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

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.