Carbohydrates in hot water extracts of soil aggregates as affected by long-term management

Microbial carbohydrates are immediate by-products of microbial metabolism and play an important role in the formation and stabilization of soil structure. The effect of long-term management on soil carbohydrate content and monosaccharide composition was investigated in five. Danish sandy loams under organic and conventional management with animal manure and mineral fertilizers. Hot-water (80°C)extraction was used to measure the distribution and composition of carbohydrates in aggregate size. Carbohydrates released to hot water were determined after hydrolysis as reducing sugars equivalent to glucose. The monosaccharide composition in hot-water extracts was analyzed as the corresponding alditol acetates. Sites with a history of long-term continuos management practices were used. Three treatments from the >100 year Askov long-term field experiment were used to show results of contrasting fertilization on soil carbohydrate content. These were all grown to a four-course crop rotation. Total carbohydrate content was signifcantly infuenced by long-term management practices, with a signifcantly higher carbohydrate content in soils fertilized with either mineral fertilizers or animal manure (1200 to 800 mg C kg-1 DM aggregate)than in an unfertilized soil (600 to 500 mg C kg-1 DM aggregate). These results were as true for micro-aggregates (,0.25 mm)as for the 0.5–1. 0mmand 4.0–8.0 mm fractions. The organically managed soil (>40years) was sited at a commercial farm with forage crop rotations, organic manure and nouse of crop protection chemicals. These results showed signifcantly higher levels of carbohydrate both in micro-aggregate and macro-aggregates (1200 to 900 mg C kg-1 DM aggregate) than an adjacent conventionally managed soil with annual cash crop, mineral fertilizers and use of cropprotection chemicals (960 to 760 mg C kg-1 DM aggregate). Carbohydrate Ccontent generally increased as aggregate size decreased in both soils. Monosaccharide distribution was generally similar among three aggregate size classes studied. In all soils the content of monosaccharide was highest in micro-aggregates and lowest in macro-aggregates. Mannose and galactose were normally the most common monosaccharides in the hot-water extracts of aggregate fractions, indicating a predominantly microbial origin

The effect of removal of soil organic matter and iron on the adsorption of radiocaesium

National audienc

Carbon and Nitrogen Dynamics in Lumbricus terrestris

The formation of macropores and litter translocation into burrows by anecie earthworms [Lumbricus terrestris (L.)] may be important in controlling the extent to which earthworms affect C and N dynamics. We conducted a mesocosm-scale laboratory experiment to assess the relationship between corn (Zea mays L.) litter incorporation by L. terrestris and C and N dynamics in burrow soil. We also evaluated the relative contribution of macropores and litter incorporation to C and N dynamics in the burrow soil. Four treatments were employed: control (CTRL), artificial burrows (ARTF), artificial burrows containing corn leaves (LEAF), and amended with L. terrestris (WORM). We measured soil C and N, dissolved organic C, C mineralization, and ammonium and nitrate-N periodically, and litter removal and litter in burrows over 16 wk. A significant, short-lived enhancement in C mineralization and in soil C and N was observed in WORM and LEAF treatments. Inorganic N increased with incubation time only in the WORM treatment. Nitrate dominated the inorganic N pool in WORM and LEAF treatments, accumulating in both, and to a lesser extent in the ARTF treatment. Strong correlations were observed between litter remaining aboveground and C mineralization, ammonium-N, and nitrate-N hi the WORM treatments, whereas only nitrate-N was correlated with litter resources in LEAF treatment. Our results indicate that C and N dynamics in the burrow soil of L. terrestris are coupled strongly to surface litter removal. Macropores and litter incorporation into macropores by themselves do not appear to explain the effects of L. terrestris on C and N dynamics in burrow soil