Incorporation of dolomite reduces iron toxicity, enhances growth and yield, and improves phosphorus and potassium nutrition in lowland rice (Oryza sativa L)

Management options to reduce the negative impacts of iron (Fe2+) toxicity in lowland rice (Oryza sativa L.) are limited. Improving productivity and ensuring sustainability of such systems requires a sound ecophysiological understanding of this widespread problem. The effectiveness of dolomite [CaMg (CO3)2] application to increase the availability of soil phosphorus (P) to rice plants, and to decrease the bioavailability of Fe2+ was tested at two locations, one with and one without effects of Fe2+ toxicity. We used a Fe2+-susceptible and a Fe2+-tolerant rice variety, with and without the application of dolomite at a rate of 1 t ha−1for three consecutive seasons. In a pot experiment, we studied the shoot and root growth, and soil and plant P and Fe nutrition with the application of 0, 1 and 10 t ha−1 of dolomite in an iron-toxicity affected soil. With the application of dolomite, both in the field and in the pot experiment, the exchangeable soil Fe2+ concentration decreased with an increase in soil pH and P availability. Plant height, shoot and root dry weight, grain yield, and P and potassium content increased, whereas the organ Fe concentration and content decreased with a greater response by the Fe2+-susceptible rice variety than by the tolerant variety, and with the greatest effect at the Fe2+-toxicity-affected site. Application of dolomite to lowland rice fields affected by Fe2+ toxicity can increase grain yield, while reducing the negative impacts of Fe2+ toxicity. The magnitude of these positive responses would vary depending on variety, season and soil conditions.