Canola Rotation Research Articles

Rotation and Cover Crop Effects on Soilborne Potato Diseases, Tuber Yield, and Soil Microbial Communities.

Seven different 2-year rotations, consisting of barley/clover, canola, green bean, millet/rapeseed, soybean, sweet corn, and potato, all followed by potato, were assessed over 10 years (1997-2006) in a long-term cropping system trial for their effects on the development of soilborne potato diseases, tuber yield, and soil microbial communities. These same rotations were also assessed with and without the addition of a fall cover crop of no-tilled winter rye (except for barley/clover, for which underseeded ryegrass was substituted for clover) over a 4-year period. Canola and rapeseed rotations consistently reduced the severity of Rhizoctonia canker, black scurf, and common scab (18 to 38% reduction), and canola rotations resulted in higher tuber yields than continuous potato or barley/clover (6.8 to 8.2% higher). Addition of the winter rye cover crop further reduced black scurf and common scab (average 12.5 and 7.2% reduction, respectively) across all rotations. The combined effect of a canola or rapeseed rotation and winter rye cover crop reduced disease severity by 35 to 41% for black scurf and 20 to 33% for common scab relative to continuous potato with no cover crop. Verticillium wilt became a prominent disease problem only after four full rotation cycles, with high disease levels in all plots; however, incidence was lowest in barley rotations. Barley/clover and rapeseed rotations resulted in the highest soil bacterial populations and microbial activity, and all rotations had distinct effects on soil microbial community characteristics. Addition of a cover crop also resulted in increases in bacterial populations and microbial activity and had significant effects on soil microbial characteristics, in addition to slightly improving tuber yield (4% increase). Thus, in addition to positive effects in reducing erosion and improving soil quality, effective crop rotations in conjunction with planting cover crops can provide improved control of soilborne diseases. However, this study also demonstrated limitations with 2-year rotations in general, because all rotations resulted in increasing levels of common scab and Verticillium wilt over time.

Biofuels agriculture: landscape‐scale trade‐offs between fuel, economics, carbon, energy, food, and fiber

AbstractFirst‐generation biofuels are an existing, scalable form of renewable energy of the type urgently required to mitigate climate change. In this study, we assessed the potential benefits, costs, and trade‐offs associated with biofuels agriculture to inform bioenergy policy. We assessed different climate change and carbon subsidy scenarios in an 11.9 million ha (5.48 million ha arable) region in southern Australia. We modeled the spatial distribution of agricultural production, full life‐cycle net greenhouse gas (GHG) emissions and net energy, and economic profitability for both food agriculture (wheat, legumes, sheep rotation) and biofuels agriculture (wheat, canola rotation for ethanol/biodiesel production). The costs, benefits, and trade‐offs associated with biofuels agriculture varied geographically, with climate change, and with the level of carbon subsidy. Below we describe the results in general and provide (in parentheses) illustrative results under historical mean climate and a carbon subsidy of A$20 t−1 CO2−e. Biofuels agriculture was more profitable over an extensive area (2.85 million ha) of the most productive arable land and produced large quantities of biofuels (1.7 GL yr−1). Biofuels agriculture substantially increased economic profit (145.8 million $A yr−1 or 30%), but had only a modest net GHG abatement (−2.57 million t CO2−e yr−1), and a negligible effect on net energy production (−0.11 PJ yr−1). However, food production was considerably reduced in terms of grain (−3.04 million t yr−1) and sheep meat (−1.89 million head yr−1). Wool fiber production was also substantially reduced (−23.19 kt yr−1). While biofuels agriculture can produce short‐term benefits, it also has costs, and the vulnerability of biofuels to climatic warming and drying renders it a myopic strategy. Nonetheless, in some areas the profitability of biofuels agriculture is robust to variation in climate and level of carbon subsidy and these areas may form part of a long‐term diversified mix of land‐use solutions to climate change if trade‐offs can be managed.

