Nitrate and potassium uptake by greenhouse roses ( Rosa hybrida) along successive flower-cut cycles: a model and its calibration

Abstract

Rose ( Rosa hybrida L.) plants grown for cut-flower production in greenhouses produce flowers in flushes year-round. Crop models for this system must handle the cyclical nature of productivity, which is determined by the horticultural production methods. Nutrition was not accounted for in previous rose growth models, since little is known about uptake of the essential nutrients by rose roots. The aim of the current study was to measure uptake rates of nitrogen and potassium by roses, to be included in a production model. Rose plants var. ‘Kardinal’ were grown in the greenhouse in aero-hydroponics nutrient solution with 3 mM nitrate (NO 3)-N and 1 mM potassium (K). After several flower growth/harvest cycles, the plants were transferred to a growth chamber in groups of three, every 10 days. The growth chamber provided 25 °C and 16 h day length. The nutrient solutions were sampled periodically while maintaining the volume constant at 5 l, and analyzed for NO 3 and K concentrations reduction. The roots were harvested at the end of each depletion series, and their lengths measured. Influx of NO 3 and K into roots was obtained by fitting a Michaelis–Menten function to the concentration depletion data. There was a cyclic rhythm of both the nutrients’ influx rates over time, with a decline in uptake after shoot harvest, and an increase during flower development, with maximal values towards flower opening. The results were incorporated in a simulation model for nutrient uptake by roses along successive flower-cutting cycles. This simulation assumes a constant number of identical flowering branches, which would be cut sequentially at flower maturity, and result in new shoot growth, assumed to follow a logistic function of time. Uptake rates of NO 3 and K were assumed to follow the changes in leaf area and shoot nutrient percentage, to compensate for N and K demand by the shoot; the root system dimensions and its effective aging are assumed constant. Simulated N and K uptake agreed with published data of their accumulation and percentage in growing rose branches along a flower-cut cycle.