Summary
The retention of crop residues at or just below the soil surface may have both a direct and an indirect influence on the development of pea root diseases (Watkins & Boosalis 1994). Sumner et al. (1981) suggested that reduced tillage would tend to increase the amount of crop residue and populations of soil-borne pathogens in the upper soil layers. Furthermore, delayed emergence as a result of reduced soil temperatures and increased moisture levels under conservation tillage could favor the development of root diseases, especially during early stages of plant development. However, in the current study reduced levels of root rot were found towards the end of the growing season under zero tillage compared with conventional tillage. Reduced root rot severity under zero tillage may have resulted from changes in soil organic matter, drainage, porosity, bulk density, and soil microbial activity. These changes may have had a negative influence on the soil-borne pathogens and restricted root rot development (Watkins & Boosalis 1994). Overall plant health also may be affected by the soil environment. Soil conditions, as affected by tillage practice, may restrict or enhance the plant's ability to withstand attack by soils-borne pathogens (Watkins & Boosalis 1994). Hwang & Chang (1989) have suggested that root rot of peas may become more of a problem when short rotations are used. Thus, farmers will need to pay particular attention to rotation to prevent the development of more severe pea root rot.
Caution must be exercised when using the results of the 1995 barley leaf survey to draw on conclusions based on tillage, variety and rotation. The trends observed in the survey represent data from one year. In addition, the survey was an observational study and it may be inappropriate to infer any cause and effect relationship. Nevertheless, certain trends were evident based on the data from the summer of 1995.
