William Deen

Carbon sequestration in a long-term conventional versus conservation tillage experiment

The impact of conservation tillage practices on carbon sequestration has been of great interest in recent years. Changes in the soil organic carbon (SOC) as influenced by tillage, is more noticeable under long-term rather than short-term tillage practices. This experiment analyzed the organic carbon status of soils sampled at depth increments from 0 to 60 cm after 25 years of five tillage treatments in a silt loam soil. Zero tillage (ZT) treatment was compared to conventional tillage practices of mouldboard and chisel plow operations conducted either during the fall or spring season in a randomized complete block design with four replications. The SOC was calculated on depth and equivalent soil mass bases. Contrast analysis showed a significantly (5%) higher soil bulk density for zero versus fall and zero versus chisel tillage operations at 5–10 cm soil depth. The SOC concentration was dependent on the depth of tillage operation and followed the trend of higher SOC for zero, chisel, and mouldboard tillage at 0–5, 5–10, and 20–40 cm depth, respectively. There were more significant differences in the SOC storage when expressed on depth compared to an equivalent soil mass basis. SOC storage was significantly higher for ZT at the 0–5 cm soil depth compared to conventional tillage practices. Contrast analysis on an equivalent mass basis showed that SOC storage was significantly higher for spring tillage compared to fall tillage at 0–60 cm depth. In conclusion, ZT practices increased SOC concentration and storage compared to conventional tillage operations only for the surface layer but not for the entire soil profile. 10 11 12 13 14 15 16 17 18 19 20 21 22

Increasing Crop Diversity Mitigates Weather Variations and Improves Yield Stability

Cropping sequence diversification provides a systems approach to reduce yield variations and improve resilience to multiple environmental stresses. Yield advantages of more diverse crop rotations and their synergistic effects with reduced tillage are well documented, but few studies have quantified the impact of these management practices on yields and their stability when soil moisture is limiting or in excess. Using yield and weather data obtained from a 31-year long term rotation and tillage trial in Ontario, we tested whether crop rotation diversity is associated with greater yield stability when abnormal weather conditions occur. We used parametric and non-parametric approaches to quantify the impact of rotation diversity (monocrop, 2-crops, 3-crops without or with one or two legume cover crops) and tillage (conventional or reduced tillage) on yield probabilities and the benefits of crop diversity under different soil moisture and temperature scenarios. Although the magnitude of rotation benefits varied with crops, weather patterns and tillage, yield stability significantly increased when corn and soybean were integrated into more diverse rotations. Introducing small grains into short corn-soybean rotation was enough to provide substantial benefits on long-term soybean yields and their stability while the effects on corn were mostly associated with the temporal niche provided by small grains for underseeded red clover or alfalfa. Crop diversification strategies increased the probability of harnessing favorable growing conditions while decreasing the risk of crop failure. In hot and dry years, diversification of corn-soybean rotations and reduced tillage increased yield by 7% and 22% for corn and soybean respectively. Given the additional advantages associated with cropping system diversification, such a strategy provides a more comprehensive approach to lowering yield variability and improving the resilience of cropping systems to multiple environmental stresses. This could help to sustain future yield levels in challenging production environments.

Control of Volunteer Glyphosate-Resistant Corn (Zea mays) in Glyphosate-Resistant Soybean (Glycine max)1

Volunteer corn in soybean can reduce yields, interfere with harvest, and cause unacceptable levels of contamination by its presence in the harvested soybean. In Ontario, soybean frequently follow corn in rotation. The use of glyphosate-resistant corn and soybean varieties has increased dramatically in Ontario. Field studies were conducted at two locations in southwestern Ontario to determine whether quizalofop-p-ethyl, clethodim, and fenoxaprop-p-ethyl can be tank mixed with glyphosate to provide effective control of volunteer glyphosate-resistant corn in glyphosate-resistant soybean. Soybean plots were overseeded with glyphosate-resistant corn and treatments consisting of glyphosate applied alone and tank mixed with full and reduced rates of each graminicide with and without a recommended surfactant. Tank mixing the graminicides and adjuvants with glyphosate did not affect glyphosate weed control or crop tolerance. Use of a recommended adjuvant significantly improved the effectiveness of the graminicides, particularly when reduced rates were applied. Quizalofop-p-ethyl was the most effective graminicide for controlling glyphosate-resistant volunteer corn, followed by clethodim and fenoxaprop-p-ethyl. Nomenclature: Soybean, Glycine max (L.) Merr. ‘Pioneer 9294 RR’; volunteer corn, Zea mays L. Additional index words: Graminicides, efficacy. Abbreviation: DAT, days after treatment.

