Abstract
To determine the feasibility of reusing waste nutrient solution as an alternative fertilizer for vegetable production, we investigated the growth and shoot nutrient content of curled mallows (Malva verticillata L.) irrigated with tap water (pH 7.8, EC: 0.5 dS·m-1), nutrient solution (pH 5.7, EC: 2.7 dS·m-1) and waste nutrient solution (pH 5.0, EC: 2.2 dS·m-1 in average) collected from plant factories. Three waste nutrient solutions were applied in sequential order to a waste nutrient solution treatment and mineral compositions of irrigation solutions were analyzed. We measured the total number of leaves, fresh and dry weight, chlorophyll content (SPAD value) and total phenolic content of curled mallow shoots and analyzed shoot and soil nutrient content using inductively coupled plasma-optical emission spectrometer (ICP-OES). Curled mallows were harvested twice during the cultivation. Curled mallows irrigated with waste nutrient solutions had a similar fresh weight (yield), total phenolic content and number of leaves compared to those grown with fresh nutrient solution, and had higher fresh and dry weight, chlorophyll content (SPAD value) and percentage dry weight compared to those grown with tap water upon first and second harvest. The dry weight of curled mallows grown in waste nutrient solution was lower than that of plants grown in nutrient solution on first harvest, but there was no significant difference between the waste nutrient solution and nutrient solution groups on second harvest. Curled mallows irrigated with nutrient solution and waste nutrient solution showed similar mineral content. These results suggest that waste nutrient solution in curled mallow cultivation could be reused and provide more efficient and sustainable nutritional solutions that improve the productive yields of crops in the agriculture sector.
Highlights
In recent years, hydroponic systems have become increasingly popular in the greenhouse industry (Savvas & Gruda, 2018)
All waste nutrient solutions applied to WNS treatment group had lower electrical conductivity (EC) and pH levels and NO3, NH4, PO4 and K concentration compared to nutrient solution, while Mg, Na, Cl and SO4 concentrations were higher in waste nutrient solution
The dry weight indicates the amount of surplus carbohydrates from photosynthesis and respiration, and the results suggest that curled mallows irrigated with waste nutrient solution can accumulate similar amounts of carbohydrates to those irrigated with nutrient solution by second harvest
Summary
Hydroponic systems have become increasingly popular in the greenhouse industry (Savvas & Gruda, 2018). As a consequence of the development of the hydroponics industry, the amount of waste nutrient solution discharged from hydroponic systems has increased. Discharged waste nutrient solution generally contains high concentrations used to increase crop yield. Nutrient solutions in closed hydroponic systems are periodically dumped during crop cultivation to prevent accumulation of salt ions, which can cause serious growth disorders (Sánchez-Guerrero, Lorenzo, Medrano, Baille, & Castilla, 2009; Savvas, Meletiou, Margariti, Tsirogiannis, & Kotsiras, 2005; Savvas et al, 2007) and plant diseases that can reduce crop yield and even eliminate all crops at once (Badgery-Parker, 2002; Grewal, Maheshwari, & Parks, 2011). The volume and concentration of applied nutrient solution are generally higher than those required for plant growth in order to satisfy variability in irrigation equipment and to maximize crop yield (Grasselly et al, 2005; Rouphael & Colla, 2009)
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