Like a troublesome rustler who refuses to leave the countryside, wild oats have developed a reputation as one of the baddest weeds in the West.It returns to farmers’ fields each spring, emerging quickly and silently to wreak havoc on yields and rob producers of their hard-earned dollars.Yet despite its reputation, the ubiquitous wild oat has remained an enigma to many western Canadian farmers and researchers.Surprisingly, little was known about its growth pattern, its competitiveness and its nutrient uptake. Jeff Schoenau is changing that.Schoenau, a farmer, soil scientist and University of Saskatchewan researcher, has spent the past two years studying the wild oat.After noticing a lack of scientific data that measured the plant’s nutritional uptake, Schoenau teamed up with U of S plant scientists Ken Sapsford and Rick Holm to take a closer look at the issue.”We knew that wild oats compete for resources and that includes water and space and nutrients, but no one had really ever documented how a weed like wild oats would compete with a crop and how its nutrient uptake would vary according to the age of the plant,” Schoenau said. “It seemed like a … fairly simple concept, but looking through the literature, there really wasn’t a lot of data available.”Schoenau’s research was conducted over two years.In the first year, the research team focused on nutrient uptake by monitoring a stand of wild oats on a 10 by 10 metre plot near Saskatoon.Soil samples were taken at 10 points in the plot before emergence and analyzed for nitrate, phosphate, potassium and water content.After wild oat emergence, sections of the plot were harvested at weekly intervals and the plant material was measured for dry weight biomass and nitrogen, phosphate and potassium uptake.To determine nutrient uptake, the harvested material was ground up and analyzed using an acidic medium to break down the plant material into its elemental constituents.The analysis showed the wild oats, like most commercial cereal crops, have a voracious appetite for crop nutrients almost as soon as they emerge.Uptake of nitrogen is especially high in wild oats’ early stage of development.In the pure stand, Schoenau’s wild oats used more than eight pounds of nitrogen per acre within the first week after emergence.After four weeks, nitrogen uptake was more than 45 lb. per acre and by the end of the eighth week, nitrogen use was approximately 108 lb. per acre.Potassium uptake maxed out at roughly 177 lb. per acre and phosphorus uptake topped out at 10.8 lb. per acre, or 22 lb. per acre of phosphorus pentoxide equivalent.”If you look at the pattern of uptake, there’s a period of very rapid … uptake that occurs over the first four weeks so by the time those wild oats are one month of age, there’s already about 50 lb. of nitrogen, about five lb. of phosphorus and about 60 lb. of potassium … in that wild oat that is no longer available for the crop to use,” said Schoenau, who farms near Central Butte, Sask.”This is indicating that the earlier you can control (wild oats), the less competition you’re going to have.”Schoenau said the pattern of nutrient uptake in wild oats is similar to that observed in other cereal crops, where a period of rapid nutrient uptake is followed by a significant increase in biomass.Nutrient uptake will vary depending on the density of the wild oat stand, he added.At maturity, the wild oats stand examined by Schoenau’s research team had produced almost nine tonnes of total biomass, suggesting a heavy infestation.The study also looked at nutrient release from the harvested biomass to determine if some of the soil nutrients used by the wild oats would be released back into the soil for planted cereals to use.The plant biomass that was harvested, ground and analyzed for nutrient uptake was then used as a soil additive to determine the rate of nutrient recovery.It was applied to the surface of potted wheat plants produced in a growth chamber under controlled environmental conditions.The results suggested that nutrient recovery rates from wild oat material left on the soil as surface trash is more likely to be used by wheat plants if the wild oats are controlled at an early stage of development.For example, trash from wild oats that were controlled one week after emergence surrendered 5.9 percent of their nitrogen to the wheat crop and 84.6 percent of phosphorus.However, after five weeks nutrient recovery rates by the wheat had fallen to 0.5 percent of total nitrogen contained in the wild oat residue and 4.7 percent of total phosphorus.In other words, the proportion of recoverable nutrients in the wild oat residue was highest in crops that received wild oat control treatments. “With the younger wild oat residue, you have a narrower carbon to nitrogen ratio and a narrower carbon to phosphorus ratio, meaning that when the micro-organisms start chewing away at that material and breaking down the carbon and converting it to carbon dioxide, you’re going to have a better opportunity for nitrogen release when the plant material is young,” Schoenau said.”With the older wild oat material, you’ve got lots of carbon there (but) … you’re not going to get any available nitrogen or phosphorus from that old material. It behaves just like mature cereal straw does in the field.”Last year, researchers turned their attention to yield impact.They planted plots of Metcalfe barley and compared overall barley yields on plots where wild oats were controlled at different stages of crop development.According to Schoenau’s data, plots that received wild oat treatments at one week after emergence yielded 2,053 kilograms per acre while plots that received no wild oat control yielded 1,706 kg per acre, an overall yield reduction of 17 percent.He said the study supported what farmers have known for years: early cereal crop establishment significantly limits wild oat nutrient uptake and improves cereal yields.”In summary, the research showed that early wild oat control will significantly reduce competition with crops for nutrients and early wild oat control will promote rapid recycling of the nutrient contained in (wild oat) residue back into available forms for crop use.”
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