“Yield Response of Corn to Crowding Stress” by Hashemi et al. (Agron. J. 97: 839-846, 2005)

J.R. KINNIRY; L. ECHARTE

AGRONOMY JOURNAL

Año: 2005 vol. 97 p. 1472 - 1472

0002-1962

Hashemi et al. have collected valuable data concerning the responses of maize (Zea mays L.) to crowding stress, especially related to harvest index (HI).  We would like to take this opportunity to demonstrate a general response of maize HI to plant density by combining their data with data from four other published studies.  This could give additional guidance as to the general response of maize HI to planting density.  For each study, the HI values were standardized by dividing each HI value by the mean HI for densities less than 10 plants m-2. For the Hashemi et al. study in MA., this mean was 0.49.  For the other studies, means were 0.58 for a dwarf hybrid in MN (Westgate et al., 1997), 0.50 for the two most recently released hybrids in Guelph, ONT in the study of Tollenaar (1992), 0.54 for a study in TX by Kiniry et al., (2002), and 0.51 to 0.55, with a mean of 0.54 for a study of Echarte and Andrade (2003) in Argentina with their two most recently released hybrids.  As shown in our figure, and as discussed by Echarte and Andrade (2003), harvest index was relatively stable and had a plateau at planting densities low enough that inter-plant competition did not reduce individual plant growth below a threshold.  The density for this threshold appeared to be near 10 plants m-2.  Above 10 plants m-2, HI decreased linearly with a slope of -0.012 units of relative HI per plant m-2 and the r2 was 0.77. This general response was for recently released hybrids in environments without drought or nutrient stresses causing reduced yields and reduced HI values. Larger HI decreases with increasing planting densities can take place in older hybrids less tolerant to high plant density stands (Echarte and Andrade, 2003). Harvest index reductions may occur at low plant densities in hybrids with lack of prolificacy and low yield potentiality of the uppermost ear. As demonstrated by Hashemi et al. with data from Iran, a much different HI response could occur in some other environments.