Ronald R. Schnabel

An evaluation of anion exchange resin used to measure nitrate movement through soil

Abstract The attribute that ion‐exchange resins remove ions from solutions moving through them can be used to measure nitrate transport through soils. The characteristics of nitrate adsorption by resins must be known to interpret nitrate accumulation on ion‐exchange resins embedded in soil. The extent to which anion exchange resins retain NO3‐ from soil leachate was measured in 15.9 cm diam.by 60 cm long intact cores of Nolin (fine silty mixed mesic Dystric Fluventic Eutrochroept) soil. A NC3 ‐‐selective resin and a non‐selective resin were tested. Columns were fertilized at a rate of 300 kg N/ha and 150 kg Br/ha and leached with 50 cm of water. Under these conditions, both resins retained approximately 80% of the NO3‐ and Br‐ leached through the soil. This compared with greater than 95% retention in laboratory columns containing only resin. The difference in retention was attributed to different flow through the resin associated with the method of resin emplacement.

Filter, inoculum and time effects on measurements of biodegradable water soluble organic carbon in soil

Abstract The biodegradation of organic carbon drives biogeochemical cycles. Incubations of water soluble organic carbon (WSOC) are popular tests for determining the amount of readily biodegradable organic carbon. However, tests differ in length of incubation, filtration prior to incubation, and method of incubation. We compared the fraction of biodegradable water soluble organic carbon (BWSOC) in soil by varying these factors. With all combinations, WSOC decreased to a minimum during the first 6 days then consistently increased at the later stages of the incubation. The mean BWSOC content of the soils ranged from 0.13 to 3.54, and depended on the length of the incubation and the combination of filters used before and after incubation. Similar amounts of BWSOC were measured during aerobic and anaerobic incubations.

Effect of Manure Management on Carbon Evolution and Water Extractable Phosphorus

Soils with excessive phosphorus (P) levels due to manure application are an environmental concern because water extractable P (WEP) in runoff from these soils can contribute to increased amounts P in surface water, which can contribute to eutrophication of freshwater. Phosphorus based manure management is an option to reduce WEP and thereby reduce agricultural P runoff. In P based manure management, manure is applied to meet the P needs of a crop or not to exceed a given soil test level. Because P base manure management does not supply enough nitrogen (N) to meet the needs of the crop, addition fertilizer N needs to be applied. Fertilizer N applied to soils may increase the rate of mineralization of organic matter and lowers soil pH and therefore may affect the solubility of soil inorganic and organic P pools. The extent to which this may affect WEP or plant P availability is not known. Thus, laboratory and greenhouse studies were conducted to determine the effects of P based manure management on WEP and on short‐term P plant availability. Phosphorus based manure management had no significant effect on the shift of organic P to WEP, but the increased acidity due to urea hydrolysis and subsequent nitrification of ammonia had a significant effect on the solubilization of P form the Ca‐bound IP pool, thereby increasing WEP. This could be a significant consideration where Ca‐bound IP dominates IP, P based manure management is implemented and increased WEP is subject to export to surface waters via runoff.