Nitrogen volatilization from grassland soils - 1989

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Ammonia volatilization was measured at three sites in the Chihuahuan Desert of southern New Mexico, U.S.A. In dry soils, ammonia volatilization ranged from 9 to 11 micrograms of nitrogen per square meter per day, but rates increased to 95 micrograms of nitrogen per square meter per day in a shrubland site after an experimental addition of water. Ammonia volatilization also increased with experimental additions of NH4Cl and decreased with additions of sucrose. Competition by nitrifiers for available NH4+ had little effect on NH3 volatilization: N-Serve, added to inhibit nitrification, decreased NH3 volatilization in a grassland site and had little effect at other sites. We suggest that NH3 volatilization is controlled by the rate of mineralization of NH4+ from soil organic matter, and mineralization is stimulated by rainfall. Overall rates of NH3 volatilization from undisturbed desert ecosystems appear to be much lower than those reported for rangeland and agricultural soils. Data set shows ammonia volatilization from the grassland soils at the base of Mount Summerford in response to a variety of experimental treatments chosen to elucidate the processes controlling the volatilization rate. Ammonia is collected in weak acid in scintillation vials placed inside PVC chambers in the field. The rate of ammonia volatilization per unit area (ugN/m2/day) is found by multiplying the concentration in the acid by 1250.

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instrumental, field data sheets

A set of experiments was established in the grassland in June 1989. Water, N-serve and CaC2-generated C2H2 were applied in a full 3-way factorial design in 8 tubes in each of 10 blocks, each of which included an unmanipulated control tube. Water and N-serve were applied as in 1988. C2H2 was applied by covering these tubes with a PVC cap and injecting 30 ml C2H2 into the headspace through a rubber septum. The volume was chosen to greatly exceed the 10 Pa level, which is found, in short-term exposures, to cause a persistent inhibition of nitrification in soils (Berg et al., 1982; Hyman and Wood, 1985). The syringe was pumped several times to ensure mixing of the C2H2 into the soil pore space. After 10 min the cap was removed, and all tubes were allowed to equilibrate in the field for 24 h. NH3 was collected during the subsequent 24 h using the 1988 procedures. Following gas collections, the columns were removed, the soil was homogenized and sieved (<2-mm), and subsamples were extracted with 0.5M K2SO4 to determine NH4+ concentrations. NH4+ was determined in the H2SO4 solutions using a TrAAcs 800 autoanalyzer and Industrial Method NO 786-86T for total N (Bran and Luebbe, 1986). Standards were mixed in aliquots of the same H2SO4 solution used in the field collections. Anomalous high values were found in 30 vials (3%) that were contaminated by ants; these were deleted from subsequent statistical treatments. Concentrations of NH4+ and NO3- in the KCl and K2SO4 extracts were determined following standard procedures on the autoanalyzer.

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Input data include experimental block (l to l0 in columns l and 2), treatments (water +/-), NSERVE (+/-), and acetylene (+/-) in columns 4,6 and 8 respectively. Application of these treatments in the field is described in the paper. Dependent variables include soil ammonium content, measured as NH4N in columns l0-l3, expressed in ugN per gram of dry soil, and the NH4 concentration recorded in the scintillation vial (mg NH4-N/liter), which (when multiplied by l250 to account for the volume of the collecting solution and the area of the collector) is equal to ugN volatilized per m2 per day. //DCALIC JOB 'DU.D02.ZI1603',SCHLESINGER,TIME=2 // EXEC SAS //SYSIN DD * DATA AMMONIA; INPUT BLOCK 1-2 WATER 4 NSERVE 6 ACET 8 SOIL 10-13 VOL 15-18; CARDS;

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Field investigations were made on the New Mexico State University Ranch, 40 km NNE of Las Cruces, N.M. in the Jornada Del Muerto Basin. The experimental plots were established at three sites along the desert Long Term Ecosystem Research (LTER) transect that crosses the alluvial piedmont of Mount Summerford in the Dona Ana Mountains. One site was located in a grassland dominated by Bouteloua eriopoda in the upper reaches of the piedmont. A second site was in a mid-slope position in a shrubland dominated by Larrea tridentata, an invasive desert species. The third site was located in an ephemeral dry lake, or playa, dominated by Panicum obtusum, at the base of the piedmont.


One period (24 hours after treatment)

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