Responses of Maize to Plant Population Density. I. Canopy Development, Light Relationships, and Vegetative Growth

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Abstract
Understanding of maize (Zea mays L.) canopy structure and light transmission over a wide range of plant population densities (PPD) is necessary in the formulation of maize intercrop associations. Experiments using a systematic (fan) design were conducted on Lake fine sand (hyperthermic, coated Typic Quartzipsamments) at Gainesville, FL (29°38′N), in 1985 and 1986 to assess the interrelationships among maize canopy structure, light interception, and vegetative growth over 15 PPD (0.8 to 15.4 plants m−2). Fractional light transmission (by canopy levels at different times up to noon), leaf area index (LAI), total dry matter (TDM) yield, plant height, and tiller number were recorded. Light interception was similar at 5 and 3 h before and at solar noon for each PPD measured at ground, ear, and below‐tassel levels. Leaf area and light interception were highly concentrated at ear level, but level of light interception shifted upward with increasing PPD. Maxima LAI were 1.7, 2.6, and 4.0 at tasseling for the 1.7, 2.6, and 6.3 plants m−2 respectively. Light interception by tassels was approximately 2, 30, and 40% for 1.9, 3.5, and 6.3 plants m−2, respectively, while that for whole canopy was 75, 90, and 97%, respectively. As early as 35 d after planting (DAP) canopy interception was 40, 60, and 75% for 1.9, 3.5, and 6.3 plants m−2, respectively. Leaf area index, TDM, crop growth rate, and plant height were significantly influenced by PPD. Tiller number decreased linearly with increasing PPD to no tillers at 3.5 plants m−2. We conclude that increasing PPD of maize increases LAI and vegetative DM yield but alters light distribution within the canopy by shifting it from lower to upper canopy strata and increasing fraction intercepted by tassels.