Increased biomass production is the major driving force leading to greater nutrient accumulation within the plant. Dr. Steinke has documented similar biomass production (lb/A) from seeding rates as low as 50,000 seeds per acre up through 170,000 seeds per acre. Additional recent research from Illinois and Wisconsin has highlighted the importance of season-long nutrient accumulation as grain tissues remobilized a majority percentage of N, P, Cu, and S to developing seed during grain fill. Much of the late-season nutrient uptake and partitioning to grain comes from the soil, emphasizing the importance of sufficient soil nutrient resources in the later reproductive growth stages to prevent yield limitations.
A primary issue with the lower plant populations, however, has been providing sufficient water resources to support the additional grain development especially lower in the plant canopy. Lack of soil moisture due to 4-8 week late-summer periods without rainfall have hindered any potential yield gains at reduced seeding rates due to pod and grain abortion. Comparing nutrient uptake and partitioning within both irrigated and non-irrigated systems at multiple seeding rates and multiple nutrient application methods will provide vital management information for Michigan soybean growers moving forward.
Application technologies have changed in such a way that growers can now apply nutrients at just about any point of the season and as a liquid, soil applied, foliar, granular, broadcast, in-row, Y-drop, etc. Questions that continue to arise are which method to use, where may a greater yield response be expected, and does soil test concentration impact performance? Our goal is to identify opportunities where soybean growers may be able to proactively modify nutrient applications and increase the potential for yield response. Current research has shown how nutrients and biomass are partitioned throughout plants in varying yield environments but fail to address nutrient application timings especially at near-critical soil test concentrations.