The Problem With Green Manure Cover Crops

#1

Most of us here are involved with helping the poor to become more self sufficient via agriculture. Green Manure Cover Crops (GMCC) are highly touted as a way for the poor to do better with their agricultural projects. We all agree with that. But, annual crops like Canavalia, Macuna, etc. are most often recommended and that is the problem….because they require large amounts of seeds which the poor seldom have. Even when money is no issue, I spent 2 years and could only find 50 lbs of Canavalia seed here in Honduras. I wanted 200 lbs but the best I could do was 50. From my many years here, I am very well connected with many seed sources in Honduras and neither money nor transportation is an issue and yet I could not buy 200 lbs of seed. So, there is no way the poor will be able to get the seeds.

I know some will say to find a few seeds and grow more but that takes a lot of time….maybe two years. And, then every year it needs to be done again. And when growing as seed, it is no longer a GMCC. So, unless one is in a location with good seed resources, it seems to me annuals are not the best choice. Just notice how many times on this list, folks are looking for those seeds. Bottom line: I think too many ag leaders are theorizing or extrapolating from their small plots in terms of what they recommend but, when dealing in hectors, it is a totally different story.

We are basically giving up of using or recommending annuals as GMCC. It is too expensive, too weather dependant, too labor intensive, too uncertain and just plain impossible for most poor families. Instead we are going exclusively with perennials. Many of the perennials are not legumes but that is the tradeoff we think is worth making.

In other posts here, I have written of Mombassa grass as being the nearly perfect cut and carry grass for livestock. We are going to begin using it a a big part of our GMCC plants. It grows thick and to about a meter tall each 35 days. That is a HUGE amount of green manure in a year. I doubt anything else compares. The great part of Mombassa is the seed is available globally and low cost. Plus, a little seed goes a long way when planting.

We have always used some legume trees for diversity but I think the mombassa will produce so much biomass in our plantain fields, lemon orchards, etc that the others will be relatively insignificant. Another good thing about mombassa is it can be walked or driven on without a problem plus it is easy to cut with a machete in our Chop and Drop system that we use on all our land. And it is very shade tolerant.

We share a lot of cuttings with the poor that serve as seed for growing many of our perennial GMCC. Mombassa is the same. It can be divided the same way that vetiver can but much, much quicker. Whereas vetiver needs about a year to form a large plant to divide, mombassa does so in about 2 months. And like vetiver, it is non-invasive. It doesn’t spread beyond a cluster size about the same size as a vetiver cluster.

#2

Greetings Glen,

I’m working on restoring about 4-5 hectares in the mountains of Haiti. We are hoping to do a demonstration at or above the kind of scale our poor neighbours would have to do. Our most promising biomass plant so far has been Napier grass (2 different types that the people were already using here before we got here). However, I’m using it mostly for soil retention and to produce something in really barren spots of the property. I’m hoping to use lablab as a perennial cover crop. It seems to do well here. Have you tried that? It probably doesn’t make as much biomass as a productive grass but it fixes nitrogen and makes good, high protein food.

I’m curious to find out more about this grass you mention. Is the Mombasa you use a cultivar of Megathyrsus maximus? What elevation are you growing it at? Have you compared it to Napier grass? Any suggestions where to get seeds in the US or Haiti?

You mention that scaling up from a small plot to many hectares is different and it obviously is, but at least where I live, anyone who is cultivating many hectares isn’t really that poor a farmer anymore.

Joel

#3

Joel good to hear from you,

I think most any of the tall grasses would work equally well. As I understand it, Napier is a hybrid while Mombasa is not. I think Mombasa tends to be more productive, but that’s not that big a deal. Also, for us growing in the shade is really important and Mombasa does that very well. And as I mentioned, mombassa is very easy to divide a plant to give to neighbors…and the original plant regrows as though it had never been touched. Not sure about Napier.

There are many sellers of Mombasa in the US and I think in most countries. A little Internet work and you’ll find it. BTW, I think Mombasa might be a trade name, but there are other very similar names that as best I can tell are either the same or nearly indistinguishable. One of them is Mombaca.

