Browsing by Subject "Soil organic matter"
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Item Effect of topography and glaciation history on the movement of carbon and nitrogen within arctic hillsides.(2010-04) Whittinghill, Kyle A.The transport of dissolved organic matter (DOM) down hillslopes to aquatic ecosystems has important implications for both terrestrial and aquatic primary productivity. DOM is an important energy and nutrient source for both terrestrial and aquatic microbes. Within watersheds, physical, chemical, and biological processes transform DOM, but it not well known how landscape heterogeneity may affect these processes in arctic watersheds. In the northern foothills of the Brooks Range, expansion and contraction of mountain glaciers over the last several ice ages have created a mosaic of landscape ages with similar climate and vegetation. My research indicates that younger landscapes (<50,000yrs) have significantly lower pH, 10x higher exchangeable base cation concentrations, and significantly lower rates of DOM production and microbial respiration than older landscapes, which could significantly affect fluxes of carbon and nutrients across the landscape. At the watershed scale, I examined patterns in soil and stream water concentrations of DOM within hillslopes across the chronosequence. I found that while concentrations of dissolved organic carbon decreased significantly moving downslope from the hilltop to the stream; dissolved organic nitrogen concentrations remain similar within the hillslope, but are significantly different among landscape ages. I also used a variety of indices to examine spatial patterns in the biodegradability of DOM within hillslopes and among landscape ages in northern Alaska. My results suggest the low biodegradability of DOM found in streams and rivers in the region is not due to microbial processing of labile DOM in terrestrial ecosystems, but rather to production of recalcitrant DOM throughout the landscape.Item Legumes and soil organic matter transformations in upper Midwest agroecosystems(2018-06) Liebman, AlexanderCover crops are an agroecological approach that can increase ecosystem service provisioning, reducing erosion, providing spatial and temporal biotic diversification, and increasing soil organic matter (SOM). However, implementation of cover crops in the upper Midwest is limited by short growing seasons and harsh winters with variable temperatures and snowfall. Our objective was to explore the potential of winter annual legume cover crops to stabilize and augment soil C and organic N stocks in upper Midwest agricultural systems in which cover crop biomass production is quite limited, and without major impacts on crop yield. We compared hairy vetch (VET), winter rye (RYE), red clover (CLO), hairy vetch/rye biculture (MIX), and bare-ground control (NOCC), planted in a randomized complete block design at two University of Minnesota Research and Outreach Centers in southwest (LAMB) and north-central (GR) Minnesota. Cover crops were established in fall and terminated in spring prior to sweet corn planting. To measure linked soil C and N dynamics, we determined microbial biomass C (MB-C), permanganate-oxidizable C (POX-C), size-fractionated particulate organic matter C and N (POM-C and POM-N), extractable soil N (EXT-N) and potentially mineralizable N (PMN). We hypothesized that 1) MIX has intermediate biomass and biomass N levels, compared to legumes (high N, low biomass) and RYE (low N, high biomass) monocrops 2) MIX treatment increases both soil C and N, legumes primarily increase N and RYE influences labile C parameters, and 3) RYE exhibit sweet corn yield declines due to low N and high residue. Our results indicate winter annual legume cover crops are a viable tool for increasing soil N but had limited impact on labile SOM parameters. Vetch biomass exceeded 2.00 Mg dry matter ha-1, resulting in > 80 kg N ha-1. Extractable N increased after cover crop termination approaching 25 mg N kg soil-1 in VET. Post-termination PMN increased at GR Y1 and LAMB Y2, to 30-65 mg N kg soil-1, from baseline values of ~ 20 mg N kg soil -1 pre-termination. Yet soil N results displayed major site differences, with PMN declining in LAMB Y1 and GR Y2 pre-termination to post-termination. Soil C results were variable, indicating significant effect of sampling time and environment yet no treatment differences for MB-C or POX-C. However, MB-C was correlated with PMN (R2= 0.24, p = 0.002), indicating labile C may be an effective indicator of N dynamics. Corn yields were highest in LAMB 2015, VET and MIX exceeded 13 Mg ha-1 and out-yielded RYE (~ 8 Mg ha-1). Our project suggests winter annual legume cover crops may achieve multiple ecosystem services including winter soil coverage, SOM development, and coupled C and N cycling.Item Soils, Soil Management and Fertilizer Monographs (Revised 1978)(University of Minnesota, Agricultural Extension Service, 1978) Overdahl, C.J.; University of Minnesota, Agricultural Extension Service; Fenster, W.E.; Simkins, C.A.; Meredith, H.L.; Swan, J.B.; True, J.A.; Swan, James B.; MacGregor, John M.; Munter, Robert C.; Grava, John; Grava, J.; Ham, G.E.; Hanson, Lowell D.; Overdahl, Curtis; Simkins, Charles; Fenster, William