Abstract
Land use and management systems are factors that control availability and nitrogen (N) forms in soil environment. The aim was to evaluate the inorganic N fractions dynamics in soil under different use and management systems in Brazilian Eastern Amazon conditions. Soils were sampled at depths of 0.0-0.1 and 0.1-0.2 m in areas under pasture (PAST), no-tillage (NT), conventional tillage (CT) and a reference area under fallow vegetation (FV). In the samples, soil organic matter (SOM), total-N, ammonium (N-NH4+) and nitrate (N-NO3-) contents were determined and the urease enzyme activity was measured. In CT and NT the SOM contents were similar to those found in FV, with an average of 36.7 g kg-1, while under PAST there was a 16.6% reduction when compared to the reference area. The total-N levels followed the same dynamics found for SOM. The ammonium concentration was 2.4 times higher in soils under FV (14 mg kg-1) when compared to other systems and nitrate followed the order NT> CT> FV=PAST. The pasture (44 µg N-NH4+ g-1 soil h-1), among soils for agricultural use, induced the highest ureolytic activity. The preserved soil conversion from native forest to pasture caused a 16.6% reduction in the SOM contents and 55.5% and 46% for ammonium and nitrate, respectively. On the other hand, the NT system has the capacity to accumulate SOM in a similar way to the area of native vegetation studied, as well as a high capacity to retain N in the soil, preferentially in the nitrate form.
Highlights
Nitrogen (N) is one of the nutrients most required by plants, due to their participation in the molecules composition such as proteins, nucleic acids and chlorophyll, which are indispensable to the metabolic plant organisms processes (Webster et al, 2016).In soil, the N total amount, in general, varies between 0.05% and 0.5%, linked to several organic compounds, and in soils of tropical climates this variation occurs between 0.02% and 0.4 % or until 2% (Rangel; Silva, 2007; Siqueira Neto et al, 2010)
The N fraction predominantly found in the soil is complexed in the organic form, this fraction being a N labile forms reservoir, while less than 5% corresponds to the inorganic fractions in the ammoniacal (NH4+) and nitric (NO3-) forms, which are the forms readily available to plants and which originate, during cultivation, through enzymatic hydrolysis produced by the activity of soil microbiota and/or nitrogen fertilizers application (Cordeiro & Hoek, 2007)
The soil organic matter (SOM) levels were higher in the superficial layer (0.0-0.1 m) and reduced, on average, 30% with the increase in depth in most systems, except in soils under conventional tillage (CT), which showed no difference between the layers (p
Summary
Nitrogen (N) is one of the nutrients most required by plants, due to their participation in the molecules composition such as proteins, nucleic acids and chlorophyll, which are indispensable to the metabolic plant organisms processes (Webster et al, 2016). The N fraction predominantly found in the soil is complexed in the organic form, this fraction being a N labile forms reservoir, while less than 5% corresponds to the inorganic fractions in the ammoniacal (NH4+) and nitric (NO3-) forms, which are the forms readily available to plants and which originate, during cultivation, through enzymatic hydrolysis produced by the activity of soil microbiota and/or nitrogen fertilizers application (Cordeiro & Hoek, 2007). These two forms are still conditioned to mineralization and immobilization processes (Cantarella, 2007; Fageria; Baligar; Jones, 2011). The aim was to evaluate the inorganic N fractions dynamics in the soil under different use and management systems in Brazilian Eastern Amazon conditions
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