Long-term tillage, straw and N rate effects on quantity and quality of organic C and N in a Gray Luvisol soil

Long-term use of soil, crop and fertilizer management practices alters some soil properties, but the magnitude of change depends on soil type and climatic conditions. A field experiment with a barley (Hordeum vulgare L.)–wheat (Triticum aestivum L.)–canola (Brassica napus L.) rotation was conducted on a Gray Luvisol (Typic Cryoboralf) loam soil at Breton, Alberta, Canada. Effects of 19 or 27 years (from 1980 to 1998 or 2006 growing seasons) of tillage (zero tillage [ZT] and conventional tillage [CT]), straw management (straw removed [SRem] and straw retained [SRet]) and N fertilizer rate (0, 50 and 100 kg N ha−1 in SRet, and 0 kg N ha−1 in SRem plots) were determined on total organic C (TOC) and N (TON), light fraction organic C (LFOC) and N (LFON), macro organic matter C (MOM-C) and N (MOM-N), microbial biomass C (MB-C), and mineralizable C (Cmin) and N (Nmin) in the 0–7.5 and 7.5–15 cm or 0–5, 5–10 and 10–15 cm soil layers. Zero tillage and SRet tended to have higher, and N fertilizer treatment usually had higher mass of TOC, TON, LFOC, LFON, Cmin and Nmin in soil compared to the corresponding CT, SRem and zero-N control treatments, especially in the surface soil layers. Soil MB-C, MOM-C and MOM-N in soil generally tended to be higher with SRet than SRem, and also with N fertilizer than zero-N. There was no additional beneficial effect of ZT in increasing MB-C in soil. There were close and significant correlations among most soil organic C or N fractions, except for MB-C which did not correlate with MOM-N, and Nmin did not correlate with MOM-C. Linear regressions between crop residue C input and soil organic C or N were significant in most cases, except for MB-C and Nmin. Compared to the 1979 data, all treatments that did not receive N fertilizer (CTSRem0, CTSRet0, ZTSRem0 and ZTSRet0) showed a decrease in TOC concentration in the 0–15 cm soil layer over time, with the highest decrease in the CTSRem0 treatment. Straw retention and N fertilizer application at 50 and 100 kg N ha−1 under both ZT (ZTSRet50 and ZTSRet100) and CT (CTSRet50 and CTSRet100) resulted in a strongest increase in TOC during the first 11 years, and since then the TOC decreased under both N rates but 50 kg N ha−1 rate under CT (CTSRet50) showed the strongest negative effect on TOC in soil. In conclusion, elimination of tillage, straw retention and N application all improved organic C and N in soil, and generally differences were more pronounced for light fraction organic C and N, and between the most extreme treatments (CTSRem0 vs. ZTSRet100) for each dynamic organic fraction. This may be better for the long-term sustainability of soil quality and productivity.

Residue burning and tillage effects on diseases and yield of barley ( Hordeum vulgare) and canola ( Brassica napus)

Crop residue is often managed by tillage or burning in western Canada. This study was conducted to test the hypothesis that burning crop residues reduces the severity of barley ( Hordeum vulgare L.) and canola ( Brassica napus L.) diseases, and increases seed or grain yield or quality. Experiments were conducted at 2 sites, a Gray Luvisol (Typic Cryoboralf) and a Dark Gray Luvisol (Mollic Cryboralf) over 5 years in northeast Saskatchewan, Canada, with treatments of: zero (ZT) and conventional (CT) tillage, and burning (B) or no burning (NB) of previous crop residue. At each site, an experiment for barley and another for canola was established in a 2-year barley–canola rotation. Severity of leaf spotting diseases of barley, mainly net blotch [ Pyrenophora teres Drechsler], and incidence of sclerotinia stem rot [ Sclerotinia sclerotiorum (Lib.) de Bary] of canola were sometimes greater in the B treatment than the NB. Leaf spot severity of barley was usually slightly reduced under CT compared with ZT, but regardless of severity, barley yields were either similar, or more often higher under ZT than CT (337–766 kg ha −1 or 11–57%). There were occasionally effects of B on barley yield, but results were inconsistent and sometimes depended on tillage system. Canola yield tended to be greater under ZT than CT (141–233 kg ha −1 or 9–44%), but the effect of B was inconsistent. Tillage system had the greatest impact on crop yields with higher yield more often under ZT than CT, most likely as a result of improved soil moisture under the ZT system. We conclude that use of fire to manage diseases of barley and canola is ineffective.

