The response of grain yield to narrow rows can be analyzed in Westgate et al., 1997).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 There are times during the crop cycle that are most on grain yield and radiation interception (RI) during the critical period critical for yield determination. These times comprise for grain set in three crop species. Ten experiments were conducted the period bracketing flowering in maize (Kiniry and with maize (Zea mays L.), sunflower (Helianthus annuus L.), or soy- Ritchie, 1985; Fischer and Palmer, 1984) and sunflower bean [Glycine max (L.) Merr.] under irrigation or under dryland con- (Chimenti and Hall, 1992, Connor and Sadras, 1992; ditions without severe drought during flowering and grain filling. The Cantagallo et al., 1997) and extend to more advanced treatments consisted of two row distances combined with other factors reproductive stages in soybean (Shaw and Laing, 1966; such as plant density, cultivar, defoliation, etc. Grain yield responses Board and Tan, 1995; Egli, 1997). Higher crop growth to decrease distance between rows were inversely proportional to RI rates during these periods would allow more grains to achieved with the wide-row control treatment during the critical pebe set and thus higher grain yields (Andrade et al., riod for grain number determination (r 2 ϭ 0.62, 0.54, and 0.86 for maize, soybean, and sunflower, respectively). Moreover, when row 1999). Crop growth rate is directly related to the amount spacing was reduced, grain yield increases and RI increases during of radiation intercepted by the crop (Gardner et al., the critical periods for grain set were significantly and directly corre-1985). Therefore, the response of grain yield to narrow lated in the three crop species (r 2 ϭ 0.71, 0.64, and 0.94 for maize, rows can be analyzed in terms of the effect on the soybean, and sunflower, respectively). For the conditions of these amount of RI at the critical periods for kernel set. In
