Fractions of nitrogen (including ¹⁵N) and also carbon in the soil as affected by different crop residues

Abstract

Returning crop residue can increase soil organic matter content, and residue quality has an influence over the rate of their turnover. However, there is a lack of information concerning the biochemical transformations of organic compounds of N and C present in the crop residues during subsequent crop growth. In this study, the contents of organic N and C fractions in soils obtained using acid and alkaline hydrolysis under two crop rotations (faba bean vs. wheat rotation) were investigated. Black fallow served as a control. The mean total N increased in the order: black fallow, wheat rotation, faba bean rotation, total C and SOM were higher in the cropped soils than in black fallow. Hydrolysable-N (1-step acid hydrolysis) reached 83.7% total N, amino acid-N and threonine+serine-N were the highest in faba bean rotation and the lowest in black fallow, ammonia-N and aminosugar-N were lower in black fallow than in cropped soils. Hydrolysable-N (2-step sequential fractionation) reached 85.3% total N and significant differ ences were noted between the cropped soils and black fallow, with respect to both the N and C contents. 15 N was mainly accumulated in the N soluble and easily hydrolysable N compounds, and these fractions were greater in cropped soils than in black fallow. N in the humic com pounds increased from black fallow to faba bean rotation. A PCA analysis showed that crop rotation and soil sampling terms had a substantial influence over cluster formation. An ANOSIM test revealed significant diff erences between the crop rotation and term treat-ments. The results indicated that soil with faba bean rotation is richer in N compounds than soil with wheat as a forecrop and this may result in a reduction in N fertilizers for the succeeding crop.Ke y w o r d s: organic nitrogen fraction, soil organic matter, crop residues, faba bean, wheat, 15 N

Spring rye as a source of biomass and carbon in the soil

“…Soils are the largest terrestrial reservoir of elements and could be the best means of removing carbon from the atmosphere (FAO, 2004). Therefore, in practice there is a need for technologies, methods, and tools which could potentially lead to the capture of CO 2 from the atmosphere, resulting in an increase in carbon (C) sequestration in the soil (Kalembasa et al, 2023). The addition of organic matter from plants or their residues contributes to a significant extent to carbon storage and sequestration in the soil which can lead to a reduction in greenhouse gas emissions (Powlson et al, 2011).…”