21. Can nitrogen fertiliser and nitrification inhibitor management influence N2O losses from high rainfall cropping systems in South Eastern Australia?

• Authors:
  • Partington, D. L.
  • Phelan, A. J.
  • Zollinger, R. P.
  • Fogarty, K. M.
  • Armstrong, R. D.
  • Hill, P. A.
  • Officer, S. J.
  • Harris, R. H.
• Source: Nutrient Cycling in Agroecosystems
• Volume: 95
• Issue: 2
• Year: 2013
• Summary: Nitrous oxide (N2O) is a potent greenhouse gas released from high rainfall cropping soils, but the role of management in its abatement remains unclear in these environments. To quantify the relative influence of management, nitrogen (N) fertiliser and soil nitrification inhibitor was applied to separate but paired raised bed and conventionally flat field experiments in south west Victoria, to measure emissions and income from wheat and canola planted 2 and 3 years after conversion from a long-term pasture. Management included four different rates of N fertiliser, top-dressed with and without the nitrification inhibitor Dicyandiamide (DCD), which was applied in solution to the soil in the second year of experimentation. Crop biomass, grain yield, soil mineral N, soil temperature and soil water and N2O flux were measured. Static chamber methodology was used to identify relative differences in N2O loss between management. In the second crop (wheat) following conversion, N2O losses were up to 72 % lower (P < 0.05) in the furrows, receiving the lower rate of N fertiliser compared with the highest rate, with less frequent reductions observed in the third crop (canola); losses of N2O from the beds was unaffected by N rate, perhaps from nitrate leakage into the adjacent furrow of the raised bed experiment. On the nearby flat experiment, nitrate leaching may have diminished the effects of N rate and DCD on N2O flux. Furthermore the extra N did not significantly increase grain yield in either the wheat or canola crops on both experiments. The application of DCD in the canola crop temporarily reduced (P < 0.05) N2O production by up to 84 % from the beds, 83 % in the adjacent furrows and 75 % on the flat experiment. Grain yield was not significantly (P < 0.001) affected however, canola income was reduced by $1407/ha and $1252/ha, compared with no addition of inhibitor on the respective bed and flat experiments. Although N2O fluxes are driven by environmental episodic events, management will play a role in N2O abatement. However, DCD currently appears economically unfeasible and matching N fertiliser supply to meet crop demand appears a better option for minimising N2O losses from high rainfall cropping systems.

22. Root:shoot ratios and belowground biomass distribution for Pacific Northwest dryland crops

• Authors:
  • Albrecht, S. L.
  • Douglas, C. L., Jr.
  • Reardon, C. L.
  • McCool, D. K.
  • Williams, J. D.
  • Rickman, R. W.
• Source: Journal of Soil and Water Conservation
• Volume: 68
• Issue: 5
• Year: 2013
• Summary: Roots, cereal crowns, and stems growing beneath the soil surface provide important resistance to soil erosion. Understanding the amount and distribution of this material in the soil profile could provide insight into resistance to soil erosion by water and improve the performance of soil erosion models, such as the revised universal soil loss equation (RUSLE) and the water erosion prediction project (WEPP). Erosion models use built-in or external crop growth models to populate crop yield and live aboveground and associated belowground biomass databases. We examined two data sets from the dryland small grain production region in the Pacific Northwest of the United States to determine root:shoot ratios, the vertical distribution of root and attached belowground biomass, and incorporated residue from previously grown crops. Data were collected in 1993, 1994, 1995, and 2000 from short-term no-till and conventional tillage experiments conducted near Pendleton, Oregon, and Pullman,Washington, and in 1999 and 2000 from long-term experiments representative of farming practices near Pendleton, Oregon. The crops sampled in the short-term data set included soft white winter and spring wheat (Triticum aestivum L.;WW and SW, respectively), spring peas (Pisum sativum L.; SP), and winter canola (Brassica napus L.;WC). Crops sampled in the long-term study included WW SW, and SP. Data were collected at harvest in both data sets and during three phenologic stages in each of the crops in the short-term data set. Soil samples were collected to a depth of 60 cm (23.6 in) in the short-term and 30 cm (11.9 in) in the long-term experiments. In both sets of measurements, we found greater than 70% of root mass is in the top 10 cm (3.9 in) of the soil profile with the exception of SP, which had 70% of root mass in the top 15 cm (5.9 in) of the soil profile.WC produced significantly more biomass near the soil surface than WW SW, or SP Root-to-shoot biomass ratios, in mature wheat ranged from 0.13 to 0.17 in the top 30 cm (11.9 in) of the soil profile, substantially lower than values suggested for use in WEPP (0.25). In the long-term experiments, soil of the conventionally tilled continuous winter wheat (CWW) plots contained significantly greater biomass than soil of conventionally tilled winter wheat/fallow (CR) and no-till winter wheat/fallow (NT) treatments. There was no significant difference between CWW and conventionally tilled winter wheat/spring pea (WP); however, CWW returned more residue to the soil than WP because SP produced less residue and these residues were incorporated with a field cultivator rather than a moldboard plow. More accurate representation of root development, particularly in winter crops, could improve RUSLE and WEPP performance in the Pacific Northwest where winter conditions have proven difficult to model.

