Partitioning of N in growing plants, microbial biomass and soil organic matter after amendment of N-ammonoxidized lignins

• Published in: Soil biology & biochemistry 2013-05, Vol.60, p.125-133
• Main Authors: De la Rosa, José M., Liebner, Falk, Pour, Georg, Knicker, Heike
• Format: Article
• Language: English
• Subjects: Agronomy. Soil science and plant productions; Biochemistry and biology; Biological and medical sciences; biopolymers; Chemical, physicochemical, biochemical and biological properties; electrical conductivity; fertilizers; Fundamental and applied biological sciences. Psychology; General agronomy. Plant production; humification; leaching; lignin; Lolium perenne; Luvisols; microbial biomass; Microbiology; N fertilization; nitrogen; Nitrogen, phosphorus, potassium fertilizations; nuclear magnetic resonance spectroscopy; nutrients; Organic matter; Other nutrients. Amendments. Solid and liquid wastes. Sludges and slurries; Physics, chemistry, biochemistry and biology of agricultural and forest soils; Plant-available N; Recalcitrance of technical lignins; seed germination; shoots; Soil amendment; soil organic matter; Soil organic N stabilization; soil productivity; Soil science; Soil-plant relationships. Soil fertility. Fertilization. Amendments
• ISSN: 0038-0717; 1879-3428
• DOI: 10.1016/j.soilbio.2013.01.024

Nitrogen (N) availability is a crucial factor for maintaining soil productivity, but application of mineral N-fertilizer raises environmental concerns. Based on earlier humification models, ammonoxidized technical lignins were suggested as potential slow N-release fertilizers. In order to obtain first insights on their efficiency as plant fertilizer, their impact on soil organic matter composition and stability, and its role within the N cycle in soils, pot experiments were performed in which perennial ryegrass (Lolium perenne L.) was grown on a typical Andalusian soil (Luvisol, chromic) after amendment of N-lignins highly enriched in 15N (Sarkanda and Indulin ammonoxidized lignins) for 75 days. For comparison, the incubation study was also carried out with soils with and without 15NO3 fertilization. Among these experiments, the addition of K15NO3 resulted in the greatest aboveground plant production. However, most of the growth occurred during the first 28 days. Thereafter, a fast decrease of the bioavailable N pool occurred. The application of ammonoxidized lignins altered the pH and electrical conductivity of the soil. At higher concentrations a retardation of seed germination was evidenced. After 75 days, the plant shoots from the pots amended with 15N-Indulin and 15N-Sarkanda accumulated 8% and 20% of the initial 15N present in the amended soils at the beginning of the experiment (15N0). In the 15N-Indulin pots the N was efficiently sequestered from fast release or leaching and most of 15N0 remained in the soil (64%). In contrast, the 15N-Sarkanda pots showed a lower efficiency in N retention. After 28 days of incubation only 42% of 15N0 was retained in the 15N-Sarkanda amended soil, but more than 17% was recovered within the soil microbial biomass. Until the end of the incubation time, the 15N0 detected in the soil microbial biomass decreased to less than 3%, whereas the amount associated with the soil matrix maintained around 37%. The notable increase of 15N in the above-ground plant production (20%) evidences an efficient use of 15N released from the 15N-Sarkanda for plant production. Solid-state nuclear magnetic resonance (NMR) spectroscopy revealed that the 15N of the added 15N-lignins was quickly transformed into peptide-type N, most tentatively of microbial origin, without major alteration of the lignin backbone. This indicates that in soils the competition for nutrients favors N immobilization into biomass with its subsequent sequestration wit