With the advent of rapid modernization and the advancement of tremendous industrialization, simultaneously arrives the invincible phenomenon of increase in population. And in the present-day earth, this is one of the most alarming problems which require long term solutions, that too, with immediate effect.
This problem of population is invariably linked with the problem of environmental hazards, because the higher the number of individuals inhabiting this land, the greater is the probability of polluting the earth and the atmosphere. It must be kept in mind that the amount of cultivable land is shrinking day by day due to increasing urbanization and growth of civilization and at the same time, the population is increasing at an alarming rate. As a result, there is an inevitable conflict between the supply and demand for agricultural land. The only way out of solving this problem is to INCREASE the yield of all the food crops per unit area.
But, increasing the yield per unit area can only be done by proper scientific methods like the application of chemical fertilizer, use of high yielding variety seeds, use of hybrid crops with disease resistance, use of chemical pesticides for the protection of the crops and so on. But in this case, also, indiscriminate use of chemical fertilizers and pesticides should be prohibited since they provide potential threats and hazards to the environment which are irreversible in nature. With the invention of chemical pesticides, individuals came out with totally uncontrolled and indiscriminate use of these chemicals in the fields which resulted in pollution of the major water sources, development of chemical resistant pests and insects which are not only harmful to the plants and crops but are also possess insane damaging potentials for human beings.
Due to this careless application of chemical pesticides for over four long decades, nowadays even an application of minimal quantities of these may pose long term hazardous effects and threats to the whole environment.
For keeping the world incredibly beautiful, and if not, at least conveniently habitable for the future generation, scientists came out with the concept of biological control of pests instead of the use of harmful chemical pesticides. Because at this phase of utmost degraded environmental condition, sustainable agriculture is the only way out or the solution to this burning problem of contamination, pollution and chemical-resistant pests.
What is green manure?
In agriculture, green manure is created by leaving uprooted or sown crop parts to decompose on a field so that they serve both as mulch in the present and manure in future. The crops are then ploughed continuously and incorporated into the soil shortly after flowering. Green manure is associated with organic and sustainable farming.
Green and un-decomposed materials when used as fertilizers are known as green manure. It is obtained in two ways, by growing green manure crops or by collecting green leaf (along with twigs) from plants grown in wastelands, marshes and forests. The plants from the leguminous family are mainly being used for the purpose of green manuring. These plants are incorporated into the soil after sufficient growth. The nitrogen-fixing bacteria (like Rhizobium sp) present in the legumes of these plants greatly help in increasing the nitrogen content of the field and thus act as perfect green manuring crops. Some important green manure crops are sun hemp, dhaincha, sesbania, alfalfa, cowpea, fava beans, sorghum, etc.
Nutrient availability from green manure –
Green manure is broken down into plant nutrient components by heterotrophic bacteria that consume and decompose organic matter. High humidity and high temperature accelerate this process of decomposition. The decomposed plant matter releases large quantities of carbon dioxide and weak acids that react with insoluble soil minerals to release beneficial nutrients. Soils that are high in calcium can be treated with green manure to generate higher phosphate content in the soil, which in turn acts as a fertilizer.
The most crucial factor that is used for considering a plant fit for being used as green manure is the carbon to nitrogen ratio of the plant. If somehow, the incorrect plants are used for making green manure, they might starve the crops of nitrogen. The C: N ratio entirely depends upon the species of the plant and the age of the plant as well. The ratio must be less than 30:1 for preventing the manure bacteria from depleting existing nitrogen in the soil.
Functions of green manure –
There are a number of advantages available for using green manure in the fields instead of inorganic fertilizers. Some of the most important functions include –
· Leguminous plants contain symbiotic nitrogen-fixing bacteria in the root nodules that fix atmospheric nitrogen into the soil in the form of nitrate and nitrite salts that the plants can use. This performs the vital function of providing nitrogen to the soil and thus fertilizing it.
· Upon decomposition, green manure plants release a large number of organic acids. As a result, areas of soil affected with alkalinity can be treated by application of green manure and thus in turn application of humic acid and acetic acid.
· Microbial activity created from the incorporation of green manure crops into the soil leads to extensive fungal growth. The fungal growth is associated with the simultaneous growth of the mycelium network under the soil surface. This in turn benefits the soil and improves the soil structure by improving the aggregation of the soil.
· The increased percentage of organic matter in the soil improves water filtration, retention, holding capacity, aeration and other soil characteristics.
· The increased amount of humus accelerates the process of decomposition in the soil and thus the cycle of manure formation continues endlessly without the need for any human intervention.
· The soils can be tilled more easily than normal soils. Also, when the green manure crops are grown as cover crops in the field along with main crops, they suppress the growth of weeds.
· Other important functions include checking soil erosion, reduction of plant pests and insects. Some green manure crops can also be used as fodder for animals.
How to apply green manure?
A green manure crop can be cut and then ploughed into the soil for further incorporation. Otherwise, the crops can be simply left in the ground for an extended period prior to tillage operations.