Green fertilizer is a kind of fertilizer made of decomposed plant remnants. In agriculture, green fertilizer is back in the game as potential organic ingredient source due to the degradation of agriculture land nowadays that is caused mostly by the extensive use of chemical fertilizers.
Based on the report from BBSDLP in 2006, Indonesia’s agriculture land only had less than 1% of organic ingredient when the ideal number should be 3-5%.
Like other organic fertilizers, green fertilizer has the ability to repair physical, chemical, and biological characteristics of soil. The use of green fertilizer in agriculture can also help environment to protect its ecological cycle because during harvest, some biomass stay in the soil and can be used for the next crop thus minimizing the use of extra products.
Basically, almost all plants can be made into green fertilizers. However, certain types of plants with packed nutrients, high nitrogen, and low C/N are more recommended.
Agro-ecosystem expert, Cheryl A Palm, explained that high quality green fertilizers have 2.5% nitrogen, less than 15% lignin, and less than 4% polyphenol.
Plants with those characteristics are easier to decompose in soil and their nitrogen will be absorbed easier. High lignin and polyphenol will cause them to need even more nitrogen to decompose thus risking a competition with your crops. Here are some examples of green fertilizers:
During harvest, not all of the biomass is for selling. Some are left on site to decompose into green fertilizers. The problem is, most farmers are not patient enough to wait until everything is decomposed. An example of that problem would be rice farmers who burn their harvest remnants, straws.
Some legumes make for very effective green fertilizers. Legumes have higher nitrogen percentage than most plants and they’re quick to decompose. Types of legumes that are popular in farming are peanuts, mung beans, soy beans, and long beans.
To get green fertilizers made out of harvest remnants efficiently, crop rotation should be done, for example by planting some soy bean crops in between rice crops.
You can get green fertilizers by planting source plants in between your crops. Farmers usually plant them in the hallways between one seedbed and another. This practice is applied by a lot of food source farmers that adopt the SALT system. Hedgerows would be more effective if they fulfill certain characteristics, such as: (1) leaves grow faster than stem, (2) grow fast, bud quickly, have deep roots as to avoid competing with the main crop, (3) are able to trap nitrogen and other nutrients really well, and (5) do not have the potential to become weeds.
Here are some legumes that can be used as hedgerows:
- Hahapaan (Flemingia macrophylla)
- White leadtree (Leuceana leucephala)
- Quickstick (Gliricidia sepium)
- Calliaandra (Calliandra callothyrsus)
There are two types of mulch plants that are usually used as green fertilizer source: the plants we plant during the rest period in the dry season to protect the soil by being sources of nitrogen and the plants we plant during crop season to decelerate soil erosion, protect water accumulation in the soil, and be sources of nitrogen.
Some mulch plants that can be used as green fertilizer sources are:
- Bunguk (Mucuna munanease)
- Lablab (Dolicos lablab)
- Cowpea (Vigna sinensis)
- Nuts (Arachis pintol)
Other than plants that we actually do plant on purpose, green fertilizer can also be made of wild plants. These plants usually grow wild around the farmland. In rice fields with high organic percentage, you can usually find water ferns (azolla) that grow very fast. During land processing, you can bury them and make them green fertilizer source.
Here are other wild plants that can be made into green fertilizer sources:
- Marigold (Tithonia diversifolia)
- Siam weed (Cromoleana odorate)
- Billy goat weed (Ageratum conyzoides)
- Ferns (Azolla caroliniana, Azolla filiculoides, Azolla mexicana, Azolla pinata)
Green fertilizer has the same characteristics as any other organic fertilizers. They can repair soil structure, increase cationic swap capacity, stimulate soil’s biological activity, and act as a source of nutrient for your crops.
Advantages of green fertilizer:
- Repairs physical, chemical, biological structure of the soil
- Prevents erosion
- Has the potential for other usage
- Is suitable for remote areas
- Promotes less use of agricultural products, resulting in better environment
Disadvantages of green fertilizer:
- Needs seeds
- Less opportunity to plant main crops
- Needs extra energy
- Has the potential to bring in pests and diseases to your crops
- Has the potential to be uncontrollable weeds
Direct burying, any green fertilizer source with low C/N ratio like legumes and azolla can be buried during land processing. These types of plants usually have high nitrogen level thus making them easy to decompose.
Use as mulch, some green fertilizers can be used as mulch. For example, straws from rice harvest leftover can be used as mulch for chili peppers or green onions. Mulch is useful to prevent erosion and protect soil humidity when your crop is young. Then, when the mulch is decomposed, it can be used as a nutrient source.
Make compost, plants with high C/N ratio (usually also high in lignin) should be made into compost first. Lignin needs a long time to decompose in soil. If you apply them directly to your crops, the decomposing process will need nitrogen and they will compete with your crops for nitrogen in soil instead of providing them with more nutrients.