Effects of urea concentration on summer maize growth and yield with sprinkler fertigation

Abstract: The direct absorption of leaf to urea is one of the main potential factors improving the nitrogen use efficiency with sprinkler fertigation. To verify the feasibility of sprinkler fertigation for summer maize, the crop growth parameters, including plant height, leaf area index (LAI), leave relative chlorophyll content (SPAD), chlorophyll fluorescence characteristics, and yield were compared among sprinkler fertigation treatments with different urea concentrations and the comparison treatment of surface irrigation with broadcast fertilization (CK). This experiment was conducted at the experimental station of China Institute of Water Resources and Hydropower Research in Daxing District, Beijing City (39.65°N and 116.25°E) in 2017 and 2018. Five solution concentrations of 0.048%, 0.105%, 0.146%, 0.178%, and 0.312% in 2017 and 0.090%, 0.146%, 0.188%, 0.219%, and 0.292% in 2018 (referred to as N1, N2, N3, N4, and N5) were used in the sprinkler fertigation of summer maize. The corresponding total N application amount in these 5 treatments was 170, 215, 248, 273, and 380 kg/hm2 in 2017 and 170, 215, 215, 248, and 273 kg/hm2 in 2018, respectively. There were 6 treatments in total, and all the treatments had 3 replicates and the same irrigation schedules. The irrigation was triggered when the difference between cumulative crop water requirement and effective rainfall was not less than 20 mm. In 2017 season, the effective rainfall was 175 mm and the irrigation amount was 70 mm. Because the precipitation (200 mm) mainly happened after the elongation stage of summer maize, the irrigation amount 150 mm was applied in 2018 season. The fertilization was applied in the flare opening stage of summer maize. The results showed that the SPAD increased in all the treatments after the fertilization, while there were no significant differences in plant height and SPAD among sprinkler fertigation treatments. There were great inter-annual variations in urea concentration effects on leaf area index (LAI) and yield. The yield of N2 treatment (12.5 t·hm-2) was significantly greater than treatments with higher urea concentrations in 2017. In these two seasons, the greatest yield of summer maize was obtained in treatment with 215 kg/hm2, which was consistent with the N application amount recommended by soil testing and fertilization recommendation technology. After the sprinkler fertigation, the influences of leave absorption to urea on PSII photosystem activity and photochemical efficiency of plant had relationship with SPAD content. In 2017 season with high SPAD value, photosystem activity and photochemical efficiency decreased firstly and then increased. When the urea concentration was less than and equal to 0.146%, the decreasing of photosystem activity and photochemical efficiency happened on the 1st day after the fertigation. While it lasted until 3 to 5 days for treatments with urea concentration greater than and equal to 0.178%. In 2018 season with low SPAD value, photosystem activity and photochemical efficiency increased firstly and then kept constant in all the treatments like in CK treatment in these two seasons. Compared with CK treatment, the sprinkler fertigation treatments with less N application than CK had similar yield and water use efficiency, and significant greater partial factor productivity from applied N. These results demonstrated that the sprinkler fertigation was feasible and had the potential to save N fertilizer and sustain yield of summer maize. To develop the sprinkler fertigation schedule, the nitrogen amount could be calculated according to soil testing and fertilization recommendation technology.