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Strategies For Boosting Yields Of Brassica And Grain Legumes Under Direct Seed Systems
George W. Clayton1*, K. Neil Harker1, John T. O'Donovan2, Newton Z. Lupwayi2, T. Kelly Turkington1, Yoong K. Soon2, Guy.P. Lafond3, Cynthia Grant4, Adrian Johnston5, Robert E. Blackshaw6, and Wendell A. Rice2

1Lacombe Research Centre, 6000 C&E Trail, Lacombe, Alberta, T4L 1W1
2Beaverlodge Research Farm, Beaverlodge, Alberta
3Indian Head Experimental Farm, Indian Head, Saskatchewan
4Brandon Research Centre, Brandon, Manitoba
5PPIC, Saskatoon, Saskatchewan,
6Lethbridge Research Centre, Lethbridge, Alberta
*Corresponding author: claytong@em.agr.ca

Abbreviations: CT, conventional tillage; NT, no tillage; ZT, zero tillage.

INTRODUCTION

Integrated crop management (ICM) must have a broad focus and combine the integrated weed management (IWM) or integrated pest management (IPM) systems with all other principles and practices of crop production that influence the ecosystem. Competitive crop stands, inoculant technology for grain legumes, seeding dates, increased diversity, tillage and rotation all combine to increase crop health and soil health. The presentation will include data supporting the effects of tillage and rotation in cropping systems, time of weed removal, pyramiding technologies.

TILLAGE, ROTATIONS AND SUSTAINABILITY

Does microbial diversity increase under direct seeding and legume-based cropping systems?

Soil micro-organisms are the least understood components of soil by both agronomists and the soil practitioners on the farm. Many soil organisms provide benefits to crops growing in an ecosystem that are not well understood, except that they contribute to soil health. Soil organisms are also responsible for a large number of deleterious effects on crop growth within the cropping system. Tillage systems and previous crops play an important role in the sustainability of soil health. Conventional tillage significantly reduced the diversity of bacteria by reducing both substrate richness and evenness of the microbial community in a study in the Peace River region. The influence of tillage on microbial diversity was more prominent at flag-leaf stage than at planting time, and more prominent in bulk soil than in the rhizosphere at flag-leaf stage. Microbial diversity was significantly higher under wheat preceded by red clover green manure or field peas than under wheat following wheat (continuous wheat) or summer fallow. The substrate utilization patterns of the bacterial communities also revealed that the bacterial community assemblages under conventional tillage had more similar structure than those under zero tillage. In addition, more carbon was sequestered under zero tillage than conventional tillage and legume-based rotations increased both the diversity and the carbon sequestered under CT. These results indicate that conservation tillage and legume-based crop rotations support diversity of soil microbial communities and may impact the sustainability of agricultural ecosystems.

Although more detailed knowledge of functional relationships among micro-organisms is required to establish the effects of diversity on ecosystem functioning and stability, it is probably safer to adopt agricultural practices that preserve or restore microbial functional diversity than to adopt practices that diminish this component of total diversity.

Is nutrient cycling affected by tillage and rotation?

Tillage and rotation also affected the mineralization of N in the cropping system throughout the life of the study. Nitrogen uptake by wheat at maturity was increased by NT and legume crops. At seeding CT plots had 28 kg ha-1 more soil nitrate-N to 100-cm depth, and was more dependent on this stored nitrate for wheat growth, than NT plots. No-tilled wheat depended more on N mineralized during the growing season. Growing season apparent net N mineralization was 71 and 22 kg N ha-1, respectively, for the NT and CT systems. Previous crop effect on net N mineralization was red clover> field pea> wheat. Approximately 18 kg N ha-1 was net mineralized from red clover residues compared to insignificant amounts from pea and wheat residues. Microbial biomass turnover's contribution to net N mineralization (28 to 40 kg N ha-1) was greater under NT and previous legume crop treatments. Soluble organic N decreased by 7 kg ha-1 between seeding and maturity, and was unaffected by tillage or previous crop. Mass balance indicated that more N was lost from CT than NT systems.

For the current study, N fertilizer recommendations were based on soil nitrate in autumn samples without regard to tillage practices. This study suggests that tillage practices must be reckoned with as growing season mineralization and crop utilization of soil N under NT were considerably greater than those under a CT system. Conversely, N mineralization between autumn and spring appeared to be greater under CT.

Is Disease Management of Crops Affected by Tillage and Rotation?

Direct seeding crop management practices reduced the level of disease compared to conventional tillage crop management practices. With legumes in rotation and using zero tillage the level of common root rot (CRR) in the first crop of wheat was reduced by approximately 30%compared to continuous wheat. Wheat yields for rotations with field pea, red clover or fallow were similar and were higher than those observed under continuous wheat. Cook and Veseth (1991) have suggested "antagonism of root pathogens in soil and around roots can be maximized by the same practices that favor the conservation or elevation of the organic matter content of the soil." Rotations that include pulse crops, especially under conservation tillage may be a method of accomplishing this. Growing pulse crops and their subsequent impact on soil quality may favour increased population levels of various soil organisms and enhance their diversity and activity. These soil organisms may then colonize crop residues before pathogens or displace pathogens from infested residues. In addition, these organisms may produce a variety of substances or actively antagonize or parasitize soil-borne plant pathogens. Ultimately, these activities would have the effect of reducing survival and inoculum production by pathogens present in the soil environment. The Fort Vermilion crop management study demonstrated increased soil microbial diversity in rotations with field pea or red clover compared with continuous wheat or the fallow rotation and may well correllate with the reduction in disease incidence.

