Weed flora in the early growth period of spring crops under conventional, reduced, and zero tillage systems on a clay soil in northern Alberta, Canada

Abstract

An understanding of tillage effects on frequency, density and species composition of the weed population could be used to improve weed management systems. This study was conducted from 1989 to 1993, to evaluate the effects of three primary tillage systems on the weed population during the early growth period of spring crops, i.e. barley ( Hordeum vulgare L.), canola ( Brassica campestris L.), and wheat ( Triticum aestivum L.), with all the three crops grown in each year. In addition, composite dry matter of the weed flora was also determined in 1991 and 1993. Field experiments were located on a Falher clay soil (Canadian = Solodized Solonetz, USDA = Natriboralf) which had been under conventional management for about 50 years in northern Alberta, Canada (55° 43′ N and 118° 41′ W). A medium duty cultivator with a working depth of 8–10 cm was used in the conventional tillage (CT, once in preceding fall and twice prior to seeding in spring) and reduced tillage (RT, once prior to seeding in spring) plots. The zero tillage (ZT) plots had preseeding applications of glyphosate (N-(phosphonomethyl) glycine). A complete factorial arrangement of the three tillage systems by three crops was laid out using a completely randomized block design, with four replications. Contribution of the various weed species to the weed flora was assessed using their frequency of occurrence (PF, zero in the absence and one in the presence of a given species), population density (PD, number of plants for the species), and relative abundance (RA, sum of the percent PF and PD for a species relative to their totals for all species present in a plot). Due to the absence of tillage by crop interactions, only the tillage effects averaged across the crops are discussed. Twenty two species of weeds were observed. Dominant weeds were wild buckwheat ( Polygonum convolvulus L.), stinkweed ( Thlaspi arvense L.), common groundsel ( Senecio vulgaris L.), wild oats ( Avena fatua L.), and dandelion ( Taraxacum officinale Weber). Annual broadleaf (fifteen species) was clearly the dominant group under all the tillage systems, compared with the perennial (six species), and annual grassy (one species) weeds. Tillage effect on the PF, PD and RA was weed species specific. The broadleaf population showed a trend as ZT>RT>CT for the PD and PF, but an opposite trend for the RA. This meant that relative contribution of the broadleaf group to the total population declined with a reduction in tillage intensity. The PD, PF, and RA of the perennial weeds were ZT>RT>CT, indicating increased contribution of this group to the total population with reduced tillage intensity. Species diversity of the broadleaf and total populations exhibited a relatively greater proportion of common and rare species under the CT and ZT, respectively. The diversity of perennial population increased with a decrease in tillage intensity, due to higher populations of both common as well as rare species. Our data indicate that the relative contributions to the size and diversity of weed flora are likely to be greater by common species under the CT and by rare species under the RT and ZT. There was no consistent increase in the weed population with time under all three systems. It is suggested that the conventional tillage can be replaced by reduced or zero tillage systems for weed control under similar soil and climatic conditions, while considering the economic, agronomic, and environmental impacts of these systems.