Effects of pruning and nutrition on growth and yield of hydroponic tomatoes (Lycopersicon esculentum Mill)

[摘要] ENGLISH ABSTRACT: The potential importance of soilless production, particularly in tomatoes, in an increasinglywater scarce South Africa prompts a need for research under local conditions. In soillessproduction systems the application and availability of nutrients is closely linked to that ofwater, necessitating the research of methods to increase water and fertiliser use efficiency insoilless production systems, while diminishing environmental pollution and maintaining, orultimately improving, tomato yield and quality. Poor management of hydroponic fertigationwater results in pollution, and wastes precious water and expensive fertiliser. Pruning is animportant cultural practise for ensuring high productivity of hydroponic tomatoes. Adaptingpruning practises to climatic conditions could be a cheap and effective manner to improveproductivity without increasing inputs. Improving water and fertiliser use efficiency is crucialto ensuring sustainable production of intensive crops, such as the tomato. Three experimentswere carried out to investigate the effects of pruning and fertilisation on growth and yield andwater and fertiliser use efficiency of hydroponic tomatoes.In the first experiment the effect of EC (electrical conductivity), irrigation frequencyand growing media on water use, nutrient uptake, yield and quality of greenhouse tomato wasexamined. A factorial design with split plots was used. Two EC treatments (1 and 2 mS.cm-1)in factorial arrangement with 3 irrigation treatments (5x, 10x, 20x) were applied to the mainplots. Plants grown in different growing media (coir, sand, sawdust) represented the splitplots. Plants grown at EC 1 mS.cm-1 were still able to uptake sufficient nutrients to achieveleaf nutrient contents associated with optimal production. Also, increasing the absolutenutrient concentration had a small effect on nutrient uptake. The organic media, coir andsawdust, reduced available N early in the tomato crop life, and tomatoes grown in coir hadreduced Ca uptake compared to plants grown in sand and sawdust. Coir grown plants usedmore water compared to sand and sawdust grown plants. Plants grown at EC 1 mS.cm-1 usedless water compared to plants grown at EC 2 mS.cm-1. Tomatoes grown at an EC 1 mS.cm-1did not differ significantly from higher EC plants in terms of marketable and green fruit yield.Plants cultivated at the lower EC had significantly lower percentage soluble solids content(Brix) compared to the higher EC treatment.The second experiment examined the effect of leaf and fruit pruning on fruit size,total yield and marketable yield of tomatoes. Plants were grown using the high wire systemand pruned to two stems. Three different leaf pruning treatments were applied: no leafpruning, pruning every 2nd young leaf after 1m plant height, and pruning every 2nd young leafafter 2m plant height. Two fruit pruning treatments were also applied: no fruit pruning and trusses pruned to 4 fruits. The experiment used a factorial design. Leaf pruning treatmentshad no effect and this was probably due to too late a removal of young leaves. Fruit pruningresulted in no significant difference between treatments in terms of marketable yield. Plantswith unpruned trusses did have a significantly higher total yield, higher early yield, loweraverage marketable fruit weight, and higher yield of unmarketable fruit (particularly smallfruit compared to the pruned treatment). From these results it can be concluded that fruitpruning isn't necessary on short tomato crops but this may be different over a longercropping cycle.The third experiment determined the combined effects of different EC and stempruning practices on nutrition, growth and early yield of hydroponically grown tomatoes incoir. A factorial design was used, with two EC treatments (1 and 2 mS.cm-1) in factorialarrangement with 2 stem pruning treatments (single and double). Stem pruning had littleeffect on plant growth but did alter plant development. Plants pruned to two stems producedsignificantly more trusses, but did not produce a significantly higher DM or leaf areacompared to single stem plants. Stem pruning's major effect appears to be influencing fruitload; this may in the long term result in differences in plant growth and nutrition. EC 1mS.cm-1 plants produced significantly lower leaf area and organ dry masses but had asignificantly higher marketable yield compared to EC 2 mS.cm-1 plants. Over fertilisation inyoung tomatoes can negatively impact on early yield, whereas lower fertiliser application inearly tomato growth improves early yield but limits canopy development which may limitplant productivity in the long term. These differences in growth are believed to be primarilyrelated to differences in N and P nutrition.

[发布机构] Stellenbosch University