Application of a Polyphosphate Fertilizer Treatment Enhances the Growth Rate of Lettuce Seedlings in a Commercial Plant Factory

Abstract

Several commercial plant factories cultivate lettuce, and the crop growth rate is an important factor related to profitability. The early development of lettuce is affected by phosphorus uptake, and plants absorb polyphosphates more stably than they do monophosphates. This study was conducted to evaluate the growth rate of lettuce (Lactuca sativa L. 'Caipira') during a polyphosphate treatment. Phosphorus was used in various combinations with potassium monophosphate (KH 2 PO 4 ) and potassium polyphosphate (K 5 P 3 O 10 ), specifically 32.4 + 15 (M2P1), 16.6 + 29.9 (M1P2), and 0.1 + 44.9 (M0P3) mg•L -1 , and 48 mg•L -1 KH 2 PO 4 as the control. The leaf length, leaf width, leaf area, and fresh and dry weights increased significantly with high polyphosphate concentrations (M0P3). The growth rate of the roots, the total root length, the root surface area, and the number of root tips were significantly increased in M0P3. Leaf growth was significantly different in the later stages of lettuce growth, whereas root growth was significantly different in the early stages. The results of this study suggest that the growth rate of lettuce can be improved by increasing the polyphosphate concentration, which could positively affect the profitability of commercial plant factories.