In Roland Bunch’s book, Restoring The Soil, which many view as “the Bible” of organic farming, he suggests companion planting as a way to rebuild the soil.
After reading what he says, it seems to me there is not much difference in terms of soil building benefits of companion planting vs rotational planting…if all or most of the plant material is harvested as human food and cattle feed… which he seems to advocate. At least he talks about it and does not discourage it.
In other words, if the farmer plants beans and corn together and harvests everything or if the farmer plants beans and harvest everything and then plants corn behind it, harvesting everything, in a rotational system which is what is normally done, it seems like the net effect on the soil would be very similar to traditional farming practices, which are credited with depleting the soil.
So that leads me to ask, how can that kind of companion planting system be taught as a soil building system? I don’t get it.
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I don’t have personal experience with this, but there is research and anecdotal experience that says companion planting/relay cropping/intercropping systems which use multiple different plant families allows the plants to maximize soil biology, root exudates and biomass. They say that the plants share DNA with the microbiology and other plants which maximizes stress resistance and increases soil carbon which maintains/increases fertility via soil biology. Dr. Christine Jones has some good podcasts on YouTube via green cover seeds which cover this idea. I don’t know how it works in the tropics in general, but it’s an idea I’m looking to explore.
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You might want to explore the ECHO website a bit more for information on GM/CCs. I work with farmers in Malawi where soil degradation is a serious issue. Over the years much of the soil organic matter has been depleted and some GM/CCs like lablab or jackbeans intercropped with grain crops are able to produce tons of green matter that can be left as mulch in the field to reverse the loss of SOM and thus improve fertility, structure, water infiltration and holding capacity greatly. GM/CCs can also include trees high in nitrogen like Gliricidia.
Watch Roland Bunch’s talk from the ECHO East Africa Conference February 2019. I think he explains well the benefits of GM/CCs.
Here are some links: Green Manure/Cover Crops: The Simplest and Cheapest Route to Achieving Adequate Nutrition | ECHOcommunity.org
https://www.echocommunity.org/resources/bb113605-b918-4bd5-88da-cf846b0eb1df
I hope this helps.
Martin
Totally agree, Martin… “when the green matter is left as mulch in the field.” But that’s not what I was describing. I was describing when everything is removed to feed people and animals. That’s what I don’t get.
I haven’t read the book, but my guess is it makes a difference in soil biology. The more diversity above the soil, the more diversity underground as well, which probably makes a difference in resilience towards pests and environmental stress.
I agree that could be it. Jaren also suggested that idea…which got me thinking. One other factor is with companion planting, there are more roots and more diverse roots. That means more organic matter below the soil after harvested. Thanks for sharing thoughts…stimulates thinking.
A polycrop may also better protect the soil from erosion, compaction, and baking in the sun, compared to a monocrop. Multiple species with different germination times, different die-back timing, different leaf shapes, and different structures will probably cover more soil for a longer duration than could a single species.
I think no mater what system you use (fallowing, intercropping, crop rotation, etc.) there needs to be some source of organic matter that exceeds the amount removed from the soil in order for soil fertility to be maintained. I don’t think there is a magic way to do that and I don’t get the impression Roland is promoting only one specific way of accomplishing this. For example, dry season cover crops (which is one of the approaches he promotes) can be either an intercropping or crop rotation system depending on how you think about it. I think it is too simplistic to say one system is better than the other because there are too many variables. For example, in an area with a long dry season, a dry season cover crop (either trees or very drought resistant temporary crops) makes a lot of sense as the land is going to be needed to be very intensively planted during the short rainy season and much of the nitrogen and organic matter produced during the rainy season is going to be gone by the beginning of the next rainy season unless it is buried or covered. On the other hand, a location with a long rainy season or multiple rainy seasons that cover most of the year, intercropping may make more sense than trying to plant another crop during the short dry season or take up the whole rainy season growing a cover crop. Roland talks about different ways to increase biomass production without diminishing the yields of the main crops. For example, planting a very short duration bean along with maize and a longer duration bean and then removing the short bean before the other crops get large and need the space. I have found here in Haiti in the mountains that there is enough land that isn’t very good for intensive agriculture that I can plant trees or Napier grass there to make biomass for areas that will be more intensively planted. If you are in an area where people have large sections of flat, rock-free farmland, it may take more creativity to increase biomass production without competing too much with the main crops people are trying to grow. It seems to me that everyone needs to evaluate the various systems in their local context and see what is going to work best.
I don’t know Roland or speak for him but I think you may misunderstand some of his argument. He does very much discourage uncontrolled grazing of crop residues for the reason you point out. It isn’t possible to take everything you produce off the field and maintain soil fertility. Roland makes the case that in places like rural Africa there is not as big a problem with nutrient loss (speaking here of basic elements, not organic matter) from fields as people like to say as most peasant farmers eat most of what they produce and as their waste goes onto the ground or into pits by their homes that most of these elements should be returned to their fields eventually. I think he is overstating this a bit. I live in an area of rural Haiti where people typically live in small villages and their farms are surrounding the villages. However, it has been my consistent observation that around their homes, the soil is almost always noticeably richer than in their fields. Maybe eventually some of the nutrients there will make their way back into the fields but I think it probably takes more intentional effort than Roland realizes for this to happen in a reasonable time frame. One thing that I see here that could make a difference is for people to learn how to grow fodder for animals so that free-grazing can be discouraged and more crop residues can be left in the field. Also, if more of the processing can be done in the fields that will leave more residue there. For example, here people take whole maize cobs, with their husks and often whole bean plants, off their fields to their homes to process there. That takes a lot of biomass off the fields and leaves it around their homes (or even worse, on the roads and foot paths!).
I would summarize Roland’s argument like this:
- fallowing is the traditional way of maintaining soil fertility and given enough land this is a reasonable way of maintaining the soil.
- as population pressure increases, fallowing land for many years is no longer possible.
- as a result, people need to find ways to grow enough biomass/organic matter in the same fields as they are producing their crops to keep soil fertility up while still producing enough food crops to feed everyone.
It seems there are two competing things here:
- poor farmer’s with very limited land are hesitant to give up land they desperately need for producing food in order to make biomass.
- land that consistently has a net nutrient loss is going to have declining yields until people adapt, starve or move.
Anyone who claims to have a solution to hunger for the rural poor of the world who doesn’t address both of those issues seems to me a bit like someone who offers one of these fad diets that promise you can eat all you want and still loose weight. There are simple chemical and biological principles that can’t be ignored.
You asked what type of companion planting system should be taught and that obviously depends on your context. However, I think a good deal of the success of such systems in land restricted areas is going to depend on how well you can take advantage of crops that are asynchronous with each other or occupying different strata (such as roots reaching deeper nutrient pools than the main crop).
Joel