Soil Organic Carbon and Silt-Clay Relationships in the Soil Orders of Northern Agriculture Region (NAR), Western Australia

Ahmed Hasson, Abdulhussien Alaskary and Muhsin Jweeg

Soil Organic Carbon and Silt-Clay Relationships in the Soil Orders of Northern Agriculture Region (NAR), Western Australia

2019

Ahmed Hasson, Abdulhussien Alaskary and Muhsin Jweeg

There are no recognized data about the relationships between soil organic carbon and soil texture in Northern Agriculture Region (NAR), Western Australia (WA). Such information is central in understanding the impact of silt and clay content of soil profile soil organic carbon. In order to describe mathematically this relation, twenty-one soil orders highly weathered soils (mostly sandy soils) in Northern Agricultural Region, Western Australia under similar climate, vegetation and topography were sampled at 120 cm depth and analyzed for texture and total SOC concentration. The SOC concentration was directly and linearly correlated with the combined clay + silt (but not to clay alone) content for all depths. The intercept and slope of these linear relations decreased with depth following exponential and logarithmic functions (P < 0.001, R2 = 0.81 and 0.76, respectively). These mathematical functions permitted the adjustment of the intercept and slope parameters of a SOC = a + b (clay + silt) function for any depth in the 0-120 cm interval. This profile pedotransfer function precisely estimated SOC concentration (P < 0.0001, R2 = 0.90) up to 120 cm of the studied soils. Using data from different soil orders, estimated vs. measured SOC relations with similarly high R2 values were obtained, despite slopes and intercepts were different than 1 and 0. This indicates that for the NAR, WA the textural control of SOC varies predictably with depth, and the proposed model can be calibrated to estimate SOC in subsurface layers of highly weathered soils.

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