We bought our lablab in the US. It was easy to find. The problem with lablab and all other beans and legumes, is for them to provide significant nitrogen, they need to be harvested before they make a bean. Preferably during the bloom phase. We find that a little tricky to do without killing the plant. And I think it can only be done a time or two. Bottom line, it not much of a perennial when used for GMCC.

We are currently growing lablab and canavalia in our plantain fields, but they don’t tolerate foot traffic, and our wheelbarrels, while we’re harvesting. Mombasa tolerates it very well and feet don’t get tangled up in the vines… Plus the lablab wants to climb and thus is difficult to control. Well, not difficult, but takes constant attention.

In terms of size of land, it’s not unusual for several poor families to rent a few hectors to grow their crops on. In other words, growing hectors is not reserve for the wealthy.

Blessings,
Glen

#4

Joel, I was looking at Hancock Seed website for something else and noticed they have Mombassa in bulk and in packs as small as 5 lbs. I would be surprise if not available in Haiti.

#5

Greetings Glen,

We initially started using Napier grass for soil retention but in retrospect, if I could restart our land recovery efforts, I would have planted as much Napier as I could get my hands on in the first year and made as much mulch as I possibly could and then transition to nitrogen fixing cover crops once the soil organic matter content was higher. We had land that was so badly degraded it barely grew Jack beans the first year. I think Roland Bunch’s book is missing some useful systems for very badly degraded land. I suspect large grasses like Napier and Guinea grass or other rapid growing large grasses that don’t reproduce from seed are a good way to start, at least in some situations.

A problem that limits more widespread use of Napier here (at least for soil retention) is that it seems to have very long lateral roots (at least in poor soil) and therefore competes with nearby plants. I’ve heard dwarf Napier is better for this and I’m working on getting some of that here. I’m curious what your impression of Mombasa grass is for that purpose. I’m interested to try it just for its biomass and fodder potential but if it was good for soil retention, that would be an added bonus. Also, what elevations have you grown Mombasa at? We are at about 1500 m so really more of a subtropical climate. I’ve heard how great Vetiver was and some of the locals had some so I planted some here for soil retention but it grew very slowly and nothing like as vigorous as Napier. I suspect it is an elevation thing. I will still use it some for soil retention but as a biomass plant here it isn’t very good.

Thanks for the pointer to Hancock Seeds, that looks promising.

My experience so far with lablab is that it is it drops a lot of leaf litter in the dry season so I’m going to try to just keep it in the ground for a while and see what it does to the soil and then when I want to intercrop something else, just hack it back before planting whatever else I want to plant there. Having a highly productive protein source is one of my main objectives for it as protein malnutrition is a huge deal here in rural Haiti.

Joel

#6

thanks for some interesting points about use of annual GM/CCs but we have not found this in Nepal - if the initial demonstrations by farmers and subsequent training is good then farmers will find a way of replicating the seed. Yes it may take time but gradual spread amongst motivated farmers is better than importing seed imo and experience. In Nepal, Sesbania was demonstrated as a GM/CC with rice and corn for example, and went from 1 farm to a few farms to thousands of farms, the seed is now sold as currency (but also gifted/exchanged for non-money resources) so farmers have been able to generate income from selling it. Meanwhile farmers have developed the best ways to save seed by planting mother plants on field/terrace edges/fallow land so they can use the GM/cc at flowering time. However I also agree using perennials is great for chop and drop/cut and carry and is obviously efficient over annuals. I think it’s not either-or, rather it’s both-and, farmers need to be able to avail the whole tool box and be able to choose what is best for them. I would like to see Roland’s opnions on this interesting thread!

#7

We have grown Mombassa at 1600 meter elevation and it did well. In hotter areas it grows faster but not that big a difference. Again the nice thing is it is easy to grow without seed by plant division which is a real benefit when sharing with those in need.

Another benefit is that it’s very high protein. In another post here on the topic I mentioned that we had it analyzed in the lab and during the dryer season it only had about 11% but in the wet season it had about 19%. As most people know protein equals nitrogen. So that means although it’s not a legume, it provides significant nitrogen from its compost…chop and drop leaf litter.

