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The influence of soil and crop management practices on soil aggregation is well documented; however very little information is available on the impact of aggregation on biological processes such as greenhouse gas emissions. Soils (Ap horizon of a Brookston clay loam) were sampled in the spring of 2002 from two treatments in a long-term study (established in 1959). The treatments included continuous corn (Zea mays L.) and the corn phase of a 4-year crop rotation which included corn–oats (Avena sativa L.)–alfalfa (Medicago sativa L.)–alfalfa. The continuous corn (CC) treatment was plowed every fall whereas the rotation corn (RC) treatment was plowed 2 out of the 4 years (in the fall following second year alfalfa and following corn). The objectives were to determine the impact of crop rotation and continuous corn on aggregate size distribution, and the influence of aggregate size on CO2 and N2O production through denitrification. The soil samples were separated into six aggregate size fractions (<0.25, 0.25–0.50, 0.50–1.0, 1.0–2.0, 2.0–4.0, and 4.0–8.0 mm diameter) using a dry sieving procedure. Each aggregate size fraction was separated into two subsamples with one subsample left intact and the other ground to <0.15 mm (100-mesh sieve). The intact and ground aggregates from each size fraction were incubated anaerobically using the acetylene inhibition technique and carbon dioxide (CO2) and nitrous oxide (N2O) production (denitrification) were determined. Nitrate was added and thus not limiting in the incubations. In both cropping treatments, the 2–4 mm aggregate size was the dominant size fraction (∼35–45% of the soil by weight) followed by the 1–2 mm size fraction (∼20–25% of the soil by weight). Crop rotation increased both CO2 and N2O production (denitrification) and the proportion of <2 mm diameter aggregates compared to continuous corn. For intact aggregates, CO2 production decreased with increasing aggregate size, while N2O production (denitrification) increased with increasing aggregate size. When the aggregates were ground, CO2 production was independent of the original aggregate size, while N2O production (denitrification) decreased as the size of the original aggregates increased. This study demonstrates that both the size distribution of natural soil aggregates and soil grinding can have substantial impacts on the CO2 and N2O production through denitrification. [Copyright &y& Elsevier]

Process-based modelling studies can help to interpret experimental results and gain more insights into CO 2 fluxes in agro-ecosystems. The objective of this study was to evaluate the ability of the DeNitrification-DeComposition (DNDC) model to predict field-measured soil temperature, moisture, and respiration (daily and seasonal) in monoculture versus rotational cropping systems. Field measurements (2003–2005) from monoculture cropping (corn, Zea mays L.; soybean, Glycine max L.; and winter wheat, Triticum aestivum L.), as well as from 2-yr (corn-soybean) and 3-yr (corn-soybean-winter wheat) crop rotations in southwestern Ontario, Canada were used for model calibration and evaluation. Model simulated soil (0–10 cm) temperature ( nRMSE = 8–9%, d = 0.97 and EF = 0.87–0.90) and moisture ( nRMSE = 15–22%, d ≥ 0.7 and EF ≥ 0) agreed well with the growing season field measurements. Predicted daily soil CO 2 fluxes were accurate for corn (under both monoculture and rotation) and winter wheat (under monoculture) ( nRMSE = 56–70%, d > 0.7, slope = 0.60–0.88, R 2 = 0.36–0.48). The overestimation in daily soil CO 2 fluxes for winter wheat phase under the 3-yr rotation could be addressed by decreasing the root: shoot ratio. The simulated temporal offset in the soil CO 2 fluxes for soybean could be improved by adjusting crop parameters (thermal degree days for crop maturity and root: shoot ratio). The simulated cumulative seasonal soil CO 2 fluxes were not statistically different from the measured CO 2 fluxes for corn, soybean and winter wheat as indicated by the paired- t test ( p = 0.17–1.00). The impacts of monoculture and rotation cropping on seasonal root autotrophic respiration (R A ), soil heterotrophic respiration (R H ) and R H /R S ratios for corn, soybean and winter wheat were attributed to the different biomass production and residue C input management systems. The R H contributed more to total soil respiration for corn (during the growing season) under monoculture (R H /R S = 42%) than when it was grown in rotation (26–29%), while ratios of R H /R S were similar among monocultural and rotational soybean (41–49%) and winter wheat (31–40%). The current litter C level and consequently annual R H were driven by the litter C input carried over from previous crop. When carbon in the harvested grain was taken into account in the carbon budget, corn would act as a strong net carbon sink (3 year average of −975, −2675 and −3151 kg C ha −1 yr −1 under monoculture, 2-yr and 3-yr rotations, respectively), while soybean and winter wheat would act as weak net carbon source under both monoculture and rotation. The DNDC model was found to be able to simulate soil temperature, moisture, and soil respiration for corn and winter wheat under both monoculture and rotation in humid southwestern Ontario, Canada but crop parameter adjustments are required to simulate soybean. [ABSTRACT FROM AUTHOR]

