मृदा खराब होने की अवस्‍था को धीमा करने तथा पलटनेे की रणनीति‍यॉं:  एग्रोफोरेस्ट्री की भूमिका

Soil degradation implies decline in the quality and capacity of soil through natural or anthropogenic perturbations. Degradation processes include erosion, compaction and hard setting, acidification, declining soil organic matter (SOM), soil fertility depletion, biological degradation, and soil pollution. Soils are the basis for more than 90% of worldwide food production. However, about 25% of the world’s arable land is degraded.

Without fertile soils, world food security is at risk. Very limited degree of agriculturally usable soil (about 12% of the total land area) is available on the earth’s surface.

The degraded soils cannot be restored within a human generation. The formation of an inch-thick (2.5 cm) layer of fertile humus soil takes approximately 500 years. With increasing population growth, the amount of agriculturally usable land especially available to us per capita is continually dropping.

Agroforestry is a collective name for land-use systems and technologies where woody perennials (trees, shrubs, palms, bamboos, etc.) are deliberately used on the same land management units as agricultural crops and/or animals, in some form of spatial arrangement or temporal sequence. In agroforestry systems there are both ecological and economical interactions between the different components.

As soil resources are essentially non-renewable, it is necessary to adopt a positive approach to sustainable management of these finite resources. Therefore, agroforestry is the important technology for reversing land degradation trends and mitigating the greenhouse effect through land and ecosystem restoration.

Extent of Soil Degradation in India

The main agencies that have estimated soil degradation in India are: National Commission on Agriculture (NCA, 1976), Society for Promotion of Wasteland Developments (SPWD, 1984), National Remote Sensing Agency (NRSA, 1985), Ministry of Agriculture (1985), and National Bureau of Soil Survey and Land Use Planning (NBSSLUP, 1984 & 2004) shown in Table.

Table. Land degradation assessment by different organizations

 Beneficial Effects of Agroforestry on Soil

Agroforestry helps in maintenance of soil fertility by the different processes such as:(i) Nutrient input: Maintenance or increase of soil organic matter (SOM) through carbon fixation and its transfer via litter and root decay, Nitrogen fixation by some leguminous and a few non-leguminous trees,

1. Nutrient uptake: the taking up of nutrients released by rock weathering in deeper layers of the soil, Atmospheric input: the provision by trees of favorable conditions for input of nutrients by rainfall and dust, including via through fall and stem flow and exudation of growth-promoting substances by the rhizosphere.
2. Nutrient loss reduction: By Protection from erosion and thereby from loss of organic matter and nutrients,
3. Improvement of soil physical, chemical and biological conditions. Reduction of acidity, through addition of bases in tree litter; reduction of salinity or sodicity.

Role of Agroforestry in Controlling Soil Erosion

The vegetation in an agroforestry practice serves two major purposes: (i) the fine root system holds soil in place, reducing susceptibility to erosion, and (ii) plant stems decrease the flow velocity, enhancing sedimentation. Vegetation strips (Panicum and Palmarosa) along with conservation tillage, application of organic amendments and weed mulching improve crop yields by reducing run-off and topsoil erosion.

Two nitrogen fixing trees species like Gliricidia sepium and Indigo feratysmani along with grass Saccharum spp. for controlling run off and erosion in the sloping agricultural lands of eastern India are found. Soil erosion can be reduced in Indogangetic sodic soil by the forestation of Prosopis juliflora and Casuarina equisetifolia by the formation of stable soil aggregates.

Role of Agroforestry in the Maintenance of Soil Fertility

The imposition of agricultural systems changes the natural equilibrium of the soil to an extent that it becomes dependent on management practices and soil resilience.

Black locust (Robinia pseudoacacia L.) and mixed species plantation [black locust (R. pseudoacacia L) + stone pine (Pinuspinea L.)] field capacity, permanent wilting point, plant available water, saturated hydraulic conductivity, soil organic matter, total nitrogen, P₂O₅, Ca were significantly greater, while bulk density and C:N ratio were significantly lower as compared to control and the planting of “black locust” and “black locust +stone pine” can be useful in soil reclamation projects in the eroded site in semi-arid regions.

The integration of trees, especially nitrogen fixing trees (NFTs) Michelia oblonga, Parkia roxburghii, Alnus nepalensis, and Pinus kesiya into agroforestry and silvo pastoral systems can make a major contribution to sustainable agriculture by restoring and maintaining soil fertility, and in combating erosion and desertification as well as providing fuelwood.

Role of Agroforestry in Reclamation of Salt Affected Soils

Biosaline (agro)forestry is the cultivation of trees and/or crops on salt-affected soils, a type of degraded land. It’s an alternative land use option for these soils because some tree species are less susceptible to soil salinity and sodicity than agricultural crops and because the cultivation of trees can help regenerate these soils.

In India so many tolerant species for saline soils are tried like Prosopis juliflora and Salvadora persica, etc. where ECe> 35 dS/m, and termed as very high salt-tolerant, Tamarix articulata, Acacia farnesiana, and Parkinsonia aculeate are high salt-tolerant (ECe> 25-35 dS/m), Casuarina (glauca, obesa, equiselifolia) and Acacia tortilis can tolerate  ECe 15-25 dS/m comes under tolerant class, under moderately tolerant class (ECe 10-15 dS/m) trees like Casuarina cunninghamiana, Eucalyptus tereticornis, and Acacia catcechu.

Role of Agroforestry in Reclamation of Acid Soil

Agroforestry systems are the appropriate management of acid soils because perennial woody vegetation can recycle nutrients, maintain soil organic matter and protect the soil from surface erosion and runoff.

Acacia mangium, Stryphnodendron microstachyum, Sclerolobium guianensis, Inga coruscans, Inga edulis, Pithecellobium idiopodum, Pithecellobium macradenium, Albizia guichapele, Pithecellobium elegans have good potential for use in reforestation and in agroforestry systems on degraded acid soils high in Al and Mn and can easily grow and produce biomass.

Conclusion

The adverse effect of soil degradation on ecosystem can be managed through strategies involving soil restoration. Human survival and prosperity depends on adequate supplies of food, land, water, energy, and biodiversity. With the adaptation of agroforestry and other management options, present global soil resources can adequately meet the food and nutritional needs of the present and future population.

Agroforestry technologies can help achieve several benefits in land-use systems, including: protection for topsoil, livestock, crops, and wildlife; greater agricultural productivity; reduced energy and chemical inputs; more efficient water use; better air and water quality; more diverse local economies; and greater biodiversity. Therefore increased adoption of agroforestry should be supported through finance for agricultural development.

Author:

Dr. Kirti Saurabh

Scientist, Division of Crop Research,

ICAR- Research Complex for Eastern Region,

Patna-800 014, Bihar, India

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