Effect of shading on the seedling growth of the leguminous shrub Leucaena leucocephala

Abstract

The growth of seedlings of the forage shrub legume Leucaena leucocephala cv. Cunningham was studied at three levels of shading (100, 57 and 35 per cent relative photosynthetic quantum flux) in a glasshouse. An additional treatment investigated the response of unshaded plants to nitrogen fertilizer applied twice weekly. Shading reduced total plant weight (3.83, 3.20, 2.46g), increased the shoot/root ratio, increased internode length and plant height. However, with increasing shade there was a linear increase in leaf area, and relative growth rate (RGR) of shoots was affected little. RGR of the roots declined sharply from 0.62 to 0.51g g -1 week-1 with shading. Only at the lowest luminance was the dry matter per cent of shoots decreased (32 per cent to 28 per cent). Leaves were larger and thinner in the shaded treatments but rate of leaf appearance was unaffected. Added nitrogen (= 225 kg N ha-1) increased uptake of nitrogen (by 68 per cent), nitrogen concentration (59 per cent) and leaf weight (24 per cent) but had no significant effect on plant height, number of leaves, RGR, or dry matter per cent of shoots. The poor seedling performance of leucaena in competition with other species does not appear to be due to a failure to tolerate shade. In this respect it appears to be better than some other tropical pasture legumes.