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close this bookSoil and Water Conservation (SWC) Technologies and Agroforestry Systems (IIRR, 1992, 171 p.)
close this folderOrganic fertilizer sources:
View the document1. Basket Composting
View the document2. Fertilizer from Livestock and Farm Wastes
View the document3. Liquid Fertilizer from Leguminous Trees
View the document4. Use of Green Manures

4. Use of Green Manures

The term green manure generally refers to the use of fresh organic materials such as leaves, twigs and small stems which are used as a soil enrichment material. The green material does not only provide the soil with needed macro elements (such as Nitrogen, Phosporous and Potassium), but trace elements as well (such as magnesium, manganese, cobalt, and iron). In addition' the green manure: (1) provides organic matter which helps improve soil structure, increases the soil's water holding capacity; (2) provides a replacement for commercial fertilizers; and, (3) helps shade weeds. Some green manures can also be grown with food crops to save land area and labor.

MATERIALS FOR GREEN MANURE

Many plants which belong to the Legume Family are commonly used as green manures. These include cover crops such as Kudzu (Pueraria phaseoloides), "Hetero" (Desmodium heterophylla), Centro (Centrosema pubescens), Siratro (Macnaptilium atropurpureum); upright legumes such as: Ipil-ipil (Leucaena diversifolia), Rensoni (Desmodium rensonil), Flemingia (Flemingia macrophylla), Madre de cacao (Gliricidia septum), Rostrata (Sesbania rostrata) and Rice bean (Vigna umbellata). Non-legumes include grasses such as Napier (Pennisetum purpureum) and Guinea grass (Panicum maximum).

Essentially, any material may be used as long as it is fresh and not very woody in form.

METHODS OF USING GREEN MANURE

There are two standard methods in using green manure. These are (1) growing the green manure crop in the crop field; and, (2) importing the green manure in fresh or processed form to the crop field.

1. Growing the green manure crop in the field. This method involves growing a cover crop, usually a legume such as spineless mimosa (Mimosa invisa) or Hetero (Desmodium heterophylla), in a field and then plowing the plant in the soil after a few months' growth. The cover crop is planted for one season, plowed under and allowed to decompose. The next crop is usually a main food crop, such as corn. The green manures should be allowed to rot three to four weeks before planting the following food crop. (See Selection of Cover Crops and Batao in the Upland Cropping System in pages 149-157 for other examples).

A second method involves planting food crops that have a short growing season and leaves which do not shade the ground too much with the green manure crop. Corn and peanuts are good examples. Since the green manure crop needs some light, the food crops should be spaced further apart but seeds should be planted closer together in a row.

A third method involves the planting of hedgerows of upright legumes such as Rensoni (Desmodium rensonii) Flemingia (Flemingia congesta) and Madre de cacao (Gliricidia septum) in the field along the contour (e.g., SALT, alley cropping). These plants are periodically harvested and the leaves and small branches placed on the soil surface between the hedgerows as a mulch. The leaves are allowed to decompose. Crops may or may not already be planted in the field. In some cases, the farmer may physically incorporate the green leaves into the soil by using a hoe. If this is done, there should be a waiting period of about one month before the field crop is planted in the field. (See Simple/Double Selection of Hedgerow Species for more examples, pages 65-69).

It is highly recommended that two different species (one with big leaves and another with small leaves, e.g., Flemingia and Rensoni) should be planted in the same hedgerow along contours. Flemingia has leaves which decompose slowly while the Rensoni leaves are soft and decompose quickly.


Legumes trees

2. Green manures imported in the field. Green manures need not be grown right in the crop field. Farmers can plant them around their field as fences or in vacant areas. The branches are pruned two to three times a year and the prunings are carried to the field where they are either incorporated into the soil or used as a mulch.


Drum and sack

3. Special methods of using green manure:

Green manure tea.

This method is described in detail as a separate topic in another section. (See Liquid Fertilizer from Leguminous Trees, pages 136-137). In general, it involves taking legume or other fresh leaves and placing them in a jute sack or the like. The sack is soaked in water for 10 days. The tea is used to water high-value crops (like sweet potato, eggplant, cabbage) while the partially decomposed leaves from the tea bag can be used as a mulch or compost material.

Compost.

This method involves using green legume leaves to activate a compost pile since the fresh green leaves have a supply of nitrogen. When the composting process is finished, the material is used as a fertilizer by placing it in a hole and covering it with soil. A seedling is planted on top. This method is generally used for high-valued crops such as vegetables.

CONSIDERATIONS:

1. Non-legumes such as wild sunflowers are used as a green manure either by incorporating the leaves and stems directly in the soil or allowing them to partially dry before incorporation. Wild sunflower is also a phosphorous trap, as it accumulates the element as it grows.

2. Cogon and other grasses or weeds can be cut before the powering stage and placed in crop fields as mulch.

3. Green manures can be applied to furrows or between the crop rows rather than as a blanket covering. This method concentrates the nutrients and the roots of the row crop, such as corn will pick up the slow released nutrients from the furrow. The weed growth in the furrow or inter-row area will also be reduced. For minimum tillage systems, placing the green manure in furrows in between rows allows easier access to the crop rows for planting and weeding.


Green manure applied between crop rows

4. farmers frequently air-dry green leaves before using them as a crop fertilizer. This is fequently done with leaves such as ipil-ipil. The drying process releases Nitrogen from the leaves but other nutrient elements such as phosphorous, potassium and trace elements remain in the dry leaf. This process prevents accidental fertilizer bum from fresh leaves.

5 Experience has shown there are several kinds of leaves which are not good for green manuring because they contain substances which are detrimental to the plants and the soil. These are Pine needles, Eucalyptus sp. leaves and Gmelina arborea leaves.