Effect of sowing date and density on sink/source relationship and canopy light transmission of summer maize (Zea mays L.)

An experiment involving 2 cultivars, and 3 sowing dates and densities was conducted in Laizhou Experimental Station of China Agricultural University in 2008~2009 with the objective of selecting the optimum cultivation pattern. The effects of sowing date and density on sink/source relationship and canopy light transmission of summer maize population were also analyzed in the experiment. The results indicate higher sink/source indices under sowing date before June 22 at a density of 6.00×10⁴~ 7.50×10⁴·hm^-2 (semi-compact variety “Jinhai No. 5”) or 6.75×10⁴~8.25×10⁴·hm^-2 (compact variety “Zhengdan 958”). At this rate, LAI is 4.88~5.97 at silking and 2.73~4.48 at maturity stage, light transmission is 21.09%~34.82% at silking and 27.97%~35.29% at maturity stage, ear-leaf Pn is 34.4~41.7 μmol(CO₂)·m^-2·s^-1. The optimum yield is 14 863.50 kg·hm^-2 for “Jinhai No. 5” sowed at June 15~17 with 7.50×10⁴·hm^-2 density, and 15 123.30 kg·hm^-2 for “Zhengdan 958” sowed at June 15~17 with 8.25×10⁴·hm^-2 density.