THE EFFECT OF ELECTRICAL CONDUCTIVITY AND STEM PRUNING ON THE GROWTH AND EARLY YIELD OF HYDROPONIC TOMATOES GROWN IN COIR

Poor management of hydroponic fertigation water results in pollution and wastes precious water and expensive fertiliser. Improving fertiliser use efficiency is crucial to ensuring sustainable production of intensive crops, such as the tomato (Lycopersicon esculentum). A better understanding of the effect of nutrition and pruning on plant growth could help achieve this. An experiment was conducted to determine the effects of different EC and stem pruning practices on nutrition, growth and early yield of hydroponically grown tomatoes in coir. A factorial design was used, and the experiment was conducted in an unheated plastic covered greenhouse. Two EC treatments (1 and 2 mS cm^-1) in factorial arrangement, with 2 stem pruning treatments (single and double) were applied. Stem pruning had little effect on plant growth but did alter plant development. Plants pruned to two stems produced significantly more trusses, but did not produce a significantly higher DM or leaf area compared to single stem plants. Stem pruning’s major effect appears to be influencing fruit load; this may in the long term result in differences in plant growth and nutrition. EC 1 mS cm^-1 plants produced significantly lower leaf area and organ dry masses but had a significantly higher marketable yield compared to EC 2 mS cm^-1 plants. Over fertilisation in young tomatoes appears to negatively impact early fruit set and reduce early yield. Lower fertiliser application during mild winter conditions, early in a tomato crop improves fruit set and early yield but limits canopy development. This may limit plant productivity in the long term. These differences in growth are believed to be primarily related to differences in N and P nutrition.