Inorganic Nitrogen Fractions in Soil Under Different Uses and Management Systems in the Brazilian Eastern Amazon

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.

Understanding the role of soil microbes and enzymes in regulating nitrogen dynamics: Promoting sustainable crop rotation systems

“…Soil acid hydrolyzable nitrogen (AHN), exchangeable ammonium (AN), nitrate nitrogen (NN), and alkaline hydrolyzable nitrogen (AAN) constitute the main forms of nitrogen, comprising ~ 2.61-14.85% of total nitrogen. These forms serve as the principal sources of nitrogen nutrition for soil plants, with direct absorption and assimilation (Torres et al, 2020;Fajri et al, 2020). Organic nitrogen (TON) accounts for more than 90% of total nitrogen (TN) in soil, representing the predominant nitrogen form.…”