The acceptance of no‐till systems for soybean [Glycine max (L.) Merr.] production following winter wheat (Triticum aestivum L.) on fine‐textured soils in Ontario has been hampered by soybean yield reductions due to unfavorable seedbed conditions. This research was conducted to identify alternative tillage and residue management systems that will enhance emergence, growth, and yield of soybean following winter wheat. Seven tillage and residue management systems, comprising fall moldboard plow, fall chisel plow, fall disk only, fall zone‐till, no‐till, no‐till (with wheat straw baled), and no‐till (with wheat straw and stubble removed), were evaluated following winter wheat on fine‐textured soils from 1994 to 1996 at six different sites near Centralia and Wyoming in southwestern Ontario. Spring soil moisture was lower in the fall tillage treatments than in no‐till with wheat residue, but moisture differences did not vary among fall tillage treatments. No‐till seedbeds had the highest soil moisture contents, the lowest proportion of fine soil aggregates (<5 mm in diameter), and the greatest penetrometer resistance. No‐till soybean growth was delayed and yields were reduced as the level of wheat residue left after planting increased. Soybean seed yield was negatively correlated with surface residue cover, but positively correlated with soil aggregates <5 mm in diameter at all sites. Fall zone‐till and fall disk systems generally improved in‐row seedbed conditions (higher fine soil aggregates and lower soil resistance), and increased seed yields by 5 to 29% relative to no‐till treatments. Fall zone‐till and fall tandem disk systems were the best conservation tillage alternatives to fall moldboard plowing.

Concerns about corn (Zea mays L.) grain yield reduction with notill following winter wheat (Triticum aestivum L.) in rotation on clay soils has been a major factor in slowing the rate of adoption of no‐till systems in Ontario. Our objective was to determine conservation tillage and wheat residue management systems that provide favorable seedbed conditions for emergence, growth, and yield of corn following winter wheat on clay soils. Seven tillage and residue management systems (fall moldboard plow, chisel plow, tandem disk, and zonetill, and no‐till bare and with straw baled and not baled) were evaluated in 1994 and 1995 at two locations in Ontario. Fall zone‐till reduced the amount of wheat residues on the soil surface. Wheat residues remaining in late fall with zone‐till, no‐till (baled), and no‐till (not baled) treatments were 3.1, 4.0, and 7.1 Mg ha−1. Volumetric soil moisture levels in the top 15 cm early in the season did not differ among fall tillage treatments, but were all lower than for no‐till with wheat residue. Modifying the no‐till system by adopting fall zonetill or fall tandem disk produced grain yields no different from fall moldboard plow or fall chisel plow treatments, and greater by 5 to 10% than for no‐till with wheat residue. No‐till yield potential was affected by the level of wheat residue present. Completely removing all wheat residue increased no‐till corn grain yields by 0.5 and 0.9 Mg ha−1 compared with baling and not baling straw, respectively. The baled and not‐baled no‐till treatments had the lowest proportion of finer soil aggregates in the seedbed, greatest penetrometer resistance up to the 20‐cm soil depth, slowest corn growth, and lowest grain yield. We recommend zone‐till or tandem disk in the fall for corn production on clay soils following wheat.

