Nitrogen Fertilization Effect on Soil Water and Wheat Yield in the Chinese Loess Plateau

Published in Agron. J. 105:143–149 (2013) doi:10.2134/agronj2012.0067 Copyright © 2013 by the American Society of Agronomy, 5585 Guilford Road, Madison, WI 53711. All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. I dryland cropping systems, soil available water and N content are some of the major limiting factors for crop production (Lenssen et al., 2007; Sainju et al., 2009). Precipitation, being the major source of available water for dryland crops, needs to be used effi ciently to sustain yields. Crops may not be able to use N effi ciently if water is a limiting factor for growth and production. Th is may result in increased residual N accumulation in the soil aft er crop harvest, which can degrade environmental quality through increased N leaching into the groundwater and emissions of greenhouse gases, such as N2O. On the other hand, soils enriched with N through manures and fertilizers can increase crop yields in the presence of abundant soil water that may result in increased soil water depletion. Nitrogen fertilization can increase dryland winter wheat yields and WUE compared to no N fertilization by better utilizing the available soil water (Singh et al., 1975; Nielsen and Halvorson, 1991; Frederick and Camberato, 1995; Hatfi eld et al., 2001; Fan et al., 2005a). Th is is because N fertilization can increase winter wheat root growth and biomass, effi ciently utilize water stored during the fallow period, and absorb more soil water during the crop growing season in water-limited semiarid regions (Frederick and Camberato, 1995; Hatfi eld et al., 2001; Fan et al., 2005a). Increased aboveground biomass as a result of N fertilization can increase water loss from the crop canopy due to greater evapotranspiration (ET) (Ritchie and Johnson, 1990; Nielsen and Halvorson, 1991). In semiarid regions of the central U.S. Great Plains and the Loess Plateau of China, increased N fertilization can increase the plant water defi cit (Nielsen and Halvorson, 1991; Frederick and Camberato, 1995; Huang et al., 2003; Fan et al., 2005b). Th erefore, N fertilization rates to winter wheat need to be adjusted to sustain WUE and grain yield in these semiarid regions. Dryland crop yields are usually infl uenced by precipitation during and aft er the growing season (Li, 1983; An et al., 2003; Stone and Schlegel, 2006). To increase soil water storage and the amount of water available to the succeeding crop, fallowing is usually practiced (Lyon et al., 1998; Moret et al., 2006; Nielsen and Vigil, 2010). Th e eff ect of fallowing on the soil water balance and PSE during the fallow period is known (Tanaka and Anderson, 1997; Lyon et al., 1998; Moret et al., 2006; Nielsen and Vigil, 2010). In the Loess Plateau of China, a short summer fallow of about 3 mo between the harvest of the previous winter wheat in late June and planting of the succeeding crop in late September is practiced to conserve soil water, increase the PSE, and sustain grain yield. While the PSE in the Loess Plateau has been reported to vary from 35 to 40% (Shangguan et al., 2002), it ranged from 12 to 43% in a winter wheat–summer fallow system in other regions (Jin et al., 2007; Wang et al., 2011). Because of the greater ABSTRACT Long-term N fertilization may increase dryland winter wheat (Triticum aestivum L.) yield but also result in adverse eff ects, e.g., soil acidity development and water storage or increased N leaching. Th is study examined if long-term N fertilization aff ected the soil water balance and dryland winter wheat yield. We evaluated the eff ect of fi ve N fertilization rates (0, 45, 90, 135, and 180 kg N ha–1) on the soil water balance, precipitation-storage effi ciency (PSE), winter wheat yield, and water-use effi ciency (WUE) from 2005 to 2010 in an experiment initiated in 1984 in a Heilutu silt loam in the Loess Plateau of China. Soil water contents at wheat planting and harvest were lower with N fertilization than without. Nitrogen fertilization increased soil water storage during the fallow period (SWSF) from 19 to 22%, water uptake during the growing season from 21 to 25%, PSE from 19 to 22%, and evapotranspiration from 7 to 8% compared to no N fertilization. Increased N rate enhanced soil organic C but had no impact on soil pH in 2005. Wheat yield increased up to 244% and WUE to 220% as the N rate increased. Although more soil water was depleted, N fertilization increased winter wheat yield and WUE by enhancing SWSF and PSE, and increased the water holding capacity by increasing soil organic matter compared to no N fertilization. Long-term N fertilization can increase winter wheat yield by utilizing soil water more effi ciently, with minimum impact on soil acidity, in the Chinese Loess Plateau.