(dehydrogenase and phosphatases) and microbial biomass C and N contents in the
monoculture soil were generally significantly lower than those in the soil from the
organic and conventional–short rotation systems, indicating that substantial disturbances may occur in the microbial activity of the monoculture soil. Crop rotations are an efficient measure to enhance microbial diversity in the rhizosphere,
increase soil organic carbon (SOC), total nitrogen (TN) and build up resistance to
disturbance and suppress root diseases [41, 42]. Cover cropping can be a useful
approach to improve diversification of soil microbial communities whether through
a form of rotation diversification or through its cover crop residues [30, 43]. Indeed,
[44] reported an increase in soil enzymatic activity around 20% in soils with a cover
crop mixture of oat/radish/vetch, with increases also in soil C and N storage.
Pasture rotated with well- managed crops can also increase enzyme activity in soil
because overgrazing leads to a decrease in soil microbial biomass [45].
Irrigation, aside from its primary function, helps to determine the enzymatic
activity of the soil with regard to dry conditions which limit the decomposition rate
and therefore microbial biomass. Protease and urease—N-cycling enzymes—seem
to be the most affected by drought [46].
It is widely reported that using organic fertilizers such as manure promotes
enzyme activity. In soils that are organically farmed crop residues and rhizodeposits
support higher microbial biomass, leading to enhanced enzyme activities [47]. For
example, it was found that enzyme activity associated with C, N and S cycling were
higher under organic farming practises compared to conventional farming [47].
More specifically, [48] demonstrated that activities of soil b-1,4-glucosidase, b-1,4N-acetylglucosaminidase, and leucine aminopeptidase increased with manure
application. Application of chemical fertilizers such as phosphorus and N negatively affects microbial activity, particularly with long term use [48]. For example,
nitrogen application may negatively affect enzyme activity, such as nitrogenase.
Nitrogenase activity provides N to the soil, through catalyzing N 2 fixation from the
atmosphere into two molecules of NH 3 —also known as biological nitrogen fixation
and [49] recorded higher activity of this enzyme with no urea-N application and
inhibition of Stenotrophomonas sp. population (significantly important for nitrogen
and sulphur cycle) with an application of 300 mg L
−1 urea-N. The way
nitrogen-based fertilizer affect nitrifying bacteria might be associated not only to the
cultivar, but also to its age and to the diazotrophs present in the environment [50].
Diazotrophs are Plant- Growth-Promoting Rhizobacteria or PGPR [51, 52],
although they can colonize the interior of plants (xylem vessels and intercellular
spaces) where the potential for nitrogenase activity increases [52].
7 Relation of Enzymes with N and C Cycles
Soil enzymatic activity plays a major role in key processes related to the quality of
SOM which, in turn, influences the efficiency of microbial nutrient assimilation
since carbon is required in microbial metabolism [54]. Moreover, soil enzymatic
Nitrogen Footprints and the Role …
143
monoculture soil were generally significantly lower than those in the soil from the
organic and conventional–short rotation systems, indicating that substantial disturbances may occur in the microbial activity of the monoculture soil. Crop rotations are an efficient measure to enhance microbial diversity in the rhizosphere,
increase soil organic carbon (SOC), total nitrogen (TN) and build up resistance to
disturbance and suppress root diseases [41, 42]. Cover cropping can be a useful
approach to improve diversification of soil microbial communities whether through
a form of rotation diversification or through its cover crop residues [30, 43]. Indeed,
[44] reported an increase in soil enzymatic activity around 20% in soils with a cover
crop mixture of oat/radish/vetch, with increases also in soil C and N storage.
Pasture rotated with well- managed crops can also increase enzyme activity in soil
because overgrazing leads to a decrease in soil microbial biomass [45].
Irrigation, aside from its primary function, helps to determine the enzymatic
activity of the soil with regard to dry conditions which limit the decomposition rate
and therefore microbial biomass. Protease and urease—N-cycling enzymes—seem
to be the most affected by drought [46].
It is widely reported that using organic fertilizers such as manure promotes
enzyme activity. In soils that are organically farmed crop residues and rhizodeposits
support higher microbial biomass, leading to enhanced enzyme activities [47]. For
example, it was found that enzyme activity associated with C, N and S cycling were
higher under organic farming practises compared to conventional farming [47].
More specifically, [48] demonstrated that activities of soil b-1,4-glucosidase, b-1,4N-acetylglucosaminidase, and leucine aminopeptidase increased with manure
application. Application of chemical fertilizers such as phosphorus and N negatively affects microbial activity, particularly with long term use [48]. For example,
nitrogen application may negatively affect enzyme activity, such as nitrogenase.
Nitrogenase activity provides N to the soil, through catalyzing N 2 fixation from the
atmosphere into two molecules of NH 3 —also known as biological nitrogen fixation
and [49] recorded higher activity of this enzyme with no urea-N application and
inhibition of Stenotrophomonas sp. population (significantly important for nitrogen
and sulphur cycle) with an application of 300 mg L
−1 urea-N. The way
nitrogen-based fertilizer affect nitrifying bacteria might be associated not only to the
cultivar, but also to its age and to the diazotrophs present in the environment [50].
Diazotrophs are Plant- Growth-Promoting Rhizobacteria or PGPR [51, 52],
although they can colonize the interior of plants (xylem vessels and intercellular
spaces) where the potential for nitrogenase activity increases [52].
7 Relation of Enzymes with N and C Cycles
Soil enzymatic activity plays a major role in key processes related to the quality of
SOM which, in turn, influences the efficiency of microbial nutrient assimilation
since carbon is required in microbial metabolism [54]. Moreover, soil enzymatic
Nitrogen Footprints and the Role …
143