503more residues from the previous crop. However, this experiment only analyzed
samples at one time point, when all treatments were planted in wheat. Therefore,
analyzing samples over an extended period will provide a better understanding of
the microbial dynamics in response to different cropping systems. Residue
management can also impact soil quality and productivity by preventing soil ero-
sion and improving soil organic matter. Spedding et al. ( 2004 ) studied the residue
management effects on total microbial biomass and observed that the retention of
crop residue increased MBC and MBN in maize monocultures. In another study,
residue retention induced higher population counts of total bacteria, fluorescent
Pseudomonas and Actinomycetes compared to residue removal (Govaerts et al.
2008 ). However, the effects of residue management on nutrient cycling, soil chemi-
cal, physical and biological properties, and crop production need to be investigated
for successful integration.
Cropping systems clearly influence soil biological properties. The specific
impacts of these practices on microbial community composition are not yet fully
known. Further in-depth research on the impact of cropping systems on soil micro-
bial communities and their functions is needed. In general, residue management
practices such as minimized fallow period, crop rotation, multiple crop sequence
and inclusion of fodder legumes/legumes, can help to restore the biological proper-
ties of soil in dryland systems.
4 Microbes in Crop Production
Biological resources such as biofertilizers, biocontrol agents, plant growth promot-
ers and other microbial products are used to improve the soil fertility and reducing
the dependence on chemical fertilizers and pesticides, form important components
of integrated nutrient management and sustainable agricultural practices. They are
cost effective and renewable source of plant nutrients. Several microorganisms with
different functional aspects are being exploited as bioinoculants in dryland agricul-
ture. They can be grouped based on their nature and function performed for the
benefit of the host plant.
4.1 Biological Nitrogen Fixation
4.1.1 Symbiotic Nitrogen Fixation
Rhizobium/Bradyrhizobium is a widely-used biofertilizer relevant to some legumi-
nous crops in dryland production systems. It forms nodules with legumes (symbi-
otic association) and fixes atmospheric nitrogen with the help of enzyme nitrogenase.
Rhizobium inoculation can meet 80 % of the nitrogen requirement of legume crops
and increase yields by 15–30 %. The nitrogen-fixing efficiency of some leguminous
Application of Microbiology in Dryland Agriculture