Influence of six successive annual applications of sulphur fertilizers on wheat in a wheat–canola rotation on a sulphur deficient soil

A 9-yr (1999–2007) field experiment was conducted on a S-deficient Gray Luvisol (Typic Cryoboralf) loam soil at Porcupine Plain in northeastern Saskatchewan. The objective was to compare the influence of six successive annual applications (1999–2004) and the following residual effects for 3 yr (2005–2007) of elemental S and sulphate-S fertilizers on yield, seed protein and total S concentration, and S uptake of wheat (Triticum aestivum L.) in a wheat–canola rotation. Treatments used were combinations of two application times (preceding autumn and before seeding in spring) with two granular elemental S fertilizers (ES-90 and ES-95), one fertilizer containing both elemental S and sulphate-S (Agrium Plus), ammonium sulphate, and a zero-S control. The S fertilizers were applied annually at a rate of 15 kg S ha–1. From 1999 to 2004, seed yield (3 yr) and straw yield (4 yr), seed protein concentration (3 yr), total S concentration in seed (4 yr), and S uptake in seed (5 yr) and straw (5 yr) of wheat showed significant response to S fertilization. In the first year (1999), ammonium sulphate and Agrium Plus were more effective than ES-90 and ES-95. In the following years (2000–2004), there was no significant effect of S source on seed and straw yield. Sulphate-S containing fertilizers produced greater total S concentration in seed and S uptake in straw (3 yr) and for S uptake in seed (1 yr). There was no effect of timing of S application on seed yield and protein concentration in any year, but autumn application was superior to spring application for straw yield and S uptake (1 yr), and for seed total S concentration and S uptake (2 yr). Residual effects of six previous S applications showed improvement in wheat seed yield until 2006, and straw yield and total S uptake until 2007. Elemental S, especially when applied in autumn, tended to have more lasting residual effects than the other S fertilizer treatments. There was some build-up of residual sulphate-S in soil in almost all S fertilizer treatments after four successive applications, but this was generally higher with sulphate-S-containing fertilizers. Recovery of applied S from 1999 to 2004 in plants was usually higher with sulphate-S fertilizer than with elemental S fertilizer in most years. Recovery of applied S in soil was higher for sulphate-S fertilizers, followed by ES-90, and finally ES-95. Residual nitrate-N in soil was significantly lower in spring-applied ammonium sulphate treatment than the zero-S or other S treatments. Key words: Elemental S, fertilizer, protein concentration, S uptake, sulphate-S, wheat, yield

Soil microbial biomass, functional diversity and enzyme activity in glyphosate-resistant wheat–canola rotations under low-disturbance direct seeding and conventional tillage

As glyphosate-resistant (GR) crops are becoming common in agro-ecosystems, their effects on non-target soil organisms need to be monitored. We evaluated soil microbial biomass C (MBC), bacterial functional diversity and community structure, and dehydrogenase enzyme activity in a field experiment conducted at six sites on the Canadian prairies. Treatments consisted of a factorial arrangement of three GR wheat and GR canola crop frequencies and two tillage systems. GR crop frequencies were arranged in 4-yr wheat-canola-wheat-pea rotations, with GR wheat and GR canola in zero of four, two of four, or three of four possible GR crop frequencies. The two tillage systems were either low soil-disturbance direct-seeding (LDS) or conventional tillage (CT). MBC increased with increasing frequency of GR crops in two of 20 site-years in the rhizosphere, and had no effects in bulk soil. Depending on tillage, GR crop frequency also affected the functional diversity of rhizosphere soil bacteria in only two of 20 site-years, and had no effects in bulk soil. Shifts in the structures of bacterial communities related to GR crop frequency were detected, but they were few and inconsistent. In three of 22 cases (10 in rhizosphere+12 in bulk soil), the activity of dehydrogenase enzyme decreased with increasing frequency GR crops in both the rhizosphere and bulk soil. In five of 20 site-years, soil MBC in the rhizosphere was greater under CT than under LDS, regardless of GR crop frequency. In bulk soil, tillage affected soil MBC in five site-years, three of which had greater MBC under CT than LDS, and vice versa in the other two. Tillage affected the functional diversity of soil bacteria in the rhizosphere in three site-years, but the effects were not consistent. Similar inconsistent tillage-related patterns were observed in the community structures of bacteria. There were no tillage effects on bacterial diversity in bulk soil. Dehydrogenase enzyme activity was greater under LDS than under CT in three of four cases in which tillage had significant effects. Overall, GR crop frequency effects on soil microorganisms were minor and inconsistent over a wide range of growing conditions and crop management.

