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Low SOM in tropical soils, particularly those under the influence of arid, semi-
arid, and subhumid climates, is a major factor contributing to poor productivity
(Katyal et al. 2001 ). Proper management of SOM is important for sustaining soil
productivity and ensuring food security and protection on marginal lands. Under
dryland conditions, the process of organic matter decomposition is faster than irri-
gated condition; organic matter disappears rapidly due to its rapid oxidation under
prevailing high temperatures, low rainfall and high potential evapotranspiration
(PET). Therefore, frequent and large quantities of added organic manure are essen-
tial to maintaining SOC concentrations. An important general strategy is to add as
much organic matter as possible through management practices (viz. crop and cover
crop residues, manures, the inclusion of legumes in the cropping sequence or as
intercrops, green manure crops, green-leaf manuring, tank silt addition, farmyard
manure, biofertilizers and vermicompost) (Srinivasarao et al. 2011 ).
Green manuring is a viable option to increase SOM. The incorporation of
Gliricidia (Gliricidia sepium Jacq. Walp.) green-leaf manuring technology in the
light soils of rainfed tribal and backward districts of Andhra Pradesh and the All
India Coordinated Research Project for Dryland Agriculture (AICRPDA) and
Operational Research Project (ORP) villages in different regions of India had a
significant and positive effect on increasing SOM and macro- and micro-nutrients
(Srinivasarao 2011 ).
The effective management of residues, roots, stubbles and weed biomass can
have beneficial effects on soil fertility through the addition of organic matter, plant
nutrition and improved soil condition. Agricultural waste is usually handled as a
liability, often because the means to transform it into an asset is lacking. Crop resi-
dues in fields can result in crop management problems as they accumulate. In India,
the availability of biomass (2010–2011) was estimated at 500 million tons/year
(MNRE 2009 ). Studies sponsored by the Ministry of New and Renewable Energy
(MNRE) in India have estimated surplus biomass availability at about 120–150 mil-
lion tons/year (MNRE 2009 ). Of this, about 93 million tons are burned each year.
The lack of availability of proper chipping and soil incorporation equipment is one
reason for the colossal wastage of agricultural biomass, and the increased cost of
labor and transport is another. Many technologies exist such as briquetting, anaero-
bic digestion, vermicomposting, biochar, but they have not been commercially
exploited.
The correction of nutrient deficiencies can be achieved through site-specific
nutrient management (SSNM) and integrated nutrient management (INM). SSNM
takes into account all nutrient deficiencies to ensure that crop demands are met, and
soil fertility is improved, which in turn ensures higher nutrient use efficiency, crop
productivity and economic returns (Dobermann 2004 ). The results of on-farm dem-
onstrations across crops and soils in India showed that S application increased grain
yield by 650 kg/ha (+24 % over NPK) in cereals, 570 kg/ha (+32 % over NPK) in
oilseeds, and 375 kg/ha (+20 % over NPK) in pulses (Singh 2001 ). Cotton yields
increased in response to balanced nutrition in the Warangal, Adilabad and Khammam
districts of India by 20, 60 and 30 %, respectively, compared with traditional farmer
practices (Fig. 4 ).
C. Srinivasa Rao et al.