Inter-row cultivation – effective weed control in field pea?

E. Johnson, B. Frick - Scott Research Farm

Problem
Some growers in western Canada have considered using inter-row cultivation as an alternative to herbicides. There has been little research in western Canada on inter-row cultivation in our commonly grown field crops. This study’s objective was to evaluate interrow cultivation as an alternative weed management system in field pea.

Background
Inter-row cultivation is commonly used in row crop production in the United States. It has been effective in corn and soybean when combined with a band of herbicide applied over the crop row. Swanson and Jacobson and Johnson reported non-weed control benefits of inter-row cultivation such as improved soil aeration and reduced soil compaction. However, most benefits of interrow cultivation are attributable to weed control. Research on inter-row cultivation of field crops in Saskatchewan is very limited. Inter-row cultivation in cereal crops was investigated at the University of Saskatchewan in the 1920’s. The purpose of that research was primarily to reduce summerfallow and manage drought, and not to manage weeds. Two to three rows of wheat, oat, or barley (spaced 15 cm apart) were separated by a 90 cm spacing to facilitate cultivation. Barley and oats appeared to respond best to the treatment; however, there were no non-cultivated checks for comparison. Subsequent wheat crops yielded similar to wheat crops grown on fallow. These results were similar to the observations of Tull, who stated that “the more successive crops are planted in wide intervals and often hoed, the better the ground does maintain them”.

Study description
The study was conducted on cereal stubble at the Scott Research Farm in 1998 and 1999. Wild oat and wild mustard were seeded on the experimental area in early spring followed by cultivation to distribute weed seeds. Field pea was seeded at a depth of 7.5 cm on May 12, 1998 and May 7, 1999. We used a hoe-drill plot seeder with adjustable row spacing and on-row packing. The crop was seeded in single rows spaced 33 cm apart to facilitate inter-row cultivation. Inter-row cultivation was conducted with a modified S-tine cultivator. Three tines were arranged in a delta formation and fitted with 10-cm sweeps to fit between the crop rows. Cultivation depth was 2.5 to 3.0 cm and was adjusted to ensure that crop rows were not covered by soil. Cultivation speed was 3.5 km/hr . Experimental design was a randomized complete block with treatments consisting of sequential inter-row cultivations (1, 2, and 3 cultivations) and an untreated check. We cultivated at field pea’s 6, 8, and 10-node stages. Inter-row cultivation before the six-node stage would have resulted in too much crop burial. A herbicide treated check was also included (seeded in 22 cm rows). Data collection included crop and weed density and biomass, and crop yield.

Major findings
Successive inter-row cultivation caused a linear reduction in wild mustard density in both years. Those wild mustard plants that remained produced as much biomass as plots where cultivation was not done. Many weed species exhibit morphological plasticity in response to environmental variation and density. Weeds can compensate for density changes so that total biomass per unit area is held relatively constant. Inter-row cultivation had an erratic effect on grass weeds' density and biomass. Field pea yield showed a linear response to successive inter-row cultivation in both years. Response magnitude was greater under the more favorable growing conditions in 1999. Inter-row cultivation improved field pea yield by 33% and 78% for 1998 and 1999, respectively. However, herbicide application resulted in respective 9 yield increases of 57 to 300%. Benefits from interrow cultivation were limited due to in-row weed growth. Most uncontrolled weed growth occurred in the uncultivated area adjacent to and within the crop row. Results cultivation provided that weed populations are low. Therefore, integration with other mechanical or cultural methods may be required for satisfactory results with interrow cultivation. from this study are consistent with research conducted in other parts of the world. A standard cultivator was not effective in controlling weeds in field bean due to intra-row weed growth. An in-row cultivator or rotary hoeing prior to inter-row cultivation was required to reduce weed populations to that achieved by a herbicide. Another study found satisfactory results with interrow cultivation.

Conclusions
Inter-row cultivation has potential as means of controlling late flushes of weeds. It should not be considered a stand-alone weed management technique since significant in-row weed growth may limit benefits. Future studies should investigate the potential of inter-row cultivation conducted on the same experimental area over a number of years to truly evaluate its potential.

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