¹AAFC and University of Manitoba, ^{2 and 3}AAFC and ⁴University of Manitoba

Fertilizer placement can directly affects a crop’s ability to compete with weeds.

For decades wild oats (Avena fatua L.) have been recognized as one of the most widespread and troublesome weed species on the Canadian prairies. It has dominated the weed community for the last twenty years (Thomas et al., 1998), and will continue to be one of the most aggressive and difficult to control weed species, as it has developed multiple resistance to herbicide groups 1, 2, 8 and 25. With resistance spreading, producers are left with fewer and fewer herbicide options. Therefore, it is necessary to develop integrated weed management (IWM) strategies.

IWM has been defined as the application of numerous weed control measures, which include cultural, genetic, mechanical, biological and chemical (Swanton and Weise, 1991). An IWM system should enhance the competitive ability of the crop to suppress weed growth (Swanton and Weise, 1991). Fertilizer placement affects the crop’s ability to compete with weeds. Placing fertilizer where the crop has access to it but the weeds do not, allows the crop to be more competitive (Kelner et al, 1996). There has been little information obtained concerning fertility interactions on weed - crop competition. This study provides information on how wild oats compete for side banded and seed placed monoammonium phosphate and potassium chloride fertilizer in spring wheat and flax.

Growth Chamber: Two growth chamber experiments (which were repeated) were conducted to assess the growth response and uptake of P and K of each species (spring wheat, flax and wild oats) separately. The experiments were organized as completely randomized designs:

1) 0, 4.37, 8.74, and 17.48 kg of actual P ha^-1.

2) 0, 8.3,16.6, and 33.2 kg of actual K ha^-1.

Destructive harvests began at 14 days after emergence (DAE) and continued on a weekly basis until 42 DAE, to determine growth responses and nutrient uptake. At each harvest date growth staging, dry matter production and tissue nutrient analysis were assessed.

Field: Four field experiments on two soil types were conducted during two years, in the Aspen Parkland Ecoregion of Manitoba. Soil types were a sandy loam soil south of Brandon and a clay loam soil north of Brandon. The experiments were conducted in a split plot factorial design. Rate and placement of fertilizer comprised the main plot effects and +/- wild oats comprised the subplots. A RCBD was used with the main plots randomized within blocks. Treatments were as follows:

1) Wheat +/- wild oats, phosphorus banded and seed placed at rates of 0, 4.37, 8.74, 17.48, 34.96 and 52.44 kg of actual P ha^-1.

2) Wheat +/- wild oats, potassium banded and seed placed at rates of 0, 8.3, 16.6, 33.2, 66.4, and 99.6 kg of actual K ha^-1.

3) Flax +/- wild oats, phosphorus banded and seed placed at rates of 0, 3.5, 4.37, 6.56, 8.74 and 17.48 kg of actual P ha^-1.

4) Flax +/- wild oats, potassium banded and seed placed at rates of 0, 8.3, 12.45, 16.6, 24.9 and 33.2 kg of actual K ha^-1.

Nitrogen (as 46-0-0) was banded, prior to seeding, across each replication perpendicular to the direction of seeding at a blanket rate of 78.4 kg ha^-1. Fertilization with P and K and seeding occurred at the same time with an air seeder on nine inch row spacing. Each plot was planted consecutively with gear settings and ratios changed by hand (ie. rate and placement of fertilizer), in a serpentine pattern. The side banded treatments were 2.5 cm to the side of the seed row and 2.5 cm down.

Data collected included: crop counts, wild oat density, biomass four weeks after emergence, biomass at heading of wheat and full boll formation of flax, crop yield, weed yield, dockage (other weed species that were not controlled), 1000 kernel weights, tissue nutrient analysis of early biomass (only 1997) and late biomass samples, grain analysis of wheat and wild oats and oil analysis of flax.

Statistics: All data was subjected to ANOVA and orthogonal contrasts with significant differences discussed in the text. In the field there was a lack of consistent fertilizer rate response (ie. linear, quadratic or cubic), therefore, regression analysis was not utilized. Similarly, in the growth chamber there was no rate response. Growth chamber experiments were combined (P and K experiments separately), after passing Bartlett’s test. Field experiments were not combined due to environmental variability across years and because different locations were selected each year.

