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close this bookAmaranth to Zai Holes, Ideas for Growing Food under difficult Conditions (Educational Concerns for Hunger Organization, 1996, 397 p.)
close this folder6: Soil health and plant nutrition
View the document(introduction...)
View the documentSoil types
View the documentGreen manures and cover crops
View the documentFertilizers

Soil types

COMPOSTING AND HILL CULTURE. There are three problems with the "proper" way to make fine compost. First, it is more work than most of us, including the subsistence farmer, have time to do. Secondly, most garden and farm residue is too big to decompose quickly unless a lot of work is done with a machete or shredder. Thirdly, humans like immediate gratification, something that only the most elegantly constructed compost piles can offer; the others take forever. We have been working on some methods to get around all of these problems, but now find they have already done that in Germany, with "hugelkultur" (hill culture). The following is taken from The Avant Gardener monthly newsletter.

"A hole 6 inches (15 cm) deep and 5 to 6 feet (1.7 m) wide is dug of any desired length and running north-south. In the bottom, twigs, branches and rotting logs are laid [I would put things like broccoli stems here too]. Then the sod removed when making the hole is laid face down on the wood layer. On top of this goes a deep layer of rotting leaves ...and green wastes.... Next comes a layer of fresh, nearly finished compost. Finally all this is topped with soil mixed with rich, mature compost. The completed mound can be as high as 30 inches (76 cm). Hugelkultur experts advise planting leaf and head vegetables such as lettuce, spinach, cabbage and cauliflower, plus tomatoes and cucumbers, the first year when there is considerable heating from the composting. The next year ... root crops can be added. The mound will last 7 years, its height gradually lessening and in the final year a perennial such as asparagus is planted."


composting and hill culture

[Subscriptions to The Avant Gardener for a year are $20 in USA; $24 overseas. Write to The Avant Gardener, Box 489, New York, NY 10028, USA. Though it is definitely oriented toward temperate horticulture, often ornamental, some of our tropical readers will find some articles helpful and interesting from time to time.]

The systems we are trying are quite similar. We make layers of whatever material we have available. By being able to plant immediately we not only get that "instant gratification" but also are able to make better use of scarce land by continuing to use the area for planting. Because it is in use, there is no hurry for the whole pile to decompose so there is no need for turning or chopping up the coarse material. You also have all the advantages of a raised bed. We are using fertilizer at least this first season because our top compost layer is thin and the decay inside may cause nutrient deficiencies at first. If we had manure tea we would water with it frequently. Instead we often use a soluble fertilizer, pouring it right over the leaves. Since we never seem to have enough compost, I will tear up some of these "hills" after a year or so rather than following the German scheme exactly.

Heat from decomposition may not be too serious a problem on a smaller scale. We have very nice carrots right now in a 12-inch (30 cm) tall 2 x 4 foot (60 x 120 cm) bottomless box that we placed on a cement slab and filled to the top with grass clippings and a bit of fertilizer. We then placed about 3 inches (7 cm) of potting mix on top and planted the seeds. By the time the roots reached the grass it had apparently cooled down.

Those of you with large amounts of rainfall are often discouraged to see the bit of fertilizer you were able to procure leached away by rains. Hill culture might help because the microorganisms that decay the organic matter in the interior of the hill use the same nutrients that plants use. As nutrients are leached into the pile they are "recycled" by these microorganisms and turned into compost.

THE HAITI MIX FOR STARTING SEEDLINGS. Many formulas for artificial potting soil give outstanding results when starting vegetable, flower or tree seedlings. The problem is that ingredients are expensive or not available in many locations. For example, at ECHO we start our seeds in a 1:1:1 mixture of peat moss, perlite and vermiculite. When Tom Post in Belize asked about using sugar cane for such a mix, I asked Jerry Larson with Double Harvest in Haiti about their experience. In the process of growing millions of tree seedlings, they have acquired a lot of experience with what they now call the "Haiti mix." His comments follow.

The basic ingredients are 5 parts sugarcane bagasse, 1 part rice hulls and 1 part sandy loam soil. Before they are mixed the sugarcane bagasse must be well decomposed. The best indicator is the color. Bagasse with a light yellow color has decomposed very little and must not be used. As decomposition proceeds the color goes through shades of red to dark brown or almost black. A dark cinnamon red color verging on brown indicates that the bagasse is acceptable, but the darker color is preferable. It is important that no undecomposed bagasse get into the mix.