Highlights: [•] DSSAT model could simulate crop yields well under a soybean–maize rotation. [•] DSSAT provided reasonable simulation of soil water content in different tillages. [•] The overall spatial and temporal patterns of soil temperature were simulated well. [•] DSSAT could simulate tillage experiment on a cool, semi-arid Black soil. [Copyright &y& Elsevier]

Abstract: In southwestern Ontario, rain-fed crop production frequently fails to achieve its yield potential because of growing-season droughts and/or uneven rainfall distribution. The objective of this study was to determine if the Decision Support System for Agrotechnology Transfer (DSSAT) v4.5 model could adequately simulate corn and soybean yields, near-surface soil water contents, and cumulative nitrate-N losses associated with regular free tile drainage (TD) and controlled tile drainage with optional subsurface irrigation (CDS). The simulations were compared to observations collected between 2000 and 2004 from both TD and CDS field experiments on a Perth clay loam soil at the Essex Region Conservation Authority demonstration farm, Holiday Beach, Ontario, Canada. There was good model-data agreement for crop yields, near-surface (0–30cm) soil water content and cumulative annual tile nitrate-N loss in both the calibration and validation years. For both TD and CDS, the CENTURY soil C/N model in DSSAT simulated water content and cumulative tile nitrate-N loss with normalized root mean square error (n-RMSE) values ranging from 9.9 to 14.8% and 17.8 to 25.2%, respectively. The CERES-Maize and CROPGRO-Soybean crop system models in the DSSAT simulated corn and soybean yields with n-RMSE values ranging from 4.3 to 14.0%. It was concluded that the DSSAT v4.5 model can be a useful tool for simulating near-surface soil water content, cumulative tile nitrate-N losses, and corn and soybean yields associated with CDS and TD water management systems. [Copyright &y& Elsevier]

Two tillage and two water table control treatments under continuous maize cropping were evaluated over a 3-year period (1992–1994) for their effects on evapotranspiration, surface runoff (SR), tile drainage (TD) and soil water content in the root-zone on a clay loam soil in southern Ontario. The tillage treatments included soil saver (SS, reduced tillage) and moldboard plow (MP, conventional tillage). The water table control treatments included controlled drainage-subirrigation (CDS) and regular tile drainage (DR). There was no significant difference (P<0.05) in evapotranspiration estimates between the SS and MP tillage treatments. The SS tillage increased SR compared with MP tillage during the non-cropping periods in 1993 and 1994, but not in 1992. Relative to MP, the SS tillage increased soil profile water content during the cropping period but decreased soil profile water content during the non-cropping period in 1992. The CDS treatment produced significantly higher (P<0.05) evapotranspiration and soil water content than the drainage treatment during the dry 1993 and 1994 years, but not during the wet 1992 year. The CDS treatment also had significantly lower (P<0.05) TD and higher SR than the drainage treatment. For all the treatments, over 65% of SR and TD occurred in the 5 month non-cropping period from November to March. Of the total annual water input (precipitation and/or subirrigation) to the field site, 8% was partitioned to SR, 30% was partitioned to TD, 55% was removed by crop and soil evapotranspiration and 7% was accounted for by changes in soil profile water content. [Copyright &y& Elsevier]