Chelated copper reduces yet manganese fertilizer increases calcium-silica fouling in brackish water drip irrigation systems

Highlights

• Effect of manganese and copper fertilizers on fouling of drip irrigation systems was analyzed.

• EDTA-Cu fertilizer significantly reduced calcium and silicate fouling in the irrigator runners.

• Use of EDTA-Cu fertilizer in brackish water drip irrigation is strongly recommended.

Abstract

Water scarcity and deficiency of trace elements (e.g., Cu and Mn) in soils of arid and semi-arid areas are major constrains to crop growth and development. The application of brackish water drip irrigation system (BWDIs), coupled with trace elements, is probably an effective way to solve this problem. However, fouling problems caused by trace elements in BWDIs were inevitable. Therefore, this paper evaluates the mechanism of different types of trace element chelated fertilizers on the fouling of emitters in BWDIs by using long-period, high-frequency periodic flow monitoring and mineral fraction analysis. The influence of chelated fertilizers such as copper (EDTA-Cu) and manganese (EDTA-Mn), and traditional micro-fertilizers copper sulfate (CuSO₄) and manganese sulfate (MnSO₄) on emitter fouling in BWDIs were investigated. Results suggested, compared with CK, the EDTA-Cu effectively alleviated the emitter fouling, increasing the average discharge ratio (Dra) and Christiansen coefficient of uniformity (CU) by 21.0%− 28.9% and 36.7%− 67.6%, respectively. Due to the strong adsorption ability, EDTA-Cu adsorb the Ca²⁺ and Mg²⁺ in BWDIs, which enhanced the structural stability, reduced the flocculation and deposition ability in the fouling, and indirectly reduced the content of calcium and silica fouling. In addition, compared with CK, the EDTA-Mn significantly aggravated the emitter fouling in BWDIs, decreasing the Dra and CU by 18.2%− 22.5% and 24.5%− 43.1% respectively. EDTA-Mn directly increased the content of Ca²⁺ and Mg²⁺ in BWDIs due to strong flocculation, which destroyed the morphology of EDTA-Mn chelates and indirectly increased the content of calcium silica fouling (calcite, muscovite, k-feldspar, dolomite and chlorite), thus reduced the anti-clogging ability of BWDIs. Considering these results, this study does not recommend the application of EDTA-Mn for manganese fertilizer in BWDIs. This study provides a new perspective on the rapid application of micronutrient fertilization in BWDIs, with potential implications for sustainable development in arid and semi-arid areas.

Introduction

Scarcity of fresh water resource and soil micronutrient in arid and semi-arid regions are major constrain, restricting the sustainable agricultural development and soil environmental safety (Oliver and Gregory, 2015, Fang and Zhang, 2020, Zhi et al., 2022). The effective utilization of inferior water could be a meaningful measure to fulfill the irrigation water demands. China's arid regions, especially in the northwest, are rich in brackish water resources. Although the abundant resources of brackish water are being extensively successfully utilized for agricultural irrigation (Xie et al., 2011, Zhu et al., 2019), the direct brackish water irrigation due to high salinity may be detrimental to the soil environment and crop health (Zhao et al., 2020). The brackish water drip irrigation systems (BWDIs) due its precision, reduce the salt stress in soil root zone(Chen et al., 2020), and improve the crop growth environment (He et al., 2017). In addition, brackish water contains high concentrations of calcium and magnesium ions, resulting in precipitate and particulate fouling in emitter flow channels of BWDIs (Zhangzhong et al., 2016). Consequently, reduced fertilization and irrigation uniformity of BWDIs, and even scrapped the whole drip irrigation system.

So far, research advances alleviation of BWDIs clogging mainly focused on changing water quality characteristics (Rohit Katuri et al., 2019) and magnetization methods (Sahin et al., 2012, Liu et al., 2021b). (Lili et al., 2021) conducted a study on the effect of water salinity on emitter clogging in BWDIs, and found that as the salinity of brackish water increases it promotes the formation of clogging substances. Only few studies have examined the effect of BWDIs on emitter clogging under different types of fertilizer application. (Liu et al., 2021a) stated that the different types of fertilizer are the key factors affecting emitter clogging in BWDIs. (Wang et al., 2020) suggested, ammonium phosphate reduced emitter clogging of BWDIs. Meanwhile, (Ma et al., 2020) and (Muhammad et al., 2021) reported that, the application of acid based phosphate (such as, ammonium polyphosphate and urea phosphate) fertilizer in saline waters significantly reduced the emitter clogging. Therefore, reasonable selection of fertilizer type would provide a new perspective to resolve the emitter clogging issue in BWDIs. Recently, chelated trace elements attracted wide attention, and broad application prospect (Souri and Hatamian, 2019). Manganese and copper are essential trace elements for crop growth and development, and their deficiency not only affects crop quality but also soil texture (Li et al., 2020). According to the survey, there is a relative lack of manganese and copper, the trace elements required by crops, in the soil of the arid regions of northwest China, especially in Xinjiang's Tarim Basin and its surrounding areas(Zhang et al., 2005; Han et al., 2010; Saifuding et al., 2010; Hu et al., 2019). Therefore, the supplementation of trace element manganese and copper fertilizer by drip irrigation, which is not only easy to operate but also harmless to crops, has become the most effective way at present. So far, the previous literatures extensively reported the effects of manganese and copper fertilizer on improving crop yield and fertilizer use efficiency(Fageria and Santos, 2014; Wang et al., 2019). However, the critical effects of aforementioned fertilizer on emitter clogging in BWDIs has not been explored yet. Chelated (EDTA) fertilizer is rich in carboxyl, hydroxyl, amino and other active functional groups, which will react with Ca²⁺ and Mg²⁺ in brackish water and produce chemical fouling (Li et al., 2019a), resulting in clogging of drip irrigation system.

Thus, two types of EDTA copper (EDTA-Cu) and manganese (EDTA-Mn) fertilizers, and two types of traditional micro-fertilizers (Copper sulfate: CuSO₄, manganese sulfate: MnSO₄) were studied. The effect of micronutrient fertilizers on fouling in BWDIs were investigated by means of X-ray diffraction. The objectives of this study were: 1) to clarify the effects of EDTA-Cu and EDTA-Mn fertilizer on hydraulic performance and fouling in BWDIs; 2) to reveal the influence mechanism and regulation pathway of EDTA-Cu and EDTA-Mn fertilizer on calcium-silica fouling in BWDIs.