The decomposed bagasse is finely shredded in a silage chopper and mixed with the other ingredients. A heating and sterilization process is initiated by adding urea to the mix at the rate of 1 pound per cubic meter of mix. [Ed: If you do not have urea, I would imagine other nitrogen sources could be used. Even ordinary fertilizer could probably be used, but it would make control of nutrients in the final mix less precise.] There is usually sufficient moisture in the bagasse to "kick off" the heating process. Within 2-3 days the temperature in the center should be about 145 F (62 C). Next the pile is turned inside out so that all parts will be heated equally. After just one more day the pile is flattened and packed down to stop the heating process. At this point the mix is in an unstable state and thorough packing is necessary if the heating process is to be controlled. Continued heating not only burns up nutrient value in the mix but, if allowed to continue unchecked, will chemically alter the mix and make it toxic to plants.

An effective method of packing is to drive over the flattened pile with a tractor. After that the pile can be left for several weeks or months with no damage. If the pile cannot be packed that tightly and if it is to be used within a short time span (several days), then it is permissible to have several men pack it by walking over it until it is as tightly packed as they can get it. Just before the mix is used, it is passed through a 3/8 inch hardware cloth to remove the larger particles. Five to six pounds of 12-35-24 fertilizer (depending on the stage of decomposition of the bagasse) is added per cubic meter along with 2 ounces of F-5-3 micronutrients. The mix should be used immediately because the fertilizer will otherwise cause it to heat up again and alter the nutrient balance. In this last stage, only as much mix as is going to be used each day should be prepared.

A PEAT SUBSTITUTE MADE FROM COCONUTS. [The following is based on an article by Alan Meerow in Country Folks Grower South, November 1993.] Coir is the fibrous part of the coconut husk. The long fibers are "extracted and sold to make brushes, automobile seats, mattress stuffing, drainage pipe filters, twine, etc. Traditionally the short fibers and dust left behind have accumulated as a waste product for which no industrial use had been discovered." Tests in Australia and Europe show that this product makes a remarkably adequate substitute for peat. "The Lignocell company in Sri Lanka (where over 2.5 billion coconuts are processed each year) has become the leading processor [of coir]."

Coir has a high lignin cellulose content, which keeps the piles that traditionally accumulate around processing plants from breaking down. The same property inhibits breakdown of coir pith when used as a growing medium.

The pith is very similar to peat in appearance. It is light to dark brown, with 0.2-2.0 mm particle size. "Unlike sphagnum peat, there are no sticks or other extraneous matter." A study in Australia found "superior structural stability, water absorption ability and cation exchange capacity compared to sphagnum peat." There are reports that coir from sources other than Sri Lanka have contained chlorides at levels toxic to many plants. Perhaps this is a result of the processing method. In any event, watch out for that if you begin using the pith.

"Lignocell processes the pith into highly compressed bricks roughly 8x4x2 inches (20x10x5 cm), each weighing 1.5 pounds (0.7 kg). They are exported for the retail market in 12-brick packages. The 12 bricks fluff out when re-wet into 4 cubic feet (0.1 m3) of ready-to-use material. Each brick absorbs about 2 gallons (7.6 liters) of water. I have been impressed by the ease with which coir pith re-wets after it has been thoroughly dehydrated."

The February 1996 HortIdeas cites research which cautions that coir can contain high levels of chlorine, which could affect seed germination. Leaching reduces chlorine levels quickly, and it is best to use coir that has been aged for at least one year.

[Ed: When I (LSM) was an intern at the Royal Botanic Gardens, Kew, we used coir rather than peat because of the adverse environmental impact on British peat bogs. Most of the horticultural staff preferred it to peat anyway. It worked well with nearly all plants, though they said it was not sufficiently acidic for the carnivorous plants. The coir surface can appear dry even when saturated below, so be careful to avoid overwatering.]

REMOVING SALTS FROM CONTAINER-GROWN PLANTS. I [MLP] vividly remember as a toddler watching my father boil down a can of saline water to show all the salt that was left behind. I think of that when week after week I water a potted plant during a long dry season or in a greenhouse where it never receives rain. As the water evaporates or is taken up by the plants, more and more salt builds up. Sometimes you can even see a white crust appear on top.

David Silber writes in the June 1992 issue of The Fruit Gardener that one way to correct this problem is to "semi- annually leach the soil with tap water (rainwater is better) that has been acidified to a pH of 4.0. I use a commercial grower's acid blend containing nitric and phosphoric acid. But you can also use vinegar as an acidifier: 2 tablespoons per gallon of water will yield the desired pH. The solution should be flushed through the growing container three times. In my experience the leaching water went in at a pH of 4 and came out at 6.5. This effectively removes lime and bicarbonates as well as sodium. I've used this on miracle fruit, coffee, pitomba, jaboticaba and lychee. The plants responded within two weeks with a new flush of normal leaves."

