Effects of elevated CO 2 concentration, irrigation and nitrogenous fertilizer application on the growth and yield of spring wheat in semi-arid areas

Abstract

In this paper, we discuss the effect of elevated CO 2 concentration, irrigation and nitrogenous fertilizer application on the growth and yield of spring wheat in semi-arid areas. A field experiment was conducted at the Dingxi Agricultural Experiment Station during 2000–2002. According to the experimental design, the CO 2 concentration increased to 14.5, 40 and 54.5 μmol mol −1, respectively, by NH 4HCO 3 (involving CO 2) application, direct application of CO 2 gas and combination of fertilizer NH 4HCO 3 plus CO 2 application, which are equal to CO 2 concentration of the Earth's atmosphere in the next 5, 15 and 20 years. The fertilizer application was divided into three levels: application of NH 3NO 3 (250 kg h m −2), NH 4HCO 3 (500 kg h m −2) and no fertilizer. Irrigation was divided into two levels: with 90 mm irrigation in the growth period and without irrigation. They can be combined as eight treatments. Each treatment was replicated three times. The results showed that elevated CO 2 concentration owing to CO 2 application leads to remarkable increase in leaf area index (LAI) and shoot biomass, and also generates the higher value of leaf area duration (LAD) that can benefit the photosynthesis in the growth stage and yield increase in crop compared than the no CO 2 application treatment. When CO 2 concentration elevated by 14.5, 40 and 54.5 μmol mol −1 with irrigation and fertilization, correspondingly, the grain yield increased by 6.3, 13.1 and 19.8%, respectively, whereas without irrigation and fertilization, the grain yield increased by only 4.2% when CO 2 concentration increased to 40 μmol mol −1. Meanwhile, irrigation and fertilization can result in larger and deeper root system and have significantly positive influences on higher value of root/shoot (R/S) and water use efficiency. The grain yields in irrigation, irrigation plus NH 3NO 3 application and irrigation plus application of NH 4HCO 3 treatments are 73.4, 148.0 and 163.6% higher than that of no-irrigated and no-fertilized treatment, suggesting that both irrigation and fertilizer application contribute to remarkable increase of crop yield. In all treatments, the highest water use efficiency (WUE, 7.24 kg h m −2 mm −1) and grain yield (3286 kg h m −2) consistently occurred in the treatment with 90 mm irrigation plus fertilizer NH 4HCO 3 and elevated CO 2 concentration (54.5 μmol mol −1), suggesting that this combination has an integrated beneficial effect on improving WUE and grain yield of spring wheat. These results may offer help to maintain and increase the crop yields in semi-arid areas.