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Fluid Journal : Fall 2017
13 The Fluid Journal Fall 2017 Table 1. Pre-plant soil characterization for all sites in US and Argentina. Soil parameters Location Ashland Ottawa Rossville Argentina pH 6.7 5.7 6.9 5.5 Mehlich P/Bray P1 (ppm) 22.0 14.0 21.0 12.0 CEC (meq/100g) 9.0 18.5 11.0 - OM (%) 1.5 4.3 2.2 2.1 K (ppm) 181 80 153 - Ca (ppm) 1599 2665 2074 - Mg (ppm) 179 393 202 - N-NO3 (ppm) 2.5 5.0 3.0 6.3 strategy 3 (S3) with a late season N application of 50 lbs. N ac-1 at R3 stage in US and R4 in Argentina. Genotypes. Twenty-one different genotypes were used during the 2016 growing season, 13 for US and 8 for ARG. Genotype-release-decades ranged from 1980’s to 2010’s (Table 2). Maturity groups (MGs) ranged between 3-4 at all sites and all seeds were inoculated at commercial rate before planting. Results Weather information. Seasonal precipitation, maximum (max) and minimum (min) temperatures and solar radiation values were documented throughout the entire 2016 growing season at all sites. In the US, similar mean temperatures were observed with max of 91, 87, and 89oF and min of 46, 47, and 44oF for Ashland, Ottawa, and Rossville, respectively. Cumulative precipitation was higher in the high yielding environments (Ashland and Rossville) with 28 and 32 inches compared to the low yielding environment (Ottawa) with 21 inches. In Oliveros, maximum temperatures were close to those in the US at 90oF but minimum temperatures were higher at 63oF. Cumulative precipitation was similar to the US high yield environments, totaling 27 inches. Solar radiation indexes were similar across locations with 82, 76, and 83 × 1,000 cumulative Langley’s (Ly), except at Ottawa with 58,000 Ly. Nodulation. Nodule counts were compiled for Ottawa and Ashland (US locations) during the 2016 growing season. Roots were collected at V4 stage and results were expressed in nodules per plant. Nitrogen strategies showed statistical effects (P ≤0.05) for this trait. Overall, Ashland presented a higher number of nodules per plant (17) than Ottawa (11) (a site without soybean history for the last 20 years). As expected, S2 resulted with the lowest number of nodules per plant at both locations (5-6 nodules per plant at Ottawa and Ashland). Genetic gain. Twenty-one soybean genotypes from different releases were used in this experiment. Results in this article will be focused on Rossville (US) and Oliveros (Argentina). Seed yields ranged from 46 to 68 bu ac-1 at Rossville and from 49 to 68 bu ac-1 at Oliveros. Superior yields were observed for modern soybean genotypes (2010’s) at both Rossville and Oliveros, while lower yields for genotypes released in the 1980’s and 1990’s (Figure 3 upper Table 2. Genotypes and decade of release for all sites in US and Argentina. Location Decade of release Cultivar Ottawa and Ashland US 1990 P39B82 2000 93Y92 2010 P34T43R2 Rossville US 1980 P3981, Williams 82 and 9391 1990 9392 and 93B82 2000 93Y92, 93B67 and 93M90 2010 P34T43R2, P35T58R, P39T67R, 94Y23 and P31T11R Oliveros ARG 1980 A4422 and Williams 1990 A3910 and DM49 2000 DM3700 and DM4800 2010 NS4955 and SRM3988 Figure 3. Genetic improvement for soybean genotypes, for yield (upper panels) and seed N content changes (lower panels) for 21 genotypes tested (1980’s, 1990’s, 2000’s and 2010’s) at Rossville (US) and Oliveros (ARG) during the 2016 growing season. Means followed by the same letter are not significantly different (P ≤ 0.05).