An economic assessment of weed control strategies in no-till glyphosate-resistant soybean (Glycine max).

Abstract: Applying glyphosate relative to the growth stage of soybean is important for maximizing weed control and profits in glyphosate-resistant soybean under no-till systems. A study was conducted in Ontario for 4 yr to evaluate the effectiveness and gross return on the timing and sequence of applications of glyphosate in glyphosate-resistant no-till soybean. Percent control of various weed species varied among years due to environmental conditions. Timing of glyphosate was critical relative to weed emergence and determined the success of the treatment in terms of optimum soybean yield and gross return. Soybean yield and gross return approximated that the critical period for weed control in glyphosate-resistant no-till soybean was the unifoliolate to the one- to three-trifoliolate stage. Sequential applications of glyphosate provided higher soybean yield and gross return than a single preplant application of glyphosate. Glyphosate applied preplant or at the unifoliolate stage followed by a second application at the one- to three-trifoliolate stage consistently provided maximum average soybean yield and gross return. Gross return of the sequential glyphosate treatments was also more consistent across variable soybean price scenarios. Competition from uncontrolled later emerging weeds resulted in soybean yield loss with the single preplant application of glyphosate. Competition from uncontrolled early-emerging weeds reduced soybean yields when glyphosate was applied only at the one- to three-trifoliolate stage of soybean. Overall, two weed control strategies were identified: (1) two applications of glyphosate, the first at preplant to the unifoliolate stage, followed by a second application at the one- to three-trifoliolate stage of soybean, (b) first application of glyphosate at the unifoliolate stage followed by a second application at the one- to three-trifoliolate stage of soybean if later emerging weeds exceeded threshold densities. Nomenclature: Soybean, Glycine max (L.) Merr. ‘S14-M7’. Additional index words: Critical period of weed control, integrated weed management. Abbreviations: DAE, days after emergence; IWM, integrated weed management; NT, no till; POST, postemergence.

A mechanistic growth and development model of common ragweed

Abstract A mechanistic model was constructed for common ragweed growth and development based on the generic plant model CROPSIM. Adaptations were made to CROPSIMs growth and development subroutines to enable common ragweed growth to be simulated. Data from field studies using a single-source common ragweed grown in monoculture and from the literature were used to parameterize the model. The influences of varying environmental conditions across years, densities, and emergence timing on leaf number, leaf area, leaf weight, height, and biomass accumulation were taken into account by the model. Deviations between simulated and measured values generally fell within a relatively narrow range. Deviations outside this range tended to be associated with common ragweed growth shortly after emergence, particularly during temperature and moisture extremes. Future versions of the CROPSIM model may need to include more detailed algorithms for upper soil surface layer temperature and moisture conditions and improved germination and emergence algorithms to reduce these deviations. Nomenclature: Common ragweed, Ambrosia artemisiifolia L. AMBEL.

Effects of photoperiod on the phenological development of redroot pigweed (Amaranthus retroflexus L.)

Mechanistic weed models focus on determining the outcome of weed and crop interference. An understanding of weed phenology is essential for simulation model development. Phenological development is a major factor determining the outcome of weed–crop competition. Growth cabinet studies were conducted to characterize the influence of photoperiod on the phenological development of redroot pigweed (Amaranthus retroflexus L.). Results indicated that redroot pigweed is a quantitative short-day species. Four development phases of redroot pigweed were described according to its response to photoperiod: (1) a juvenile phase of 1.1 d; (2) a photoperiod-sensitive inductive phase of 7.9 d; (3) a photoperiod-sensitive post-inductive phase of 39.9 d; and (4) a photoperiod-insensitive phase of 2.2 d. This information is useful for the development of mechanistic models and for comprehending the distribution and competitive ability of redroot pigweed with crops. The utilization of these results could help in predicting th...

Effect of temperature and photoperiod on the phenological development of common lambsquarters

Abstract The goal of a mechanistic model is to determine the outcome of weed–crop interference. An understanding of weed phenology is essential for construction of such models because phenological development is a major factor determining the outcome of weed–crop competition. Growth cabinet studies were conducted to determine the influence of temperature and photoperiod on the phenological development of common lambsquarters. Common lambsquarters is a short-day species adapted to a temperature range of 6.5 to 44.5 C. Phenological development of common lambsquarters grown under a constant temperature of 20 C and an 8-h photoperiod was described in terms of biological days (Bd: chronological days at the optimum photoperiod and temperature). Three development phases of common lambsquarters were described as (1) a juvenile phase of 6.3 Bd, (2) a photoperiod-sensitive inductive phase of 8.2 Bd, and (3) a photoperiod-sensitive postinductive phase of 34.4 Bd. The photoperiod sensitivity of rate of development did not differ among phases of development across the life cycle. Interpretation of constant sensitivity to photoperiod will simplify simulation of weed phenology in mechanistic models. Nomenclature: Common lambsquarters, Chenopodium album L. CHEAL.