23. Limited potential for soil carbon accumulation using current cropping practices in Victoria, Australia

• Authors:
  • Robertson, F.
  • Nash, D.
• Source: Agriculture, Ecosystems & Environment
• Volume: 165
• Year: 2013
• Summary: The extent to which soil C storage can be increased in Australian agricultural soils by adoption of improved management practices is poorly understood. There is a pressing need for such information in order to evaluate the potential for soil C sequestration to offset greenhouse gas emissions. In this study we used the RothC model to assess whether soil C accumulation under cropping using stubble retention and pasture rotations could be a significant offset for greenhouse gas emissions. We chose eight regions to represent the climatic range of the Victorian cropping industry: Walpeup, Birchip, Horsham, Bendigo, Rutherglen, Lismore, Bairnsdale and Hamilton (annual rainfall 330-700 mm). For each region, we chose two representative soil types, varying in clay and total organic C contents. For each region x soil combination, we compared the effects of five rotations: Canola-wheat-pulse-barley (C-W-P-B); Canola-wheat-triticale (C-W-T); Canola-wheat-barley-5 year perennial pasture (C-W-B-Pt5); Canola-wheat-fallow (C-W-F) and Continuous pasture (Pt). We compared the cropping rotations with cereal stubble burnt and with cereal stubble retained and, for two regions, with cereal stubble grazed by sheep. The results of the simulations showed that, across all scenarios, the equilibrium C density varied between 19 and 135 t C/ha to 300 mm depth, with potential soil C change being strongly influenced by crop yield, crop rotation, climate, initial soil C content, stubble management and continuity of management The simulations suggested that soil C stocks could be increased under a crop-pasture rotation (C-W-B-Pt5) with stubble retention, with rates of increase of 0.3-0.9 t C/ha yr over 25 years. If all of Victoria's cropland were converted to C-W-B-Pt5 rotation with stubble retention, and if 50% of the modelled potential C change were achieved, this would represent 3.0-4.5 MtCO(2)-e/year, equivalent to 2.5-3.7% of Victoria's greenhouse emissions. Less C accumulation would be possible under continuous cropping with stubble retention; even using the most conservative rotation (C-W-T) rates of C change varied from loss of 0.3 t C/ha yr to accumulation of 0.5 t C/ha yr over 25 years. If all of Victoria's cropland were converted to C-W-T rotation with stubble retention, and if 50% of the modelled potential C change were achieved, this would be equivalent to 0.8-2.3 MtCO(2)-e/year, or 0.7-1.9% of Victoria's greenhouse emissions. It would generally take 10-25 years for the soil C changes to become measurable using conventional soil sampling and analytical methods. Thus we conclude that, with current technology, the potential for significant and verifiable soil C accumulation in Victoria's croplands is limited.

