that some yield can be sacrificed without a negative effect on profits.
These studies all focus on short-term yield effect which is an important financial consideration. However, long-term soil health and future yield potential is undoubtedly improved with regular cover cropping. And so, I like to think of cover crops as investors that want to see future returns. They want to build an environment in which their future selves or their offspring can thrive.
They are somewhat fussy
Cover crops can be a little fussy and there is a risk that they don't establish or grow enough, which wastes money and time. To determine the viability of cover crops on your farm, you need to take a multi-season approach. Over 5 years, there might be 3 successes and 2 failures. Therefore, if short-term profits are the only factor, then you need to ensure that those 3 cover crops bring in enough financial gain to cover all 5 of those years. This is generally possible through grazing and carbon credits.
However, you need to decide what you view as a successful cover crop. What biomass are you aiming for? Do you just want some living roots? Some cover? Grazing? It's important to define for yourself what a successful cover crop would look like in your context.
Winter cover planted in Mpumalanga - the green is a nice contrast to the brown winter veld
To conclude - cover crops sound like a surprisingly valuable tool to have in your shed - I guess it just comes down to how you use and view them. Direct value is gained through carbon credits, grazing and savings in chemical costs while indirect value is achieved through protecting top soil, promoting soil life, nutrient and water conservation, pest management and many other aspects. Although cover cropping is easier in some areas than others, it is a viable strategy to consider in any area! If weeds can grow in your winter, so could a cover crop...