Green leaf manures (GLMs) are organic manures made from leaves collected from all available sources and used to supply essential plant nutrients to the soil and increase soil fertility in a healthy manner. Using GLMs to grow crops is not a recent concept at all and has been used in many South Asian countries for centuries. Green leaf manuring can be defined as the pruning and collecting of green leaves and twigs from various trees, herbs and shrubs and then applying them elsewhere as fertilizers. Forest tree leaves are major sources of these manures while herbs and shrubs growing in field bunds, wastelands etc. are some other mentionable sources. Using green leaf manures is very useful practice especially in hilly areas.
Why Green Leaf Manures
Using chemical fertilizers as a nutrient source for plant growth is not at all a good way to treat the soil. Chemical fertilizers are being used worldwide, especially in third world countries, to negotiate the extra food requirement by the huge world population.
This indiscriminate use of various chemical fertilizers is causing a number of environmental and health hazards along with permanent damage to the most precious natural resource ‘soil’. If this terrible chemical using goes unrestrained, the soil will no longer be available for crop production after a certain period.
So, it is time to shift the agricultural system from chemicals to organic manures to maintain a healthy soil for the upcoming generations.
As organic manure, green leaf manure is capable of supplying the required plant nutrients with maintaining very good soil health. For instance, in an experiment rice yield was increased significantly due to the application of GLMs. The result of that experiment concluded that application of GLM N at 120 kg/ha from Leucaena and Gliricidia is capable of producing yield and other outputs of rice to that obtained from N at 60 kg/ha from urea. So, GLMs can replace chemical fertilizers and protect the world from numerous hazards the chemicals bring.
Advantages of using GLMs
Using GLMs instead of chemical fertilizers gives a number of advantages-
• GLM plants add a huge quantity of N to the soil. Around 120 kg N can be added to the soil from 400 trees placed 2 m apart on the bund.
• GLMs ensure balanced nutrition for plants and improve soil fertility to a great extent.
• GLM trees are perennial and supply leaves 2-3 times in a year for manuring; so, they need not to replant.
• GLMs are slow releasing fertilizers and act as plant nutrient source for a long time after their application.
• Soil structure is improved to a great extent due to the application of GLM.
• GLMs encourage the development of earthworms by acting as food material to them.
• GLMs produce very high quality and safe food materials.
• GLMs possess no threat to water and air quality.
• GLMs stimulate the growth of various beneficial microorganisms in soil and thus improve the soil biodiversity.
• GLMs are very useful in reclaiming salinity affected soils.
• The woody branches of GLM trees are used as fuel.
• They are cheap and easily affordable.
• GLMs are readily available and very easy to use.
Plant species useful for green leaf manures
To produce green leaf manures a number of trees and plants are used; among them trees like- Pungam, Gliricidia, Mahua, Erukku, Subabul, Vahai, Karanji, Wild indigo, Wild dhaincha, Neem, Colatropis, etc.; and weeds like Water hyacinth, Calotrophis, Trianthema, Cassia, Ipomoea, Parthenium, etc. are used widely.
Preparation of Green Leaf Manures
Producing green leaf manures is very easy and cheap. Different green manuring trees and plants are grown in live fences or on barren lands. When they are well grown, their leaves are simply cut and brought to the crop fields in bundles. Leaves of green manuring crop like Thespesia are needed to wither for two days before incorporating them into the soil.
Application of Green Leaf Manures
Application of green leaf manures to a soil is dependent on the moisture content of the soil. Enough moisture content is necessary to apply this manure to a soil. Farmers who use GLMs, measure moisture content with their own technique. To determine the moisture status of soil, they dig to a depth of 5cm and take a soil sample from there. They make clod from that soil sample using their hands. They press the clod between their hands and if the clod crushed immediately, they consider the moisture content insufficient to apply GLMs. They apply GLMs to the soil only when they found the moisture content sufficient. They also determine the organic matter level of the soil before applying GLMs to that.