This report examined the economic performance of tillage management systems for summerfallow - spring cereal crop rotations at two sites. The first was the Dark Brown soil zone, using 16 years of summerfallow - wheat and summerfallow - barley data from a site near Lethbridge, Alberta. The second was the Black soil zone, using 25 years of summerfallow - wheat data from a highly fertile silty clay soil near Melfort, Saskatchewan.

The Lethbridge site had eight tillage systems, including conventional, minimum and zero tillage. Conventional systems included one-way disc, heavy duty cultivator and wide blade during the fallow phase. Minimum till systems had one tillage pass and the remainder of the weed control was by herbicides. The zero tillage systems used herbicides only to control weeds. The tillage plots were split into two during the crop phase with half seeded to wheat and half seeded to barley. On average, production was highest on the minimum till and while generally lowest on the zero till, these differences were usually not significant. The economic results showed that the returns were highest for the conventional till systems and lowest for the zero till, but over the 16 years the difference between the conventional and the reduced tillage systems declined as more effective herbicide control was used. The substitution of herbicides for mechanical tillage provided some resource savings for the reduced tillage systems, but these savings were more that off-set by higher herbicide costs. The minimum and zero till systems had returns that were $20 to $40 ha-1 lower than the conventional till systems. Changes in the prices of wheat and barley had little impact on the relative profitability because of the small yield differences that existed among treatments. Herbicide expenditures were the primary factor limiting the profitability of minimum and zero tillage. If the herbicide costs of controlling weeds during the summerfallow phase were kept low, the economic returns from minimum tillage was comparable to conventional tillage.

The Melfort site had seven tillage management systems for summerfallow - spring wheat. During 1969 - 76, areas planted to wheat had the seedbed prepared with a cultivator and harrow. After 1977 one-half of each plot received conventional seedbed preparation and the other half was sprayed with herbicide and zero till seeded. Overall, wheat yields averaged 2916 kg ha-1 for tillage only, 2957 kg ha-1 for reduced tillage (combinations of tillage and herbicides), and 3016 kg ha-1 for herbicide-only treatments. During 1977-93, preparation of a tilled seedbed significantly increased yields (compared to zero till seeding) in 8 of 17 years, but it resulted in significantly lower yields in 5 other years. Results of the economic analysis showed that average variable and total costs for the complete rotation systems were lowest for the tillage-only treatment ($138 ha-1), intermediate for reduced tillage ($147 to $159 ha-1), and highest for herbicides-only ($163 to $175 ha-1). Although the substitution of herbicides for mechanical tillage provided resource savings of up to $7 ha-1 because of fewer field operations, this was more than offset by increased expenditures for herbicides. Net returns (at a wheat price of $147 t-1) were generally highest for tillage-only (avg. $76 ha-1) and lowest for herbicide-only treatments in which paraquat or glyphosate was used in combination with bromoxynil plus MCPA ester (avg. $47 ha-1) or with dicamba plus 2,4-D ester (avg. $51 ha-1) for summerfallow weed control. The reduced tillage systems generally produced net returns that averaged $1 to $12 ha-1 lower than the traditional tillage system. Changes in wheat price had little impact on the relative profitability of the tillage management systems because of the small yield differentials that existed. The maximum expenditure that could be made for herbicides, to break even with the tillage-only treatment, ranged from $25 to $35 ha-1 for the reduced tillage systems, and from $36 to $42 ha-1 for the herbicide only systems.

It was concluded from the study that although the substitution of herbicides for some or all of the mechanical tillage of summerfallow is attractive to producers from an agronomic and soil conservation perspective, the absence of significant and consistent yield advantages, and the high expectations for herbicides remain as major deterrents to widespread adoption of conservation tillage management for fallow-type cropping systems in this region. Producers will continue to have an economic incentive to use conventional tillage on summerfallow-cropping systems until herbicide costs in the summerfallow phase can be reduced.