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been reported on microbial biomass carbon (MBC), available soil moisture content
and enzymatic activities in long-term field experiments involving different dryland
cropping systems under the All India Coordinated Research Project on Dryland
Agriculture (Srinivasarao et al. 2012 ). Bandick and Dick ( 1999 ) compared enzy-
matic activity in long-term residue utilization plots (RUP) in semi-arid eastern
Oregon under a winter wheat (Triticum aestivum L.)–summer fallow supplemented
with inorganic N, green manure and beef manure treatments. Soils under the organic
treatment or cover crop had higher α-glucosidase, β-glucosidase, amylase, arylsul-
fatase, invertase and urease activities than inorganic N treatments due to greater C
inputs and the subsequent stimulation of microbial activity.
Soil organic carbon (SOC) pools are important for maintaining soil productivity
and reducing the net CO 2 loading in the atmosphere. In a 21-year field experiment
conducted in inceptisol under subhumid tropical conditions in India, the impact of
mineral fertilizers and manuring treatments on crop yield sustainability was assessed
for a rice (Oryza sativa L.)–lentil (Lens esculenta Moench) cropping sequence.
Application of farmyard manure (FYM) with and without mineral fertilizers
increased C input and SOC concentration and SOC stock. The 100 % organic
(FYM) treatment had significantly higher SOC and more C build up and C than the
control treatment. The application of 50 % organic (FYM) + 50 % recommended
dose of fertilizer (RDF) increased grain yields in rice and lentil. Thus, the applica-
tion of FYM (or other organics) in conjunction with mineral fertilizers is essential
to maintain and enhance SOC stock in rice-based cropping systems (Srinivasarao
et al. 2012 ). Srinivasarao et al. ( 2014 ) conducted another long-term (18 years) field
experiment involving a pearl millet (Pennisetum Glaucum L.)–cluster bean
(Cyamopsis tetragonoloba L.)–castor (Ricinus communis L.) sequence on an Entisol
in western India to examine the effects of chemical fertilizers and manuring on car-
bon pools in relation to crop productivity and C sequestration. The study revealed
that use of chemical fertilizers combined with farmyard manure produced higher
agronomic yields and reduced the rate of SOC depletion. Carbon pools were signifi-
cantly correlated with SOC, which increased with the application of organic
amendments.
The use of inorganic fertilizers in dryland areas over the years has not signifi-
cantly improved crop productivity due to the inherent risk factors in dryland agricul-
ture and poor economic base of dryland farmers (Venkateswarlu and Srinivasarao
2005 ). The adverse effect of the indiscriminate use of fertilizers on soil productivity
and environmental quality is of concern. Products of biological origin can be advan-
tageously blended to replace part of the energy-intensive and market purchased
inputs. Biofertilizers or microbial inoculants are living-nutrient availability systems
present in soil which provide available major and minor nutrients such nitrogen,
phosphorous, potassium, zinc and copper to crops. These microbes help to fix atmo-
spheric nitrogen, solubilize and mobilize phosphorous, translocate minor elements
like zinc and copper, produce plant growth-promoting hormones, vitamins and
amino acids and control plant pathogenic fungi, thereby helping to increase crop
production and soil health.
M. Grover et al.