Small grains stubble burning and tillage effects on soil organic C and N, and aggregation in northeastern Saskatchewan

Field experiments were conducted over 5 years (2000–2004) at two sites (Star City and Birch Hills) in the Saskatchewan Parkland region to determine the effects of tillage and crop residue burning on soil total organic C (TOC), total organic N (TON), light fraction organic matter (LFOM), light fraction organic C (LFOC), light fraction organic N (LFON) and dry aggregation. Two tillage (ZT, zero tillage; CT, conventional tillage, with one tillage in autumn and another in spring) and two burning (B, residue burnt in autumn; NB, residue not burnt and returned to the soil) treatments were combined in a barley ( Hordeum vulgare L.)–canola ( Brassica napus L.) rotation. After five crop seasons, the mass of TOC and TON in the 0–15 cm soil tended to be greater, whereas mass of LFOM, LFOC and LFON was significantly greater in NB than B treatments at both sites. Zero tillage resulted in greater TOC, TON, LFOM, LFOC and LFON in soil than CT, in both B and NB treatments. The mass of TOC, TON, LFOM, LFOC and LFON in soil was the highest in the ZT–NB treatment, and lowest in the CT–B treatment. Zero tillage had a lower proportion of fine aggregates (<0.83 mm diameter) and a greater proportion of large aggregates (>6.4 mm diameter) at both sites, but the mean weight diameter (MWD) was greater under ZT than CT only at Birch Hills. Although the tillage × burning interaction was not significant in most cases, the ZT–NB treatment usually had the lowest proportion (22.6%) of fine aggregates and the greatest proportion (47.1%) of large aggregates, compared to the highest (34.9%) and the lowest proportion (35.6%) of these aggregates, respectively, in CT–B treatment. This indicated reduced potential for wind erosion when tillage was omitted (ZT) and crop residues were returned to the soil (NB). Returning crop residue to soil rather than burning usually increased soil organic C and N, and aggregation, but the differences between treatments were of greater magnitude between tillage treatments (ZT versus CT) than between burning treatments (B versus NB). Overall, returning crop residues along with ZT improved soil organic C and N, and aggregation, while burning in combination with CT resulted in the deterioration of these soil properties.

Rotation length, canola variety and herbicide resistance system affect weed populations and yield

A 4-year study was initiated in 1997 to provide canola producers with information on the consequences of various rotational intervals with the use of new disease and herbicide-resistant canola varieties. The study was conducted at three locations in Alberta, Canada (Ellerslie, Strathmore, and Warburg). At each location, four canola rotations were established: continuous canola, and canola seeded in 1 of 2, 3, or 4 years. Canola varieties included the conventional varieties ‘AC Excel’ and ‘Quantum’, the glyphosate-resistant variety ‘Quest’, imidazolinone-resistant ‘45A71’, and a glufosinate-resistant hybrid, ‘Invigor 2153’. In the fourth year of the study, when canola was grown in all treatments, weed densities, weed species diversity, and evenness were determined preseeding and before and after in-crop herbicide application. Canola yield was greatest in the northern ecoregions of the Boreal Transition (Warburg) and Aspen Parkland (Ellerslie), and lowest in the Moist Mixed Grassland ecoregion (Strathmore). Weed populations increased and population diversity decreased and became less even where rotations were less diverse; in continuous canola and in the 1-in-4–year rotation. As expected, weed densities increased in poorly competitive, conventional canola varieties compared to herbicide-resistant varieties sprayed with their broader-spectrum herbicides. Where weed densities were high, variety/herbicide system became a critical factor affecting crop yield. Under these conditions, the herbicide-resistant varieties ‘Quest’ and ‘Invigor 2153’ typically outyielded the conventional varieties of ‘AC Excel’ and ‘Quantum’. Canola yield was highest when grown in a 1-in-3– or a 1-in-4–year rotation, although the 1-in-3–year rotation generally had lower weed densities, and allowed high-value canola to be grown more frequently in rotation.

