The Problem With Green Manure Cover Crops

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.

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

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