Existing models of leaf-area expansion of Gramineae species are empirical and species-specific. To increase understanding of the mechanisms involved in leaf-area expansion, effects of environmental factors on leaf growth of the non-tillering species maize (Zea mays L.) were analysed quantitatively. A growth chamber experiment was carried out with the cultivar Luna including different combinations of temperature (day/night temperatures 13/8, 18/13, 23fl8 and 28/23°C) and photosynthetic-photon-flux density (PPFD) (104, 185 and 277 JUDol m-2 S-I). At 13/8°C, a large proportion of the plants died due to prolonged exposure to cold stress. Both high temperatures and high PPFDs increased leaf-appearance rate. Maximum leaf width was highest at intermediate temperatures and high PPFDs, and was strongly related to specific-leaf weight (R2. dj = 0.88). Leaf-elongation rate increased and leaf-elongation duration decreased with temperature, the resultant being a maximum final leaf length at 23fl8 °C. Leaf length decreased slightly with PPFD, caused by a shorter leafelongation duration. Leaf shape has been described with a new function and was different for Leaves I and 2 than for higher-positioned leaves. Leaf width was closely associated with specific leaf weight. The observed relationships can be used in dynamic simulation of leaf area based on plant morphology.

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A two-year field experiment was undertaken on an Alfisol in the forest-savanna transition zone of southwestern Nigeria, to study the effect of alley cropping, root barrier, application of N fertilizer and Leucaena leucocephala (Lam.) de Wit. prunings, on N utilization by maize and Leucaena hedgerows. The trial was conducted using a split-plot design with three replications. Mainplot treatments were alley cropping with Leucaena leucocephala planted at 4m interhedgerow spacing and control (no hedgerows). Four subplot treatments were with and without addition of hedgerow prunings, and with and without presence of root barriers. There were no significant effects of presence of Leucaena hedgerows and root barriers on maize grain yield. Leucaena hedgerows recovered about 7% of the 30 kgN/ha applied as (15NH4)2S04 to maize during one year. Application of hedgerow prunings increased maize yield by 82% and N-uptake in the grain by 50% over the treatment without prunings. Recoveries of 15N-labelled prunings and fertilizer N by maize plants were about 10 and 16% respectively. Prunings addition increased ~SN-fertilizer recovery in main season maize and the residual value during the minor season by about 36% over the treatment without prunings. Pruning N-use efficiency was higher for plants grown adjacent to the hedgerows than in the middle of alleys during main season and the reverse was observed during the minor season. Absence of a root barrier increased N-use from prunings. Large amounts of applied N in the system were unaccounted for. Results of the trial showed, that without root barrier there was no measurable below-ground N competition between Leucaena hedgerows and maize.

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