Nitrate retention and physiological adjustment of maize to soil amendment with superabsorbent polymers

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 (psi(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. (C) 2013 Elsevier Ltd. All rights reserved.