Green manure is a fertilizer derived from the decomposition of plant residues. In the world of agriculture, green manure is re-glimpsed as a potential source of organic materials, considering that agricultural land has been degraded. This is due to the loss of organic matter in the soil due to the massive use of chemical fertilizers.
Based on the BBSDLP (2006) report the level of organic matter on agricultural land in Indonesia is less than 1%. Whereas a good agricultural land ideally has a content of organic materials 3-5%.
Just like other types of organic fertilizers green manures have the ability to improve the physical, chemical and biological properties of the soil. The use of green manure in agriculture, helps the environment maintain its ecological cycle. Because at harvest, some of the biomass remains in the field and is used again for the next growing season. So that the outer intake in agricultural production can be kept as low as possible.
The types of green manure
In general, almost all types of plants can be used as a source of green manure. However, it is best to use plants that have a high total humus content, high nitrogen content and a low C / N (nitrogen carbon to nitrogen ratio) ratio.
Cheryl A Palm agroecosystem expert explains that high quality green manures have nitrogen content of more than 2.5%, lignin content less than 15% and polyphenol content less than 4%.
Plants with such characteristics will easily decompose in the soil and nitrogen elements can be absorbed by plants easily. If the content of lignin and high polyphenols will require more nitrogen in the weathering process. So it has the potential to compete with core plants. Here are some types of plants commonly used as a source of green manure.
The rest of the production plant
At harvest time not all plant biomass is transported for sale. Some are left on the ground and left to decompose as green manure. Obstacles, some farmers are impatient waiting for the fallow (rest) until all the rotten plants. Like rice farmers who often burn the remaining straw of harvest. This is done because some types of plants are long term penguraiannya. Actually this can be accelerated by way of composting the plant first.
Some plants of the legume type are more effective to be used as green manure. Nutrient content of legume crops, especially N elements higher than other types. Provision of nutrients from legume plants faster because this plant is easier to decompose. Legumes are often cultivated crops such as nuts, peanuts, green beans, soybeans and long beans.
To get the green manure from the rest of the production plant efficiently, we have to crop rotation. For example, soybean crops planted on the sidelines of the rice planting season. So when soybeans are planted, the rest of the plant can be buried directly for rice plants.
Green manure can be obtained by planting source crops on the sidelines of the nucleus. The farmers used to plant it in the passage between the main plant beds. This practice is widely applied by food crop farmers who adopt the SALT system . The fence plant will work effectively when it meets the properties (1) The percentage of leaf growth is greater than the wood, (2) Rapid growth, easy to sprout and roots in order not to compete with nucleus plants, (4) High-ability nitrogen and nutrient Other, (5) Not potential to weed.
Plants suitable for fence plants as a source of green manure is a legume crop species. Some of them are:
- Hahapaan ( Flemingia macrophylla )
- Lamtoro ( Leuceana leucephala )
- Gamal ( Gliricidia sepium )
- Kaliandra ( Caliandra callothyrsus )
Plants cover ground
There are two types of cover crops commonly used as a source of green manure. First, plants grown in fallow periods or periods when land is not used. This green manure is usually planted ahead of the dry season, its use as mulch to protect the soil. This plant is expected to conserve soil and forage is a source of nitrogen for the next planting season.
Second, plants grown side by side with core plants, usually applied in coffee or palm plantations. In order for this plant to withstand the rate of soil erosion, maintain soil moisture, and forage can be used as a source of nitrogen.
Some suitable cover crops used as a source of green manure are:
- Bunguk ( Mucuna munanease )
- Komak ( Dolicos lablab )
- Cowpea ( Vigna sinensis )
- Kacacangan ( Arachis pintol )
Apart from the plants that we are cultivating, green manures can also be taken from wild plants. These plants usually grow wild around the farmland, biomass can be used as a green manure. In rice fields that have high organic content is usually found a kind of water fern ( azolla ) that grows rapidly. When processing the soil, this plant can be immersed directly as a green manure.
Some of the wild plants commonly used as a source of green manure are:
- Kipait or paitan ( Tithonia diversifolia )
- Kirinyu ( Cromoleana odorate )
- Babadotan or Wedusan ( Ageratum conyzoides )
- Azolla ( Azolla caroliniana, Azolla filiculoides, Azolla mexicana, Azolla pinata )
Characteristics of green manure
Green manure has characteristics like organic fertilizer in general. Can improve soil structure, increase cation exchange capacity, trigger soil biological activities, and provide nutrients for plants. Viewed from the side of farming, green manure has a number of advantages and disadvantages to use.
The advantages of using green manure:
Has advantages such as other organic fertilizers, improving the physical, chemical and biological structures of the soil
Able to prevent soil erosion
Potential to bring other benefits, such as firewood, animal feed, or edible fruit
Suitable for areas that are difficult to reach, because it can be grown in situ
Lowering intake of agricultural ingredients, better for the environment
Weakness of green fertilizer use:
- Require seeds and plant them
- Eliminates the opportunity to plant more core crops more often
- Need more energy to grow it
- Potential to bring pests and diseases in the core plants
- Potentially weed
Use of green manure
Direct embedding, green manure sources of low-C / N-type plants (such as legume and azolla ) can be buried directly on the land during tillage. Plants of this type usually have high nitrogen content and easily decompose in the soil.
Used as mulch, several types of green manure can be applied as mulch. For example, the remaining straw of rice crops used as mulch of chilli or leek. Mulch is useful for maintaining soil erosion and moisture when the core plants are young. When mulch begins to decompose it will be used as a source of plant nutrients by core plants.
Composted, plants with a high C / N ratio (usually high lignite levels), should be composted first (see how to make compost ). Lignin takes a long time to break down in the soil. If such a source of green manure is applied directly to the field, a decomposition process that requires nitrogen takes place. This led to competition for the struggle for nitrogen with core plants. As a result, core plant growth is disrupted.