Year of Publication

2015

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Agriculture, Food and Environment

Department

Plant and Soil Sciences

First Advisor

Dr. Chad Lee

Abstract

In an effort to maximize yields, many soybean growers have begun moving to intensive, input-based soybean management systems. However, limited reliable information exists about the effect of these inputs on soybean yield. The purpose of this study was to evaluate the effect of individual inputs and combinations of inputs as part of high-yield management systems on soybean seed yield and to determine the effect of one of these inputs, lactofen, on soybean physiology. Small plot studies were established in nine states across the Midwest. A number of commercially available soybean inputs were evaluated individually and in combination to determine their effect on soybean yield and quality. Lactofen and comparison treatments were applied to soybeans at multiple growth stages and yield and yield components were determined. When examined across environments, input-intensive combination treatments increased soybean yields from 3.9 to 8.1 %. However, break-even economic analysis indicated that the combination (SOYA) treatments evaluated had 0% probability of breaking across a wide range of yield levels and soybean prices, due to the high input costs. The foliar insecticide showed the highest probability of breaking even across a range of yield levels and crop prices (40% to 99%). Yield increases and breakeven probabilities were generally greatest in the northern states (Minnesota, Wisconsin, Michigan) and similar in the central and southern states. Lactofen application did not kill the apical meristem and had minimal effect on yield components compared to untreated soybeans at any growth stage. Meristem removal increased node m-2 in some environments, but did not increase pods m-2 and seeds m-2 or seed yield.

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