Irrigation and nitrogen effects on the leaf chlorophyll content and grain yield of maize in different crop years

Abstract

For economic as well as environmental reasons, the determination of optimal nitrogen (N) fertiliser application rates under field conditions is of great importance, especially under irrigated conditions. A two-year field experiment was conducted in Hungary (47°33′N, 21°26′E, 111 m) with six N fertiliser rates (0–150 kg ha⁻¹) under irrigated and non-irrigated conditions with the aim to compare the chlorophyll (Chl) concentration of maize (Zea mays L.) leaves at different growth stages to the soil nitrate-N, the amount of N applied as fertilizer and grain yield. The effect of irrigation and N fertilisation on the soil water and nitrate-N dynamics, grain yield and water use efficiency (WUE) was also examined. In the drought year of 2007, the volumetric soil water content increased from the surface (8.5–9.5, v/v%) to a depth of 1.2 m (15–20, v/v%) in both water treatments. In the extremely wet year of 2008, an opposite tendency was observed. In 2007, N applied without irrigation accumulated in the 0–0.2 m depth and nitrate-N did not significantly decrease, due to minimal crop N uptake. Under irrigated conditions, nitrate-N was significantly reduced by crop uptake during the growing season of both years. In 2007, chlorophyll meter readings were related to the plant available N at the R1 stage in both water treatments (P < 0.001). The CMR value and yield were in close correlation with each other at the R1 growth phase in the drought year in the irrigated treatment (P < 0.001; R = 0.724), and in the wet year both in the non-irrigated (P < 0.001; R = 0.735) and the irrigated treatments (P < 0.001; R = 0.782). The soil nitrate content could be concluded to in the dry year (2007) at the R1 growth stage in both irrigation treatments (R = 0.614; R = 0.648), and in the wet year (2008) in the non-irrigated treatment at the V12 growth stage (R = 0.763).

In 2007, the lack of rainfall caused yield stress in the non-irrigated treatment, in contrast to the significantly reduced yield in every N treatment in comparison with the non-irrigated treatment recorded in 2008, due to the extremely high amounts of rainfall. The yield surplus per 1 mm irrigation was negative and the level of WUE was also significantly lower.

Introduction

Maize is one of the most important cultivated crops in the world, due to its basic role in feeding the population and its ability to be rapidly expanded into high levels of production. Hungary ranks 11th in the World's average maize yield and 8th in the category of yearly average yield increase. Indeed, Hungary has the 4th largest maize production area in the world (more than one million hectares), following the USA, France and Canada (FAOSTAT, 2009).

Intensive crop nutrition is indispensable for ensuring yield increase. Determining the optimal fertiliser application rate is a difficult task due to its interaction with soil water and other factors. One has to consider the nutrient management history and nutrient binding ability of the soil, as well as the yield potential and nutrient requirement maize hybrid and residual soil N from the previous crop (Hansen and Djurhuus, 1996, Delphin, 2000, Ichir et al., 2003, Nakamura et al., 2004, Körschens, 2006, Széll et al., 2005, D’Haene et al., 2007). Of the three macroelements (NPK), nitrogen fertilisation has the highest yield increasing effect in maize on most soils (Shaahan et al., 1999, Fabrizzi et al., 2005, Nagy, 2008). Nitrogen plays a key role in several physiological crop processes. As a result of increasing N doses, the photosynthetic activity, leaf area index (LAI) and leaf area density (LAD) increase (Anderson et al., 1985, Dwyer and Anderson, 1995, Earl and Tollenaar, 1997, Tóth et al., 2002, Ma et al., 2005, Uribelarrea et al., 2009).

Efficient nutrient utilization and high yields require favourable water supply. Limited water supply during vegetative growth reduces the development of stem and leaf cells, resulting in reduced crop height and leaf area (Lauer, 2003). Drought during tasseling could potentially cause even a 40–50% yield reduction. Water deficiency during tasseling and flowering reduces the grain number of cobs per row, whereas post-pollination stress decreases kernel weight, resulting in significant yield reduction (Westgate and Boyer, 1986, Lauer, 2003).

In the case of insufficient natural water supply, irrigation is a significant element, being the most effective intervention in a crop population (Wienhold et al., 1995, Márton, 2005, Bharati et al., 2007, Kumar, 2008). In addition to its yield increasing effect, irrigation also reduces yearly yield fluctuation and moderates the risks of crop production (Pandey et al., 2000, Rockström and Falkenmark, 2000, Zwart and Bastiaanssen, 2004, Nagy, 2008). As a result of irrigation, not only will the available water content of soil be higher, but it will also have a favourable effect on the dissolution processes and increase the biological activity of the soil. Nevertheless, it is a fundamental requirement that the applied irrigation should not deteriorate the soil structure and soil fertility, cause permanent anaerobic conditions in the soil, reduce the activity of microorganisms, result in the leaching of N and mineral nutrients or induce secondary salinisation (Díez et al., 1997, Kengni et al., 1994, Pang et al., 1997, Cameira et al., 1998, Feng et al., 2004).

The aims of our investigation were to evaluate the effect of N fertilisation and irrigation on the soil water and nitrate-N content, the chlorophyll content, grain yield of maize and water use efficiency, as well as to evaluate the correlation between the chlorophyll content, the soil nitrate-N content and grain yield in the growing seasons of 2007 and 2008.