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Light Requirements of Yellow Nutsedge (Cyperus esculentus) and Light Interception by Crops

The influence of artificial shading (0, 30, 47, 70, 80, and 94% shade) on growth of yellow nutsedge (Cyperus esculentus L.) and the time required for developing canopies of several crops to intercept a given amount of light were investigated in field studies to estimate the potential of crops to compete with yellow nutsedge for light. Average number of shoots and tubers and total dry matter production of yellow nutsedge increased in direct proportion to increased amounts of light (correlation coefficient (r ≥.98). Compared to no shade, flower production was substantially reduced by 30 and 47% shade and was essentially absent under more dense treatments. Photosynthetically active radiation (PAR) measured at weekly intervals indicated that light interception occurred first within the drill row of crops, then on shoulders of planting beds, and finally in furrows. The most rapidly developing canopies studied [corn (Zea mays L.), potatoes (Solanum tuberosum L.), and safflower (Carthamus tinctorius L.)] intercepted 90% or greater PAR, including illumination in furrows, within 8 to 9 weeks after planting. About 12, 12, and 16 weeks were required for 80% interception for cowpeas [Vigna unguiculata (L.) Walp.], milo [Sorghum bicolor (L.) Moench.], and cotton (Gossypium hirsutum L.), respectively. Fall-planted barley (Hordeum vulgare L.) intercepted about 90% PAR by March 12. Alfalfa (Medicago sativa L.) intercepted about 90% PAR within 2 to 3 weeks after individual cuttings. Although onions (Allium cepa L.) planted in December intercepted 95% of the PAR in each of the two drill rows per bed about 26 weeks after planting, only 20 to 30% interception occurred in furrows and row middles.