But our motive in growing it is to increase the organic matter in the soil. I don’t think anything else can match it. With more organic matter in the soil, the soil, microorganisms flourish, and thus comes much of the nutrition the plants need. Mombassat has extensive roots that are excellent at erosion control because they are very fine and extensive and deep. So that means they are also mining minerals, etc. from the deep zone. I assume it’s because of its deep roots that it tolerates drought so well.

For us, it’s not an either or. We always do multi cropping of various different green manure plants. My point in this article is we are going with perennials. We are currently have some annuals, namely, canavalia and lablab and macuna but we will discontinue that in favor of perennials for among other reason is as we are helping poor farmers, annuls is an expense and complication they don’t need.

#8

Greetings from Florida. On green manure crops. There are alot of different seed types out there. What you can buy maybe the problem. I work in a seed warehouse. What is there today maybe bought out tomorrow.
Velvet bean seems to be a hard one to buy in large amounts. Iron and clay cowpeas on the other hand is a gardeners nightmare for growth. And can be bought by ton. But importing it into yours country is maybe a cost you are not ready for.
Maybe ECHO can help with seed companies that sell Velvet bean.
And on growing guinea grass/ ti Napier. I would look to the elephant grass/ gross napier grass. Or look into a hybrid grass Mulato 2 grass.
I’m always growing more mulch/ green manure here where I live. I hope this helps, Kevin Fall
ECHO knows how to reach me with more questions.

#9

@Neil_Rowe_Miller / @Neil_Rowe_Miller1 or @Nathan_Deboer do you have thoughts to share around the topic of best practices for annual cover cropping in farmer fields? What size/scale do you see annual cover cropping successful in low-resource contexts? How have you both overcome seed source and price hurdles in your experiences?

#10

In my experience, the problem of seed availability with Canavalia, Mucuna & Lablab is just at the initial stages. Once farmers are convinced of the benefits, they will keep their own seed, pass it on to neighbors and friends, and the whole thing becomes self-replicating. The key is finding a niche in the local cropping system where the GMCC can add value without greatly disrupting traditional food crops. The solution will vary from location to location. In NW Tanzania, for example, thousands of farmers are intercropping mucuna with maize, then allowing it to grow to maturity after maize harvest then planting the next crop directly into the mucuna residue. Hundreds of thousands of Central Tanzanian farmers use a similar approach, but with densely planted pigeon pea and/or lablab intercropped in their maize. Central Kenya farmers grow the pigeon pea in alleys with a rotation of millet and short-season legumes in between. Eastern Uganda cassava farmers relay crop Canavalia under their cassava and allow it to grow until cassava harvest. In northern Ethiopia it’s white lupin planted in rotation with small grain cereals.

As you’ll see from all these success stories, the GMCC is NOT incorporated at peak flowering. Yes, that would probably increase nitrogen production, but it eliminates many other benefits: food production, soil protection through the dry season, soil microbial increase associated with growing plants, etc. The effect on the following crop is the combination of all these factors, not nitrogen alone.

I’m also a big fan of perennial GMCCs, but please don’t give up on annuals. Farmers need access to all the options out there.

1 Like
#11

Neil and all others, thanks for taking time to share your insights. I think of the old adage that two heads are better than one.

It seems to me that what Roland Bunch and others in this discussion are describing a traditional system that reflects… “the way we’ve always done it.” And also the thinking of “If it ain’t broken, don’t fix it.”

I’m suggesting there is a better way to do it. I’m an old guy and I’ve been doing it the traditional way for many decades. A system based on seeds works much better in the States than it does in underdeveloped countries. That seed system is fraught with problems. Just think of all the problems that are involved with seeds. Source supply, cost, often difficult if not impossible to find, spoilage problems, storage problems, rodent and insect problems, weather dependent for germination. The list goes on. And, they need to be planted over and over and over. So those problems don’t go away. Just trying to store the seeds from one year to the next in a hot, humid tropical climate is challenging by itself.

