Interview with Mike Hands:
Q: What was the path that led to your interest and involvement with agricultural practices in these regions of the world?
A: My first contact in the tropics came when I was a surveyor making maps of the region, and then later, mainly in development projects, I spent a lot of time in Africa and also quite a bit of time in Central America. Really, as a child I was completely engaged with nature. I just lived in nature, in a country village in Gloucestershire in England and just inhabited woods and streams and open places – always in engagement with nature. So, when I was particularly in some parts of Africa, walking through miles and miles of burnt Guinea savannah forest it was just devastating seeing the effects. I was already interested in organic production and gardening when it came to a time in my life where a change was due. I was getting kind of restless, sort of like a midlife crisis, but I sensed it before it hit me. So, I went back to school, Cambridge, where I enrolled in a two year masters specifically to get my teeth into this. The more I got into reading about this the more I realized that no one really had any conclusions. There was some good work out there, but in the ecology of slash and burn, information was not just inconclusive but sometimes contradictory. I began to focus on the availability of nutrients being the major factor in slash and burn. It’s the reason that the systems fail that was the real question to me.
Q: How many years have you been working specifically to combat slash and burn agriculture?
A: I’ve had my teeth into this problem for about thirty years. After quite a long time, and the usual blunders, I began to get my teeth into not only the work I had set myself in but also the problem. And I made a couple of breakthrough discoveries. Firstly that the well-known technique for determining total phosphorous in soil is thoroughly flawed. It produces bad data.
Q: Can you elaborate more on the problems you encountered relating to the soil test results that you were producing?
A: It took me a while to disentangle that. I tried all kinds of extraction techniques, most of which are very difficult to interpret even if you succeed, but I then sort of simplified things. I thought well what I’m going to do instead of looking at fractions and extractions and microbial biomass and all the rest, I’m just going to look at the total; ask the simple question first. What’s happened to the total phosphorous in this soil? I’d cracked the problem of laboratory methodology, gotten that right so that I was getting very consistent results if I put samples of phosphorous through the digestive system that I was running. The way that I discovered the original system was flawed was that I wasn’t getting consistent results back. The moment I was able to crack that problem I then went back to the original soil that had come from my sample plot, I made a massive discovery that a huge amount of phosphorous had actually left the soil profile. I think I know what had happened, but it went against all received wisdom in tropical soils. So there was a heck of a lot to get out of the way and disentangle. You couldn’t get straight from a position of ignorance to a position of immediate insight. I wrote it all up as thesis, and then went through the nail biting time of trying to raise funds for a real project.
Q: When developing your experiments and programs how did you determine the best approach, and can you give some examples of other systems that didn’t lead to the outcomes you have achieved using Inga?
A: This was going to be an alley cropping experiment because I’d already seen a lot of reference to alley cropping with legume trees claiming to be a sustainable alternative to slash and burn. They were advocating the use of very small leaved legumes, the idea being that the foliage that you grow must be decomposing at the correct time and therefore available to the crop so that the whole bloody thing had to be fine-tuned. I set out an alley cropping experiment with the two species recommended by the so-called experts in Costa Rica at that time which incidentally turned out to be a complete failure. Those being Gliricidia sepium and Erythrina fusca. There were 16 big plots – 400 square meters each. I had also already encountered Inga and was very impressed by what I was seeing and how this thing was functioning very differently to any of the other legume trees. It wasn’t being used in our alley cropping trials, but it was used very much, and widely, as shade over coffee up in the highlands of Costa Rica and elsewhere – Honduras, Columbia, and so on for the same purpose. Against advice I was determined to at least trial some Inga, so we added another 14 plots (of the same size) around the main experiment. We started a regime of cropping. Maize was the first in, which is what farmers would do (after the slash and burn) followed by beans six months later, and then we’d just repeat the whole process trying deliberately to exhaust the soil of its available nutrients. The objective being to test further down the line to see whether there was a response – to see whether the crop was short of any one particular nutrient. And because I had already fingered phosphorous as most likely the key, it was a phosphorous experiment. On half the plots we applied one single application of 100 kilos of rock phosphate, and then we just cropped, monitoring everything that grew – weeds, trees, and the crop of course. The two conclusions were extremely rapid and extremely clear. There was no response to anything other than the rock phosphate. It was key, and the alley cropping systems that were recommended were clearly failing fairly early on. They didn’t control the weeds anyway, but (in contrast) the Inga was clearly coming out head and shoulders above the other species. We had eight species of Inga in trial, and all of them out-performed the others species in trial, but four or five of them were absolutely outstanding – real tigers.