Effect of temperature and photoperiod on the phenological development of wild mustard (Sinapis arvensis L.)

The development of mechanistic weed models focuses on determining the outcome of weed‐crop interference. Phenological development is a major factor determining the outcome of weed and crop competition. The influence of temperature and photoperiod on phenological development of wild mustard (Sinapis arvensis L.) was studied in growth cabinets. The life cycle of wild mustard was defined in terms of biological days (Bd: chronological days at the optimum photoperiod and temperature). Wild mustard was a long-day species adapted to a wide temperature range of 1.5‐488C. Four phases of development of wild mustard were described: (1) a juvenile phase of 12.7 Bd; (2) a photoperiod-sensitive inductive phase of 6.2 Bd; (3) a photoperiod-sensitive post-inductive phase of 12.8 Bd; (4) a photoperiod-insensitive phase of 33.9 Bd. When effects of photoperiod on rate of development were normalized across phases of development, photoperiod sensitivity did not vary among phases of development. Interpretation of constant sensitivity to photoperiod will simplify simulation of weed phenology in mechanistic models. # 2001 Published by Elsevier Science B.V.

Weed Control in Pea with Reduced Rates of Imazethapyr Applied Preemergence and Postemergence1

Broad-spectrum weed control options for pea are limited. Field experiments conducted from 1998 to 2000 evaluated reduced rates of imazethapyr for selective control of grass and broadleaf weed species in pea. Imazethapyr was applied preemergence (PRE) and postemergence (POST) at 20, 40, 60, 80, and 100% of the PRE rate of 75 g ai/ha currently labeled in Ontario. A rate of 45 g/ha or greater was required to maintain consistent control of common lambsquarters and wild mustard when imazethapyr was applied PRE. Green foxtail and redroot pigweed control was excellent at all PRE rates 56 d after treatment. The 75-g/ha rate was required to maintain effective and consistent control of common ragweed. No injury or yield reductions were observed for any of the PRE application rates of imazethapyr. Reduced rates as low as 30 g/ha of imazethapyr applied POST maintained high levels of weed control. Pea tolerance to low rates of imazethapyr applied POST was acceptable except when applied in a year of low rainfall when peas experienced moisture stress. Nomenclature: Imazethapyr; common lambsquarters, Chenopodium album L. #3 CHEAL; common ragweed, Ambrosia artemisiifolia L. # AMBEL; green foxtail, Setaria viridis (L.) Beauv. # SETVI; redroot pigweed, Amaranthus retroflexus L. # AMARE; wild mustard, Sinapsis arvensis L. # SINAR; pea, Pisum sativum L. ‘Bolero’, ‘Sanchos’. Additional index words: Herbicide efficacy, pea yields, reduced herbicide rates. Abbreviations: DAT, days after treatment; OCHU, Ontario corn heat units; POST, postemergence; PRE, preemergence.

Effects of 30 Years of Crop Rotation and Tillage on Bacterial and Archaeal Ammonia Oxidizers.

Ammonia-oxidizing bacteria (AOB) and archaea (AOA) both mediate soil nitrification and may have specialized niches in the soil. Little is understood of how these microorganisms are affected by long-term crop rotation and tillage practices. In this study, we assessed abundance and gene expression of AOB and AOA under two contrasting crop rotations and tillage regimes at a 30-yr-old long-term experiment on a Canadian silt loam soil. Continuous corn ( L.) (CC) was compared with a corn-corn-soybean [ (L.) Merr.]-winter wheat ( L.) rotation under-seeded with red clover ( L.) (RC), with conventional tillage (CT) and no-till (NT) as subplot treatments. Soil sampling was performed during the first corn year at four time points throughout the 2010 season and at three discrete depths (0-5, 5-15, and 15-30 cm). Overall, AOA abundance was found to be more than 10 times that of AOB, although AOA transcriptional activity was below detectable levels across all treatments. Crop rotation had a marginally significant effect on AOB abundance, with 1.3 times as many gene copies under the simpler CC rotation than under the more diverse RC rotation. More pronounced effects of depth on AOB abundance and gene expression were observed under NT versus CT management, and NT supported higher abundances of total archaea and AOA than CT across the growing season. We suggest that AOB may be more functionally important than AOA in this high-input agricultural soil but that NT management can promote enhanced soil archaeal populations.