The Timing of Irrigation and Fertilization Affects Fertilizer Distribution and Rice Growth

【Background】 China is one of major rice-growing countries in the world. Excessive use of nitrogen fertilizers has led to eutrophication, increase in greenhouse gas emissions and groundwater pollution. Improving fertilizer utilization efficiency and reducing its adverse impact on the environment is hence essential to sustaining rice production. Differing from crops in dryland, paddy field has a water layer on its surface which has a significant impact on efficacy and consequence of irrigation and fertilization. Previous studies on water-nitrogen coupling in paddy field focused on its impact on rice growth while overlooking the impact of timing of irrigation and fertilization. 【Objective】 The objective of this paper is to investigate the impact of fertilizer types, timing of irrigation and fertilization on nitrogen distribution and traits of rice, aimed to improve water and fertilization management of paddy fields and reduce their detrimental impact on environment. 【Method】 The experiment used liquid fertilizer and sprinkler irrigation. The treatments included: applying the fertilizer in the first two hours after irrigation (T1), applied the fertilizer between 2~4 hours following irrigation (T2), and applied the fertilizer between 4~6 hours after irrigation (T3). Traditional surface-broadcasting was taken as the control (CK). During the experiment, we measured the uniformity of fertilizer distribution, traits, yield and water use efficiency of the rice in each treatment. 【Result】 When irrigation and fertilization amount were the same, T1 was most effective for making fertilizer distribution uniform, increasing tiller numbers, yield and water utilization efficiency at significant level (P<0.05). In CK, nitrogen content peaked three days after the fertilization, while in other treatments it maximized just one day after the fertilization with the associated fertilizer distribution uniformity increased by 5.63%~21.65% compared to CK. After the booting stage, the treatment increased plant height by 6.37%~6.53%. T1 increased tiller numbers and dray matter by 11.25%~23.17% and 5.75%~8.48%, respectively, compared to CK. T1 also increased the yield and water utilization efficiency by 13.73%~17.46% and 14.15%~17.47%, compared to other treatments and CK. 【Conclusion】 Considering fertilizer distribution uniformity and increase in yield and water use efficiency, the best fertilization timing is to apply the liquid fertilizer in the first two hours following irrigation.