Nitrate retention and physiological adjustment of maize to soil amendment with superabsorbent polymers A. Egrinya Eneji a, * , Robiul Islam b , P. An c , U.C. Amalu a a Department of Soil Science, University of Calabar, Nigeria b Department of Agronomy and Agricultural Extension, Rajshahi University, Rajshahi 6205, Bangladesh c Laboratory of Plant Ecophysiology, Arid Land Research Center, Tottori University, Japan article info Article history: Received 12 October 2012 Received in revised form 14 February 2013 Accepted 21 February 2013 Available online 21 March 2013 Keywords: Stress physiology Irrigation Maize Nitrate leaching Drought stress Superabsorbent polymer abstract Underground water pollution associated with nitrate leaching has become a major concern in areas with intensive cereal production; in areas with dry climates, water scarcity is the main limitation to crop production. We thus hypothesized that use of super absorbent polymers (SAP) may effectively increase nitrogen use efficiency by minimizing leaching and enhancing water and nitrate retention in the soil. Here, we evaluated nitrate movement in soils amended with SAP and determined changes in maize growth based on enzyme activities and physiological parameters. Nitrate retention was studied in six undisturbed soil lysimeters under different fertilizer (standard, medium or 75% and low, or 50% of standard) rates with (30 kg/ha) or without SAP. Maize yield decreased 20% under medium and 38% under low fertilizer rates but SAP application increased yield (P < 0.05) by 44% at medium and 80.3% at low fertilizer levels. Use of SAP plus only half the standard fertilizer rate (150 kg urea, and 33 kg each of superphosphate and potassium sulphate) minimized nitrate leaching and enhanced uptake with little change in yield relative to the standard fertilizer rate. On the evaluation of SAP at three irrigation levels (adequate, moderate and deficit), we found that the relative water content (RWC) and leaf water potential (j 1 ) were much higher in plants treated with SAP and under deficit irrigation, the SAP increased maize biomass by 99% compared with only 11% under adequate irrigation and 39% under moderate irrigation. Plants treated with SAP under deficit irrigation showed reduced stress signals based on the superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX) and glutathione reductase (GR) activities in leaves. The improved growth of maize treated with SAP under deficit irrigation was ascribed to maintenance of higher RWC, intercellular carbon dioxide concentration and net photosynthetic and transpiration rates. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction The ever increasing rate of inorganic fertilizer use in modern agricultural production has raised quite some concern about environmental safety and sustainability. Some studies (e.g. Yuan et al. 1995; Zhu and Chen, 2002; Li and Li, 2000) have shown that much of the excessively applied fertilizer was lost through leaching, resulting to serious environmental hazards, including soil acidifi- cation, heavy metal contamination and greenhouse gas emission. Nitrate leaching and the resulting ground water contamination are related to N fertilizer use in agricultural land worldwide (Ibnoussina et al., 2006). Although necessary for profitable cereal production, excessive use of N fertilizer may have adverse effects on groundwater quality (Schepers et al., 1991); much of the nitrogen leached from soil is in nitrate form and the leaching losses were influenced by the amount applied (Brandi-Dohrn et al., 1997; Owens et al., 1999; Kuo et al., 2001; Ibnoussina et al., 2006). In some countries like China, overuse of N fertilizer has caused a decline in pH and soil acidification far in excess of that caused by acid rain (Zhao et al., 2010). Thus, the challenge is to develop timely and viable alternative soil-water-crop management system to mitigate the worsening trends in environmental degradation and agricul- tural productivity. Use of water-saving super absorbent polymers (SAP) may be an effective way to increase nutrient use efficiency in crops (Lentz and Sojka, 1994; Lentz et al., 1998). When polymers are incorporated with soil, they presumably retain large quantities of nutrients, which are released as required by the plant. Thus, plant growth * Corresponding author. E-mail address: aeeneji@yahoo.co.uk (A. Egrinya Eneji). Contents lists available at SciVerse ScienceDirect Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro 0959-6526/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jclepro.2013.02.027 Journal of Cleaner Production 52 (2013) 474e480