Yield responses to narrow rows depend on increased radiation interception

The response of grain yield to narrow rows can be analyzed in terms of the effect on the amount of radiation intercepted by the crops. The objective of this work was to study the effect of row spacing on grain yield and radiation interception (RI) during the critical period for grain set in three crop species. Ten experiments were conducted with maize (Zea mays L.), sunflower (Helianthus annuus L.), or soybean [Glycine max (L.) Merr.] under irrigation or under dryland conditions without severe drought during flowering and grain filling. The treatments consisted of two row distances combined with other factors such as plant density, cultivar, defoliation, etc. Grain yield responses to decrease distance between rows were inversely proportional to RI achieved with the wide-row control treatment during the critical period for grain number determination (r(2) = 0.62, 0.54, and 0.86 for maize, soybean, and sunflower, respectively). Moreover, when row spacing was reduced, grain yield increases and RI increases during the critical periods for grain set were significantly and directly correlated in the three crop species (r(2) = 0.71, 0.64, and 0.94 for maize, soybean, and sunflower, respectively). For the conditions of these experiments, grain yield increase in response to narrow rows was closely related to the improvement in light interception during the critical period for grain set.