Herbicide program, seeding rate, and seed technology interactions were analyzed using yield and irrigation tradeoffs for soybean [Glycine max (L.) Merr.] Maturity Groups (MG) II through IV. Profitmaximizing seeding rates were calculated and sensitivity analyses were performed. Results suggested that high seeding rates, affordable as a result of low seed cost, led to fast canopy closure which largely eliminated the need for postemergence herbicide use. Postemergence herbicide applications or early weed interference (in the case of the postemergence-glyphosate [N-(phosphonomethyl) glycine] program) may have resulted in some yield loss. Using MG IV soybean as opposed to earlier-maturing soybean with lower water requirements was optimal over a wide range of soybean price and input cost assumptions. Larger, later-maturing plants at high plant density contributed to competitiveness of soybean with weeds.
JustificationS oybean seed cost is an ever growing budget item for estimating cost of soybean production. The recent ability for growers to lower seed cost by saving biotech seed no longer protected by patent opens the possibility of using high soybean plant density to reduce the need for postemergence weed control as a production strategy. This study offers insights about this approach and also provides estimates of returns foregone by choosing earlier-maturing soybean with lesser irrigation needs than the profit-maximizing soybean cultivar maturity.
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