Strip cropping strategies to increase Maize yields

Strip cropping is an unfamiliar term for most farmers, but early results in South Africa show promising signs of increasing yields and profits when managed correctly. If you are a grain farmer, it might be worth considering...

Strip cropping is the practice of planting different crops on the same field in strips that are multiple rows wide. For example, a farmer could plant 8 rows Maize next to 8 rows Soybeans next to 8 rows Maize and so on. Although similar to intercropping, where each row is alternated between complimentary crop species, strip cropping serves a completely different purpose.

The main idea behind strip cropping is to harvest more sunlight (as illustrated below) and to reduce soil erosion from wind and water on sloped lands. The additional sunlight means more photosynthesis and a higher likelihood of producing 2 or more cobs per maize plant. Additional sunlight is mostly absorbed in the early and late hours in a day as the sunlight penetrates a few maize rows on each strip instead of only penetrating a few rows of a whole block of monoculture Maize. Around mid-day, the sun shines down almost vertically and therefore there is not much additional photosynthesis or heat stress during the hottest parts of the day when compared to block planting.

What results can I expect to see?

It is important to take note that each farm is unique, and we strongly encourage farmers to test different "recipes" (planting angles, rotations, cultivars, plant densities, planting dates, and other variables) that ultimately influence the viability and profitability of strip cropping.

An important aspect to consider, is that the most significant yield gains will only be made where sunlight is the most limiting factor to crop growth and seed fill. In other words, if water or nutrients are lacking, strip cropping might not deliver significant yield increases. Therefore, it might be best to trial on higher yielding fields with a better water-holding capacity.

We have seen varying results, but have summarized some of the expectations below:

Long-term strip cropping farmer in the US, Dean Sponheim, has seen an average increase of 12-15% in 8-row Maize yields when compared to block planting. His Soybean yield has decreased by only 3.5%.

A Northern-KZN farmer in South Africa yielded almost 4t / ha more Maize on his dryland strip cropping compared to his conventional fields. while losing 1t / ha on his Soybean. He believes that with a few minor adaptations in strategy, the decrease in Soybean yield can be reduced to <0.5t / ha while his Maize yield can be increased even more. There was a 300m strip on which he harvested 18.9t / ha on dryland, which is 85% higher than the farm average.

Early trial results for another South African farmer, on the Mpumalanga highveld, who strip cropped 8-row Maize with mixed cover crop strips of about 2m, show promising results. Yield estimations show the outside rows yielding double compared to the inside rows. The expected result is that there will be no yield loss despite giving up about 20% of the surface area to a cover crop. After harvest, the maize residues will be complemented by green strips with living roots which will help keep soil structure, reduce wind erosion, form valuable grazing for his livestock and will keep on growing throughout the winter.

A strip-cropping study revealed that strip cropping can use water and sunlight more effectively even in semi-arid regions with similar rainfall to many relatively dry South African cropping regions.

Let's do the math

At the time of writing, the Maize price was R3,800 and the Soybean price R8,100.

Let's assume that the long-term averages from strip cropping are a 12% increase in Maize and a 4% decrease in Soybean. And that a 2-year rotation of Maize and Soybean is replaced by annual strip cropping (e.g. 50ha of Maize and 50ha of Soybean is replaced by 100ha strip cropping) resulting in similar planting costs as effectively the same area is planted to each crop.

Although over-simplifying, at a 2t/ha average, the yield drop in Soybeans would reduce revenues by R648 per hectare. The gain relating to Maize would be R2,736. This results in an additional net revenue of R2,088 per hectare per year for growing the same crops on the same area.

So what's the catch?

As with any good thing, there are always down-sides...

• Soybean yields typically decrease due to reduced sunlight.
• The management can become quite tricky, especially with the spraying programme. Precision implements help but the system still requires active management to ensure no errors are made.
• Mistakes made with spraying or fertilising can be very costly.
• As mentioned before, where sunlight is not the most limiting factor when it comes to yields, the Maize yield gains might not be significant enough to make up for the Soybean yield loss and management effort. We expect that the drier areas without irrigation might not benefit as much as wetter areas.
• Depending on available equipment, there may be additional costs of planting and managing the crop.
• If you are already planting a very low density Maize stand, this might not benefit you. However, while low plant stands allow sun to penetrate, there are less leaves that can use this sunlight. Therefore, higher stands in strips are still expected to result in higher yields than low plant stands across an entire field.

How do I manage a strip cropped field?

Although a little intimidating, managing a strip cropped field is not too difficult with the right equipment and some determination and innovation.

• It is important to select your cultivars to allow for simpler management. For example, if your programme includes herbicide applications after or just before planting, then it would be wise to ensure both crops are roundup ready.
• Precision planting equipment is necessary as one would first plant the one crop (e.g. Soybeans) and leave exactly the right spacing in between the strips to allow for planting of the other crop (e.g. Maize).
• When other spraying activities are required (such as foliar feeds / fungicides etc.), precision spraying is also recommended with the option of either turning off the nozzles that run over the crop that should not be sprayed or to have a 2nd tank with a separate mix being sprayed onto each crop. While the one first option does not require additional capital expenses, it does increase the cost of spraying. We recommend that you only commit to capital costs once you have decided this will be a common practice on your operation.
• Depending on the product being applied, it is important to throw caution to the wind as chemical residues might affect growth of neighbouring strips.
• Combines will also need to be the right size for the operation. For Soybean-Maize strips the Soybean will likely be harvested first so the size of the Maize combine is less important. Or for stripping Maize with Lucerne for example, you need to ensure that your mowing and baling equipment is the right width.
• Rotating between Maize & Soybean (or other species) will bring additional benefits. Alternating the strips each year will decrease fertiliser costs and should improve yields further.
• The planting angle is very important and depends on what your goal is. If your goal is to reduce wind erosion, then the strips should be planted perpendicular to the wind direction. If your goal is to minimise water erosion, then you could plant your strips parallel to contours. If you simply want to increase yields, the best angle might be at a slight offset to the sun's movement between sunrise and sunset (see below illustration). We recommend doing multiple trials and determining what works best in your context.

Improving Maize yields even further and reducing the loss in Soybean yields

Although we are still learning, there are several strategies that seem reasonable to use to improve yield performance further.

• Planting a longer-grower Soybean variety should reduce yield losses as the Soybean has more time to utilise the heat units (there is less heat units and sunlight available per day due to the taller neighbouring Maize).
• Variable planting / seeding rates could be used to increase the density of the outside rows of each strip. This will mean more plants which make 2 or more full cobs.
• Decreasing the planting density of the Soybean strips so that each plant is able to get more sunlight.

Is this strategy only for regenerative farmers

Although not necessarily considered a regenerative practice, strip cropping improves in-field diversity, reduces erosion, captures more sunlight for photosynthesis and increases the biomass potential per hectare. The increased biomass and photosynthetic activity can help grow your soil organic carbon and so, strip cropping can form an important strategic component in any regenerative farmer's plan to improve soil health and decrease input costs

For the regenerative farmers out there, one could try planting some strips (e.g. 8 rows per 72 rows or 10% of the surface area) to a mix of permanent / perennial pollinator-friendly plants. These strips can be maintained for years, can serve as livestock fodder, reduce erosion, and most importantly act as an ecosystem buffer to host predator pests and pollinator species.

We would encourage farmers, especially those in higher-rainfall areas, to give this strategy some attention and dedicate some hectares to strip cropping trials.
Let us know what your experience with this is!