The impacts of expansion and degradation on Australian cropping yields-An integrated historical perspective

Using a 'stocks and flows' model of Australian cropping we show that the expansion of aggregate cropping area has effectively masked landscape degradation impacts associated with continual production activity on “ageing” land. We estimate yield loss from combined land degradation to have increased to 9%, though the aggregate impact has effectively been masked by the introduction of new land. The model tracks the vintage of land since its first introduction to the agricultural system and calculates landscape degradation for four modes (dry-land salinity, irrigation salinity, acidification, and soil structure decline) according to historical production and ameliorating activities on each vintage. The model is calibrated with over 140 years of varied historical data from the 1850s. Modelled farm-gate production volumes also incorporate technological factors, such as genetic and other yield increases. Despite the introduction of many technological advances in the cropping industry through the middle of the 20th century, production yields of Australian cereal grain remained relatively unchanged for decades. This can be explained by the rapid ageing and degradation of the cropping land due to a period of halted expansion. This perspective has important implications for future scenarios of the Australian cropping industry, which are unlikely to maintain land expansion at the long-term average of about 2% pa. Without major change, land degradation in our model results in yield loss of nearly 30% by 2060.