In order to address the concerns regarding the effects of tillage systems on rate of crop establishment , plant development in spring wheat was monitored every year by measuring Haun stage at about the 4-5 leaf stage. Haun stage determines the number of leaves on the main stem and is highly correlated to rate of crop emergence. The results in Table 2 shows that the type of stubble had an effect but not tillage system and surprisingly the plants growing on field pea were slightly less developed than those on cereal stubble. In absolute terms, the differences were very small. We can therefore conclude that with proper residue management and seed to soil contact, negative effects from conservation tillage should not be experienced with regards to crop establishment.

With regards to seeding depth, shallower planting was always obtained with zero followed by minimum then conventional tillage. However, in absolute terms, the differences were small between tillage systems.

The first observation is that the type of stubble that a crop is seeded on has a large influence on soil water conserved, irrespective of the tillage system used. For instance, in the case of field pea stubble, the amount of water stored is similar between the three tillage systems because of the inability of this stubble to trap very much snow. As well the extra amount of spring soil water conserved, if any, is similar to the extra amount of water used which in turn results in greater yields with zero and minimum tillage, providing that extra moisture is conserved. Increases in water use efficiency was only observed for flax with zero and minimum tillage being better than conventional tillage. It is important to note that the size of the plots may preclude some of the advantages of standing stubble or else the stubble was cut to short to derive the true benefits. The research of Cutforth and McConkey at Swift Current [Can. J. Plant Sci. 77:359-366] stresses the benefits of tall stubble when developing water management strategies, especially in the drier areas of the prairies.

A summary of crop yields and crop water use values is given in Table 3 for all crops, tillage systems and crop sequences (sequences for spring and winter wheat). With field pea, total crop water use corresponded closely to the extra moisture conserved with zero and minimum tillage relative to conservation tillage. There was no effect of tillage systems on crop water use efficiency.

With flax, the difference in total crop water use as a function of tillage systems corresponded almost entirely to the extra spring soil moisture conserved in the 0-24" soil layer. Of interest also is how much more efficient flax grain yields were with zero and minimum tillage relative to conventional tillage for a given unit of water. This is the only crop in the study where increases in crop water use efficiency were recorded because of changes in tillage systems.

Winter wheat was seeded using the same tillage system because of the requirement for maintaining standing stubble to avoid low temperature injury. The results presented in Table 3 are for the various sequences. In sequence 1, winter wheat was seeded on spring wheat stubble as opposed to flax stubble in the other two crop sequences. Crop water use, grain yield and water use efficiency were less for winter wheat on spring wheat stubble than on flax stubble. Much of these differences can be explained on the basis of root and leaf diseases.

With spring wheat, fallow management had no effect on the variables measured. In the case of spring wheat on field pea stubble, the yields were equal for minimum and conventional tillage but 7% less for zero tillage. This difference cannot be explained on the basis of soil water stored or crop water use.

With spring wheat on cereal stubble, soil water, crop water use and grain yield were higher for zero and minimum tillage than conventional tillage. Total crop water use was higher than the difference in soil moisture storage in the top 24" between tillage systems. This is a reflection that spring wheat can extract water beyond the 0-24" soil layer.

The results, to a large extent, speak for themselves. It is interesting to note that when the economic analysis was last done for the period 1987-1990, the average cost of production has increased for all three tillage systems since that time. It is also interesting to note that during this period, there has been an increase in herbicide use with the largest increase observed for conventional tillage. When herbicide and fuel use are taken together, the amount is much less for zero and minimum tillage than conventional tillage. In our study, herbicide use has increased because of the widely used technique of pre-harvest application of glyphosate which can be used on all tillage systems. At the farm gate level, we are seeing a lot of zero tillage technology and management is being applied to conventional tillage systems.

The results for all crops and tillage systems are given in Table 4 and 5.

The overall message is that total production costs, as measured by purchased inputs costs, are very similar between all three tillage systems. What this means is that radical changes in production technology did not result in greater production costs. The increased costs of herbicides with zero tillage were off set with the reduced costs due to the elimination of tillage.

Fuel use (li/ha) and herbicide use (g ai/ha) were also quantified as a function of tillage system. For crops grown on stubble, moving from a tillage based production system to a zero tillage system resulted in a significant decrease in fuel use with a concomitant increase in herbicide use (Table 6).

Weediness increased over time, as measured by total weed density, especially in wet years following dry periods e.g. 1991 (Table 7). Zero tillage was weedier in wet springs regardless of fall conditions while conventional tillage was weedier when a dry spring was preceded by dry fall conditions. Minimum tillage was weedier when a dry spring was preceded by wet fall conditions i.e.: conditions between those favouring zero and conventional tillage (Fig 4)

Differences in moisture availability for weed seedling recruitment may explain the differences in relative weediness. For example, during wet springs seeds germinating in the trash layer of zero tillage may establish before dessication, while incorporating the seed-trash mix from a wet fall into the dry soil in minimum tillage may promote seedling establishment. Conversely, the relative weediness of conventional tillage in a dry conditions may be due to reduced crop competition compared to the other tillage systems.