ECHO used this technique in the greenhouse where we grow rain forest plants. Plants were not thriving and leaf margins were turning brown on some species. They seemed generally healthier after the treatment.

The Fruit Gardener is published six times yearly by the California Rare Fruit Growers chapters. Membership/subscriptions: $16 in USA; $25 Canada/Mexico; $30 foreign surface mail; $40 foreign airmail. Write: California Rare Fruit Growers, The Fullerton Arboretum, California State University at Fullerton, Fullerton, CA 92634 USA.

SALINE AGRICULTURE: SALT-TOLERANT PLANTS FOR DEVELOPING COUNTRIES is a 143-page book published by the National Academy of Sciences (1990). Like the other NAS books of this nature, it is a very readable overview of lesser-known resources for a difficult situation. Salt-tolerant crops (halophytes) might utilize land and water that are unsuitable for salt-sensitive plants. Looked at from a different angle, farmers whose poverty limits them to their present location where soils or water are salty might eke out a better living.

There are limitations, in part because relatively little agricultural research has been done with these crops. Salt- tolerant plants usually have poor agronomic qualities (e.g. there may be wide variations in germination and maturation times). Seeds of grasses and grains tend to shatter and fall to the ground. The foliage may not be suitable for fodder because of its high salt content. Nutritional (or anti-nutritional) characteristics have, in many cases, never been studied in the laboratory.

Sections are devoted to food, fuel, forages, and fibers.
FOOD: grains and oilseeds, tubers and foliage, leaf protein, fruits, traditional crops.
FUEL: fuelwood trees and shrubs, liquid fuels, gaseous fuels.
FODDER: grasses, shrubs, trees.
FIBER ET. AL.: essential oils, gums, oils and resins, pulp and fiber, bioactive derivatives, landscape plants.

Some of the plants we have talked about in EDN are discussed as having some degree of salt tolerance. The leucaena tree, Leucaena leucocephala, has been grown on coastal sandy soil in Pakistan through irrigation with saline water. Trees even survived when 20% seawater was used in the irrigation water, although yields were reduced by 50%. [See below for more information.] Jojoba (Simmondsia chinensis) is relatively salt tolerant, growing near the Dead Sea with brackish water irrigation in Israel. Quinoa (Chenopodium quinoa) germinated in a mixture of 1/3 sea water and 2/3 fresh water, though it would not continue to grow at that salinity. In the salt flats of southern Bolivia, quinoa is one of the few crop plants grown. In this arid region (230 mm/9 inches) rainfall, quinoa is planted in holes about 40 cm (16 inches) deep where the soil is damp. As the plant grows, soil is filled in around it. With wide stretches of salt beds nearby, the environment is certainly saline, but no measurements have been reported. [The book does not say whether they are using specially selected strains of quinoa.] Neem (Azadirachta indica) seedlings have been grown successfully in Pakistan on sandy soil using irrigation water with approximately 10,000 ppm salt. [Pure sea water is 35,000 ppm.] A neem plantation has been established near Mecca in Saudi Arabia to provide shade for Muslim pilgrims. Water with approximately 2500 ppm salt was used for irrigation.

Only two conventional crops have halophytic ancestors: beets and date palms. Both can be irrigated with brackish water without serious loss of yield. Asparagus is remarkably tolerant of salt. In Tunisia, where irrigation water contains 6,500 ppm salt, asparagus yields are about the same as in areas irrigated with fresh water. [ECHO staff Cory Thede comments that he remembers reading somewhere about applying salt for weed control in asparagus.] Barley is the most salt-tolerant cereal grain. At the University of Arizona, a special strain of barley yielded 4,000 kg per hectare when irrigated with groundwater with half the salinity of seawater. Selected strains were grown at the University of California on sand dunes with the following yields in kg/ha and salinities: 3,102 with fresh water; 2,390 for 1/3 sea water; 458 for 100% seawater. (Unfortunately the book says very little about vegetables. For some help on that subject, see "Helpful Facts About Salinity" below.)