The other key finding, if I didn’t say anything else today, was when we were getting the site prepared — I don’t know if you’re familiar with slash and burn, but what you do is under-brush the under-story so that you can move around. Then you drop the trees, leaving an even spread of fuel (for fire). You leave that for about six weeks until there is a short dry period. Then you fire it, hoping the whole lot will go up — before I dropped the trees I did a massive soil sampling, 96 points on a grid, down to 60 cm because I wanted to catch everything that was happening. Then I took the rest of the steps towards firing it and removed the remaining branches, leaving a clear flat site. I forgot to mention that I chose deliberately an Ultisol which is one of the most acid and difficult soil environments but typical of where the problem is in Amazonia. I continued to do this massive soil sampling, and it almost killed me to be honest, but what we found was that there was not a molecule difference in the amount of phosphorous (before and after burning). All of the phosphorous – approximately 100 kilos of phosphorous that I’d estimated to be in the canopy – was gone from the system. This was a very serious and surprising loss. Then suddenly in year three there was an apparent rise in the phosphorous, which in theory can’t happen but in fact did and couldn’t be denied. We figured out that this had to come from the decomposition of the roots of all those trees that has been previously killed, and it took until now for the phosphorous in their roots to become available. But, the key finding that I’ve never properly published was that in years four and five there was a drop in total phosphorous in the soil, and it’s huge and highly significant. In total, in the bare soil plots (not in the Inga plots), by year 5 there was a loss of 200 kilos of phosphorous plus what I’m estimating is another 100 kilos from the original forest that was lost. That’s 300 kilos of phosphorous, and a single crop of maize wants about five kilos of phosphorous. So, not only is it the key nutrient, and the experiment showed long term that the only response to nutrients was to phosphorous applied as rock phosphate. It’s key and absolutely vital. That’s the equivalent of 60 crops of maize that had left the soil profile in that period of time, and no one had ever picked it up before.
No one had ever reported anything like that before. I can remember one paper to this day that reported this apparent loss but said that it wasn’t possible, and kind of left the sentence hanging, that it didn’t happen. Well it did happen, and not only can it happen but it was key. To round the story off, the Inga plots didn’t lose any phosphorous. They held on to it. What I think is happening is that the phosphorous that was lost was lost from the soil microbial biomass as a result of exposure (under bare soil conditions). With the Inga system being extremely productive. These are extremely acid soils, 4.1 pH. They are the soils which slash and burn farmers get. The other (higher quality land) goes to cattle, bananas, and sugar, and all the rest of it. Inga has, somehow, very high tolerance to acid soils, and it is producing as much biomass in the system that I put in place as in a rainforest. And that’s actually the key observation because I’m certain that the phosphorous that was lost from the soil over those years actually originated in the soil microbial biomass. You have stopped adding fuel to the (microbial) biomass, and the predation that goes on in the soil all the time hasn’t stopped. But the fuel supply has stopped. The soil microbial biomass is actually being eaten, and it’s a finite resource and it eventually runs out. When it does the phosphorous that it contains and recycles also runs out. I think that’s where it comes from but can’t prove it because the standard techniques for determining microbial biomass phosphorous don’t work on those soils. There is a huge absorption of phosphorous by these soils in the lab. When you shake a soil like that with a solution it is fantastically hungry to absorb phosphorous chemically and lock it up. If you take a sample of soil and shake it in the normal way soil scientists do, add a shot of soluble phosphorous, shake it another five minutes, spin it down, and analyze how much phosphorous you have in the solution it’ll be zero. There will be nothing there because it’s all taken up by the clays, but what happens in the live soil is not what happens in the laboratory. That’s part of the confusion in the literature with soils of this kind – (thinking) they absorb phosphorous, so therefore they can’t leach. Well, that’s not what happens. We saw powerful leaching, and then the phosphorous that’s released from the soil microbial biomass also leaches. It wasn’t even there down to 60 cm. It just disappeared from the soil profile. The conclusion is that the Inga, it’s the only thing that worked, and the only nutrient response we saw was to phosphorous in the form of rock phosphate.