Growing carrots hydroponically using perlite substrates

Perlite substrate and nutrient solution were studied for growing carrot [Daucus carota L. cv. Dr. Carotene 5] hydroponically. Three independent studies were conducted to determine the size of perlite particle and concentrations of nutrient solution for growing carrot in hydroponics by evaluating their effects on growth, root yield and qualities of carrot. In the first study, carrots were grown in 1.2 or 5.0 mm with 12.5, 25, 50 and 75% ‘Enshi’ nutrient solution. Plants grown in 1.2 mm perlites with 50 and 75% nutrient solution produced about 15 and 28% higher root yield, respectively than those plants grown in 5.0 mm with same concentration, which was attributed by its longer roots. In the second study, carrots were grown in 0.6, 1.2, 2.5, and 5.0 mm perlites and with 25, 50, 100, 200, and 300% of nutrient solution. It was found that, carrot plants grown in 0.6 mm perlite supplied with 100% nutrient solution produced significantly higher root yield compared to larger perlite particles and higher concentrations of nutrient solution. In the third study, once used perlites of 0.3, 0.6, and 1.2 mm particle and 50, 75, 100, and 150% nutrient solution were investigated and greater root yield was obtained from carrots grown in 0.6 mm than in 0.3 or 1.2 mm perlite with 75% nutrient solution. Carrots grown in 0.3 mm perlites produced shorter roots, wider near the proximal end and whitish in the distal end due to excessive water content causing oxygen deficiency. Carrot root length was greatly hampered leading to decreased root yield in plants grown in 0.3 mm perlites compared to other perlite sizes at all concentrations except 100%. This ultra fine perlite hold excessive water causing oxygen deficiency in the substrate air zone and as a result roots become whitish with reduced amount of carotenoids content. Reused perlite culture in the third study lead to maximum root yield at 75% nutrient solution whereas it was with 100% in the second study, which was possibly due to residual nutrient available in the reused perlite which in turn lowers the demand of nutrients in the second culture. Year and growing season along with reused perlite has results in lower root yield and quality in the last two cultures in autumn 2009 and 2010. Therefore, we recommended 0.6 mm perlite and 100% (for first culture) or 75% (for second culture) ‘Enshi’ nutrient solution for growing carrots hydroponically with maximum yield and higher quality.