Do legumes support endophytic bacteria in subsequent crops?

Recently, N-fixing bacteria, including rhizobia, have been detected inside roots (and shoots) of non-legumes without formation of nodule-like structures. These endophytic bacteria are likely to be more effective in providing the host plant with N than associative rhizosphere bacteria. Therefore, there is new emphasis on establishing stable endophytic associations between N-fixing bacteria and non-legumes. The objective of our recent work was to determine if wheat and barley grown in rotation with field pea or lentil develop an endophytic association with pea or lentil rhizobia (Rhizobium leguminosarum bv. viceae), and to assess the potential of the rhizobial association to promote cereal growth.

In a field experiment at Beaverlodge, Alberta, soil and plant samples were collected at flag-leaf stage in barley plots that previously had: (a) inoculated peas, (b) uninoculated peas or (c) barley. Rhizobia were enumerated in the bulk soil, rhizosphere, rhizoplane and root-interior. Crop yields were also recorded. At Swift Current, Saskatchewan, soil and plant samples were collected in wheat plots that previously had: (a) inoculated lentil or (b) wheat. The results show that the roots of cereal crops contain endophytic rhizobia that were introduced to the soil by a previous legume crop, and the populations of the endophytic rhizobia seem to correlate with cereal N accumulation. Whether this is symbiotically fixed N remains to be determined, but it is a significant contribution nonetheless.

Summary

Producers, simply by including a pulse crop in their rotation, especially under zero tillage may be able to manipulate the soil environment to enhance the population levels and activities of various soil organisms and thus reduce the impact of cereal root diseases. In addition, the synchrony of N availability may be enhanced in this type of management.

TIME OF WEED REMOVAL - Canola & Peas

Does timing of herbicide application improve the bottom line?

Recently, crop producers have relied mainly on post-emergence herbicides, and have tended to delay application of herbicides to accommodate a single treatment for all weeds. This practice encourages early weed interference and irrecoverable yield loss before the first herbicide is applied. Since 1995, an extensive research program on early weed control was initiated. Hand-weeding experiments were conducted at Lacombe and Lethbridge (Harker et al., 2001) and the encouraging results led to further experiments employing herbicides for weed removal in peas, canola, barley, and wheat. Early weed removal involves no additional herbicide inputs, but simply more judicious use of existing inputs. The benefit to growers, who implement early weed control compared to a standard timing, can be as much as $75/acre depending on crop values and the magnitude of the time of weed removal effect in the particular year/environment. In some years/environments there are slightly negative or minimal benefits to the grower after early weed removal, but only in extremely rare situations would producers benefit by waiting until late leaf stages to control weeds. A conservative estimate of the value of this improved management practice probably averages between $10 and $20/acre for canola r peas alone. Given 12 million acres of canola in western Canada, adoption of this practise could increase canola revenues by $240 million annually. Extensive benefits for the adoption of this technology are also common in other field crops. These will be discussed during the presentation.

PYRAMIDING TECHNOLOGIES

Can I manipulate inputs to enhance the whole production system?

Pyramiding technologies by combing technologies and cultural practices together results in the integration of technology tools in a strategic system. Knowledge can be gained in a single growing season and over many years when combined with rotation. Single factor studies often produce results that indicate 5-10% yield increases. Often a producer never realizes the incremental gain from each factor when these factors are combined independently. Generally, when a technology is not utilized to it's greatest potential the benefits from the other technologies in the system are reduced or eliminated. Data collected from multi-factor studies, where integration of disciplines such as agronomy, weed and disease management and breeding, will be presented to provide some discussion on the integration of technologies. These studies are very complex to understand, when numerous interactions occur, consequently, it is difficult to make recommendations compared to single-factor studies. However, as margins become slimmer in primary production the understanding of an ecosystem can provide insight into utilizing cost-effective farm inputs and may possibly provide answers to reducing inputs that are perceived to be harmful to the environment.

Factors that can be combined include competitive crop stands that impact on weed and disease management. Competitive crop stands vary depending on cultivar differences, rapid emergence (vigour), seeding rate and row space and seeding dates. Varietal differences can have a profound effect on the competitiveness of the growing plant in the field. Hybrid vs. open-pollinated canola or semi-leafless and leafed field peas will contribute to the effectiveness of other technologies required to grow successful crops. Herbicides appear to work better when combined with competitive crops. However, plant diseases may become more prevalent under such circumstances. Strategies to increase the competitiveness of crops may include vigour for rapid emergence (variety or quality of seed) and possibly more plants (seeding rate and/or row space). The impacts of these strategies on weed and disease management need to be determined by eco-zone. Technologies such as fertilizer rate and placement, herbicide rate and timing, fungicides and agricultural equipment require strategies that produce the greatest potential benefits in the companion technologies required to grow a crop.

