An alternative approach to the analysis of mixed cropping experiments. 2. Marketable yield.

The effects of competition on marketable yield are derived from those on biomass by means of the relation between individual plant biomass and harvest index. A method is presented to estimate competition effects and advantage of mixed cropping directly from the data of marketable yield. The effect of spp. composition and population density on the advantage of mixed cropping, measured by the land equivalent ratio, is partitioned into an effect due to better resource exploitation (niche differentiation), a favourable influence of mixed cropping on harvest index and an effect due to density which can also be achieved by growing monocrops at a higher density. The approach is illustrated with the results of an experiment on mixed cropping of maize and groundnuts. (Abstract retrieved from CAB Abstracts by CABI’s permission

Effects of light and temperature on lettuce seedlings.

In the first of 2 experiments lettuces were grown either under natural light conditions in the glasshouse in December and January or under 8- or 16-h daylengths, with several temperature regimes, and the leaf area per plant was measured after 22 and 45 days. Under natural light growth during the first 22 days was slight but subsequent growth was greatest with a light/dark temperature regime of 13/13 deg C, followed by one of 17/17 deg . With an 8-h day growth with diurnally changing temperatures was much greater than with constant ones, the best results being obtained with a regime of 25/17 deg . With a 16-h day the effect of diurnal temperature was much less marked and a constant high temperature regime of 21/21 deg gave better results than one of 25/17 deg . In the second experiment the plants were grown for 4 weeks under the same temperature regimes with 8- or 16-h daylengths, but the light intensity was varied by placing the plants at 2 vertical distances from the overhead lamps and all plants receiving a 16-h daylength were shaded by cheesecloth. The best results were obtained with a 16-h daylength with the plants placed close to the lamps; the effects of temperature were not so marked, but regimes of 25/17, 21/13 or 17/17 deg were the most satisfactory. (Abstract retrieved from CAB Abstracts by CABI’s permission