Effect of fertilizer solution concentrations on filter clogging in drip fertigation systems

Highlights

• Fertilizer solution concentrations affect the clogging of filter in drip fertigation systems.

• The clogging substances of filters were silicates, carbonate precipitates, and insoluble phosphates.

• The mechanism of clogging was physical and chemical coupling process.

Abstract

Drip irrigation using fertilizers is one of the commonly used methods to save fertilizer and minimize the impacts of fertilizer on the soil and the environment. However, the clogging issue of drip fertigation systems has been the major limitation and may lead to system damage if fertilizer solution concentrations are not appropriately selected. Therefore, the head loss, flow rates, and clogging substances of screen and disc filters were analyzed to evaluate the effect of different fertilizer solution concentrations on filter clogging under different injection rates (2%, 3%, and 4%) and fertilizer-water ratios (1:4, 1:5, and 1:6) in drip fertigation systems. The surface morphology and chemical composition of the clogging substances were analyzed by scanning electron microscopy and energy dispersive spectrometry (EDS). The results showed that the large injection rate caused uneven fertilization, and the recommend injection rates of the proportional fertilizer pump were 2% and 3%. In the same fertilizer solution concentration range, the difference in head loss of the screen filter (0.09–7.75 m) was larger than that of the disc filter (0.32–3.88 m), indicating that the anti-clogging performance of the disc filter was better. Meanwhile, the application scope of the fertilizer solution concentration of the screen filter was less than 0.117% and that of the disc filter was between 0.117% and 0.296%. There was a significant effect of the fertilizer solution concentrations on filter clogging (P < 0.05). The interaction between the fertilizer solution concentrations and filter types had a more significant effect on filter clogging (P < 0.01). The clogging substances consisted of undissolved phosphate fertilizers and silicates as well as carbonate and phosphate precipitations generated by chemical reactions. The clogging mechanism was a physical and chemical coupling process when using phosphate fertilizers. Therefore, the use of fertilizers, especially phosphate fertilizers, contributed to the generation of clogging substances. Fertilizer solution concentrations and type of fertilizers should therefore be considered in the anti-clogging performance of filters in drip fertigation systems.

Introduction

Drip irrigation systems can be used for fertilization, which can reduce fertilizer use, increase crop yield, and minimize the impact of fertilizer on the environment (Hernandez et al., 1991, Hanson et al., 2006, Ajdary et al., 2007, Li et al., 2016, Jayakumar et al., 2017). Therefore, drip fertigation is an efficient and precise fertilization method. However, the use of fertilizer contributes to the formation and development of clogging substances in the drip fertigation systems, and excessive fertilizer solution concentration aggravate the clogging process (Liu et al., 2017, Tang et al., 2018), reduce the service life of the system, and cause uneven fertilization, eventually resulting in a decrease in economic benefits. Meanwhile, drip fertigation is a commonly used method in arid and semi-arid regions for water and fertilizer-saving. Consequently, research on the anti-clogging performance of drip fertigation systems has practical significance for the widely use of the system.

To enhance the anti-clogging performance of drip fertigation systems, it is necessary for the used equipment to have efficient performance. Filters are the key equipment to prevent impurities in drip irrigation systems (Oron et al., 1979, McDonald et al., 1984, Tripathi et al., 2014), and their good hydraulic performance can ensure the efficient operation of the systems. Wu et al. (2015) found that the filtration efficiency of sand filters was 11.4–48.0%, which increased when used with disc filters. Many scholars have studied filter hydraulic parameters to evaluate the anti-clogging performance of different filters. Duran-Ros et al. (2009) concluded that the flow rate of emitters protected by disc filters had the smallest change when compared with other filters. Ribeiro et al. (2008) showed that the head loss changes in disc filters were more significant than those in non-woven synthetic fabric filters. Zong et al. (2012) studied the relationship between the filter head loss and flow rate when using muddy water, and thought that the head loss was a key parameter to evaluate filter performance.

Fertilizer solution concentration is another key factor that affects the clogging of drip fertigation systems. Various ions and impurities in fertilizer solutions react with the ions in water to form insoluble precipitates, thereby increasing the clogging degree of the drip fertigation system (Haynes, 1985, Li et al., 2007). Tang et al. (2018) stated that the fertilizer solution concentration was one of the factors affecting fertilization uniformity, and poor fertilization uniformity can lead to the clogging of drip irrigation systems. Li et al. (2015) inferred that the clogging effect of emitters was more obvious at higher fertilizer concentrations. Phosphorus is an essential nutrient for the growth of crops (Yamaji et al., 2017); however, the excessive use of phosphate fertilizer can easily cause water and soil pollution. Therefore, it is best to use drip irrigation systems to effectively use phosphate fertilizer. Studies have shown that phosphate fertilizer aggravate the clogging of drip irrigation systems, but the clogging risk of drip fertigation systems can be reduced by setting appropriate system operation patterns (Zhou et al., 2015, Tang et al., 2018). The anti-clogging performance of drip fertigation systems can be improved when fertilizer solution concentrations are matched with the performance of the filtration systems.

Research on the anti-clogging performance of drip irrigation systems has focused on the independent performance of each device and emitter clogging (Pei et al., 2014, Zhou et al., 2016, Feng et al., 2017). Studies on the filter anti-clogging performance are mostly based on the impurities in the water source, without considering the effect of fertilizers. Therefore, the fertilization process, filtration performance, and clogging substances of filters in drip fertigation systems need further study.

The objectives of this study were to (1) evaluate the uniformity of the fertilizer solution concentration under different combinations of injection rates and fertilizer-water ratios in drip fertigation systems; (2) explore the effects of different fertilizer solution concentrations on the hydraulic performance of filters, and the clogging substances of screen and disc filters. The results of this study will provide a reference for the anti-clogging research, aiming to promote the integrated water and fertilizer technology of drip fertigation systems in arid and semi-arid regions.