Nitrogen immobilization and mineralization during initial decomposition of15N-labelled pea and barley residues

Abstract

The immobilization and mineralization of N following plant residue incorporation were studied in a sandy loam soil using 15N-labelled field pea (Pisum sativum L.) and spring barley (Hordeum vulgare L.) straw. Both crop residues caused a net immobilization of soil-derived inorganic N during the complete incubation period of 84 days. The maximum rate of N immobilization was found to 12 and 18 mg soil-derived N g-i added C after incorporation of pea and barley residues, respectively. After 7 days of incubation, 21% of the pea and 17% of the barley residue N were assimilated by the soil microbial biomass. A comparison of the 15N enrichments of the soil organic N and the newly formed biomass N pools indicated that either residue N may have been assimilated directly by the microbial biomass without entering the soil inorganic N pool or the biomass had a higher preference for mineralized ammonium than for soil-derived nitrate already present in the soil. In the barley residue treatment, the microbial biomass N was apparently stabilized to a higher degree than the biomass N in the pea residue treatment, which declined during the incubation period. This was probably due to Ndeficiency delaying the decomposition of the barley residue. The net mineralization of residue-derived N was 2% in the barley and 22% in the pea residue treatment after 84 days of incubation. The results demonstrated that even if crop residues have a :relative low C/N ratio (15), transient immobilization of soil N in the microbial biomass may contribute to improved conservation of soil N sources.

Leaves Material Decomposition from Leguminous Trees in an Enriched Fallow

“…Calculation of net ammonification (a, Figure 3) and net nitrification (n), in order to have a comparative parameters between treatments, was performed by subtracting soil NH 4 + -N in the time x (t x ) from soil NH 4 + -N in the initial time (t 0 ) and NO 3 --N in the time x (t x ) from soil NO 3 --N in the initial time (t 0 ), respectively. Apparent microorganism NH 4 + -Nimmobilization (i) was calculated by subtracting soil NH 4 + -N microbial biomass in the organic amendment treatment from NH 4 + -N microbial biomass in the control treatment (soil without organic amendment) (Jensen 1997), using the fumigation-extraction method. NO 3 --N consumption (c) was calculated by subtracting soil NO 3 --N in the control treatment from soil NO 3 --N in the organic amendment treatment.…”

“…NO 3 --N consumption (c) was calculated by subtracting soil NO 3 --N in the control treatment from soil NO 3 --N in the organic amendment treatment. This is based on the assumption that the mineralization and losses of indigenous soil N were similar in control and residue-treated soils (Jensen 1997). Apparent ammonification (a) was significantly different (P < 0.05) during the incubation period for the majority of treatments (Table 2).…”

“…Transient immobilization of soil N in the microbial biomass may contribute to improved conservation of soil N sources (Jensen 1997). …”

Potential nitrogen immobilization as influenced by available carbon in Japanese arable and forest soils

“…A high N concentration in soil solution is necessary for plant growth but facilitates N loss via leaching (Jensen 1997). Soil microbial biomass N plays an important role as a sink and source of N (Singh et al 1989), and microbial immobilization of soluble N would contribute to a decrease in N leaching when crop residues were added to soils (Herai et al 2006;Sugihara et al 2012).…”

Intervalo de tempo para semeadura de milho pós-dessecação da cobertura de aveia-preta com herbicidas

“…Estas reduções são atribuídas, principalmente, ao efeito da alta relação C/N. A imobilização líquida de nitrogênio poderá ocorrer nos períodos iniciais da decomposição (JENSEN, 1997). Entretanto, a continuidade do processo de decomposição dos resíduos diminui a relação C/N no solo, uma vez que o carbono é perdido na forma de CO 2 e o nitrogênio é conservado pela formação de massa celular microbiana (VICTORIA et al, 1992).…”