Planting Patterns and Soybean Yields1

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Abstract
No satisfactory explanation for the effect of planting patterns on soybean [Glyclne max (L.) Merr.] seed yields under favorable growing conditions has been proposed. The purpose of this paper is to suggest two postulates that together explain soybean yield response to various planting patterns. They are: (1) seed yields continue increase with plant density to a limit that is well above that needed for almost complete light interception, and (2) yield is directly related to vegetative plant weight, all other conditions remaining the same. To illustrate the application of the first postulate, interplant competition is divided into three parts: Phase I in which there is no interplant competition for light among fully developed plants, Phase II in which canopy light interception is complete while seed yield increases with plant density, and Phase III in which yield per unit area is at a maximum for the planting patterns and is independent of plant density. The second postulate explains whyields per unit area differ with row width even when there is no difference in either plant density or canopy light interception. The validity of the postulates is tested using published data. No proof is offered for the postulates other than that they explain the data and seem physiologically possible.