Ecological and agronomic aspects of a pear and vegetable interculture system

Abstract

The objectives of this study were to characterise the productivity and resource use efficiency of an experimental interculture system and to develop methods for the evaluation and optimisation of interculture. The experimental system consisted of a mature pear orchard intercropped vegetables. The first experiment used a phytometer technique in order to evaluate the response of a range of understorey vegetables (carrot, onion, pea, radish and lemon balm) to the aerial environment created/modified by the trees. The main conclusion was that most vegetables could be intercropped given a suitable soil environment. Some changes in crop morphology were identified in positions directly under the canopy. Radish was selected for further study. Novel techniques for the measurement of the transmissivity of the tree canopy to photosynthetically active radiation (PAR) were developed and tested. The canopy was found to be around 70% transmissive when averaged over the orchard floor. Areas directly under the canopy received around 50% of the incoming radiation. The response of radish to various levels of PAR was characterised using a shade experiment. A 50% reduction in PAR resulted and a 65% reduction in yield measured as mean bulb diameter but did not affect the mean total dry weight of the plants. This was due to the plants partitioning proportionately more dry matter to the leaves. A few individual plants, when grown at 30% PAR had bulb diameters equivalent to the 100% mean. This was taken as an indication of the potential for increasing yields by genotype selection. The land equivalents ratio for the system when calculated indicated that 50-100% more land would be required in order to obtain the same yield from monocultures, depending on the spatial arrangement selected. The radish component did underyield in positions directly beneath the canopy. Experiments with artificial fertiliser (NPK) and shade indicated that PAR intensity coupled with some soil factor other than NPK concentration were implicated.