Yield Response of Corn to Crowding Stress

Plants grown at noncompetitive densities (isolated plants) can be used to relate competitive pressure on yield and yield components at high plant densities. The main objective of this research was to quantify the sensitivity of grain yield and its components to manipulation of crowding stress in corn (Zea mays L.). The experiment was conducted in Deerfield, MA (1986, 1987, and 2000), and Shoush, Iran (1998 and 1999). Three single-ear corn hybrids were planted at six densities (0.25, 3, 4.5, 6, 9, and 12 plants m -2 ), the lowest density being considered an isolated density. The higher three densities (6, 9, and 12 plants m -2 ) were combined with three removal treatments, consisting of removal of alternate plants in rows at different stages of growth. Intensity of competition was quantified by comparing grain yield and its components of plants in these densities with those of isolated plants. The highest grain yield in all experimental sites was obtained from 9 plants m -2 and for total biomass yield between 9 and 12 plants m -2 . Kernel yield per plant decreased linearly in all hybrids as plant density intensified. All yield components had a linear decline in response to increased competition pressure. The reduction in kernel yield was attributed most to the reduction in number of kernels per row. Removal treatments indicated that early competition during vegetative growth had no or little effect on final grain yield. Plant competition between the vegetative stage and anthesis had a large effect on grain yield reduction, which ranged from 8 to 21% in different hybrids and experimental sites. Increased assimilate supply through plant removal again confirmed that adjustments in grain yield occurred primarily through kernel number per row.

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