Identification of optimum potassium nutrition of greenhouse plants grown in recirculating subirrigation

Abstract

Recirculating subirrigation has the potential to reduce run-off of water and fertilizers when growing greenhouse plants. Past studies have focused on nitrogen and phosphorous nutrition of plants grown in subirrigation. The overall objective of this research was to determine the optimum potassium nutrition of greenhouse plants grown in recirculating subirrigation. New Guinea impatiens 'Ovation Salmon Pink Swirl' were grown in recirculating subirrigation trays using 0 -12 mM K, with constant 1.5 mM P and 8.0 mM N. Optimum growth was noted at 1.0 - 1.5 mM K, which was half the recommended rate for New Guinea impatiens grown with top water. Growing medium conductivity and K concentration were highest in the top layer extract compared to the middle and bottom layer extracts. Experiment 2 was conducted to test the effects of increased K levels, up to 24 mM K, on different types of greenhouse plants. New Guinea impatiens 'Cameo' and 'Illusion' grew the best at 2 mM K, vinca 'Pacifica Apricot' at 2 - 8 mM K and petunia 'Trailing Wave Misty Lilac' at 4 - 16 mM K. At the upper range of optimum fertilizer levels, salinity damage was not a problem due to "upward leaching" which sequestered the salts in the top layer out of the active root zone. Experiment 3 compared the optimum K fertilizer rates of vinca 'Pacifica Red' grown in recirculating subirrigation and top water. The plants grew the best in subirrigation at 2 mM K and in top water at 4 mM K. Fertilizer salt stratification occurred in the top layer of the growing media of both irrigation techniques, but was most evident in subirrigation. Experiment 3 also focused on the nutrient analysis of these plants. Subirrigated plants were more efficient in accumulating total available K in the most functional plant parts, without leachate loss. In the top watered plants, 50 to 80% of the total available K was lost in the leachate. The nutrient analysis reemphasized that a recirculating subirrigation system is more efficient, due to no leaching and the use of lower fertilizer levels to obtain optimum growth.