Register      Login
Crop and Pasture Science Crop and Pasture Science Society
Plant sciences, sustainable farming systems and food quality
RESEARCH ARTICLE

Factors influencing the availability of mineral nitrogen in clay soils of the brigalow (Acacia harpophylla) region of Central Queensland

PR Grace, IC MacRae and RJK Myers

Australian Journal of Agricultural Research 43(5) 1197 - 1215
Published: 1992

Abstract

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).

Keywords: mineral N; brigalow; microbial biomass; bacteria; fungi; leaching; models

https://doi.org/10.1071/AR9921197

© CSIRO 1992

Committee on Publication Ethics


Export Citation Get Permission

View Dimensions