Flax: Flax did not show a positive or negative response to P or K addition, on either soil type or in either year. It has been shown that flax is notorious for poor response to phosphorus fertilizer in a broad range of experiments (Lafond et al., 1996). General recommendations are for very low rates of phosphorus fertilizer for flax, with the consensus that flax does not efficiently use phosphorus from fertilizer sources (Bailey et al., 1980). Flax did not show toxicity or damage at the high fertilizer rates.

Wheat: Wheat showed a response to both P and K addition, on both soil types and in both years. There was a significant yield increase to P addition even at the highest fertilizer rate (soils were marginal and average in background P, ie. 12 - 19 ppm). However, addition of K provided a yield decline on soils with high background levels of K (>600 ppm), but slight yield increases to K addition at low application rates on soils with average background K levels (300 - 600 ppm). Lack of a significant increase in yield to KCl addition may be due to a varietal response, increased toxicity due to less water holding capacity on light textured soils, and the presence of wild oats. Teal wheat, the variety used in this study, may show yield declines with KCl application (Grant, 1997).

Wild Oat Fertility Interaction: Side banding provided the highest crop yields in all trials, and therefore, was better than seed placed fertilizer application in giving the crop a competitive advantage. It was thought that seed placed fertilizer would give the crop a head start ("pop up" effect) at the lower rates. This may have occurred at low rates, but was not found consistently.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Growth Chamber Experiments

Wild oats’ uptake of both P and K was significantly higher than spring wheat and flax, even though the wild oats produced approximately the same dry matter as the spring wheat. Therefore, many questions arise when we look at fertilizer management practices: When we apply P and K fertilizer in field situations are we giving wild oats a competitive advantage? Is the higher uptake ability due to wild oats’ phenotypic plasticity and/or genetic variability?

Environment, both climatic and edaphic, play extremely important roles when dealing with immobile nutrients. 1997 was dry, whereas, 1998 was excessively wet, but, there was not a significant difference between the wet and dry years when looking at rate responses and overall trends in yield. However, there was more competition from wild oats in the dry years. The greatest difference between seed placed and side banded fertilizer placement occurred in 1998, likely due to excess moisture increasing the mobility of the P and K applied.

This research has led to the re-evaluation of IWM and fertilization rates in direct-seeding systems. It has shown the need for further KCl research in wheat, particularly in the Aspen Parkland Ecoregion, and the need to incorporate different wheat varieties and weed species with these studies. Fertilizer recommendations may no longer be accurate because soils have changed due to changing management systems. New information regarding the uptake potential of P and K by wild oats was provided. Mechanisms of nutrient uptake, as well as, the probability of mycorrhizal associations need to be investigated. Could the wild oat problem on the Canadian prairies be directly associated with a genotypic need for K and the inherently high levels of K in the soil?

Bailey, L.D., H. Ukrainetz, and D.R. Walker. 1980. Effect of phosphorus placement on crop uptake and yield. Proc. Western Canada Phosphate Symposium. Alberta Soil Science Workshop. pp. 200-229. Calgary, Alberta.

Grant, C.A. 1997. Chloride’s role in maximizing wheat variety performance: 1997 Report. Agriculture and Agri-Food Canada, Brandon, Manitoba.

Kelner, D., L. Juras and D. Derksen. 1996. Integrated weed management: making it work on your farm. Canada - Saskatchewan Agricultural Green Plan, Saskatchewan Agriculture and Food and Manitoba Agriculture.

Lafond, G.P., D. Wall, A. Johnston, C. Grant, D. McAndrew, and D.Derksen. 1996. Increasing flax yields: a closer look at fertilizer utilization and weed management. An annual report.

Swanton, C.J. and S.F. Weise. 1991. Integrated weed management: the rational and approach. Weed Tech. 5:657-663.

Thomas, A.G., B. Frick, R. Van Acker, S.Z. Knezevic and D. Joosse. 1998. Manitoba Weed Survey: Cereal and Oilseed Crops 1997. Weed Survey Series, Publication 98-1. Agriculture and Agri-Food Canada, Saskatoon Research Centre, Saskatchewan.