PRODUCTION AGRICULTURE Yield Responses to Narrow Rows Depend on Increased Radiation Interception Fernando H. Andrade,* Pablo Calvin ˜ o, Alfredo Cirilo, and Pablo Barbieri ABSTRACT Blamey and Zollinger, 1997; Ottman and Welch, 1989; Rumawas et al., 1971; Nunez and Kamprath et al., 1969; 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 pe- be set and thus higher grain yields (Andrade et al., riod for grain number determination (r 2 = 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 = 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 experiments, grain yield increase in response to narrow rows was some cases, full RI during these periods may not be closely related to the improvement in light interception during the achieved with wide rows. Examples of this situation critical period for grain set. could be late soybean plantings, early maize plantings, defoliation or stress at early stages, use of short-season cultivars, use of erect-leaf maize hybrids, etc. D ecreasing row spacing at equal plant densities Our working hypothesis is that the yield increase in produces a more equidistant plant distribution. maize, soybean, and sunflower in response to decreased This distribution decreases plant-to-plant competition distance between rows is a result of an increase in light for available water, nutrient, and light and increases ra- interception at the critical periods for grain set. Re- diation interception (RI) and biomass production (Shi- sponses are expected to be inversely proportional to RI bles and Weber, 1966; Bullock et al., 1988). It also re- achieved with the wider row spacing at those critical duces the leaf area index required to intercept 95% of periods for grain yield determination. the incident radiation due to an increase in the light extinction coefficient (Flenet et al., 1996). However, the MATERIALS AND METHODS benefits of more equidistant spacing for crops grown The experiments were conducted at Balcarce (37 °45' S lat), without important water and nutrient deficiencies are Tandil (37 °15' S lat), and Pergamino (33 °56' S lat), Argentina, variable. Some researchers reported grain yield increases during different growing seasons. The soils were typical Argiu- (Hunter et al., 1970; Scarsbrook and Doss, 1973; Olson dols with an organic matter content of 6 to 8% in Balcarce and Sanders, 1988; Bullock et al., 1988; Porter et al., and Tandil and 2% in Pergamino in the first 25 cm of depth. 1997; Ethredge et al., 1989; Parvez et al., 1989; Board Nitrogen and P were applied following fertilizer recommen- et al., 1992; Egli, 1994), but others have not (Robinson, dations derived from soil analysis. Soybean seeds were inocu- 1978; Beatty et al., 1982; Zaffaroni and Schneiter, 1991; lated with Bradirhizobium japonicum. In Exp. 3, 4, 5, and 6, soil water in the 1-m depth was kept above 50% of maximum F.H. Andrade and P. Barbieri, Unidad Integrada INTA Balcarce- available water by sprinkler irrigation. In Exp. 1, a comple- Facultad de Ciencias Agrarias UNMP, CC 276, 7620 Balcarce, Bue- mentary irrigation of 45 mm was applied at flowering. The nos Aires, Argentina; P. Calvin ˜ o, Unidad Integrada INTA Balcarce- rest of the experiments (2, 7, 8, 9, and 10) were conducted Facultad de Ciencias Agrarias UNMP and AACREA, CC 276, 7620 under dryland conditions; however, plants were not exposed Balcarce, Buenos Aires, Argentina; and A. Cirilo, INTA Pergamino, to severe drought during flowering and grain filling. In all CC 276, 7620 Balcarce, Buenos Aires, Argentina. This work was cases, weeds, insects, and diseases were controlled. The size supported by Instituto Nacional de Tecnologı ´a Agropecuaria (INTA), Facultad de Ciencias Agrarias UNMP, CREA Tandil, Consejo Na- of the experimental plots ranged from 28 to 39 m 2 , and the cional de Investigaciones Cientı ´ficas y Te ´ cnicas (CONICET), and number of replications varied from three to four. Monsanto Argentina. Received 27 Nov. 2001. *Corresponding author (fandrade@balcarce.inta.gov.ar). Abbreviatons: MG, maturity group; PAR, photosynthetically active radiation; RI, radiation interception. Published in Agron. J. 94:975–980 (2002). 975 Published September, 2002