Wickings, K.G. and A.S. Grandy
Presented at the All Scientist and GLBRC Sustainability Meeting (2009-05-05 to 2009-05-07 )
Nitrogen (N) fertilization is known to alter soil biological processes and many land managers believe that the addition of N will increase litter decomposition rates in no-till systems. We assessed the effects of N fertilization, applied by subsurface, side-dress injection, on biological activity within the litter layer in a no-till corn agroecosystem at the W.K. Kellogg Biological Station LTER. Our overall objective was to determine if soil N application alters decomposition processes within surface litter. A litterbag experiment was conducted from June through September 2008 using corn leaves and stems and wheat straw applied to the soil surface in no-till plots under three rates of 28% urea-ammonium-N (0, 134 and 291kg/ha). At monthly intervals between June and October 2008, replicate bags were collected and sub-sampled for physical and biological analysis. Decomposition rate was determined using the percent of ash free dry mass remaining. Soil invertebrates were extracted from litter bags using Berlese funnels. Microbial extracellular enzyme activity was assessed for common enzymes that serve as indicators of the decomposition of cellulose, chitin and lignin-containing compounds. Although N-addition did not affect total litter mass loss it did enhance the decomposition of corn litter during August 2008. This may have been due to the concurrent increase in enzyme activity under N-addition. The activity of cellulose, chitin and lignin degrading enzymes was significantly increased by the addition of N. Enzyme activities did not differ between litter types; however, the abundance of decomposer invertebrates was higher in corn than in wheat (July-August). This suggests that the differences in total mass loss between wheat and corn may be due to the enhanced activity of decomposer invertebrates. Differences in enzyme activity between 2-month and 13-month-old wheat residue demonstrate that the effects of N-addition on hydrolases (glucosidase, cellulase, chitinase) happen quickly. Conversely, oxidative enzymes (lignin breakdown) are much slower to respond to N-addition and the effects may only be apparent under higher levels of N than traditionally applied by land managers.
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