Quantification of competitive interference by neighboring plants in a crop population.

A method of quantifying density effects in crop populations is proposed. Since microenvironments around a plant in a population are created by interference from neighboring plants, this interference was quantified based on these microenvironments. As an indicator reflecting microenvironments around a focal plant in a population, evaporation rate from wet filter paper set close to the focal plant (Ei) was used. The ratio of Ei to the evaporation rate from wet filter paper placed outside the target population (Eo) was assessed for its relationship to the interference from those neighboring plants. Firstly, the Ei/Eo ratio was compared for consecutive fine and cloudy days with soybean and rice populations and with a mixture of maize and teosinte plants. In all cases, the Ei/Eo ratio did not differ between days of different evaporation demand at the probability level of 50%. Secondly, in artificial populations of different densities in square planting carried out using similarly-sized potted soybean plants, the values of 1 – Ei/Eo always had a rigid linear relationship with reciprocals of the plant distance. A proposed index defined as 1 – Ei/Eo consistently responded not to weather changes but to the change in interference from neighboring plants.