Population studies with wheat: II. Propinquity

An investigation of the problem of propinquity has shown that the yield of any unit of 6 in. of drill row of wheat is significantly affected by the number of plants in adjacent units. The “competition correlation”, which measures the intensity of this effect, is greatest with medium plant densities, and low and often insignificant for units of high or low plant density. Competition is primarily underground for water, soil nutriments and soil air; of these, competition for water is most important in determining yield.