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Project Abstract: Comparison of dry bean and soybean for agronomic traits, inputs, diseases and nitrogen-fixing benefits to following crops, water use and harvest losses

This study is set up to compare agronomic practices for soybean production and quantify their nitrogen benefits in comparison to dry bean. It is a collaborative effort between Agriculture & Agri-Food Canada and Alberta Agriculture & Forestry, conducted over two sites, at Bow Island and Lethbridge, AB.

With the advent of new short-season glyphosate-tolerant cultivars, soybean [Glycine max (L.) Merrill] has expanded westward into southern Alberta but local soybean yield is still low, compared to other locations. Adjusting seeding rate and row spacing to maximize soybean growth and yield is well-documented but mostly for rain-fed conditions. Current information on seeding rate and row spacing for irrigated soybean in Alberta is lacking. We conducted randomized complete block design experiments with 4 replications at two sites (Bow Island and Lethbridge) in two years (2014, 2015) using two glyphosate-resistant soybean genotypes (Co-op - F045R #3 and NSC Tilston), two row spacings (narrow, 17.5 cm; wide, 35 cm) and three seeding densities (30, 50 and 80 seeds m-2); The results indicate that compared to Co-op - F045R #3, NSC Tilston flowered and matured earlier, had lower pod clearance, but higher seed yield (2639 vs 2615 kg ha-1) and lower total N uptake (197 vs 182 kg ha-1). There were inconsistent results in seed yield and N uptake with row spacing where narrow row yielded more than wide row (by 229 kg grain ha-1 and 28 kg N ha-1) at Lethbridge in 2014 but wide row yielded more than narrow row (by 216 kg grain ha-1 and 21 kg N ha-1) at Lethbirdge in 2015. Maximum yield of 2965 kg seed ha-1 and net gain of $772 ha-1 were achieved at highest seeding density. Thus, soybean producers should grow Co-op - F045R #3 at Bow Island and NSC Tilston at Lethbridge for grain yield but consider Co-op - F045R #3 for a higher N uptake. Row spacing effects were inconsistent and may be genotype-, weather- or site-specific. Soybean production in southern Alberta would benefit from high seeding densities of 50 seeds m-2 but this may also increase production costs. 

Numerous studies have reported the effects of plant density on yield of soybean and dry bean (Phaseolus vulgaris L.), but effects of density on N fixation are less well documented. We conducted experiments in four environments (Bow Island and Lethbridge, AB in 2014 and 2015) using soybean, dry bean and barley (Hordeum vulgare L., a non-legume control) in Year 1 (2014, 2015) followed by wheat (Triticum aestivum L.) with no N fertilizer in Year 2 (2015, 2016). In Year 1 there were two soybean genotypes, at two row spacings (wide row, 35 cm; narrow row, 17.5 cm); and three seeding densities (30, 50, 80 seeds m-2). Dry bean was planted in narrow (35 cm, 25 seeds m-2) or wide rows (52.5 cm, 40 seeds m-2), at 0 and 60 kg N ha-1. Across all environments, genotypes, and row spacings, N fixation (using the N difference method) by soybean was greatest at highest plant density (111 kg ha-1, 80 seeds m-2), followed by 75 kg ha-1 (50 seeds m-2), and 53 kg ha-1 at 30 seeds m-2. Results indicate that despite dry bean having a lower N fixation ability compared with soybean, wheat following dry bean resulted in greater N uptake than wheat following soybean. This may be related to faster decomposition and N release from dry bean residue. Our results will provide some comparative N benefits for growers interested in growing soybean vs. dry bean in southern Alberta’s irrigation districts.

Through biological N fixation, both soybean and dry bean provide an N credit or N fertilizer replacement value to following crops in rotation. However, N credits have not been quantified for soybean or compared with dry bean for the region. Therefore, we conducted experiments at two sites (Bow Island and Lethbridge) using soybean, dry bean and a non-legume (barley, Hordeum vulgare L.) as main plots in the first year, and wheat (Triticum aestivum L.) with six N rates (0, 30, 60, 90, 120 and 150 kg N ha-1) as sub-plots in the second year. TwoYear 1-Year 2 data sets were collected (2014-2015 and 2015-2016) in which we compared two methods of estimating N credits: (1) a traditional method where N credit = N rate required to produce a wheat yield following barley which is equivalent to unfertilized wheat yields (0 N rate) following soybean or dry bean; and (2) a difference method where N credit = economic optimum N rate (EONR) of wheat following soybean or dry bean minus EONR of wheat following barley. The EONR is the point where additional fertilizer N still returns a yield increase large enough to cover the extra fertilizer costs. Our preliminary results indicate that N credits (mean of 2 sites) estimated by the traditional method were 18 kg N ha-1 for soybean and 49 kg ha-1 for dry bean. Using the difference method, mean values were 18 kg N ha-1 for soybean and 54 kg N ha-1 for dry bean. Results showed that the N credit estimation method had little effect while dry bean showed an ~3 times higher N credit) than soybean.

 

Project lead: Dr. Francis Larney (403) 317-2216 francis.larney@agr.gc.ca

 

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