Nutrient uptake of cut roses grown on substrate

A continuous monitoring of nutrient uptake in crops is studied as a means to facilitate a more efficient nutrient application strategy and improve the control of product quantity and quality. Six years of data were collected from six glasshouse compartments on the cultivation of cut roses (Rosa hybrida L.). Data consisted of 7- and 21-day averages of solar radiation, air temperature and air humidity, glasshouse data on assimilation light and irrigation, and harvested number of stems and their biomass. Substrate consisted of cocos or rockwool. Nutrient composition in the substrate solution was maintained at a constant, recommended level by controlling the fertilizer dosage. Daily nutrient uptake was calculated from the difference in volume and electrical conductivity (EC) of supply and drainage water. Nutrient uptake of rose varied strongly with time and ranged from 0 to 5 meq per gram fresh weight growth. Variations were caused by technical disturbances like blocked sprinklers, diseases or heat stress. A strong variation in nutrient uptake may hamper product quality and quantity. The uptake data were analysed with a stepwise multiple regression. Nutrient uptake could be explained by a combination of climatic conditions, water supply and nutrient contents of the substrate solution. The combination of the total of all input variables explained 95 to 99% of the variation in nutrient uptake rate. Additionally, a more detail analysis was performed on a two-year series from three glasshouses on nutrient composition of the supplied water, the substrate water and the corresponding nutrient uptake rates. The uptake rate of the separate nutrients could partly be explained by their concentration in the supplied water and in the substrate water. The total, summed uptake of all nutrients correlated predominantly to nutrient concentrations in the substrate, and not to those in the supplied water. In a 100% recirculating fertigation system, the nutrients are added in response to their plant uptake and thus ideally result in a nutritionally balanced supply. Such a balanced nutrition may lead to maximum growth without nutrient shortages, in parallel with a low use of water and nutrients with minimum environmental losses.