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The best crop row spacing is…

A multi-year study suggests there is no one-size-fits-all answer to the question

The question of the best row spacing has been asked even more often in recent years, and it turns out that the answer is the same as for many other questions in farming — “It depends.” But on what? A multi-year study by researchers at Agriculture and Agri-Food Canada and the Indian Head Agricultural Research Foundation (IHARF) has shed some light on some of the factors.

The studies involved row spacing from 12 to 24 inches in no-till production, and combined other agronomic factors such as different nitrogen rates, seeding rates, weed control and fungicide applications. The trial results are now available, and suggest that yield sensitivity to row spacing is highest for flax followed by wheat, oats, soybeans and canola.

Canola

While canola appears to be relatively insensitive to row spacing, the research indicates that growers should still consider several factors when choosing the optimal spacing on their farm, including seeding rates, nutrient application rates and weed control.

Indian Head’s three-year study evaluated the impacts of wider row spacing on canola yield and quality, and investigated the potential interactions between row spacing and other management considerations such as seeding rate, side-banded N fertilizer and weed control.

Researchers conducted three separate field trials with row spacings of 10, 12, 14, 16 and 24 inches combined with side-banded N rates of 0, 45, 90, and 134 lbs./ac., seeding rates of 30, 60, 90 and 120 seeds per square metre (approximately 1.3 to 5.5 lbs./ac.) and no in-crop versus an in-crop herbicide treatment.

Canola plant populations generally declined as row spacing increased. On average, plant populations declined by 19 per cent (from 85 to 62 plants per m²) when row spacing increased from 10 to 24 inches. Increased row spacing also delayed flowering and maturity, but the effect on final seed yield was not significant.

The results also suggest that growers should not generally reduce canola seeding below typical rates as row spacing increases, with the exception being the 24-inch row spacing, where there was little potential benefit to seeding at rates higher than 90 seeds per m².

The study suggests canola N response is similar regardless of row spacing, although high N rates in wide rows can increase the risk of seedling injury. In all four years, increased rates of side-banded N significantly reduced plant densities across all row spacing, although the 24-inch spacing showed a decline in plant populations at lower rates of N than other row spacing. Apart from emergence, canola responded well to side-banded N with yields increasing on all applications, up to 134 lbs. N/ac. including on the widest row spacing.

Weed competition not a factor

Researchers also compared row spacing with and without herbicide to assess potential impacts on weed competition. Although it’s generally thought that crops are less able to compete with weeds at wider row spacing, the study did not bear this out, particularly when weeds were controlled with an in-crop herbicide. There was evidence of higher weed biomass with wider row spacing when no in-crop herbicide was applied, but not every year. Well-timed herbicide applications could manage weeds in all row spacing but it is worth recognizing that reduced crop competition does put more pressure on herbicides and could increase the potential for resistance to develop or escapes. When weeds were not controlled, average yield loss across all row spacing treatments was similar at about 21 per cent.

The consistently highest yields were on narrower row spacing, combined with high rates of side-banded N, but all row spacing — even 24 inches — produced viable yields as long as environmental conditions were conducive and weeds effectively controlled.

Canopy closure took longer in canola growing on wider row spacing, which can either give treated weeds an opportunity to grow through the herbicide or allow weeds to germinate, but the effect on maturity was small. Narrow row spacing, however, may be an important component of an integrated management strategy that uses multiple approaches to controlling weeds such as herbicides, crop competition, crop rotation and tillage. An integrated strategy generally results in better long-term control and reduces the likelihood of weeds becoming resistant to a single technology or control method.

Wheat

From 2013 to 2016, AAFC researchers compared row spacings of 10, 12, 14 and 16 inches with rates of N at 18, 36, 71, 107 and 142 lbs./ac. in a no-till system. Seedmaster also conducted a three-year, no-till wheat trial comparing 10- and 15-inch spacing at its research farm.

