Effect of Longwall Mine Subsidence on Plant Production on Cropping Land

The effect of longwall mine subsidence on crop yield and critical soil factors affecting plant growth were investigated in central Queensland to improve the understanding of subsidence on agricultural production. To achieve this, specific objectives were to:

1. measure the agricultural productivity (crop yield) of specific crops grown on subsided and unsubsided land;
2. measure the effect of critical soil physical factors (moisture extraction and bulk density) that affect plant growth on subsided and unsubsided land; and
3. examine the relationship between crop yield and soil physical characteristics on subsided and unsubsided land.

Two mines (Crinum and Kestrel) near Emerald were included in the two-year study. Four surface attributes were identified and included unsubsided land, subsided pillar land, subsided panel land and subsided middle panel land. Wheat (Triticum aestivum) was harvested in the first year (2000) at both mine sites, and a second harvest in 2001 at the Kestrel site. Crop yields at the Kestrel site during 2000, a wet year, and 2001, a dry year, were not significantly different between unsubsided land and the three subsided attributes. Crop yields during year one (2000) at the Crinum site were significantly different but did not follow any clear trend related to the degree of subsidence. Seed protein and moisture levels were also measured and were comparable across all attributes at both sites.

Throughout the growing seasons, critical soil physical factors of soil moisture content and soil bulk density were monitored. Subsidence from longwall mining did not notably affect these properties, and there were no signs of the inundation and ponding of subsided regions. The results of this study indicate that the affects of subsidence are likely to be very site specific and localised.