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Understanding the soil bacterial communities involved in carbon (C) and nitrogen (N) cycling can inform beneficial tillage and crop rotation practices for sustainability and crop production. This study evaluated soil bacterial diversity, compositional structure, and functions associated with C-N cycling at two soil depths (0–15 cm and 15–30 cm) under long-term tillage (conventional tillage [CT] and no-till [NT]) and crop rotation (monocultures of corn, soybean, and wheat and corn–soybean–wheat rotation) systems. The soil microbial communities were characterized by metabarcoding the 16S rRNA gene V4–V5 regions using Illumina MiSeq. The results showed that long-term NT reduced the soil bacterial diversity at 15–30 cm compared to CT, while no significant differences were found at 0–15 cm. The bacterial communities differed significantly at the two soil depths under NT but not under CT. Notably, over 70% of the tillage-responding KEGG orthologs (KOs) associated with C fixation (primarily in the reductive citric acid cycle) were more abundant under NT than under CT at both depths. The tillage practices significantly affected bacteria involved in biological nitrogen (N2) fixation at the 0–15 cm soil depth, as well as bacteria involved in denitrification at both soil depths. The crop type and rotation regimes had limited effects on bacterial diversity and structure but significantly affected specific C-N-cycling genes. For instance, three KOs associated with the Calvin–Benson cycle for C fixation and four KOs related to various N-cycling processes were more abundant in the soil of wheat than in that of corn or soybean. These findings indicate that the long-term tillage practices had a greater influence than crop rotation on the soil bacterial communities, particularly in the C- and N-cycling processes. Integrated management practices that consider the combined effects of tillage, crop rotation, and crop types on soil bacterial functional groups are essential for sustainable agriculture. [ABSTRACT FROM AUTHOR]

On-farm field trials were conducted on sandy loam soils in Ontario and Quebec, Canada for three years to quantify N2O fluxes and cumulative N2O emissions as affected by the amount and timing of N fertilizer application to corn (Zea mays L.). Using the static chamber method, gas samples were collected and analyzed after preplant or sidedress N fertilization. In general, both N2O flux and total emission increased with the amount of N fertilizer applied at preplant or sidedress at the V6-V8 growth stage with peak flux rate from 30 to 900 μg N m-2 hr-1. Depending on N levels and timing of application, the cumulative emission ranged from 0.05 to 2.42 kg N ha-1 over the 28-d monitoring period, equivalent to 0.03 to 1.45% of the total N fertilizer applied. The amount and temporal distribution of rainfall played a major role in stimulating the rate of N2O emission. The flux of N2O was negligible when soil mineral N in the 0-15 cm layer was 15ºC, during early plant growth stages. Cumulative N2O emission was generally higher for sidedress incorporated N than preplant application probably because of higher soil water contents and temperatures later in the growing season induced higher rates of N2O production.

Climate change, resulting from increased atmospheric CO2, will affect temperature and precipitation amount and regularity. Changes in solar radiation have been observed in the recent past. Precipitation irregularity is a measure of rainfall distribution during a growing season (calculated as the standard error of the slope from regression of cumulative precipitation on day of the growing season). We investigated whether precipitation irregularity and solar radiation contributed to soybean yield. Fourteen short-season cultivars, released from 1930 to 1992, were grown from 1993 to 2019 at Ottawa, Canada. Stepwise multiple linear regression was used to investigate the contribution to seed yield of precipitation irregularity and solar radiation, and also previously modeled parameters genetic improvement, annual [CO2], and cumulative precipitation and average minimum temperature during the vegetative, flowering and podding, and seed filling growth stages. While solar radiation and precipitation irregularity did not trend over the years of our study and precipitation irregularity was not related to growing season precipitation, both were significant factors in our model, accounting for 2.5% and 6.5%, respectively, of the seed yield variability. Precipitation during all three stages were similar as they each accounted for 4%–7% of seed yield variability. We observed contrasting temperature effects where higher minimum temperature during vegetative and seed filling reduced yield, while during flowering and podding increased yield. Estimated yield improvement due to elevated [CO2] was 7.8 kg ha−1 ppm−1 and to genetic improvement over time was 7.1 kg ha−1 year−1. Over the extremes of our study we found that precipitation irregularity could cause up to a 30% yield reduction. [ABSTRACT FROM AUTHOR]

Abstract: Charles Edward Saunders was born in London, Ontario, in 1867. His father, Sir William Saunders, was the first director of the Dominion Experimental Farms (1886-1911). Charles received his B.A. [...]

