Soil Carbon and Nitrogen Mineralization: Influence of Drying Temperature

samples. When a soil analysis requires field-moist soil, a pre-incubation time of 7 to 10 d after rewetting dried Carbon and N mineralization in dried soils that are rewetted has soil may be used to equilibrate the samples before analybeen proposed as a rapid index of C and N mineralization potential sis (Franzluebbers et al., 1996). and to reflect soil management, but further research is needed on effects of soil type and drying temperature for this approach. The Rewetting dried soil is thought to alter the soil physioobjective of this study was to determine the effect of maintaining soil chemical environment and make it an unrealistic treatfield moisture or drying soil at 40, 60, or 100 C followed by rewetting ment (Martens, 1995). On the other hand, laboratory and a 3-d incubation on C and N mineralization across diverse soil drying and rewetting tends to produce a uniform release types. Strong correlations between C mineralized in 24 d from field of C and N and is a natural process that occurs under moist soils vs. C mineralized in 24 h from soils dried at 40 or 60 C field conditions (Birch, 1958, 1959, 1960). Furthermore, were observed. Carbon mineralization values for 24 vs. 3 d resulted short-term C mineralization (1–3 d) of soil after drying in nearly linear relationships for all drying treatments. Nitrogen miner(40 or 60 C) followed by rewetting correlates strongly alization in 24 d from moist vs. dried at 40 or 60 C and rewetted soils with longer-term (100-d) CO2 evolution and soil microwere also highly correlated with field moist N mineralization. The drying and rewetting pre-incubation of soil followed by a 3-d incubabial biomass C (Franzluebbers et al., 2000; Haney et tion was shown to be a useful indicator of longer-term (24 d) C al., 1999). mineralization potential. Nitrogen mineralization potential may also Marumoto et al. (1982) and Sparling et al. (1995) have be obtained after drying/rewetting at 40 or 60 C without the need for shown that it may be possible to estimate soil C and N keeping soil in a continuously field-moist state. mineralization potential by monitoring the fluxes of CO2 following the rewetting of dried soil. Other authors have stated that the amount and quality of substrates availC and N mineralization can be a useful tool able for mineralization may be quantified using CO2 for quantifying the impact of various organic and evolution (Sorensen, 1974; Sparling and Ross, 1988). inorganic amendments on soil functions. Carbon minerAnderson and Domsch (1978) suggested that the size alization is generally determined by monitoring CO2 of the soil microbial biomass is reflected by the shortfluxes from field-moist samples that are wetted to term flush of CO2 after amending labile substrates. This roughly 50% of field capacity and subsequently incuis the basis for substrate induced respiration (SIR) bated in the laboratory for various periods of time. The method for determination of soil microbial biomass. If incubation period is generally several weeks long, dethe evolution of CO2 following rewetting of dried soils pending on the objective of the study. Short incubations can be related to soil microbial biomass and potential and air-drying soil facilitate routine soil testing procemineralizable C and N for different soils under different dures and for certain tests air-drying avoids biochemical environments then this method might serve as a rapid artifacts that could occur if soils are kept moist beindicator of potential C and N mineralization. fore analysis. Chemical and physical disturbances of soil organic Adopting a technique that uses dried soil may signifimatter have been proposed as mechanisms for increascantly reduce variability within the same soil sample ing the flush of CO2 associated with soil drying and and reduce the amount of refrigerated space necessary rewetting (van Gestel et al., 1991). For example, Franzfor storage of moist soils. Soil samples from the same luebbers and Arshad (1999) ground dry soils to a powder site can vary greatly in moisture content, depending on then rewetted the soils and trapped evolved CO2. This season or short-term weather patterns. Drying soil holds treatment resulted in a greater flush of CO2 than from potential to minimize this variability. Drying and rewetundisturbed soil. However, C mineralized in 3 d from ting soil may also permit researchers to determine C the disturbed soils was strongly correlated with 24-d C and N mineralization potentials on dry, archived soil mineralization in undisturbed samples. Similar results were observed when comparing N mineralization as afR.L. Haney, USDA-ARS, 808 E. Blackland Rd, Temple, TX 76502; fected by drying temperature. E.B. Porter, F.M. Hons, and D.A. Zuberer, Dep. of Soil & Crop Currently, most soil incubations use field-moist soil. Sciences, Texas A&M University, Texas Agricultural Experiment StaThe flush of C and N after drying and rewetting could tion, College Station, TX 77843; A.J. Franzluebbers, USDA-ARS, possibly become a rapid assessment tool for monitoring 1420 Experiment Station Road, Watkinsville, GA 30677-2373. Rechanges in C and N mineralization potential due to ceived 15 Jan. 2002. *Corresponding author ([email protected]. gov). organic or inorganic inputs as well as inputs from different management strategies. The objective of this study Published in Soil Sci. Soc. Am. J. 68:489–492 (2004). was to compare soil C and N mineralization after drying  Soil Science Society of America 677 S. Segoe Rd., Madison, WI 53711 USA and rewetting with those maintained field-moist to ex-