24. Net CO2 exchange and carbon budgets of a three-year crop rotation following conversion of perennial lands to annual cropping in Manitoba, Canada

• Authors:
  • Fraser, T. J.
  • Amiro, B. D.
  • Taylor, A. M.
• Source: Agricultural and Forest Meteorology
• Volume: 182-183
• Year: 2013
• Summary: Eddy covariance flux towers were used to measure net ecosystem production over three adjacent agricultural fields in Manitoba, Canada, from 2009 to 2011. Two fields were converted from long-term perennial hay/pasture to annual cropping, while the third field served as a control field that was maintained as hay/pasture. One converted field had a rotation of oat-canola-oat crops, while the second was hay-oat-fallow. Weather was an important driver of inter-annual variability, with poor yields on all fields in 2011 because of dry conditions in summer, with the summer-fallow condition on one field caused by excess spring moisture not allowing planting. The cumulative net ecosystem production of the oat-canola-oat field showed a net CO2 emission of 100 g Cm-2, the hay-oat-fallow field emitted 500 g Cm-2, and the hay field gained 550 g C m(-2) by the end of the 30-month study period. The hay field had the highest cumulative gross primary production of 2500 g C m(-2), whereas the oat-canola-oat and hay-oat-fallow fields had only about 1400 g C m(-2). The perennial field had the advantage of both early- and late-season growth when crops were absent on the other fields. The hay and hay-oat-fallow fields had comparable cumulative ecosystem respiration (1400 g Cm-2). Manure additions contributed 300 g C m(-2) on the two converted fields. With harvest exports and manure additions included, the oat-canola-oat field was a carbon source of 240 g Cm-2, the hay-oat-fallow field was a source of 415 g C m(-2), and the hay/pasture field was a sink of 120 g C m(-2) over the 30-month period.

25. Twenty-five years of changes in soil cover on Canadian Chernozemic (Mollisol) soils, and the impact on the risk of soil degradation.

• Authors:
  • Huffman, T.
  • Coote, D. R.
  • Green, M.
• Source: Canadian Journal of Soil Science
• Volume: 92
• Issue: 3
• Year: 2012
• Summary: Agricultural soils that are covered by vegetation or crop residue are less susceptible to degradation by wind and water erosion, organic matter depletion, structural degradation and declining fertility. In general, perennial crops, higher yields, reduced tillage and continuous cropping provide more soil cover than annual crops, lower yields, intensive tillage, residue harvesting and fallowing. This study presents a model for estimating the number of days in a year that the soil surface is protected and demonstrates its application on the Canadian prairies over the period from 1981 to 2006. Over the 25-yr study period, the average soil cover on Canadian prairie soils increased by 4.8% overall. The improvement came primarily as a result of widespread adoption of no-till and a decline in the use of summerfallow, but the gains were offset to a great deal by a shift from higher-cover crops such as wheat, oats and barley to more profitable but lower-cover crops such as canola, soybeans and potatoes. The implication of these trends is that, even though protection of prairie agricultural soils has improved over the past 25 yr, soil cover could decline dramatically over the next several decades if crop changes continue, the adoption of conservation tillage reaches a peak and residue harvesting for biofuels becomes more common.

26. Twenty-five years of changes in soil cover on Canadian Chernozemic (Mollisol) soils, and the impact on the risk of soil degradation.

• Authors:
  • Huffman, T.
  • Green, M.
  • Coote, D.
• Source: Canadian Journal of Soil Science
• Volume: 92
• Issue: 3
• Year: 2012
• Summary: Agricultural soils that are covered by vegetation or crop residue are less susceptible to degradation by wind and water erosion, organic matter depletion, structural degradation and declining fertility. In general, perennial crops, higher yields, reduced tillage and continuous cropping provide more soil cover than annual crops, lower yields, intensive tillage, residue harvesting and fallowing. This study presents a model for estimating the number of days in a year that the soil surface is protected and demonstrates its application on the Canadian prairies over the period from 1981 to 2006. Over the 25-yr study period, the average soil cover on Canadian prairie soils increased by 4.8% overall. The improvement came primarily as a result of widespread adoption of no-till and a decline in the use of summerfallow, but the gains were offset to a great deal by a shift from higher-cover crops such as wheat, oats and barley to more profitable but lower-cover crops such as canola, soybeans and potatoes. The implication of these trends is that, even though protection of prairie agricultural soils has improved over the past 25 yr, soil cover could decline dramatically over the next several decades if crop changes continue, the adoption of conservation tillage reaches a peak and residue harvesting for biofuels becomes more common.

