A 12-week greenhouse experiment was conducted to determine the effect of the polyphenol, lignin and N contents of six legumes on their N mineralization rate in soil and to compare estimates of legume-N release by the difference and 15N-recovery methods. Mature tops of alfalfa (Medicago sativa L.), round leaf cassia (Cassia rotundifolia Pers., var. Wynn), leucaena (Leucaena leucocephala Lam., deWit), Fitzroy stylo (Stylosanthes scabra Vog., var Fitzroy), snail medic (Medicago scutellata L.), and vigna (Vigna trilobata L., var verde) were incorporated in soil at the rate of 100 mg legume N kg -1 soil. The medic and vigna were labeled with 15N. Sorghum-sudan hybrid (Sorghum bicolor, L. Moench) was used as the test crop. A non-amended treatment was used as a control. Net N mineralization after 12 weeks ranged from 11% of added N with cassia to 47% of added N for alfalfa. With the two legumes that contained less than 20 g kg ~ of N, stylo and cassia, there was net N immobilization for the first 6 weeks of the experiment. The legume (lignin+polyphenol):N ratio was significantly correlated with N mineralization at all sampling dates at the 0.05 level and at the 0.01 level at 6 weeks (r 2= 0.866). Legume N, lignin, or polyphenol concentrations or the lignin:N ratio were not significantly correlated with N mineralization at any time. The polyphenol:N ratio was only significantly correlated with N mineralization after 9 weeks (r 2= 0.692). The (lignin + polyphenol):N ratio appears to be a good predictor of N mineralization rates of incorporated legumes, but the method for analyzing plant polyphenol needs to be standardized. Estimates of legume-N mineralization by the difference and ~SN recovery methods were significantly different at all sampling dates for both 15N-labeled legumes. After 12 weeks, estimates of legume-N mineralization averaged 20% more with the difference method than with the 15N recovery method. This finding suggests that estimates of legume N available to subsequent crops should not be based solely on results from 15N recovery experiments.

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.

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Sodium thiosulphate was used in a modification of the regular Kjeldahl method for the determination of total N in soil and plant samples containing NO�-N and NO;-N. Quantitative recoveries of added 15 N-labelled and unlabelled NO;-N (1000 �g N), NO;-N (500 �g N), and NO;-N (500 �g N) + NO;-N (Z50 �g N) were obtained from soils, plant materials and adenine, even in the presence of water (up to 50 ml H Z O/sample) when 5 g of_ Na Z S Z 0 3 .5H Z O as Z5% aqueous solution was added to each sample before digestion. Moreover, this procedure does not require additional pretreatment of samples as does the salicylic acid-sodium thiosulphate or KMn0 4-Fe modification of the Kjeldahl method, and therefore saves considerable time.