At the Seedmaster site, there was no significant impact on grain yield with wider row spacing.

At Indian Head, yield response at the different row spacings was similar and there seemed to be no interaction between row width and N. In one year out of the four-year study, yield was lower at 14- and 16-inch row spacing than at 10 and 12 inches. But study lead William May of AAFC says it’s too early in the research to know if such a yield reduction one year in four is what can normally be expected. In the other three years, yields at 14 and 16 inches were similar to the 10- and 12-inch row spacing.

Makes a difference with flax

The three-year flax trial at Indian Head compared spacings at 10, 12, 14, 16 and 24 inches, with and without foliar fungicide. Flax plant populations and yields consistently and linearly declined with increasing row spacing. While yield differences between row spacing treatments were not always significant in individual site-years, on average flax yields decreased by two per cent for every one-inch increase in row spacing. From 10- to 24-inch row spacing there was a 37 per cent, or 10 bu./ac., reduction in yield. The use of a fungicide increased yield over the untreated control by six per cent regardless of row spacing, and there were no interactions between row spacing and fungicide application. The flax response to fungicide varied from year to year but not with row spacing. Plant maturity also lengthened by a few days as row spacing increased, but had no appreciable effect on yields.

Soybean

Analysis of the three-year soybean trial at IHARF is still underway but preliminary results suggest there can be advantages to going narrow, at least with some varieties under certain conditions although the crop is well adapted to wider rows. This trial compared row spacings of 10, 12, 14, 16 and 24 inches and seeding rates of 40, 50 and 60 seeds per m². Plant density was usually reduced with wider rows, and increased at higher seeding rates regardless of row spacing.

Yield responses to date have varied with the highest yields at 16- to 24-inch spacing in 2014, a slight advantage to 10- to 12-inch spacing in 2015 and no effect of row spacing on yield in 2016. The yield advantage to increased row spacing was attributed to improved nodulation (better inoculation) as unusually strong responses to granular inoculant were observed that year and the rates applied were somewhat limiting.

In 2015, while there was a slight advantage to narrower spacing, canopy closure was still achieved at 24-inch spacing and yields were nearly 40 bu./ac. and did not significantly differ for 14- to 24-inch row spacing. While the results suggest the soybeans can do well at wider row spacing, it may be beneficial to choose varieties with a more branching as opposed to upright growth habit.

Plant maturity lengthened with wider row spacing, but decreased at higher seeding rates, and while maturity is important for long-season crops like soybeans, the range from the narrowest to widest row spacing treatments was always within a few days. Row spacing is unlikely to have nearly as much impact on maturity as other factors such as variety selection and weather conditions.

Oats

The row spacing study in oats was conducted at Indian Head by AAFC from 2009-11. Oats were compared on 10, 12, 14 and 16 inches and at N rates of 18, 36, 53, 71 and 197 lbs./ac. On average, oat yields were similar for 10- to 14-inch row spacing and slightly lower at 16 inches, but results varied somewhat from year to year with no effect in 2009 and greater reductions in 2010 and 2011. Protein was not affected by row spacing.

Plant density (emergence) decreased at wider row spacing, but was not affected by N rate, regardless of row spacing (which means there was no interaction between these factors).

Other considerations

Research demonstrates that sound agronomic practices such as adequate seeding rates and fertility along with thorough weed control are likely more important for yield and quality. Row spacing can delay things slightly but the impact is less than other factors such as high fertility and low plant populations. Seedling mortality generally increases with wider row spacing, but not to the degree where optimal plant populations for top yield and quality cannot be achieved.

Yield variability does increase with wider row spacing in most crops, but could be offset by other factors such as reduced equipment costs and fuel consumption as well as by reduced need for tillage harrowing or burning under high residue conditions. Wide rows may also permit earlier seeding by reducing land preparation, and covering more area faster with larger seed drills.

Wider row spacing is also better suited for inter-row seeding that results in better seed placement and moisture availability for seed germination.

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