Compost Input: A Technology for Soil Restoration

Soil degradation may be one of the most important constraints to food production. Degraded soils are often characterized by low organic matter status, poor microbial diversity and activity of microbial population, low water retention capacity, and low nutrient content and declined soil fertility. Intensive farming practices and inadequate efforts to replenish nutrients and restore soil quality have resulted in stagnation of crop yields. Restoration of degraded soil is necessary for meeting the increasing demands for food and avoiding risk of irreversible soil degradation. It is also essential to reestablish the soil's long term capacity for infiltration and to enhance the vitality of the soil as it hosts all types of microbes and plant root systems in complex, symbiotic relationships.

Soil restoration refers to the process of repairing and returning the degraded soil to a level similar to pre degraded level of capability for supporting plant growth and maintaining environment quality. A degraded soil can be restored with in 4-5 yrs of its production by following improved management/farming practices. A combination of soil fertility restoration technologies and conservation tillage practices can offer opportunities to sustainable land use. Amendment of soil with additives such as compost, animal manure, bio-solids, fly ash, green manure, organic wastes, and sewage and paper sludge are some of the appropriate strategies to improve the organic matter status of soil that supports the biological activity of different organisms. The soil low in organic matter has poor microbial diversity that leads to poor plant productivity. Healthy soil inhabits microscopic and macroscopic organisms that convert dead and decaying matter as well as minerals to plant nutrients. Nutrient exchanges between organic matter, water and soil are essential to soil fertility and need to be maintained for sustainable production purposes. When the soil is exploited for crop production without restoring its organic matter and nutrient contents and maintaining a good structure, the nutrient cycles are broken, soil fertility declines and the balance in the agro-ecosystem is destroyed.

Application of un-decomposed wastes or unstable compost to land may lead to immobilization of plant nutrients and cause phytotoxicity that may inhibit the seed germination and needs to be restricted. However, soil application of well decomposed organic residues in the form of mature and stable compost can help to restore its fertility. Being a rich source of active microorganisms, organic matter and nutrients, compost improves soil resilience. Soil microorganisms through their dynamic activities, play an important role in moderating soil organic matter decomposition and enrichment and contribute to soil fertility concentration. Application of compost reduces soil bulk density; increases soil aggregation, water retention capacity and soil macro porosity. A pore size improvement of 46% and 24 % in soil treated with stabilized manure and vermicompost respectively as compared to unfertilized soil has been reported. Amendment of soil with stabilized manure improves the wettability of soil surface. Organic matter added through compost has been found more effective in controlling the soil temperature by reducing the thermal conductivity and heat capacity of soil. Improved water retention as well as reduced temperature fluctuations in soil amended with compost has been found more important in improving the nutrient uptake than increased availability of soil nutrients. Integrated use of poultry manure and chemical fertilizer provided higher neutralization of alkalinity in tropical soils. At low pH (3.3-5.5), addition of 10 % humified organic matter in the form of compost to soil reduced aluminium toxicity.

Increase in organic matter content results in improved soil microbial biomass, increased biodiversity and biological activity of soil organisms; and plant nutrient availability. Application of compost improves the proliferation of non-symbiotic nitrogen fixers and phosphate solubilizers. The peak in microbial activity may be attributed to preferential stimulation of microbes by different constituents of organic residues in soil. These bacteria compete with pathogens for space and nutrients. They may also produce lytic enzymes, antibiotics as well as siderophores that can be implicated in the biological control of plant diseases. Changes in soil organic carbon, nitrogen concentration and microbial biomass are often used as sensitive parameter to monitor the soil recovery. Microbial biomass carbon, pH, cation exchange capacity of soil, mineralizable nitrogen, total and available phosphorus concentration has shown an improvement of > 70 %. However, increase in biological activities as invertase, arylsulphatase, dehydrogenase, FDAse and soil respiration has shown an improvement of 60- 80 %. But the compost with high content of heavy metals can inhibit soil biological quality measured in terms of enzyme activities.

A key to soil restoration is to maximize the retention and recycling of organic matter and plant nutrients, and to minimize the losses of these soil components through leaching, runoff and erosion. Conservation agriculture practices through combining no tillage or minimum tillage with a protective crop cover and crop rotations maintains surface residues, roots and soil organic matter, helps control weeds, and enhances soil aggregation and intact large pores. Therefore, by practicing the proper soil management technology along with organic amendments as compost, productivity of soil can be improved.

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