Elucidating distinct oxidative stress management, nutrient acquisition and yield responses of Pisum sativum L. fertigated with diluted and treated wastewater

Highlights

• Influence of different wastewater irrigation types on Pisum sativum productivity was investigated.

• Used wastewater fertigation types triggered modulations of soil characteristics.

• Fertigation with biologically treated or diluted wastewater decreased soil pH.

• Diluted and treated wastewater maintained optimum retention of nutrients by P. sativum.

• Application of treated or diluted wastewater conferred growth and yield enhancement to P. sativum.

Abstract

Fertigation of crops with untreated wastewater predominates in developing countries. Use of wastewater for crop irrigation poses a potential risk of food chain poisoning with toxicants. However, direct and indirect interaction of wastewater with soil properties and crop productivity has been rarely investigated. The current work was, therefore, planned to quantify the impact of canal water, biologically treated and untreated wastewater on soil properties, growth, biochemical, nutrient turnover and yield of pea (Pisum sativum L.) plants. Seeds of P. sativum were sown in soil filled pots irrigated with five different water types [canal water (CW), biologically treated wastewater (BTW), 50%, 75% and 100% wastewater (WW50, WW75 and WW100)]. The plant samples were collected after 35 days for biochemical analysis, while yield parameters were recorded at maturity. The results revealed a significantly higher growth and yield of pea plants irrigated with BTW followed by WW50 and CW irrigated plants as compared to other wastewater treatment types. Application of untreated wastewater (WW75 and WW100) resulted in stunted growth due to decrease in total chlorophylls, carotenoids, activities of SOD and POD enzymes, and increase in lipid peroxidation (MDA and H₂O₂) as compared to CW, BTW, and WW50. Pre- and post-harvest soil analysis revealed that application of concentrated wastewater caused soil alkalinization and subsequently limited the nutrient absorption by P. sativum plants. Growth enhancement of P. sativum under BTW might be a direct consequence of balanced accumulation of nutrients owing to alteration of soil properties. It was concluded that wastewater must be treated biologically or diluted with 50% of fresh canal water before application to agricultural fields in order to maintain soil nutrient level and sustainable crop productivity in the areas with less availability of fresh canal water.

Introduction

The agricultural sector, mainstay of Pakistan's economy (18.5% of GDP in 2019–20), ensures food safety and poverty alleviation. It engages 37.4% of manpower employment and is one of the chief sources of profit for rural society (Agriculture Statistics of Pakistan, 2020). Pakistan is amongst the countries which are facing severe water scarcity and per capita available water was 1000 m³ in 2016 which is estimated to be decreased up to 700 m³ in 2025 (Akhtar et al., 2018). About 93% of total freshwater available in Pakistan is utilized for crop irrigation, therefore, it is necessary to seek water recycling sources to ensure sustainable water supply for crop productivity (Sleet, 2019). Moreover, urban and industrial wastewater production is 6.8 billion m³ per annum, out of which 0.876 billion m³ was directly used for crop production on an agricultural land area of 32500 ha (Khan et al., 2020). Besides, about 26% of total vegetables production is based upon wastewater fertigation in the country (Naz et al., 2016).

Increasing scarcity and continuous pollution of freshwater sources compelled the farming communities to increase the urban and industrial wastewater utilization for crop irrigation (Ashraf et al., 2018). Judicious use of wastewater in agriculture, especially in areas where underground water is unsuitable for irrigation, may be helpful in nutrients recycling, cost reduction, water conservation and reduction in water pollution up to some extent (Ahmed et al., 2016, Kausar et al., 2017); however, its long-term application reported to modify soil properties and be noxious for plant growth, development and productivity (Alderson et al., 2015). Wastewater fertigation to crops may change physico-chemical characteristics of soil, its fertility, and elevation in concentrations of salts which subsequently alter the osmotic pressure in the rhizosphere (Elgallal et al., 2016, Farhadkhani et al., 2018). These salts include salts of trace elements i.e. (Cu, Mn, Cd, As, Pb, Zn, Cr, Mo, B, Co), polycyclic aromatic hydrocarbons (PAHs), organic pollutants, detergents, fertilizers and pesticides which are non-essential and highly poisonous to plants together with animals and humans (Egbuikwem et al., 2020).

Besides, use of wastewater raises the levels of toxicants in soil, which may subsequently enter into edible plant parts such as vegetables and cereals and imposes health hazard to consumers (Ghosh et al., 2012, Libutti et al., 2018). A continuous use of untreated wastewater is not only hazardous for efficient plant metabolism but also harmful for humans due to contaminated food. In planta, it affects photosynthesis, respiration and water balance. Together with mineral unbalance, high production of reactive oxygen species and/or altered enzymatic activities has been reported by Singh and Laura, 2014, Ain et al., 2019. Furthermore, the adverse effects arisen from reuse of industrial wastewater are species specific and depend upon plant nutrient uptake capabilities and patterns of applied wastewater (Ayoub et al., 2016, Ain et al., 2019). In Vigna radiate L. and Pisum sativum L., the fertigation with industrial and sewage wastewater decreased nutrient uptake, biomass accumulation, enzymatic activities, rate of photosynthesis and yield as compared to biological treated wastewater irrigation (Yasmeen et al., 2014, Singh and Laura, 2014). Diminished growth and yield was the result of less photosynthesis and less mineral acquisition by the plants (Hajihashemi et al., 2020).

Pea (Pisum sativum L.) is an important legume vegetable which is cultivated for food and fodder purposes. In Pakistan, the average yield is 55 t per ha and the cultivated area is 26,600 ha. Irrigation of P. sativum crop with municipal wastewater is a common practice in the peripheral areas of various industrially-centered cities of Pakistan. Seeds of P. sativum are composed of essential proteins but wastewater irrigation may result in uptake of toxicants posing serious risks to the consumers.

The present study is investigating the effect of canal water, biologically treated and various dilutions of untreated wastewater (blackish water) on soil properties, physio-biochemical attributes, nutrient translocation and yield of P. sativum. The specific objectives of current study were (a) to monitor the changes in physico-chemical properties of soil under various wastewater fertigation regimes (b) to establish correlations among plant’s morpho-physio-biochemical attributes to find out which parameters in biomass production and yield are affected by the treatments by using P. sativum as a test plant and (c) finally to determine the applicable dilution levels for municipal effluents to be practiced as low cost fertigation strategies for growing vegetable and other crops cultivation.