CHANGES IN NATURAL ¹⁵N ABUNDANCE OF SOILS ASSOCIATED WITH TILLAGE PRACTICES

Abstract

The objective of this study was to determine changes in N dynamics in an Orthic Black Chernozem as a result of two tillage practices (conventional and zero tillage) using the variations in the natural 15N abundance of different soil-N fractions. After 14 yr, no significant differences in isotope composition of total soil-N between the two tillage practices could be found. However, changes were detected in the natural 15N abundance of the acid-hydrolyzable N and various organo-mineral size fractions which led to useful comparisons of the nature of N under the two systems. The N-content of the hydrolyzable-N fraction was similar at the 0- to 4- and 8- to 16-cm depth under both tillage practices, while it was significantly different at the 4- to 8-cm depth. The δa15N of this fraction was consistently higher than that of total soil N at all depths only under zero tillage. This was associated with the presence of more labile N compounds under zero tillage. No differences in the isotopic composition of the organomineral size fractions were found at the 0- to 4-cm depth. At the 4- to 8- and 8- to 16-cm depths, the δa15N values of the finer particle size fractions were higher under zero tillage than under conventional tillage. This indicates a more labile nature of the N associated with these size fractions under zero tillage. Key words: δa15N, conventional tillage, zero tillage, total N, acid-hydrolyzable fraction, particle size fractions

Long‐term effects of cropped vs. fallow and fertilizer amendments on soil organic matter II. Nitrogen

“…The C : N ratios generally decreased from coarse to fine fractions, thereby indicating the tendency of fine fractions to be relatively more important as N sink than as organic-C sink. These results are in agreement with previous studies where decreasing C : N ratios with smaller particle sizes were observed (Selles et al, 1984;Stemmer et al, 1988;Kandeler et al, 1999;Gerzabek et al, 2001b). Gener-…”

“…Comparing N contents in particle-size fractions with the N content in bulk soil by calculating their ratios (N concentration in the respective fraction divided by N concentration in bulk soil; data not shown), we observed on average enrichment in fine fractions (silt: 1.36; clay: 2.14) and depletion in coarse fractions (coarse sand: 0.20, fine sand: 0.53). Several authors have confirmed that N contents increase with decreasing particle size (e.g., Gerzabek et al 2001b;Selles et al, 1984;Stemmer et al, 1998). Schulten (1998, 2000) gave evidence for several longterm (5±108 yr) studies in Germany that this pattern is influenced by the adsorption of organic N on reactive surfaces of soil compounds (silicates, pedogenic oxides, alkali-extractable organic substances).…”

Complexities of nitrogen isotope biogeochemistry in plant-soil systems: implications for the study of ancient agricultural and animal management practices

“…Selles et al (1984) tested this premise directly and found no significant change in soil δ 15 N at any depth due to tillage (Figure 7C). It is therefore unlikely that soil tillage is a significant contributor to variation in ancient plant N isotopic compositions.…”

Nitrogen partitioning and cycling in barley-soil systems under conventional and zero tillage in central Alberta

“…Reduced tillage concentrates crop residues, organisms and organic matter (Selles et al 1984;Doran et al 1987), increases immobilization of fertilizer N, and decreases carbon and net N mineralization over time in the 0-to 5-cm layer of soil (Doran 1980;Linn and Doran 1984;Coleman 1985). In the shortrun, the mineralization-immobilization turnover (MIT) of N slows under ZT and organic matter accumulates (Fredrickson et al 1982: House et al 1984Rice and Smith 1984; Carter and Rennie 1987: Doran et al 1987).…”