The most important aspect in successful management of soilless produced vegetables is the management of total NC (Maboko and Du Plooy, 2017). For optimal growth and development of the crop, it is essential that all the nutrient elements required for plant growth are present in optimal quantities in the nutrient solution. Nutrient solution concentration plays an important role in determining yield and quality of vegetable crops (Fallovo et al., 2009; Siddiqi et al., 1998). Many growers continue to adopt a liberal approach to fertilizer management, by applying high NC in an attempt to maximize crop yield with no attention to nutrient uptake by the crop (Li et al., 2001; Sonneveld and Voogt, 2009). Excessive application of NC results in saline or iron toxicity and nutrient excess or imbalance and increases osmotic pressure, whereas too low NC generally leads to nutrient deficiencies (Savvas and Adamidis, 1999; Sonneveld and Welles, 2005).
The environmental sustainability of open hydroponic systems has been questioned because a less consistent fraction of applied nutrient solution is discharged into the environment (Sonneveld, 2002). This fraction varies largely as a function of several parameters, but in normal growing conditions, it ranges between 20% and 50% (Grewal et al., 2011). Niederwieser and Du Plooy (2014) recommended that 10% to 20% of the volume of irrigated nutrient solution must drain freely out of the growing medium to leach excessive fertilizer and salts that might otherwise build up to toxic levels. This leads to an uncontrollable leakage of concentrated nutrient solution to the soil and then to the ground- or surface water, causing severe environmental pollution (Breś et al., 2013; Kläring, 2001).
As a supplement, foliar fertilizer application is gaining popularity among growers as a standard practice in agricultural crop production because it is more purposeful and environmentally friendly as opposed to soil fertilization (Maboko and Du Plooy, 2017). Foliar fertilization is mostly used to correct nutritional deficiencies in plants caused by improper supply of nutrients to plant roots (Ling and Silberbush, 2002). It offers a complementary means of providing nutrients during a critical phase of restricted nutrient supply (Mengel, 2002). The effects of strong binding of plant nutrients in soils and the difficulties in the acquisition of nutrients because of a particular soil condition can be alleviated by foliar fertilizer application (Kolota and Osińska, 2001; Mengel, 2002; Santos, 2013). It is also recognized that supplementary foliar fertilization during crop growth can improve the mineral status of plants and increase the crop yield and quality (Fageria et al., 2009; Kolota and Osińska, 2001). The beneficial effects of applying foliar plant nutrients, expressed as an increase in yield and improvement of crop quality, have been noted in many vegetable species such as gherkin (Cucumis sativus) (Abeyrathna et al., 2013) and tomatoes (Solanum lycopersicon) (Maboko and Du Plooy, 2017; Roosta and Hamidpour, 2011). Other advantages of foliar fertilizer application over soil application include a lower input of fertilizers due to improved utilization of nutrients and reduced risk of leaching from the soil (Kolota and Osińska, 2001; Komosa, 1990). However, the use of foliar nutrition with the aim of reducing NC through fertigation in hydroponic/soilless systems is limited.
The objective of this study was to decrease the NC used for fertigation while applying foliar fertilizer on mini-cucumber grown in sawdust growing medium.
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