Combining agronomic practices and herbicides improves weed management in wheat–canola rotations within zero-tillage production systems

Development of more comprehensive and cost-effective integrated weed management systems is required to facilitate greater integrated weed management adoption by farmers. A field experiment was conducted at two locations to determine the combined effects of seed date (April or May), seed rate (recommended or 150% of recommended), fertilizer timing (applied in fall or spring), and in-crop herbicide dose (50% or 100% of recommended) on weed growth and crop yield. This factorial set of treatments was applied in four consecutive years within a spring wheat–spring canola–spring wheat–spring canola rotation in a zero-till production system. Both wheat and canola phases of the rotation were grown each year. Weed biomass was often lower with May than with April seeding because more weeds were controlled with preplant glyphosate. However, despite fewer weeds being present with May seeding, wheat yield was only greater in 1 of 7 site-years, and canola yield was never greater with May compared with April seeding. Higher crop seed rates had a consistently positive effect on reducing weed growth and the weed seedbank. Crop yield was sometimes greater, and never lower, with higher seed rates. Fertilizer timing did not have a large effect on crop yield, but applying N in the spring compared with fall was less favorable for weeds as indicated by lower weed biomass and a 20% decrease in the weed seedbank. In-crop herbicides applied at 50% compared with 100% doses often resulted in similar weed biomass and crop yield, especially when higher crop seed rates were used. Indeed, the weed seedbank at the conclusion of the 4-yr experiment was not greater with the 50% compared with 100% herbicide dose at one of two locations. This study demonstrates the combined merits of early seeding (April), higher crop seed rates, and spring-applied fertilizer in conjunction with timely but limited herbicide use to manage weeds and maintain high crop yields in rotations containing wheat and canola.

Crop Seeding Rate Influences the Performance of Variable Herbicide Rates in a Canola–Barley–Canola Rotation

Glyphosate-resistant canola was seeded at Vegreville, Alberta, in 1997 and 1999 and barley in rotation with the canola in 1998 at three seeding rates. The effects, at each crop seeding rate, of variable glyphosate (canola) and tralkoxydim plus bromoxynil plus MCPA (barley) rates on crop yield, net economic return and seed production by wild oat, wild mustard, and wild buckwheat, and the amount of weed seed in the soil seed bank was determined. Crop seeding rate influenced the response of canola and barley yield and weed seed production to herbicide rate. At the lowest crop seeding rates, yield responses tended to be parabolic with yields increasing up to one-half and three-quarters of the recommended herbicide rates and trends toward reduced yields at the full rates. This response was not evident at the higher crop seeding rates, where, in most cases the yield reached a maximum between one-half and the full recommended rate. The effects of the herbicides on weed seed production, especially at the lowest rate, were often superior at the higher crop seeding rates. The results indicate that seeding canola and barley at relatively high rates may reduce risk associated with lower crop yields and increased weed seed production at lower than recommended herbicide rates. However, the current cost of herbicide-resistant canola seed may preclude the adoption of this integrated weed management practice by growers.

Water use and root growth by annual and perennial pastures and subsequent crops in a phase rotation

Perennial pastures and trees have been proposed as a means of increasing water use, reducing groundwater recharge, and therefore reducing the spread of secondary salinity in southern Australia. This paper investigates comparative water use throughout a 5-year rotation involving 3 years of pasture (either annual subterranean clover ( Trifolium subterraneum L.) or perennial lucerne ( Medicago sativa L.)) followed by wheat ( Triticum aestivum L.) and then by canola ( Brassica napus L.). Within the pasture phase, lucerne reduced soil water content during summer and autumn by approximately 60 mm more than the annual pasture. Lucerne in its second year produced 1.7 times more root biomass than the annual pasture, and also grew roots deeper into the soil. Wheat after lucerne produced 15 t ha −1 dry matter compared with 8 t ha −1 for wheat after clover, but grain yields were similar due to a combination of frost damage and water stress. There was a small difference in canola dry matter production, but no differences in canola grain yield or 1000-grain weight in the second year after pasture. Canola root distributions were similar on the two blocks. Average annual water leakage was 45 mm for the annual pasture–wheat–canola rotation and 17 mm for the lucerne pasture–wheat–canola rotation. Wheat after lucerne extracted 20 mm more water from the ‘B’ horizon than wheat after clover, and this extended the period of protection against water leakage. Water leakage under the lucerne block commenced before the dry soil buffer was completely refilled, indicating the possibility of bypass flow.