activity can impact the availability and/or storage of C and N in SOM pools.
Because a lot of the enzymatic activity occurs in the rhizosphere from associations
between soil microorganisms and root exudates (plant-soil interaction) enzymes
may be used as a proxy for potential plant growth and for nutrient availability [55],
especially for nitrogen. While this may not directly promote crop nutrient uptake
and thus, crop growth, it does so indirectly by improving the availability of soil
microorganisms that play a key role in nutrient availability for plant nutrition. These
degrade complex organic carbon compounds to release simple utilizable C compounds for microorganisms’ survival and growth (e.g. sugars, organic acids).
Moreover, the enzymes involved in nutrient (e.g. N, P and S) cycle processes,
mineralize organic compounds of the respective nutrients into inorganic compounds, which can be readily used by microorganisms and plants. The influence of
soil enzymatic activity in soil nutrient cycling is a relatively well-researched topic
(e.g. [56–59]). By playing a vital role in initiating and maintaining nutrient biogeochemical cycles, enzymes play a vital role and ensure soil fertility for plants
development [60, 61]. Enzyme activity is more intense in the rhizosphere than in
the bulk soil due to the direct contact with plant roots and influence of root exudates, as well as with bacteria and mycorrhiza. The rhizosphere is a uniquely rich
environment where enzymes and microorganisms mediate the biogeochemistry of
minerals and better nourish the soil–plant ecosystems [62].
8 The Importance of Nitrogen Fertilization
Nitrogen (N) is the most important of nutrients within the structural and functional
molecules that make up the plant structure, and is also essential for the biosynthesis of structural molecules such as the nucleotides and amino acids that are
building blocks for plants, animals and other organisms. Despite this important role
of nitrogen, fertilizer application can negatively affect the enzyme activity, such as
for nitrogenase, that catalyzes atmospheric N fixation as mentioned before. Similarly, atmospheric deposition of reactive nitrogen reportedly reduces the activity of
lignin-modifying enzymes and hence of C decomposition, which positively affects
terrestrial C sequestration [63]. While ligninase activity increases in soils with low
SOM quality under nutrient deficiencies, its activity is progressively reduced as
nutrient deficiency is replenished [64]. By contrast, cellulase activity derived from
N deposition was reported by [63] not to correlate with changes in soil C stocks.
One of the main anthropogenic factors affecting soil enzymatic activity is both
organic and mineral fertilization that has a crucial influence on soil biological status
and the enzymatic activity in soils. The application of organic fertilizers such as
farmyard manure, has a positive effect by increasing organic C and N concentrations in soil and affects the quality and quantity of SOM. On the contrary, if manure
is too rich in inorganic N (NH 4
+
), it may promote immobilization and N losses and
have a negative effect. Data shows that the impact of agricultural nutrient management practices on enzyme activity depends on the type of fertilizer (i.e.
144
C. M. d. S. Cordovil et al.
Because a lot of the enzymatic activity occurs in the rhizosphere from associations
between soil microorganisms and root exudates (plant-soil interaction) enzymes
may be used as a proxy for potential plant growth and for nutrient availability [55],
especially for nitrogen. While this may not directly promote crop nutrient uptake
and thus, crop growth, it does so indirectly by improving the availability of soil
microorganisms that play a key role in nutrient availability for plant nutrition. These
degrade complex organic carbon compounds to release simple utilizable C compounds for microorganisms’ survival and growth (e.g. sugars, organic acids).
Moreover, the enzymes involved in nutrient (e.g. N, P and S) cycle processes,
mineralize organic compounds of the respective nutrients into inorganic compounds, which can be readily used by microorganisms and plants. The influence of
soil enzymatic activity in soil nutrient cycling is a relatively well-researched topic
(e.g. [56–59]). By playing a vital role in initiating and maintaining nutrient biogeochemical cycles, enzymes play a vital role and ensure soil fertility for plants
development [60, 61]. Enzyme activity is more intense in the rhizosphere than in
the bulk soil due to the direct contact with plant roots and influence of root exudates, as well as with bacteria and mycorrhiza. The rhizosphere is a uniquely rich
environment where enzymes and microorganisms mediate the biogeochemistry of
minerals and better nourish the soil–plant ecosystems [62].
8 The Importance of Nitrogen Fertilization
Nitrogen (N) is the most important of nutrients within the structural and functional
molecules that make up the plant structure, and is also essential for the biosynthesis of structural molecules such as the nucleotides and amino acids that are
building blocks for plants, animals and other organisms. Despite this important role
of nitrogen, fertilizer application can negatively affect the enzyme activity, such as
for nitrogenase, that catalyzes atmospheric N fixation as mentioned before. Similarly, atmospheric deposition of reactive nitrogen reportedly reduces the activity of
lignin-modifying enzymes and hence of C decomposition, which positively affects
terrestrial C sequestration [63]. While ligninase activity increases in soils with low
SOM quality under nutrient deficiencies, its activity is progressively reduced as
nutrient deficiency is replenished [64]. By contrast, cellulase activity derived from
N deposition was reported by [63] not to correlate with changes in soil C stocks.
One of the main anthropogenic factors affecting soil enzymatic activity is both
organic and mineral fertilization that has a crucial influence on soil biological status
and the enzymatic activity in soils. The application of organic fertilizers such as
farmyard manure, has a positive effect by increasing organic C and N concentrations in soil and affects the quality and quantity of SOM. On the contrary, if manure
is too rich in inorganic N (NH 4
+
), it may promote immobilization and N losses and
have a negative effect. Data shows that the impact of agricultural nutrient management practices on enzyme activity depends on the type of fertilizer (i.e.
144
C. M. d. S. Cordovil et al.