Abstract
The ‘packed bag-fertilization (PF)’ method of controlled-release fertilizer was applied to tomato sand culture using a root-proof capillary wick watering system for ease of media reuse. Plant growth, marketable fruit yield, and elution percentage of fertilizer were compared in four treatments, which were combined with growing media (mixed soil and sand) and the nutrient supply method (mixed fertilizer (MF) and PF method). Plants of medium-fruited tomato were grown for 132 days from September 2009 to February 2010, up to the 7th fruit truss. There were no differences in the plant growth and marketable fruit yield in soil and sand media, and in MF and PF. In sand media, the incidence of ‘green back’, a fruit-colouring disorder, increased at the later trusses compared with soil media. Also, fruit acidity of sand media at all trusses was lower than that of soil media. This reduction in fruit quality was probably caused by K2O deficiency in sand media. At the end of the experiment, the fertilizer bag was removed from the media and analyzed. The elution percentages of total-N (T-N) and K2O were more than 80%, which were slightly lower in sand than in soil media. There was little difference in the elution percentages between MF and PF of sand media. Apparent K2O absorption per plant in the sand decreased by 4 g compared to that in the soil media. This difference was caused by the nutrient contents of the media before planting. As a result, fruit quality in the sand media was lower than that in the soil media. In conclusion, the PF in sand can sustain plant growth and yield at similar levels as soil or MF and with a similar elution percentage of fertilizer. However, sand media should be designed to show an improved fertilizer effect of K2O from the first to end of the growth stages greater than for soil media to decrease the incidence of ‘green back’ fruit and improve fruit quality.
