Harker: Input Study and Recovery
Date: April 2013
Term: 4 years
Status: Completed
Researcher(s): K. Neil Harker, John O’Donovan, Kelly Turkington, Agriculture and Agri-Food Canada (AAFC), Lacombe AB, Robert Blackshaw, Newton Lupwayi, AAFC Lethbridge, AB, Eric Johnson, AAFC Scott SK, Randy Kutcher, University of Saskatchewan
SaskCanola Investment: n/a
Total Project Cost: n/a
Funding Partners: n/a
Project Summary
Growers may wish to limit herbicide use to reduce costs, crop injury, environmental concerns and herbicide-resistance selection pressure. However, reducing herbicide inputs can increase crop production risks. Economic losses can occur when low herbicide rates substantially reduce weed control and increase weed competition with crops. Overall, the study results showed that for relatively competitive, narrow-row crops such as barley and canola, the negative effects of high soil weed seedbanks can be mitigated if growers achieve healthy crop canopies with appropriate seed and fertilizer rates in combination with judicious herbicide applications to adequately manage recruited weeds.
Growers may wish to limit herbicide use to reduce costs, crop injury, environmental concerns, and herbicide-resistance selection pressure. However, reducing herbicide inputs can increase crop production risks. Economic losses can occur when low herbicide rates substantially reduce weed control and increase weed competition with crops.
Researchers with Agriculture and Agri-Food Canada (AAFC) in Lacombe, Alberta conducted four-year Initial Input study at five locations in Alberta and Saskatchewan, followed by a two-year Recovery Study to determine weed interference impacts and barely and canola yield recovery after four years of variable crop inputs (seed, fertilizer, herbicide). Reduced-input plots were considered to have “recovered” when yield was not lower than that in “standard” input control plots.
Direct-seeding experiments were conducted at Lacombe, Lethbridge and Beaverlodge, Alberta, and Scott, Saskatoon and Melfort, Saskatchewan. In the Initial Input Study (2005-2008), main plots were split between canola and barley. Subplots were given various input treatments including “standard” and “basic” input packages (seed, fertilizer and herbicides) as well as various treatments with one optimal practice removed from the standard package or added to the basic package. The same input strategy was imposed on each plot for a period of 4 years to evaluate cumulative effects in a canola-barley or barley-canola rotation. After 4 years of the initial input study, all plots received full inputs for two years (2009-2010) in the recovery study.
Table 1. Treatment descriptions for canola and barley in the original input study
(# of optimal factors).
a In canola, the premium hybrid cultivar from 2005 to 2008 was glufosinate-resistant ‘InVigor 5020’; the suboptimal open-pollinated cultivar was glufosinate-resistant ‘LBD 2393LL’ in 2005 to 2006 and ‘74P00 LL’ in 2007 to 2008. In barley, the premium and suboptimal cultivars were ‘AC Metcalfe’ and ‘Harrington’, respectively from 2005 to 2008.
b Highest and suboptimal seeding rates in canola were 150 and 75 seeds m-2, respectively. Highest and suboptimal seeding rates in barley were 300 and 150 seeds m-2, respectively.
c Herbicide treatments on two- to three-leaf canola were 50 or 100% rate tank-mixtures of glufosinate (250 or 500 g ai ha-1), clethodim (7.5 or 15 g ai ha-1) and Amigo adjuvant (0.5% v/v). Herbicide treatments on two- to three-leaf barley were 50 or 100% rate package mixtures of tralkoxydim plus bromoxynil/MCPA (100 + 140/140 or 200 + 280/280 g ai ha-1) and Turbocharge adjuvant (0.5% v/v).
After four years without herbicides in the Initial Input Study, weed biomass levels exceeded 2,000 and 4,000 kg/ha in barley and canola plots, respectively. Barley was more competitive with weeds than canola, with generally lower weed biomass levels in all situations where herbicide was reduced or excluded. Weed biomass levels tended to be highest in plots that received fertilizer in the absence of other inputs, possibly due to better utilization of nutrients by the weeds compared to the crops.
When comparing barley and canola plots, all barley plots receiving at least a 50% herbicide rate except one (B+50H) had weed biomass levels similar to the standard treatment. In contrast, in canola, half rates of herbicides combined with all other optimal inputs (S-50H) and low inputs with a 100% herbicide rate (B+100H) both led to weed biomass levels greater than the standard treatment.
In the recovery study, weed biomass levels were similar in barley and canola in the first recovery year, but by recovery year two, weed biomass levels were substantially lower in barley than canola. Across all treatments, average weed biomass levels in barley and canola in recovery year two were 31 and 171 kg/ha, respectively.
After four years of one or zero (Basic) optimal inputs, barley and canola yields were significantly lower than the treatment with four optimal inputs. The study also showed that after four years with all optimal inputs but herbicides led to only 77% yield recovery for both crops. After standard optimal inputs were restored, most barley and canola plots recovered to optimal yield levels after one year. The recovery occurred despite high weed biomass levels prior to the first recovery year and despite high wild oat seedbank levels that persisted at the end of the study.
Canola oil concentration in the first year of standard inputs for all plots was usually highest in plots that had been subjected to low fertility treatments in the original four years of the study. After two years of standard inputs, no difference in canola oil concentration was detected. However in barley plots, after two years of standard inputs, there were still some protein concentration differences. With some exceptions, most of the barley plots with low protein concentration in recovery year two were those that had less than 100% fertility treatments in the first four years of the study. It is interesting that fertility deficits influenced barley protein concentration even two years after standard inputs were imposed.
The study shows that herbicide application can optimize yields in weedy fields despite relatively high weed seedbank levels. Therefore, it is probably more important to optimize yield by managing weeds early in the growing season and put less emphasis on repeated herbicide applications that may reduce weed banks and recruitment in the following year. Repeat herbicide applications will definitely increase selection pressure for weed resistance to herbicides.
Overall, the results show that for relatively competitive, narrow-row crops such as barley and canola, the negative effects of high soil weed seedbanks can be mitigated if growers achieve healthy crop canopies with appropriate seed and fertilizer rates in combination with judicious herbicide applications to adequately manage recruited weeds.
Scientific Publications
Harker, Neil K., John T. O'Donovan, T. Kelly Turkington, Robert E. Blackshaw, Eric N. Johnson, Stewart Brandt, H. Randy Kutcher, and George W. Clayton. (2013). Weed Interference Impacts and Yield Recovery after Four Years of Variable Crop Inputs in No-Till Barley and Canola. Weed Technology. 2013. 27:281-290.
Full Report PDF: n/a