Anyone working with salinity problems will surely want this book. If you are working with a governmental or non-profit organization, you may write the NAS on official letterhead, explain your work in no more than one paragraph, and ask if they might send you a free copy. The price in the US is $15. The address is Board of Science and Technology for International Development, Publications and Information Services (HA-476E), Office of International Affairs, National Research Council, 2101 Constitution Avenue, Washington, D.C. 20418, USA.

SALT TOLERANCE IN LEUCAENA? Dr. James Brewbaker at the University of Hawaii commented on the note above that leucaena has salt tolerance. "Leucaena's salt tolerance is effective only along shore lines where calcium levels are high. As with many other plant species, the tolerance of 'salt' is a complex subject, for salt can represent a great assortment of chemicals. Generally, the major difference is seen when comparing coastal salinity (highly calcareous) with inland evaporative salinity (e.g. Salt Lake), which is usually not calcareous. Leucaena tolerates the former, not the latter."

Calcareous refers to soils with high calcium content, primarily coral-derived soils with accompanying high pH. Arid regions naturally have areas of high salinity due to evaporation and salt accumulation; such soils are often lower in calcium, higher in sodium, and thus more toxic to plants.

A few nitrogen-fixing trees do handle the salty non-calcareous soils. The best work with these is at CAZRI (Central Arid Zone Research Institute of India) in Jodhpur, India. (Please send us their complete address and more information about their work if you know it. Thanks!)

SOME HELPFUL FACTS ABOUT SALINITY. I pulled the following facts from Knott's Handbook for Vegetable Growers. On units of measurement: The following gives a helpful perspective when reading salinity literature that talks about ppm and millimohs per cm (sometimes written mmho/cm). 1 ppm (part per million) = 1 gram in 1,000 liters of water; ppm x 1,000 = 1%; 1,000 micromhos per cm (a unit of measure for electrical conductivity) = approximately 700 ppm; 1,000 micromohs per cm means that one ton of salt would be in the water that would cover one acre of land to a depth of 1 foot.

The handbook lists several vegetables and the mmho/cm in the soil that reduce yields by 25%. Beet (10), spinach (7), tomato and broccoli (6), cabbage, cucumber, muskmelon, potato, corn and sweet potato (4), lettuce, pepper, radish, onion and carrot (3), bean (2). So beets would be the best vegetable for saline soils, beans the worst.

Some general rules listed for likely crop response to salinity follow. 0-2 mmho/cm, mostly negligible; 2-4, yields of very sensitive crops may be restricted; 4-8, yields of many crops restricted; 8-16, only tolerant crops yield satisfactorily; above 16 only a few very tolerant crops yield satisfactorily.

PLANTING IN FRESH VOLCANIC ASH. Two members of our network in the Philippines asked what we could find out about this subject. Planting season is now near for farmers near Mt. Pinatubo. We called Dr. Allen Busacca at Washington State University about gardening in volcanic ash and what impact layers of ash will have on agricultural soils.

"Most of our experience has been with revegetation of natural areas (Mt. St. Helens) rather than agricultural lands. While we generally think of volcanic soils as rich agriculturally, that is only after thousands of years of weathering. It has been my experience that ash is relatively neutral. Initially it is silica-rich, like crushed glass. In the case of the Mt. St. Helens volcano it was not very toxic. It is probably best to incorporate it up to maybe 6 inches (not an easy thing to do without equipment)."

"Not all volcanic ash is created equal. The best way to deal with a larger quantity depends upon whether it is light and fluffy or a fine, coarse pumice."

He referred us to Dr. Jeff Smith who was involved in some agricultural studies for the USDA. Dr. Smith said that there has been surprisingly little study of agriculture in fresh volcanic ash. "It will probably be a bit on the alkaline side and almost certainly will contain a lot of salts. So the first year only the most salt tolerant vegetables and grains should be grown. He is pretty sure that if they plant salt sensitive vegetables directly into the ash they will not thrive. On the other hand, there are volcanos where the ash was more like glass. Incorporating into the soil seems to help a lot."

There are no extension bulletins on the subject that he knows about. This would be a good research topic for one of our readers in the scientific community. If anyone has ever seen an extension bulletin or especially helpful research paper, or if you have had personal experience, we would like to hear from you.

ECHO's network shared quite a few helpful experiences. Ken Turner with Mercy Corps sent an interesting letter and pictures. "I guess I'm your reporter on the spot. Our community and my home (until the eruption) is 15 km from Mt. Pinatubo. We evacuated June 7, two days before the first major eruption. One of our staff returned a few weeks later. It looked pretty dismal.