Wheat straw placement effects on total phenolic compounds in soil and corn seedling growth. Can. J. Plant Sci. 77: 301-305. The effects of placement of wheat (Triticum aestivum L.) straw on the release of phenolic compounds potentially phytotoxic to corn (Zea mays L.) seedling growth were examined in plastic pots under controlled conditions in growth cabinets. The treatments were soil only (control), soil with straw only in the top 2.5 cm, and soil with mixed straw. Each of these treatments was either sown or not sown with corn. Corn radicle length and seedling biomass were significantly reduced, relative to other treatments, when wheat straw was present only in the top layer of soil. Water extracts from soil with surface straw had higher amounts of total phenolic compounds than the other treatments at each of the sampling times. The concentration of phenolic compounds increased with time, with average amounts at 14 and 28 d being 53 and 77%, respectively, of the concentration at 42 d. The presence of corn reduced the amount of phenolic compounds at 14 and 42 d compared with when corn was absent (P = 0.01). Water extracts prepared from soil after 42 d from all the treatments were used to investigate germination of corn seeds. Germination of corn seeds and radicle extension were inhibited by water extracts from all the above soils at 42 d compared with the control (deionized water). Coleoptile length was inhibited when concentration of phenolic compounds exceeded 10 ppm. Soil NO 3 -N differences among the treatments were insignificant at the various sampling times. This indicated that the observed corn growth differences were mainly due to the presence of phenolic compounds.Key words: Wheat (winter), straw replacement, phenolic acids, seedling, allelopathy Opoku, G., Vyn, T. J. et Voroney, R. P. 1997. Effets du mode d'enfouissement de la paille de blé sur les composés phéno-liques totaux dans le sol et sur la croissance du maïs au stade jeune. Can. J. Plant Sci. 77: 301-305. Nous avons examiné en pots de plastique en enceinte de croissance les effets du placement de la paille de blé (Triticum aestivum L.) sur le dégagement de composés phénoliques éventuellement phytotoxiques envers les plantules de maïs (Zea mays L.). Les traitements comparés étaient : sol sans paille, sol avec paille seulement dans les 2,5 cm supérieurs et sol mélangé à la paille. Chacun des traitements étaient combinés ou non avec un semis de maïs. La longueur de la radicule et la biomasse de la plantule étaient significativement plus basses dans le traitement avec paille seulement dans la couche supérieure du sol que dans les deux autres traitements. L'extrait aqueux du sol dans le premier traitement contenait de plus fortes quantités de substances phénoliques totales à toutes les dates de prélèvement. Les concentrations de substances phénoliques augmentaient en fonction du temps, donnant à 14 et à 28 jours des quantités moyennes respectives de 53 et 77 % des valeurs mesurées à 42 jours. La présence du maïs dans le sol abaissait les quantités ...

Opoku, G. and Vyn, T. J. 1997. Wheat residue management options for no-till corn. Can. J. Plant Sci. 77: 207-213. Corn (Zea mays L.) yield reduction following winter wheat (Triticum aestivum L.) in no-till systems prompted a study on the effects of tillage and residue management systems on corn growth and seedbed conditions. Four methods for managing wheat residue (all residue removed, straw baled after harvest, straw left on the soil surface, straw left on the soil surface plus application of 50 kg ha -1 N in the fall) were evaluated at two tillage levels: fall moldboard plow (MP) and no-till (NT). No-till treatments required at least 2 more days to achieve 50% corn emergence and 50% silking, and had the lowest corn biomass at 5 and 7 wk after planting. Grain yield was similar among MP treatments and averaged 1.1 t ha -1 higher than NT treatments (P < 0.05). Completely removing all wheat residue from NT plots reduced the number of days required to achieve 50% corn emergence and increased grain yields by 0.43 and 0.61 t ha -1 over baling and not baling straw, respectively, but still resulted in 8% lower grain yields than MP treatments. Grain yield differences among MP treatments were insignificant regardless of the amount of wheat residue left on the surface or N application in the fall. Early in the growing season, the NT treatments where residue was not removed had lower soil growing degree days (soil GDD) compared with MP (baled) treatment, and higher soil moisture levels in the top 15 cm compared with all other treatments. The application of 50 kg N ha -1 in the fall to NT (not baled) plots influenced neither the amount of wheat residue on the soil surface, nor the soil NO 3 -N levels at planting. Our results suggest that corn response in NT systems after wheat mostly depends on residue level.Key words: Winter wheat, straw management, no-till, corn, soil temperature, soil moisture Opoku, G. et Vyn, T. J. 1977. Choix de gestion des restes de culture du blé pour la production de maïs sans travail du sol. Can. J. Plant Sci. 77: 207-213. La baisse de rendement du maïs (Zea mays L.) observée après une culture de blé d'hiver (Triticum aestivum L.) en système de culture sans labour nous a inspiré une étude sur les effets du mode de travail du sol et de la gestion des restes de culture sur la croissance du maïs et sur l'état du lit de semence. Nous avons évalué quatre méthodes de gestion des restes de culture de blé : enlèvement total des résidus, mise en balle de la paille après la moisson, paille laissée à la surface du sol, la même chose avec épandage de 50 kg N ha -1 en automne. Ces traitements étaient combinés à deux régimes de travail du sol : labour d'automne à la charrue à versoir (Lcha) et semis direct (SD). En régime SD, le maïs requérait au moins 2 jours de plus pour arriver à 50 % de levée et à 50 % de floraison femelle. Et en outre sa biomasse à 5 et à 7 semaines après le semis était toujours la moins abondante. Le rendement grainier était du même ordre dans tous les traitements en régime de travail cla...