MPa, Robinson (1957) found little mineralization at <-1.5 MPa. Some workers (Miller and Johnson 1964;Reichman et al. 1966) Stanford and Epstein (1974) except that all samples were mixed with a spatula before incubation. Five replicates were prepared, two of which were sampled at time zero for nitrate plus nitrite-nitrogen and exchangeable ammonium-nitrogen. The remaining three replicates were covered tightly with a double layer of parafilm with two pin holes for aeration and incubated at 35'C for 14 days.They were then analyzed for mineral nitrogen.In Australia, the entire sample was extracted with 2 M KCI and mineral nitrogen was de-termined (Henzell et al. 1968 (Throughout the remainder of this paper the term "net" will not be used in describing mineralization, but it is implied in all cases.)The soil moisture contents were calculated from the known air-dry moisture content plus the water applied. The equivalent SPWPs were estimated from the moisture release curves as measured by pressure membrane and pressure plate (Campbell et al. 1981 For personal use only.

The procedure of Stanford and coworkers was used to quantitatively relate net nitrogen mineralization in five Queensland semi-arid soils to temperature. The concentration of potentially mineralizable nitrogen (No) (1) ranged from 67 �g nitrogen g-1 for a red earth subsoil to 256 for a recently cultivated cracking clay surface soil, (2) was directly proportional to total soil carbon, (3) was greater in surface than in subsurface soil, and (4) was greater in subtropical than tropical soils. Expressed as a fraction of total nitrogen (No/Total N), it ranged between 8 and 21%, and was directly proportional to cation exchange capacity, perhaps implicating expanding lattice clays in stabilization of cell lysates and metabolites. The mineralization rate constant (k) was directly proportional to total carbon, the fuel for microbially mediated reactions in soil. The average k for surface soils was interpolated to be 0.058, 0.031, and 0.018 week-1, corresponding to half-lives of 11.9, 22.4 and 38.5 weeks, at 35�, 25� and 15�C, respectively; these values are similar to those reported for U.S.A. and Chilean soils. The Arrhenius relationship between k and temperature for surface soils (log k = 6.14-2285/T) was similar to that reported by Stanford for U.S.A. soils, and indicates that this relationship might be a general one.

Ammonia volatilization from artificially applied cattle urine was measured in a fertilized (374 kg nitrogen ha-1 year-1) and grazed (4 beef steers ha-1) pasture of Nandi setaria (Setaria sphacelata var. sericea) in south-eastern Queensland. Microplots (0.5 by 0.5 m) of pasture were treated with 1.4 1. of urine (= 37-48 g nitrogen m-2) and evolved ammonia measured with a flow-through chamber system that maintained near ambient temperatures and air flows. Calculated volatilization over a 14-day period was 18.8 % of the applied urine nitrogen in June, 14.4 % in November-December and 28.4 % in February-March. More than half of the volatilization occurred within 48 h of applying the urine. Measurements of soil mineral nitrogen in February-March showed that more than 80% of the urinary urea was hydrolysed within 2 h and only traces remained unhydrolysed after 24 h. Soil ammonium declined from 700 to 1000 �g nitrogen cm-3 in the surface 2.5 cm on the first day to near-background levels on the 14th day. Accumulation of nitrate was rapid after the 2nd day, and accounted for one-third of the applied nitrogen by the 14th day. Nitrite reached a maximum of 2.3 % of the applied nitrogen on the 7th day and had virtually disappeared by the 14th day. Only traces of nitrite were detected below 2.5 cm depth.

The effect of acidity on denitrification and nitrous oxide production in six soils from the Atlantic Coastal Plain was estimated using laboratory incubations of flooded soil for periods up to 21 d. Increased denitrification rates were associated with a decrease in acidity in all soils but most of the effect occurred above pH 6.5. Some accumulation of NH+4‐N occurred in all soils and was positively correlated to the NO‐3‐N lost from the system. Small quantities of NO‐2‐N were formed in all soils. Larger amounts of NO‐2‐N were found at pH 5.0 and 4.7 for two soils. Nitrite‐N accumulation corresponded to the release of large quantities of N2O suggesting a possible relationship between NO‐2‐N accumulation and N2O production. Nitrous oxide evolved, as a percentage of NO‐3‐N lost, increased with increasing acidity with maximum N2O being evolved at pH values ≤5.8. Above pH 5.8, evolution of N2O virtually ceased. Since all six Coastal Plain soils are generally <pH 5.8, a high percentage of nitrogen being lost from these soils through denitrification is as N2O.

The objective of this study was to determine the effect of acidity on mineralization, nitrification, and N2O evolution during these processes on naturally acid soils from the lower Coastal Plain of North Carolina. Six acid surface soils (pH ≤4.5) from the Tidewater region of North Carolina, with a range of organic matter (OM) contents (28‐850 g kg−1) were limed to give a range of pH values so that the effect of acidity on mineralization of organic N and nitrification of (NH4)2SO4 could be studied under controlled conditions in the laboratory. Cumulative net mineralization over 21 d was significantly (p <0.01) influenced by acidity in four of the six soils. However, no soil exhibited a significant net mineralization increase between the very acid initial pH value and the pH value to which liming is recommended (pH 4.8‐5.2 for Histosols) for crop production. Liming to pH values <7 increased net mineralization in only one soil. Adding a small increment of lime tended to decrease mineralization although this effect was significant in only one soil. Essentially all organic N mineralized was converted to NO‐3 at all pH values. However, the very high acidities tended to inhibit the nitrification of NH+4 added as (NH4)2SO4. There was apparently no influence of organic matter content on any of the processes studied except N2O evolution where the soils with <120 g OM kg−1 evolved the highest amounts of N2O during nitrification. Much of the N2O evolution was apparently due to denitrification because addition of nitrapyrin did not eliminate the evolution. It was concluded that the liming of acid soils in the Tidewater Region of North Carolina would have little influence upon N mineralization rates. The recommended pH values of 4.8 to 5.2 for Histosols appears to be adequate for both mineralization and nitrification.