
%0 Journal Article
%A Grace, PR 
%A MacRae, IC 
%A Myers, RJK 
%T Factors influencing the availability of mineral nitrogen in clay soils of the brigalow (<I>Acacia harpophylla</I>) region of Central Queensland
%J Australian Journal of Agricultural Research
%D 1992/08/01
%V 43
%N 5
%P 1197-1215
%K mineral N;brigalow;microbial biomass;bacteria;fungi;leaching;models
%R https://doi.org/10.1071/AR9921197
%U https://www.publish.csiro.au/paper/AR9921197 
%X Microbiological and chemical assays were performed on clay soils from woodland (Acacia harpophylla-Casuarina cristata), grassland (Panicurn maximum var trichoglume-Chloris gayana) and cropland (Vigna mungo) in the brigalow region of Central Queensland. Over a 15 month period, the microbial biomass C in the top 3.5 cm of native brigalow woodland soil was on average 3630 8g C g-l, 50% more than an associated perennial pasture and over 400% more than an annually cropped soil. Microbial biomass N (575 8g N g-l) in woodland soil was on average 41% and 270% higher than in pasture and cropped soils respectively and highly correlated with seasonal soil moisture content. Viable counts of bacteria were consistently lower (average 69.2%) in the 0-3.5 cm and 3.5-7.5 cm strata of woodland soil compared with pasture and annual crop sites. Soil NO-3- N levels increased two fold in the upper 3.5 cm of the woodland site during low rainfall periods. This increase may be attributed to a more efficient distribution of mineral N mediated by the increased presence of a fungal population in this community. Leaching may also play a significant role in the distribution of plant available N in the brigalow region as suggested by the inverse relationship N = 54.11-0.67 R (P<0.01), where N is soil NO-3-N (8g N g-l) and R is rainfall in the preceding 3 month period (mm month-1). 