Operational diversity is another tool that may be used to provide the greatest potential benefits from a technology. Seeding date effects on crops contributes to the diversity of timing of herbicides and fungicides. Seeding canola in the fall just before the ground freezes results in the early emergence of canola the following spring. How might fall seeding or April seeding affect weeds that have adapted to mid-May seeding dates? One of the reasons crop rotations and alternate seeding dates can improve weed management is that weeds are not given a chance to build-up in repeated crop seeding dates. Fall seeding can influence weed control because of the early crop emergence relative to weeds resulting in better crop competition after herbicide application. Most weeds have also been selected for emergence with the crop at spring planting and/or have adapted to mid-September harvests. Earlier emergence and earlier harvest dates provide an operational diversity that can "confuse" weeds.

Combining cultural practices, costly technologies and operational diversity provide a means to understand the ecosystem and the role management contributes to the health of the system.

GRAIN LEGUMES - INOCULANT FORMULATION, RATE, PLACEMENT AND SUBSEQUENT EFFECTS: ARE THE BUGS THERE WHEN YOU NEED THEM?

Is starter N required in field pea?

The 12-station years of results involving central Alberta and Saskatchewan did not provide any support for the practise of using starter nitrogen fertilizer in field pea. These results also support those from Northern Alberta.

In farm scale trials, inoculant trials were conducted to evaluate soil inoculation with seed-applied and uninoculated treatments. Plot size was a minimum of five acres, where granular inoculant was applied at 5 and 10 pounds / acre and compared to seed-applied inoculant (either peat powder or liquid) and an uninoculated test strip. Field pea nodulation, as measured by visual assessment, was greater from soil inoculation than from seed-applied or uninoculated treatments. Field pea nodulation was least on the uninoculated treatment, as expected. Field pea yield was greater from the field peas treated with granular inoculant than from field pea treated with seed-applied inoculant or the uninoculated treatments.

Do soil applied inoculants differ in their effectiveness relative to seed applied inoculants?

The results from Fort Vermilion, Beaverlodge and Indian Head clearly show that soil applied inoculants , in this case, peat granules are superior to liquid inoculants and at times better than the peat powder applied to the seed. The grain yields from the peat granule (soil applied) > peat powder (seed) > liquid (seed) > uninoculated check. The results from Stettler, Calahoo and Melfort showed no differences between inoculant formulations but also no differences between the uninoculated check and the other inoculant formulations. These higher organic matter soils did not respond to inoculant formulations even though these fields have no history of field pea.

Does rate and placement effect soil-applied inoculant effectiveness?

Studies at Fort Vermilion, Beaverlodge, Melfort and Indian Head indicated that placement of the peat granules in the seed row, in a band below and to the side of the seed or spread with a sweep with the seed resulted in similar grain yields at all sites. This occurred at at all rates tested. Applying at 5 lbs./acre ensured consistent results.

Can I mix peat granule inoculant with fertilizer?

There is no recommendation for mixing an inoculant with fertilizer. Studies have shown that under good environmental conditions there may be opportunity to mix fertilizer and granular inoculant. These opportunities will be discussed during the presentation. There is no data to indicate that mixing fertilizer and granular inoculant will be effective where environmental stresses occur, consequently, there is a great risk of mixing these two products unless the conditions in the two week period around seeding are known or if it is known that environmental stresses exist such as low soil pH.

What impact do high yields of field pea yields have on subsequent spring wheat crops?

The trials from Indian Head showed that the field pea grain yields of the granular peat inoculant yielded 4000 kg/ha versus 3000 kg/ha for the uninoculated check in 1996 yet the yields of spring wheat were the same the following year. In 1997, the field pea yields for the granular inoculant were 2622 kg/ha while the uninoculated check was 2000 kg/ha and yet the yields of spring wheat were the same for those treatments the following year. The effects on grain protein were not consistent. It is important to note that the wide range of field pea yields did not have a negative effect on subsequent field pea yields. In the case of Melfort, the lack of an inoculant formulation effect in field pea resulted in a corresponding no yield effect in spring wheat. Again the effects on grain protein were not consistent. It would appear that the rotational benefits of field pea on cereals in the short term may be associated more with the reduction of leaf and root diseases rather from the extra nitrogen being supplied by the pea residues. However, in the longer term, that may not necessarily be the case.

Do we need to use inoculants again when re-cropping field pea on land previously seeded to field pea i.e. two years previous?

This is a frequently asked question by producers because of the potential cost saving of not having to use any inoculants. At most sites in central Alberta and Indian Head in 1998, there were no benefits from using inoculants on land seeded to field pea two years previously. However at Indian Head in 1999, an important benefit was observed when using inoculant. In 1999, immediately after seeding the field pea plots, cold, rainy and snowy weather conditions prevailed for a five-day period. The presence of these stresses may explain the benefits observed from using inoculants, even though field pea was seeded two years previously.