Effects of earthworms on nitrogen mineralization |
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Authors: | J J G M Willems J C Y Marinissen J Blair |
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Institution: | (1) Department of Soil Science and Geology, Agricultural University Wageningen, PO Box 37, 6700 AA Wageningen, The Netherlands;(2) Division of Biology, Kansas State University, 66506 Manhantten, KS, USA |
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Abstract: | The influence of earthworms (Lumbricus terrestris and Aporrectodea tuberculata) on the rate of net N mineralization was studied, both in soil columns with intact soil structure (partly influenced by past earthworm activity) and in columns with sieved soil. Soil columns were collected from a well drained silt loam soil, and before the experiment all earthworms present were removed. Next, either new earthworms (at the rate of five earthworms per 1200 cm3, which was only slightly higher than field numbers and biomass) were added or they were left out. At five points in time, the columns were analyzed for NH
4
+
, NO
3
–
, and microbial biomass in separate samples from the upper and lower layers of the columns. N mineralization was estimated from these measurements. The total C and N content and the microbial biomass in the upper 5 cm of the intact soil columns was higher than in the lower layer. In the homogenized columns, the C and N content and the microbial biomass were equally divided over both layers. In all columns, the concentration of NH
4
+
was small at the start of the experiment and decreased over time. No earthworm effects on extractable NH
4
+
were observed. However, when earthworms were present, the concentration of NO
3
–
increased in both intact and homogenized cores. The microbial biomass content did not change significantly with time in any of the treatments. In both intact and homogenized soil, N mineralization increased when earthworms were present. Without earthworms, both type of cores mineralized comparable amounts of N, which indicates that mainly direct and indirect biological effects are responsible for the increase in mineralization in the presence of earthworms. The results of this study indicate that earthworm activity can result in considerable amounts of N being mineralized, up to 90 kg N ha–1 year–1, at the density used in this experiment. |
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Keywords: | Earthworms N mineralization Agroecosystems Soil structure Microbial biomass Lumbricus terrestris Aporrectodea tuberculata Soil cores |
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