The traditional cropping system in semiarid regions of the Canadian prairies involves frequent summer fallowing with several tillage operations to control weeds during the fallow period. Recently, there has been a trend toward reduced tillage and more intensive cropping, but the impact of this shift in management on sequestration of atmospheric CO2 remains uncertain. In 1995 and 1996, we measured fluxes of CO2 in a tillage experiment that had been initiated in 1982 on a silt loam (Typic Haploboroll) in southwestern Saskatchewan. The experiment comprised two spring wheat (Triticum aestivum L.) rotations (continuous wheat [Cont. W] and fallow–wheat [F–W]), each with conventional tillage (CT) and no‐till (NT) treatments. In Cont. W, CO2 fluxes tended to be lower under NT than under CT (mean annual flux was ≈20 to 25% less for NT than CT). In F–W, tillage effects on mean annual CO2 flux were significant (P < 0.05) in the wheat phase only (NT ≈ 10% less than CT). Tillage had negligible effect on C inputs in crop residues. Lower CO2 fluxes under NT than under CT were attributed to slower decomposition of crop residues placed on the surface of NT soil than when they were incorporated. With good growing conditions (and thus large inputs of residues) between 1989 and 1996, there was an accumulation of partially decomposed residues on the surface of NT soil. Carbon in surface residues represented about one‐half of the C gained by NT soil. In Cont. W, surface residue C (in 1996) amounted to 3.6 t ha−1 under NT vs 1.4 t ha−1 under CT. Residue C amounts were smaller in the F–W system: 1.7 t ha−1 (NT) and 0.7 t ha−1 (CT). Based on our results, producers on medium‐textured soils in the semiarid Canadian prairies who switch from the traditional wheat production system (conventionally tilled fallow–wheat) to continuous no‐till cropping could, potentially, sequester 5 to 6 t C ha−1 in soil organic matter and surface residues in 13 to 14 yr.

Wheat functions as a complex wellintegrated organism with adaptation to many environments. Traits of wheat may be correlated to each other in a positive or a negative manner. The direction of the correlation is independent of breeding objectives and may change from one production environment to another. Grain yield is correlated positively with time to maturity in environments without terminal stress. The negative correlation between grain yield and grain protein concentration exemplifies an undesirable relationship in a wheat quality type in which protein concentration is positively correlated with bread loaf volume. However, this same correlation has an advantage to those end-products that are favored by low protein concentration such as confectionary products. To shift the negative correlation between grain yield and protein concentration requires assembling a more photosynthetically efficient, nitrogen-use efficient and\or water-use efficient genotype in combination or separately. Simultaneous selection for quantitative and quality traits is a breeding strategy, which with the inclusion of marker assisted selection, can shift undesirable correlations.

Carbon exchange between soil and the atmosphere plays an important role in the global C cycle, but partitioning soil CO2 emissions by source (soil organic matter mineralization, crop residue decomposition, and root respiration) is difficult. Our objective was to determine the contribution of decomposing wheat (Triticum aestivum L.) straw to CO2 emissions from a Swinton silt loam (fine‐silty, mixed, mesic Typic Haploboroll) under controlled conditions (constant 20°C). Two types of straw (i.e., fresh straw collected shortly after harvest and standing stubble that had “weathered” in the field for a year) were either incorporated into or placed on the soil surface at a rate equivalent to 2800 kg ha‐1. One set of soils was watered every 2 or 3 d to 90% of field capacity and a second set was allowed to dry (from 90% field capacity) to below the permanent wilting point before watering. Emissions of CO2 were measured every 2 or 3 d with a vented chamber connected to a portable CO2 analyzer. Within 2 d, incorporation of straw increased CO2 flux from 0.3 to ≈ 1.5 µmol CO2m‐2s‐1. Surface straw had significantly increased fluxes, but the effect was small compared with incorporated straw. Straw type had little effect on emissions. Total CO2‐C emitted in 77 d from continuously moist soil was 25 g m‐2 with no added straw, 41 g m‐2 with surface straw, and 73 g m‐2 with incorporated straw (values are averages for two straw types). In all, 38% of incorporated‐straw C and 13% of surface straw C was emitted as CO2. Soil subjected to moist‐dry cycles emitted from 36 to 62% less CO2 than continuously moist soil. The Douglas‐Rickman residue‐decomposition model simulated the amount of straw C remaining in the soil as a function of time. In the absence of straw, CO2‐C emitted was similar to the amount by which light‐fraction C decreased, suggesting that this labile fraction of organic matter was a major source of respired C.

. 2002. Effect of leaf spotting diseases on grain yield and seed traits of wheat in southern Saskatchewan. Can. J. Plant Sci. 82: 507-512. Although leaf spotting diseases have been reported to have a negative effect on grain yield and seed characteristics of wheat (Triticum spp.), the magnitude of such effects on wheat grown on dryland in southern Saskatchewan is not known. A fungicide experiment was conducted at Swift Current (Brown soil) and Indian Head (Black soil) from 1997 to 1999 to determine the effect of leaf spotting diseases on yield and seed traits of wheat. Two fungicides, Folicur 3.6F and Bravo 500, were applied at different growth stages on three common wheat (Triticum aestivum L.) and three durum wheat (T. turgidum L. var durum) genotypes. Fungicide treatments generally did not affect yield, kernel weight, test weight or grain protein concentration, and these effects were relatively consistent among genotypes. Folicur applied at head emergence in 1997 and at flag leaf emergence and/or head emergence in 1998 increased yield at Indian Head (P < 0.05). Fungicides applied at and before flag leaf emergence tended to increase kernel weight. Grain protein concentration increased only in treatments of Bravo applications at Indian Head in 1998. These results suggested that under the dryland environment and management in southern Saskatchewan leaf spotting diseases generally have a small effect on yield, kernel weight, test weight and protein concentration.

No abstract