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Soil N transformations after application of 15 N‐labeled biomass in incubation experiments with repeated soil drying and rewetting
Author(s) -
Olfs HansWerner,
Neu Anni,
Werner Wilfried
Publication year - 2004
Publication title -
journal of plant nutrition and soil science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.644
H-Index - 87
eISSN - 1522-2624
pISSN - 1436-8730
DOI - 10.1002/jpln.200320348
Subject(s) - loam , incubation , soil water , mineralization (soil science) , moisture , chemistry , zoology , water content , biomass (ecology) , agronomy , temperate climate , incubation period , environmental chemistry , botany , environmental science , soil science , biology , biochemistry , geotechnical engineering , organic chemistry , engineering
The effects of repeated soil drying and rewetting on microbial biomass N (N bio ) and mineral N (N min ) were measured in incubation experiments simulating typical moisture and temperature conditions for soils from temperate climates in the post‐harvest period. After application of in vitro 15 N‐labeled fungal biomass to a silty loam, one set of soils was exposed to two drying‐rewetting cycles (treatment DR; 14 days to decrease soil moisture to 20 % water‐holding capacity (WHC) and subsequently 7 days at 60 % WHC). A control set (treatment CM) was kept at constant moisture conditions (60 % WHC) throughout the incubation. N bio and N min as well as the 15 N enrichment of these N pools were measured immediately after addition of 15 N‐labeled biomass (day 0) and after each change in soil moisture (day 14, 21, 35, 42). Drying and rewetting (DR) resulted in higher N min levels compared to CM towards the end of the incubation. Considerable amounts of N bio were susceptible to mineralization as a result of soil drying ( i.e. , drying enhanced the turnover of N bio ), and significantly lower N bio values were found for DR at the end of each drying period. Immediately after biomass incorporation into the soil (day 0), 22 % of the applied 15 N was found in the N min pool. Some of this 15 N min must have been derived from dead cells of the applied microbial biomass as only about 80 % of the microbes in the biomass suspension were viable, and only 52 % of the 15 N bio was extractable (using the fumigation‐extraction method). The increase in 15 N min was higher than for unlabeled N min , indicating that added labeled biomass was mineralized with a higher rate than native biomass during the first drying period. Overall, the effect of drying and rewetting on soil N turnover was more pronounced for treatment DR compared to CM during the second drying‐rewetting cycle, resulting in a higher flush of mineralization and lower microbial biomass N levels.