"Now it is a different story. Some pretty amazing harvests have drawn a lot of attention. Banana planted a few weeks before the eruption produced a good crop. Most amazing was the watermelon harvest--more than twice the yields of past years, melons (sugar baby variety) twice the size on the average and still sweet, and vines more than twice the usual length.

"The ash is now about 8 inches (20 cm) deep. The soil has remained moist (and I suspect cool) under the sand, even after 3 months of dry weather. I did not check the pH, but 30 km from the mountain the pH is about neutral. It appears that sweet potato is thriving in rice fields 30 km from the volcano.

"The crops and generally lush growth is encouraging farmers to return, even though the road is likely to become impassible early in the rainy season. "

Victoria Coronel with IRRI sent very specific and helpful recommendations. Highlights are summarized. The eruption of Mt. Pinatubo brought havoc to more than 38,000 ha of farmland. Even though the Philippines has several active volcanos, they could find no published reports of studies on revegetation.

Some findings from the Mt. St. Helens volcano in the United States are relevant. (1) Ash has a lower permeability than soil. This means that flood water will remain longer on the surfaces of the ash-covered soils. (2) The ash layer acts as a surface mulch both reflecting solar radiation (increasing photosynthesis) and impeding water flow and evaporation from the soil to the atmosphere. An estimated 40-60% of the light is reflected. Peak daytime soil temperatures beneath 2-3 cm of ash were 6-10 C lower than adjacent sites where ash had been incorporated into the soil. (3) The abrasive effect of ash particles is harmful to insects. Unfortunately beneficial insects were the most affected.

Studies from Mt. Galunggung in Indonesia provided the following insights. (1) Crop yields were still high in areas with up to 20 cm of volcanic materials. Productivity declined with greater amounts. (2) Yields of rice and other food crops were high when the ratio of volcanic materials to soil were as high as 5:5 and 7:3. If there is less than 20 cm of ash, plowing into the soil seems the easiest solution. If deposits are deeper, adding organic matter may be needed (20 t/ha manure or other organic materials). Dumping organic waste from Manila has been suggested, but transportation is a problem. Green manure crops may be the answer.

The following cropping pattern was suggested if volcanic materials are less than 20 cm and the irrigation system is intact. After plowing 30 cm deep (a 7:3 ratio of volcanic materials to soil), plant rice-rice-corn/ soybean or rice- rice-leaf onion. For 20-30 cm thick deposits, plow the volcanic material when dry, incorporating any organic material that is available. Food crops can be planted in the early rainy season. Rice and corn are not generally recommended. If volcanic materials exceed 50 cm, pineapple would be suitable since it thrives well in sandy soil with pH range of 4.5-7.l5 and requires minimum care and inputs. Hybrid coconuts can also be planted. Fruits like guavas, nangka [jackfruit], papaya and banana grew well, even better than before the eruption of Mt. Galunggung.

Preliminary tests show some rice varieties do better than others. The top 3 were all varieties grown in acidic areas of Indonesia. In one area, corn exhibited early leaf yellowing (corn requires a lot of nitrogen). Sweet potato gave the best growth, followed by kangkong and cassava. Green manures also gave initial excellent growth. A second eruption destroyed the experiment.

IRRI recommends that the above fruit trees be planted as quickly as possible for the longer term; that sweet potato, cassava, kangkong and green manures be planted for the intermediate term; that livestock that eat roots (e.g. swine) be associated with sweet potato and cassava growing; that aerial seeding of green manures, including ipil-ipil [leucaena], be considered.

Scientists desiring to see the entire report, "Mt. Pinatubo--Controlled Revegetation" by B. S. Vergara and V. Coronel can write to Dr. Coronel at IRRI, P. O. Box 933, 1099 Manila, PHILIPPINES. Workers outside of Asia can write to ECHO.

RESOURCES ON SOIL HEALTH. We asked Marianne Sarrantonio, author of the handbook Methodologies for Screening Soil-Improving Legumes and professor of agroecology at Slippery Rock University, Pennsylvania, USA, to recommend a few hands-on resources from the emerging science of soil health (or soil quality). (This book is available in English and Spanish from Rodale Institute, 611 Siegfriedale Rd., Kutztown, PA 19530, USA.) "Local extension groups in your area are a good place to check for hands-on manuals on composting and green manures. I think that Grace Gershuny's books The Soul of the Soil and Start with the Soil are excellent for those without science training." Contact John Doran (ARS-Nebraska, USA, 402/472-1510) after mid-1996 about his how-to manual for measuring and monitoring soil health.