Planting date (PD) studies with cotton (Gossypium hirsutum L.) have not been conducted in Louisiana since the introduction of BT varieties and eradication of the boll weevil. Eight cotton varieties were planted at eight dates (25 Mar; 5, 15 and 28 April; 6, 20 and 27 May; and 7 June) on Gigger silt loam (fine-silty, mixed, thermic Typic Fragidaulf) in 2003 and 2004. Soil and air temperature and photosynthetically active radiation (PAR) were recorded hourly from planting through harvest for each PD. The rate of seedling emergence and emergence percentage were lower at 25 March and 5 April PD because of low soil and air temperature and high rainfall. Lint yields were highest at PD between 15 April and 6 May. Cultivar x PD yield interactions were significant because earlier maturing cultivars had a wider optimal planting window than later maturing cultivars. Yield reductions at late May and early June PD were associated with lower total seasonal PAR values, but especially with lower PAR during boll fill. Cotton at the earliest planting dates had the highest levels of PAR but the reduced stands prevented full utilization of PAR in yield production.
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