The odyssey of my colleagues and I started in 1982, the day Conrado Zavala, a villager in Central America, sheepishly showed us his experiment. Skeptical about the value of the organic matter we had recommended, he had piled a huge quantity of compost into several rows of his maize field. The last two rows he left as a control, untilled and unfertilized. There, before our eyes, stood a field of maize 2-1/2 meters tall, with the last row less than 40 cm tall. That was the day we began to realize the incredible degree to which organic matter can restore soils.
Maximize organic matter production
Little by little, work in a dozen countries has convinced us that the vast majority of soils can be made highly fertile. How? By using our first principle: maximize organic matter production.
Conrado’s particular approach, however, was anti-economic. The cost of using compost on basic grains exceeds the benefit. But intercropped green manure/cover crops (gm/cc’s) can produce from 50 to 140 tons per hectare (green weight) of organic matter with very little work: no transporting of material and no cutting up, layering or turning over of compost heaps. In fact, sometimes, because of the gm/cc’s control of weeds, net labor costs decrease. And soil quality often improves visibly each year. Then, as often happens, we found we were far from the first to employ intercropped gm/cc’s. Gradually, between 1985 and 1992, we learned that villager farmers from Veracruz State in Mexico through Guatemala, El Salvador and Honduras were intercropping velvetbeans (Mucuna pruriens), cowpeas (Vigna spp.) and jackbeans (Canavalia ensiformis) with their maize and sorghum.
Keep the soil covered
To our amazement, these systems, virtually all of them in the supposedly infertile humid tropics, allow farmers to plant maize every year for decades, with productivity increasing over time up to four tons per hectare. In other words, these farmers have found an answer to slash-and-burn agriculture. Migratory agriculture is most frequently motivated by decreasing fertility, increased weed problems, or both. In the Mesoamerican gm/cc systems, nitrogen fixation and biomass recycling maintain soil fertility. Mulches of crop residues and fast-growing gm/cc’s drastically reduce the weed problem. We had learned a second principle: keep the soil covered.
Gm/cc mulches provide a whole series of additional benefits. They protect the soil from irradiation and the heat of the tropical sun, thereby also reducing burnout of organic matter. They save a tremendous amount of work; farmers can sow into the plant residue rather than tilling the soil. They keep the excess nitrogen from acidifying the upper soil horizons. And they largely prevent soil erosion, even on slopes of 40 degrees. In the meantime, we had been reading Fukuoka’s book, The One-Straw Revolution. However, his recommendation of zero tillage failed to convince us. After all, most of the traditional agriculture in Latin America uses zero tillage, yet is far from productive. In mid-1993, I visited the work of EPAGRI in southern Brazil.
Having visited over 160 agricultural development programs through the years, I found this largely unpublicized effort to be the finest of its size I had seen in Latin America. Literally tens of thousands of farmers were producing harvests approaching those in the U.S.-with gm/cc’s and zero tillage.
Valdemar de Freitas, EPAGRI’s manager, showed us that the secret to achieving zero tillage is applying massive amounts of organic matter to the soil. Brazilian farmers, after some four years of applying gm/cc’s to the soil, are able to quit plowing. (This is now outdated as corroborated recently by Valdemar. “We now know that plowing down green manure is a much, much slower way to improving soil structure than going straight to zero tillage. The enhanced biological activity under ZT is the key to soil structure renovation.” August, 2001) The advantages, in terms of better soil structure, reduced soil compaction, higher fertility, and decreased cost, are impressive. Interestingly, farmers often use non-leguminous gm/cc’s to increase biomass in order to quit plowing sooner. That is, they spend scarce income on nitrogen fertilizer for three or four years in order to achieve zero tillage sooner. The Brazilians’ discovery explains why the zero tillage gm/cc systems of northern Honduras-and Fukuoka’s-produce so well, while many traditional zero tillage systems do not. Thus we added a third principle: use zero tillage.
Maintain biological diversity
EPAGRI’s investigation and dissemination of over 60 species of gm/cc partly to avoid diseases and insect pests, confirmed another, more widely known fourth principle: maintain biological diversity.
This last principle was discovered by Martha Rosemeyer, a Cornell doctoral candidate working in Costa Rica. For several years, agronomists working with a low-cost, traditional, mulched-bean (Phaseolus vulgaris) system had been trying to solve a phosphorus deficiency problem. With highly acid (pH = 4.0 to 4.5) soils, virtually all the phosphorus applied became tied up almost instantly. Farmers’ harvests averaged 500 kgs/Ha.
Feed plants through the mulch
Martha and a group of farmers tried broadcasting the phosphorus on top of the mulch. The results, since confirmed in numerous additional experiments, were astounding. Bean yields rose to between 1.5 and 2.5 T/Ha. This would help explain the success of Mesoamerica’s gm/cc systems, and coincides with the fact that plants as diverse as maize, manioc, and tropical trees tend to develop a heavy mass of feeder roots immediately under thick mulches. Furthermore, it makes simple sense: when soils are as hostile to plant growth as are the humid tropic’s acid soils, feeding plants through a mulch would seem a much more promising alternative. The fifth principle is undoubtedly the most unconventional: feed plants through the mulch.
These five principles enjoy a nice synergy. For example, if we are going to feed our plants through a mulch, we certainly cannot plow our fields. Nevertheless, the most important relation between these principles is precisely the one that took us the longest to figure out: They describe quite well the way a humid tropical forest functions. That is, all we discovered in our 12-year odyssey is something we should have guessed all along. In order for humid tropical agriculture to be both highly productive and sustainable, it must imitate the highly productive, millions-of-years-old humid tropical forest (Roland Bunch, COSECHA, Honduras).
The above works in temperate climates as well. In Honduras, farmers, working alone and using hand tools only, farm up to 10 acres using no-till. In a video that trains extension service people, the statement is made “The worst thing that can happen to a soil is the use of a rototiller.” Or a mouldboard or oneway or disk, etc. [KH]
Morrison, an ag engineer in Temple, TX, did several years of research with 100″ wide permanent beds using farm machinery. He later used 80″ and 40″ to accommodate harvesting equipment. It increased yield 10%.
No-till is great once the soil is loaded with organic matter and has become healthy with microbes and earthworms. Walking on and compacting the soil will ruin them so you need to establish permanent walkways and beds. Keeping mulch on the ground year-round is critical with any garden. Without mulch, rain can compact and erode the soil.
To do the plant-through-the-mulch procedure, you’ll have to start by planting the cover crop. Cut the plants off in the spring, leaving the cuttings on the soil to serve as a mulch. Then plant the tomatoes or other crops right into the undisturbed roots without tilling or adding fertilizer. Additional mulch might need to be added after planting if any soil is left exposed.
Tests by the USDA showed that this technique gave a 100% increase in production over conventional fertilizer and tilling. (Howard Garrett, dirtdoctor.com, Dallas Morning News, 3 March 00.)
The above principles apply to very steep field. In Honduras I visited a farm on land with a 73° slope. During Hurricane Mitch, when almost a meter of rain fell in just a few days, this farm had no soil erosion with the permanent beds. They had been built some six years before. Each bed was approximately one meter wide with each bed some one meter below the next one and on the contour. A small channel to carry runoff water, when it was needed, was on the uphill side of each bed. Each bed was made to slope just a little to the channel. On less-sloped land the beds could be wider. No grass, rocks, trees, alley cropping, etc., were used.
Ken teaches workshops in organic, no-till mini-agriculture (urban and rural): gardening, mini-farming, mini-ranching worldwide in English and Spanish.