Amending sodic soils using sub-soil manure: economic analysis of crop trials in the high rainfall zone of Victoria

In this paper the question is answered about how profitable it was to incorporate 10 and 20 tonnes of poultry litter (manure) per ha to amend sodic sub-soil used for high rainfall cropping on two farms in south western Victoria over the four years 2009 to 2012. The subsequent four crop yield responses were measured in plots from replicated field trials on the two farms, and the costs and benefits analysed. The costs of growing crops using sub-soil manure were high. Incorporating the full rate of 20 tonnes of manure cost $1244 and $1345/ha at the two farms, with the difference resulting from the distance the manure was transported. Applying half the rate of manure at 10 tonnes/ha greatly reduced the cost of the sub-soil treatment. Despite the high costs, the practice was profitable at both sites, because significant increases in crop yields were achieved in each crop over the four years from 2009 to 2012. Incorporating 20 t/ha of manure in the sub-soil resulted in an extra annual net return of $419 or $546/ha, in present value equivalent terms at 8% nominal discount rate, above the return from conventional cropping each year for the four years. This extra net return represents a return to the extra capital invested above a cost of capital of 8% nominal per annum. Cumulative net cash flows were from $1800-$2400/ha over the four years. Incorporating 10 t/ha of manure in the sub-soil resulted in an extra annual net return of $309 to $336/ha above the conventional cropping for each year for the four years. Cumulative net cash flows were $1300-$1400/ha.