Abstract
Utilization of organic matter and synthetic fertilizers in soil generally influences the diversity and dynamics of microbial
mass bearing the amino acids, which contain carbon as well as nitrogen being stable components of soil organic matter. This
long-term field study initiated in 1989 compared the sole and collective use of compost and NPK fertilizers for exploring
microbial amino acids as signatures of carbon turnover in soil exhibited by macro-aggregates formation. Treatments in
quadruplicated randomized complete block design experiment were: whole N from organic manure (OM); half N from
organic manure + half N from inorganic fertilizer (HOM); mineral NPK fertilizers (NPK), NP, NK, PK, and no fertilizer
(control) applied to raise wheat and maize continuously. Classified as calcareous Fluvo-aquic soil (Aquic Inceptisol) and
located in Fengqiu County, Henan province, North China Plain, it has sandy loam texture and average pH 8.2. After 23 years
of fertilization treatments (in 2012), randomly drawn soil samples from 0–20 cm profile were subjected to various physicochemical and biochemical determinations. Contents of majority amino acids, viz., arginine, asparagine, aspartic acid, cystine,
glutamic acid, leucine, lysine, methionine, proline, and tyrosine were statistically higher under OM and HOM compared to
NPK and control treatments. Among the mineral fertilizers, N and P addition but not K mainly contributed to amino acid
synthesis / residues in soil; more importantly the cysteine, phenylalanine and serine. Quantitatively increased amino acids
positively correlated with improved SOC content that promoted the formation and count of macro-aggregates in soil. These
results suggest that accrual of organic and microbial residues largely the amino acids associated with soil micro-aggregates
enhance the carbon sequestration in surface soil concurrent with an increased formation and stability of macro-aggregates.
