Organic fertilization integrated with water management to remediate As and Cd contamination in a paddy soil

Abstract

Soil heavy metal pollution is the main risk for sustainable agriculture, especially the combination of As and Cd pollution in paddy fields which may lead to the superimposed accumulation in rice. There is an urgent need for environmental-friendly and cost-effective strategies to remediate the contamination of As and Cd in soils. In this work, a pot culture experiment was conducted in a As and Cd polluted paddy soil to explore the effects of organic fertilization (OF) and two water managements (continuous flooding, CF; intermittent irrigation, II) on the fractionation of As and Cd in soil, and the uptake of As and Cd by rice. The results showed that OF integrated with intermittent irrigation performed best in reducing the contents of As and Cd in rice grains by 58.9 % and 69.3 %, respectively, under compound pollution. The significant conversion of available As and Cd to stable species (specifically adsorbed and Fe-Mn/Al oxide bound) under OF + II were supported by the changes in an array of soil attributes such as pH, Eh, soluble Fe and dissolved organic carbon (DOC). Intermittent irrigation was more conducive to the accumulation of As outside the roots, and Fe-plaque prevented As uptake by roots and the translocation to shoots. While more accumulation of Fe-plaque along with Cd on root surface induced by continuous flooding is helpful for depressed assimilation of Cd by rice. Considering the combined contamination of As and Cd polluted in paddy soils, a management approach was proposed based on intermittent irrigation and application of organic fertilizer at the rate of 0.1 % (∼ 2.3 t/ha) in two phases (two weeks before planting or drainage). Organic fertilization will hold great promise in restoring polluted soils and maintaining soil health via suppressing the lability of heavy metals and providing nutrients.