Permaculture Designers Manual
CHAPTER 10 –
THE HUMID TROPICS IN PERMACULTURE
Section 10.4 –
Earth Shaping in the Tropics in Permaculture
On level ground or gentle slopes (2 – 8°) in the wet dry tropics, a series or large contour banks or swales have an excellent soil preservation effect.
Coupled with the gradual development of a terrace, the retention of wet season water and mulch providing hedge row, this ensures a stable situation.
Between the main hedges, mulch hedgerow and borders can be developed in crop or the terraces can be flooded seasonally for irrigated crops. (Figure 10.8)
On very flat sites (less than 4°), a series or raised mounds or ridges can operate to drain crops in very wet areas, or to impound water for absorption in drier areas.
Pits can also be used only where rainfall is less than 76cm (30 inches), or where soil drainage is good.
Thus, cassava, yam and cucurbits are mounded in areas where drainage is a problem and rainfall intense and pitted in dry areas or savannah dry seasons.
Pits retain mulch and moisture, as they do in desert areas. (Figure 10.9) (Figure 10.10)
Almost every slope benefits from earth shaping for soil conservation.
Hand-made slope terraces need to be narrower (to 3.5 – 6.5m – 12 -15 feet) than machine made systems.
Garden terraces on very steep humid slopes must be kept narrow, and in sets of 6 – 8 down slope, otherwise instability may result.
Borders can be kept vegetated with trees. (Figure 10.11)
Classical wet rice and taro terrace has water continuously led into the top terrace of the series.
Each has a drain and sump to regulate water level. Fish may be grown in the deeps of such terraces. (Figure 10.12)
In stable clay or clay-loam soils, terraces not only hold and infiltrate water, but permit mulch application with minimal leaching losses.
Where no streams exist to feed the terrace system, DRY TERRACE holds the soil against erosion in cropped areas.
Lacking streams, deep mulch keeps terrace soils moist. Where a stream, or part of a stream, can be led to upper terraces, wet crop such as rice, taro, watercress, kangkong and water chest nuts (Indian or Chinese) can be cultivated in water-level controlled paddy.
This is the rich WET TERRACE culture of Asia and Oceania.
About one-half to one third of the total terraced area should be devoted to mulch tree crop providing fodder for livestock or direct leaf and branch mulch to terraces.
Ideally, the upper one-third of hills, the very steep slopes of 30° or greater, terrace side-borders and the outer faces and crowns of bunds (walls) should be planted to productive and mulch producing tree and ground crop.
This not only adds to the terrace stability – many of which have existed in production for up to 5000 years, e.g. the wet terrace cultures of the lfugao people of the Philippines – but will also provide a local manure-mulch crop for terrace cultures.
Included in such mulches are the crop wastes of the proceeding crop.
Specific Growing Situation on Terraced Lands
- Banks and bunds: The rim of the terraces and stepped bunds made for tree crop.
- Slope faces and walls.
- On trellis out from bunds.
- In and around ditches and drains.
- On steep (un-terraced) slopes.
- The flat area of the terrace itself.
Dry Terrace Crop Species
- Millet: summer or dry periods.
- Dryland rice: spring-summer.
- Barley, wheat, rye: winter and cool periods, spring wheat varieties, Brassicas, fava beans.
- Amaranth: summer grains, spring greens.
- Quinoa: summer grains.
- Rape/mustard: winter oils and oil seed.
- Lentils, peas: intercrop and nitrogen fixing grain legumes.
- Grams and pulses: intercrop and nitrogen fixing.
- Tagasaste, banna grass, comfrey, Leucaenana, crop wastes and straw.
Garden Terraces near Homes
- Banana, papaya, melons, chilies, peppers, cucurrbits, maize, beans, sugar cane, cultivated green-crop Brassica, edible Chrysanthemum, edible Hibiscus, rosella, horseradish tree (Moringa), coconut, mango.
Vine Crop off Bund Faces
- Chayote, cucurbits, beans, passion fruit, kiwi fruit.
- Bamboo on borders provides trellis material, as do rot-resistant timbers.
Mulch Crop and Fodders Above to the Borders
- Tree legumes, banna grass (Pennisetum), lemongrass, Vetiver grass, comfrey, bamboo and palm fronds, Aleurites spp., Cinnamonum spp.
- Contour strips of Vetiver grass, lemongrass, banna grass with tree legumes not only replace contour ridges but trap soil particles and are a cheap way to “terrace”, even on steep slopes.
- These strips provide mulch for trees and intercrop. (Figure 10.13)
Essentials and Variations on Terrace Systems
(Figure 10.14) (Figure 10.15)
- Borders; and uphill, sleep-slope, forest crop planted and selected for mulch value and fodder or:
- Animal sheds (ducks, pigeon, poultry, pigs, bees) over top terraces; manure on a “wash down” system.
- In-crop mulches such as beans, Azolla, clovers.
- Staggered, short sets of terraces for steep slopes and high rainfall, compared with more continuous and longer series for winter dry irrigated terrace.
- Deep areas in Terraces for fish/crayfish/ shellfish refuges.
- Vines over all or part of the terrace to aid such crops as taro.
- Bunds planted in clover, beans, comfrey, lemongrass, fruit crop.
- Splash stones or splash plates for falling water; methods or draining terrace.
- Border drains in terrace to keep soil dry for midseason crop.