27. Effect of planting methods on spring canola ( Brassica napus L.) establishment and yield in the low-rainfall region of the Pacific Northwest.

• Authors:
  • Alldredge, J. R.
  • Long, D. S.
  • Young, F. L.
• Source: Crop Management
• Issue: March
• Year: 2012
• Summary: Growers are becoming interested in producing canola ( Brassica napus or B. rapa) in the dryland, wheat-fallow region of the Pacific Northwest. Currently, agronomic research for spring canola in this region has not been initiated. This study evaluated the effect of no-till planting methods on stand establishment, crop yield, and seed oil quantity of spring canola in Washington and Oregon in 2009 and 2010. The treatments included: double disk opener; broadcast; broadcast plus rolled; Kile opener; Cross-Slot opener; and hoe opener (at Washington only). In this study, canola establishment was generally greatest with the double disk opener and least in the broadcast or broadcast plus rolled treatments at all four site-years. Yield was least in the broadcast treatment and rolling broadcast seed increased yield only 50% of the time. In three out of four site-years, canola planted with the various no-till openers yielded higher than broadcast seed. The adoption of spring canola in the wheat-fallow region of the Pacific Northwest would improve pest management strategies, diversify markets, and increase sustainability.

28. Ground beetle (Coleoptera: Carabidae) diversity, activity density, and community structure in a diversified agroecosystem.

• Authors:
  • O'Donovan, J.
  • Harker, K.
  • Clayton, G.
  • Dosdall, L.
  • Hummel, J.
• Source: Environmental Entomology
• Volume: 41
• Issue: 1
• Year: 2012
• Summary: Diversity and abundance of ground beetles (Coleoptera: Carabidae) can be enhanced in vegetable and field intercropping systems, but the complexity of polycultures precludes the application of generalized assumptions of effects for novel intercropping combinations. In a field experiment conducted at Lacombe and Ellerslie, Alberta, Canada, in 2005 and 2006, we investigated the effects of intercropping canola ( Brassica napus L.) with wheat ( Triticum aestivum L.) on the diversity and community structure of carabid beetles, and on the activity density responses of individual carabid species. Shannon-Wiener diversity index scores and species evenness increased significantly as the proportion of wheat comprising total crop plant populations increased in one site-year of the study, indicating a positive response to enhanced crop plant species evenness in the intercrops, and in that same site-year, ground beetle communities in intercrops shifted to more closely approximate those in wheat monocultures as the percentage of wheat in the intercrops increased. Individual carabid species activity densities showed differing responses to intercropping, although activity densities of some potential root maggot ( Delia spp.) (Diptera: Anthomyiidae) predators were greater in intercrops with high proportions of wheat than in canola monocultures. The activity density of Pterostichus melanarius (Illiger), the most abundant species collected, tended to be greater in canola monocultures than high-wheat intercrops or wheat monocultures. We conclude that intercrops of canola and wheat have the potential to enhance populations of some carabid species, therefore possibly exerting increased pressure on some canola insect pests.