Although agricultural charities have been working here in Honduras for decades, the seeds are nearly impossible to find and expensive in the rare occasions they are found. It’s a very difficult challenging system. If it were the only way, then we would just buckle down and do the best we can. But there is an alternative. Perennial plants do away with the need for seeds…and all the problems involved with seeds.

With all due respect, growing beans, intercropped with corn, and then eating the beans and the corn, is not GMCC. If it is, it’s not in any significant way. When the farmer grows corn and harvest the corn, that’s not GMCC. Neither it is it when he does the same thing, but adds beans to the mix. Excuse one more old phrase, but, “there is no free lunch”. If you’re harvesting, then it’s not GMCC. However, if one is growing perennials and particularly legumous perennials, then it’s almost automatically going to be GMCC because no one’s going to be eating and harvesting those perennials.

We could share many examples, but here is just one. When we grow Leucena within our plantain plantation. We cut it approx each 45 days in a chop and drop system. That is GMCC because there is no taking away from the land. To my way of thinking GMCC is when one is giving a gift to the land… not taking from the land by harvesting and hauling away.

One of the best things about perennials is they are readily available in most areas and they are generally free and they have no storage requirements. They only need to be planted once. They survive droughts. The list goes on.

This is a part of the GMCC for our lemon and plantain orchards. Intercropped with our Mombasa grass is leucaena, arachis pintoi, gliricidia, Erythrina berteroana, Commelina diffusa, etc. All of those except for the mombassa are legumes. Some grow very low to the ground basically taking up no space. We do the same in our cut and carry fields where we call the mix “salad” for our animals. That is, they get a salad each time they are fed because all those plants and more are growing together and being cut together.

Bottom line. I think perennials is much better and more efficient way of helping the poor to do better farming.

#12

Greetings Glen,

I can understand your point of view on this. I live in Haiti where sourcing things in country has become much more difficult as gangs take over increasing areas of the country. Even before that problem, sourcing stuff here wasn’t easy (unless it was produced in our local area). However, I see a different aspect of seeds. I can fly here on a plane out of the US with a single seed of less than 1 g or a small pack of seeds that is enough to introduce an entire new species of plant (including a tree that grow to 30-40 m in height) and then reproduce thousands and thousands of that plant over time. That seems like a huge blessing to me. Also, I really appreciate that the Napier grass we use doesn’t often propagate by seed or it would take over all our garden beds. However, I’ve been struggling to source dwarf Napier grass here and in one failed attempt a dwarf Napier grass root ball and some stalks rotted in transport to the point that they wouldn’t take here. If I could have just brought a single dwarf Napier grass seed here that would have been a huge blessing.

To me it seems like the biggest problem with seeds is the initial acquisition which is the same with annuals and perennials. Once you can produce your own seed the issue just becomes about storage (which I acknowledge isn’t a trivial problem). I really like perennials, which is why I’m focusing on lablabs, Phaseolus dumosus and pigeons peas here for legumes. However, I don’t see the same problems you see with annuals. Everyone around here plants maize every year and don’t seem to generally have trouble sourcing the seed for it. It is also worth noting that most the world’s major calorie sources are annuals (or used like annuals): rice, wheat, maize, sweet potatoes, potatoes, cassava, yam, various annual oil crops, etc… I think sugar cane, banana, palm oil and pigeon peas are notable exceptions.

I’m curious what makes you think that. The total mass of corn kernels and beans is a fraction of the total mass of the plants that produce them. How is the remaining plant residue not acting as a GM/CC? To me the “no free lunch” principle would apply more to taking all of the plant residue out of the field or burning it. Even from a nitrogen perspective, most, if not all, of the nitrogen that remains in bean plants after removing the beans has presumably come from nitrogen fixation. So even if the total amount of nitrogen remaining has been decreased by harvesting the beans, I still don’t see how the beans plants don’t serve as a nitrogen source for future plants.

To me the fact that people are successfully using GM/CCs to maintain soil fertility while harvesting some part of the plants for food, seems to suggest that this concern is more theoretical, at least in some situations.

Joel

#13

That is very useful info. I’ll try to give it a try.

I’m curious to see how it compares to Napier.

Joel

#14

Joel, when I said I don’t think anything else could produce as much GM as Mombassa, I was thinking of all the tall grasses…not just mombassa.

