Factors influencing the availability of mineral nitrogen in clay soils of the brigalow (Acacia harpophylla) region of Central Queensland.
1992
Grace P.R. | MacRae I.C. | Myers R.J.K.
Microbiological and chemical assays were performed on clay soils from woodland (Acacia harpophylla - Casuarina cristata), grassland (Panicum maximum var trichoglume -Chloris gayana) and cropland (Vigna mungo). Over a 15 month period, the microbial biomass C in the top 3.5 cm of native brigalow woodland soil was on average 50 percent more than an associated perennial pasture and over 400 percent more than an annually cropped soil. Microbial biomass N in woodland soil was on average 41 and 270 percent higher than in pasture and cropped soils respectively and highly correlated with seasonal soil moisture content. Viable counts of bacteria were consistently lower in the 0-3.5 cm and 3.5-7.5 cm strata of woodland soil compared with pasture and annual crop sites. Soil nitrate N levels increased 2 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.
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