29. Yield and weed suppression of crop mixtures in organic and conventional systems of the western Canadian Prairie.

• Authors:
  • Quideau, S.
  • Pswarayi, A.
  • Nelson, A. G.
  • Frick, B.
  • Spaner, D.
• Source: Agronomy Journal
• Volume: 104
• Issue: 3
• Year: 2012
• Summary: To investigate intercropping as a management strategy to increase crop productivity and weed suppression in organic systems, spring wheat ( Triticum aestivum L.), barley ( Hordeum vulgare L.), canola ( Brassica napus L.) and field pea ( Pisum sativum L.) monocultures were compared with two-, three-, and four-crop intercrops containing wheat at two organic and one conventional site in 2006 and 2007, central Alberta, Canada. We measured crop and weed biomass, grain yield, and crop competitiveness against weeds from a replacement design in a completely randomized block experiment. Pea and canola monocrops on organic sites yielded the least of all crop treatments. Conventional crop treatments generally yielded higher than organic treatments. Few land equivalent ratios (LERs) on organic sites were significantly >1.0. Some wheat intercrops without barley showed overyielding (LER >1.0) potential. Most of the significant LERs were from three- and four-crop intercrops. More than 50% of the intercrops on organic sites significantly suppressed weeds (based on relative weed biomass) and most of these intercrops had barley in the mixture. Barley as a sole crop and in intercrops suppressed weeds better than all other intercrops and sole crops. The wheat-canola intercrop exhibited the best weed suppression of the two-crop intercrops on organic and conventional sites. The crop densities used in this study may have contributed to the extremely low pea and canola monocrop yields as well as low LERs. Due to this, our findings should be regarded as showing trends and potential from intercrops only. We therefore recommend further studies to establish ideal densities for the intercrops used.

30. Nitrous oxide emissions in response to ESN and urea, herbicide management and canola cultivar in a no-till cropping system.

• Authors:
  • O'Donovan, J. T.
  • Blackshaw, R. E.
  • Hao, X. Y.
  • Li. C. L.
  • Harker, K. N.
  • Clayton, G. W.
• Source: Soil & Tillage Research
• Volume: 118
• Year: 2012
• Summary: Environmentally Smart Nitrogen (ESN), a type of polymer-coated urea, synchronizes N release with crop demand to increase N use efficiency and potentially reduce N 2O emissions. This study investigated the effects of ESN and weed management on N 2O emissions from soil under a canola ( Brassica napus L.) no-till cropping system. The experiment was conducted from 2005 to 2008 at three sites: Lethbridge, Lacombe, and Beaverlodge, located in southern, central and northern Alberta, Canada. Treatments included a hybrid and an open-pollinated canola cultivar, with ESN and urea applied at 1 and 1.5 times (*) the recommended rate, and herbicide at 50 and 100% of registered in-crop application rates. Canola was grown in rotation with barley ( Hordeum vulgare L.) and both phases of crop rotation were present each year. The N 2O fluxes from soil were measured using vented static chambers at 2-week intervals during the growing season from 2006 to 2008. Except for a few occasions with higher fluxes from urea than ESN earlier in the growing season and higher fluxes from ESN than urea later on, N 2O fluxes were similar among all treatments for all three years and three sites. The N 2O fluxes also varied over the growing season, and peak flux occurred in response to rainfall events. Similarly, cumulative N 2O emissions, expressed as either per land area or per canola seed yield, over the three growing seasons were low (0.15-2.97 kg N ha -1 yr -1 or 0.05-1.19 g N kg -1 seed) for all treatments and sites, and unaffected by weed management or crop variety ( P>0.05). The N 2O emission across the three sites from ESN averaged 20% lower ( P=0.040) than from urea although the differences between fertilizer types or application rates were not significant ( P>0.05) at each site. Elevated N 2O emissions (72% higher; P=0.028) from 1.5 * ESN (0.83 kg N ha -1 yr -1 or 0.33 g N kg -1 seed) relative to 1 * ESN (0.26 kg N ha -1 yr -1 or 0.16 g N kg -1 seed) were only observed at Beaverlodge while emissions were similar ( P>0.05) at the other two sites. The higher N 2O emissions at 1.5 * ESN at Beaverlodge were due to excess N accumulation in soil caused by unfavourable weather conditions that reduced canola N uptake and yield. Our results suggest that ESN fertilizer could reduce N 2O emissions in Alberta, Canada, but reductions will depend on rainfall events and canola N utilization.