#15

“I’m curious what makes you think that. The total mass of corn kernels and beans is a fraction of the total mass of the plants that produce them. How is the remaining plant residue not acting as a GM/CC?”

While they represent a fraction the total mass, they represent the bulk of the nutritional value. Corn stover is basically just filler feed…not much energy or protein. The bulk of the energy and protein went into the grain. The nutrition of the soil has been moved into the grain and not much into the stover. So, if the grain is harvested, that removes the majority of the nutrition of the soil. Soil quickly gets degraded when grain is removed and only the stalks are left…unless an outside source of nutrition is added to the soil…manure, etc.

To my way to thinking, the purpose of a GMCC is to add fertility to the soil. When harvesting rather than returning to the soil, there is a negative gain…a loss of soil nutrition/fertility. How can that kind of a system or process be considered feeding the soil if it creates a net loss?

I totally agree with you that the plant residue after harvesting the grain has GM value but it is rather low. It leaves the land with less nutrition as opposed to more which is the goal of GMCC. If harvesting the grain and leaving the stubble behind is a form of GMCC, then most commercial farming is a form of GMCC because that’s what most commercial farming does.

#16

When I said the seed system is filled with problems, I was speaking of the normal GMCC system that depends on hundreds of pounds of seeds per hectar every year or more often and those are often seeds the poor farm family could eat.

Certainly, seeds are helpful and easy to transport. When they are perennial, that is all the better. Many perennial seeds and cutting are available for free. We harvested most of our initial supply from along side the road. Because they are perennial, they are abundantly available compared to the seed of annuals.

A related topic is we grow maybe 20 different perennials for chicken feed. Most of them we harvested seed or cuttings for free.

God give us eyes to see the abundance you surround us with. Amen

#17

Greetings Kevin,

Could you elaborate on why you would make this recommendation? I’ve had good success with two varieties of Napier/Elephant grass but why do you think they are better than Guinea grass? I know that in addition to Glen’s experience, the Mombassa cultivar of Guinea grass is used in some syntropic agriculture systems for biomass.

Also, what do you see as the advantage of a grass like Mulato 2? Can it be reproduced from tillers or does it produce fertile seed or do you always have to buy seed?

Joel

#18

This is certainly relevant for human nutrition but is it for soil nutrition? I have never read a clear explanation of what chemicals or organic molecules in organic matter make the biggest difference in soil fertility. My understanding is that in all plants the bulk of the mass of the plant dry matter is carbon and oxygen. I’ve not yet heard a good explanation of how exactly soil organic matter increases soil fertility. It is obvious it does but by what mechanism? Perhaps just the increase in carbon in the soil is enough to increase soil microbial life enough to encourage plant growth significantly. In which case corn stover may be a significant advantage to the soil. Probably it isn’t for soil N content but I don’t see why bean plant residue wouldn’t be, even with all the beans harvested. Obviously beans have a higher N concentration then the rest of the plant but because the plant mass is so much more (at least for some legumes) than the mass of the beans, it is probably the case that the addition of N to the soil from bean plant residue is significant, even if it is less than what would be added to the soil if none of the plant was harvested. The fact that it seems to be an observed fact that some systems that combine maize and an edible legume like lablab can sustainably maintain soil nutrition without external inputs, seems to give evidence that this is the case. I have no doubt that you are right that putting the entirety of a plant back into the soil will do more for the soil fertility but soil fertility is not an end in itself but a means to an end and if you just have fertile soil and never take food from it, you will eventually be back to a natural ecosystem where there are no humans to manage it (because they have all starved). Since the bulk (perhaps all?) of the C, O, H in plants comes from the atmosphere and rainwater and not the soil (and with nitrogen fixers, this is true of N as well), it doesn’t seem like the equation of soil fertility is a zero sum situation: for example, if you take anything away then you must end up with a decrease in soil fertility. Maybe this could be true for elements like potassium, calcium, magnesium, phosphorus, etc. but I haven’t yet heard of any good evidence that these elements will eventually be lacking in soils that are high in soil organic matter. If we learn good ways to return the excrement of the humans or animals eating the produce from our soil, I don’t see how soil chemical nutrient composition could possibly go down, even with sustained harvesting. Also, most (if not all) of the energy in the plants came from the sun, not the soil so this too is an addition to the soil, even if edible parts of the plants are harvested. The fact that soils can be heavily degraded and then returned to good fertility by fallowing is evidence to me that you can take nutrients out of the soil and then fix the soil without any external inputs other than sun and rain and the atmospheric gases.

