Zai holes can increase the growth of grains, vegetables and trees, especially in compacted infertile soils in drier climates or seasons. De luxe Zai hole invention and illustration by David Clode. In addition, some of the subsoil or stones is then used to make a surrounding ridge or rim to hold water on flat ground , or on the down slope edge on sloping ground, in order to catch more water runoff from the paths in between the Zai holes. The same or similar techniques have been used extensively and successfully by the author in suburban ornamental landscaping, and tree planting on farms and degraded land in Australia. Ideally groundcovers would be species that root at the nodes e.
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Zai holes can increase the growth of grains, vegetables and trees, especially in compacted infertile soils in drier climates or seasons. De luxe Zai hole invention and illustration by David Clode. In addition, some of the subsoil or stones is then used to make a surrounding ridge or rim to hold water on flat ground , or on the down slope edge on sloping ground, in order to catch more water runoff from the paths in between the Zai holes.
The same or similar techniques have been used extensively and successfully by the author in suburban ornamental landscaping, and tree planting on farms and degraded land in Australia. Ideally groundcovers would be species that root at the nodes e. Ipomoea spp. In the Sahel region, for example, suitable trees could be Acacia holosericea, A. These trees and shrubs also provide edible seeds. In slightly wetter regions, some other possibilities include Acacia auriculiformis, Gliricidia sepium, Leucaena leucocephala and Sesbania sesban.
At around year 5 — 10, the soil should have been improved even more by the Faidherbia or other trees and crops could be grown under the canopy of the Faidherbia trees, with greatly increased yield probably twice as much and perhaps much more with Faidherbia trees. Direct seeding Faidherbia albida in the Sahel final Zai holes: Size and shape An example of a rock dust, made from volcanic basalt rock.
This has been tested in North Queensland by James Cook University, and proven to provide long-term fertility improvement to a variety of soils in a high rain fall, tropical climate where nutrients tend to be leached. In very dry areas, there are usually larger paths a greater surface area to catch more runoff , and fewer Zai holes.
Other appropriate amendments could include compost, vermicompost, fertilizers, biochar, rock dusts, burnt bone, clay in sandy soils, etc. In Western Kenya, a depth and diameter of 60 cm 2 feet is popular, with paths of the same size between the plantings Orodho, Zai holes can be as little as 20 cm in diameter and 10 cm deep, while Tumbukiza used to grow the very large Napier grass in Kenya, can be as much as 90 cm deep, and up to 90 cm long.
See the Napier grass photo below. Cairns, North Queensland, Australia. Many plant species absorb most of their water and nutrients from the top 60 cm 2 feet of soil. Larger holes require more work, which is a consideration where many holes are to be dug, and in Africa where the farmer may be a woman and perhaps not as strong as they were in their younger years.
Generally hoes or mattocks are used to make the holes, but in some soils but not very sandy soils , and for some people, a garden fork may be easier, since you are using your body weight to push the fork into the ground, and levering the fork upwards using the principle of the lever , rather than the relatively hard work of lifting a hoe above your head, and then striking the ground to make holes.
If four stakes are to be used to enclose each hole with clear plastic or non-woven polypropylene fleece, then fewer, larger holes would be more economical, since four stakes and other materials are needed for each hole.
The size and shape of paths should allow easy access for people, and possibly wheelbarrows, mowers and trolleys. In dry areas, the most important function of paths may be to provide a large and impermeable surface area to collect water. Plants could also be grown on paths, to be mowed with a lawn mower and produce mulch for example, perhaps subterranean clover, Biserrula pelecinus in Mediterranean climates, or other nitrogen-fixer , or to attract beneficial insects such as bees e.
However, in drier areas, plants grown between the holes would reduce runoff into the holes. The higher figures would be from results in dry, infertile soils, often with a hard surface crust. In good soils with favorable climates, a lower response should be expected. The pits themselves contributed more to yield increases than the nitrogen inputs, indicating the significant role that water can have on crop growth and the use of existing soil nutrients.
Shelter to increase plant growth Non-woven polypropylene garden fleece also called frost protection blanket. This material provides some shade, and protection from extremes of hot sun, winds, sandblast etc. In addition, the material is relatively cheap, and could also perhaps be provided by overseas aid organisations as an alternative mosquito net material. To gain an appreciation of what shelter can do in colder climates the U. Mulch Mulches of plant materials organic mulches on the surface of the soil generally keep the soil cooler, insulated against temperature extremes, and moister for longer.
Mulches usually reduce weeds which compete for light, water and nutrients, and so reduce plant growth and need to be topped up as they decompose. Mulches can greatly increase plant growth. In my experience, mulches of pea straw or alfalfa lucerne hay are particularly good for growing vegetables, and encouraging a population explosion of earthworms, and hence their beneficial activity.
The leaves preferably small leaves and twigs of most nitrogen-fixing plants are likely to be good, e. Gliricidia sepium for example, is tried and proven. The leaves of Tithonia species are high in both nitrogen and phosphorus and the related Montanoa and other daisy family plants may be similar and should make a good mulch. Tithonia, Montanoa and Tagetes are all in the daisy family Asteraceae, so it is reasonable to assume that other plants in the daisy family may have leaves high in NPK.
Pigeon Pea prunings make a good nitrogen rich mulch. Photo: Shannon Drive, Bayview Heights. Mulch from plant materials should be kept away from plant stems as this may promote rotting of the stems, however, some plants such as maize and tomatoes, will benefit by growing additional adventitious roots if mulch or compost is piled up against the stem, later in the growing season.
These very high figures should porbably be viewed as a best case scenario. In some climates, where it is cold in winter and hot in summer, it may pay to use black plastic mulch initially to warm up the soil, which could then be removed and replaced with an organic mulch as the weather and soils get warmer.
Partially decomposed compost should preferrably not be in direct contact with the soil, as this may cause nitrogen draw-down, where micro-organisms outcompete plants for the nitrogen they use in breaking down plant materials and so plant growth is reduced due to nitrogen deficiency. It would be best to place fully decomposed compost onto the soil first, and partially decomposed compost on top of this, preferably with additional nitrogen, which could come from human urine.
Once the partially decomposed compost has fully decomposed, more could be added on top to keep up the carbon dioxide concentration, but results are likely to be diminished as the plants grow taller, and become adapted to CO2 enrichment.
Around twenty sheets of newspaper in a bowl shape at the bottom of the hole e. For plants that grow best in very wet conditions, an impermeable layer of plastic sheet or similar could be used. Zai holes are designed to catch water runoff, but additional watering is possible and may increase growth.
Zai holes, Tumbukiza, Roof gardens, Circle gardens, Vertical gardens
Meitzner and Martin L. See web site for order form. The authors have organized and connected together articles and letters from a quarterly newsletter put out by the Educational Concerns for Hunger Organization, Inc. ECHO which contains reports and questions from diverse locations and situations about the success and failure of an array of experimental agricultural ideas. Many of the topics are presented as works-in-progress, with one subject in a newsletter issue often getting updated by the response of the readers, presenting sometimes conflicting experiences. So it is quite useful to have these observations on, say, a particular crop or water management, now grouped together. The book is easily enjoyed in the usual linear manner of reading from front to back but subject-matter chapters provide a good organizational basis for specific research.