The Impact of Irrigation and Fertilization on Bioavailability of Chromium and Its Absorption and Enrichment in Paddy Rice

【Background and objective】 Sewage irrigation and extensive use of chemical fertilizers have resulted in soil pollution by heavy metals in many countries including China, threatening food safety and security. Understanding the impact of agronomic managements on bioavailability of heavy metals and their adsorption by crops is hence important to mitigate their impact on food production. Taking chromium in paddy soil as an example, this paper investigated how irrigation and fertigation combined to mediate its uptake by paddy rice. 【Method】 The experiment was conducted on a site that has been contaminated by chromium for eight years. We compared two irrigations: conventional irrigation (F) and controlled irrigation (C). In each irrigation, there were two fertilization treatments: conventional chemical fertilization (F) and organic fertilization (OF). In each treatment, we measured pH and chromium in different forms in the soil, as well as chromium content in roots, shoots and rice grains. 【Result】 Compared with conventional irrigation and chemical fertilization, controlled irrigation and organic fertilization significantly reduced soil pH. Compared with F+F, C+OF increased the content and proportion of exchangeable, reducible and oxidizable chromium in soil by 54.31%, 43.06%, and 39.33%, respectively, while reducing the content and proportion of residual chromium by 2.84%. Improved fertilization and irrigation also enhanced the transfer coefficient of chromium from below-ground to above-ground, and increased chromium content in the roots and grain by 46.31% and 59.43% respectively, compared to F+F. Under the same irrigation, soil pH was negatively correlated with the exchangeable and reducible chromium content, and the difference in the impact between different fertilizations was significant. Under the same fertilization, different irrigations did not show noticeable impact on the correlation between soil pH and exchangeable and reducible chromium. 【Conclusion】 Compared with conventional fertilization, organic fertilization brought exogenous chromium into the soil thereby significantly enhancing its bioavailability and absorption and enrichment by the rice. Compared with conventional irrigation, controlled irrigation did not show noticeable effect on chromium bioavailability.