This is a very interesting point. I don’t have much exposure to mechanized commercial farming. Where I live in Haiti no farming is mechanized and slash and burn is the normal system of farming. Most maize stover is removed from the fields by the next planting season in order to burn for cooking food and almost all of the bean plant residue has either been removed from the fields to be taken to the area around peoples homes where they use a flail to get the beans out or has been eaten by animals. In that system, especially combined with large-scale, uncontrolled erosion, it isn’t hard to see why the soil organic matter is going down. But your point does raise an interesting point I hadn’t considered: what is the difference between tradition mechanized farming where presumably most of the plant residue remains in the field (at least initially) and systems like are being promoted by Roland Bunch or in syntropic agriculture? Is it just the amount of biomass or the quality of nitrogen fixation? Is it the amount of photosynthesis that happens in a year per square meter of land? What do you think?

#19

What kinds of systems are you thinking of? We got lablabs from our neighbours here in Haiti and in a single year, on very poor soil we grew enough lablab seed that we could have planted most or all of our 4-5 hectares in lablab this year if we had wanted to. I haven’t had as good success with mucuna but I suspect if I put more effort into it, I could do the same with that plant too.

Could you share what plants you are using for this? I’m interested in trying to grow more here for our chickens and teaching our neighbours to do the same and I’m happy to have more perennials. P

#20

Joel, I appreciate your thinking, questioning, challenging, etc. Thanks for stimulating my thinking. I haven’t figured out how to do the quote system that you do, so I will just go from your first to last post.

Obviously, for the sake of brevity, I have over simplified everything and will do it again now. The residual organic material is certainly beneficial. That is the main purpose of GMCC. Most farming leaves residual organic matter on the land. But, that farming is not GMCC. It is growing and harvesting. When harvesting the grain, most of the NPK that was removed from the soil went into the grain. If the grain is harvested, the NPK is removed. That represents a net lost of soil nutirtients…a very, very large net loss. I think the whole topic is a matter of degree. In a GMCC a significant degree of nutrition is added to the soil. In farming that harvests the crop, a small degree of nutrition is added to the soil…or more frequently depletes the soil of nutrition.

Sure, a person can plant a garden full of seed and harvest enough to plant a large field. But, what has that accomplished? Instead of eating the harvest, the poor family plants that seed. And, in my experience, that cycle ends because the poor families are too hungry and focused on planting food to continue that cycle. In other words, when I go back to visit families and communities that I gave seeds, the cycle has ended for the reasons/problems I listed previously. However, when I go back even many years later, almost without exception, their perennials are still there…growing even if forgotten. An annual seed based GMCC system can’t be forgotten and come back years later to find it doing well. I think that is why here in Honduras, although tons and tons of GMCC seeds have distributed by ag charities and yet finding those seeds is almost impossible. It is a very fragile system. It is a system that works well in the USA because there are businesses dedicated to providing (selling) those seeds. At the same time, most perennials do well even if forgotten and neglected.

To me the choice is to teach a system that is low effort and low competition for food…not having to decide… do we eat these seeds or plant them. Do we teach a system that is higher in cost and labor and needs discipline to continue to produce or do we teach one that is low cost (most perenial seeds/cuttings are free) and less work ( only needs planting once vs annually). To my way of thinking it is basically a choice of teaching a system that is easy to fail (seed system of annuals) vs a system that is difficult to fail. For most of our veggies, we are forced to grow annual via seeds but why do that with GMCC?

For me, it has been a slow transition but I don’t see myself going back to teaching the seed based GMCC system.

It will take me awhile to put together the list of perennials we use as chicken feed but I will.