Genetic diversity assessment of improved crop germplasm can facilitate the expansion of the genetic base in a plant breeding program, but little effort has been made to assess the Canadian soybean [Glycine max (L.) Merr.] gene pool established over the past century. Simple sequence repeat (SSR) markers were applied to assess the genetic diversity of 45 Canadian soybean cultivars released from 1934 to 2001 and 37 exotic germplasm accessions. Thirty-seven SSR primer pairs were applied and 234 polymorphic bands were scored for each accession. The frequencies of the scored bands ranged from 0.01 to 0.90 and averaged 0.17. The proportion of total SSR variation occurring between exotic and Canadian germplasm was 9%; among the Canadian cultivars of three breeding periods 10%; and between the cultivars of maturity groups 0 and 00 4%. More diversity was found for exotic germplasm than the Canadian. More diversity was observed in the cultivars of the recent breeding period than the early. The Canadian cultivars were clustered into seven major groups, partially congruent to the known pedigrees, and they were more related to germplasm from Russia, Sweden, and Ukraine and less to the Asian germplasm. The six genetically most distinct cultivars were PS86 RR, Gaillard, Manitoba Brown, Beechwood, Maple Isle, and 92B91. These findings are useful for the selection of genetically distinct or less related soybean materials to improve the genetic background of the soybean gene pool.

Studies with a series of historic soybean [Glycine max (L.) Merr.] cultivars have found genetic improvement rates for seed yield of about 0.5% per year since soybean was first cultivated in Canada. Work with maize (Zea mays L.) has shown seed yield differences between old and new hybrids are more pronounced under higher seeding rates. The objective of our research was to determine the effect of plant populations on the rate of genetic improvement of short-season soybeans. Soybean cultivars released from 1934 to 1996 were grown in 40-cm-wide rows at several seeding rates (Exp. 1, 42 cultivars grown at 25, 50, 75 seeds [m.sup.-2] in 1998 and 1999; and Exp. 2, seven cultivars grown at 25, 50, 100, 150, 200 seeds [m.sup.-2] in 1999 and 2000) in two fields for 2 yr at Ottawa, ON. Genetic improvement rates were based on cultivar year of release and were compared across plant populations. In Exp. 1, seed yields did not reach a plateau. In Exp. 2, a seed yield plateau was reached and genetic improvement rates generally increased with plant population. Maximum rates of genetic improvement occurred at plant populations three to four times greater than current commercial practice (40 plants [m.sup.-2]). A plateau for seed yield was reached at lower plant populations compared to plateaus for genetic improvement rates which were reached at higher plant populations (>80 plants [m.sup.-2]). Higher plant populations also resulted in earlier maturity, increased plant height, and increased lodging. Seed protein increased and seed oil decreased with higher plant populations. New soybean cultivars appear more tolerant to plant population stress than older cultivars., ACCORDING to Donald (1963) a successful crop plant should be intraspecifically noncompetitive while still exhibiting sufficient plasticity to respond in size and shape to available conditions. Duncan (1969) concluded that [...]

Temperatures greater than 27°C, in a growth cabinet, have resulted in floral sterility and yield loss in Brassica napus L. Maximum daily temperatures often exceed this in the major canola growing regions. Our objective was to examine the effects of heat stress during flowering on yield and yield components of B. napus, B. rapa L., and B. juncea (L.) Czernj. & Cosson. Cultivars of the three Brassica species were grown in a split-plot design in the field for 3 yr at Ottawa, Canada. Three seeding dates were used each year to obtain different levels of heat stress during flowering. The number of flowers on the main raceme and the first and second branch racemes were counted at anthesis, from 10 plants per plot. At maturity, pods from the sampled plants were counted and seed numbers and weight determined. Two rows of the remainder of each plot was harvested for seed yield. A heat stress index was developed on the basis of the accumulation of daily maximum temperatures greater than a threshold temperature. The threshold temperature during flowering, which resulted in seed yield losses, was 29.5°C for all Brassica species. High mean maximum temperature during vegetative development resulted in a reduction in flower number for all Brassica species. Seed yield decreased as heat stress during flowering increased. The reduction in seed yield was primarily due to a reduction in flower number and in the number and size of the seeds produced per flower. Plant breeders should actively select for heat stress tolerance in future canola cultivars., HIGH AIR TEMPERATURES during reproduction cause a reduction in fertility and seed yield in wheat (Triticum aestivum L., Saini et al., 1983), corn (Zea mays L.; Schoper et al., 1987; [...]