Wheat yield and weed population as influenced by three tillage systems on a clay soil in temperate continental climate

Abstract

The potential benefits of conservation tillage practices depend mainly on the soil and climatic conditions of the site. A study was conducted to determine the effects of three tillage systems (conventional, CT; reduced, RT; zero, ZT) on spring wheat ( Triticum aestivum L.) and weed growth on a clay soil in temperate continental climate, northern Alberta (55°43′N, 118°41′W), Canada. A medium duty cultivator with 25 cm sweeps spaced 22 cm apart and a working depth of 8–10 cm was used for tillage in the CT (once in fall and twice in spring) and RT (once in spring) plots. The ZT plots received a harrowing to spread straw and a preseeding application of Roundup (glyphosate) to control weeds. Experimental design was a randomized complete block with four replications and the tillage systems were fixed in space for the 1989, 1990 and 1991 seasons. The RT treatment resulted in higher yields than the CT or ZT treatments. However, the differences were not always significant. The ZT treatment produced higher yields than CT in 1989 and 1991, whereas its yields were lower than CT in 1990. The 3 year means of total dry matter (TDM) were 3899 kg ha −1, 3640 kg ha −1 and 3331 kg ha −1 for the RT, ZT and CT treatments, respectively. The corresponding grain yields were 1728 kg ha −1, 1573 kg ha −1 and 1530 kg ha −1. The concentration of total N in plants and grains of wheat, amounts of extractable NO 3-N, NH 4-N and P in soil and soil moisture and bulk density were not significantly affected by tillage. The mean weight diameter of aggregates in surface soil was significantly greater under ZT than under the other systems. Wild buckwheat ( Polygonum convolvulus L.) was more abundant under CT, but common groundsel ( Senecio vulgaris L.), dandelion ( Taraxacum officinale Weber), hemp nettle ( Galeopsis tetrahit L.), field horsetail ( Equisetum arvense L.) and smartweed ( Polygonum scabrum Moench) tended to have higher populations under the ZT system. The populations of foxtail barley ( Hordeum jubatum L.) wild rose ( Rosa sp.), stinkweed ( Thlaspi arvense L.) and wild oats ( Avena fatua L.) showed no consistent effect of tillage. Tillage or preseeding application of glyphosate did not provide an effective control of all weed species. The spring tillage of the RT system improved crop yields and weed control relative to ZT, whereas the fall tillage of the CT system (in addition to spring tillage) reduced crop yields and had no significant effect on weed population relative to RT. The overall results showed that tillage intensity could be reduced to the level of RT without any adverse influence on crop yields, soil properties or weed populations. The RT system is also economical and environmentally desirable owing to lower tillage and herbicide requirements.