Effects of organic matter and water regime on the kinetics of iron and manganese in two high pH rice soils

Abstract

A greenhouse experiment studied the effect of different rice (Oryza sativa L.) straw application levels on the pH, Eh, Fe²⁺, and Mn²⁺ in soil solution, on Fe and Mn content in plant tissues, and on rice growth and grain yield under continuously flooded and flooded at 4 weeks after transplanting (WAT). Two high pH soils, Le. San Manuel clay loam (Fluva-quentic Haplustolls) and Guadalupe clay (Typic Pellusterts) were used in the experiment. Applying rice straw increased IR36 straw and grain yields and the Fe²⁺ and Mn²⁺ yields at different growth stages. With 0.5% rice straw, Fe2+ and Mn2+ in the soil solution peaked early; high Fe and Mn contents were obtained. Soil solution pH and Eh of San Manuel soil were lower under continuously flooded condition than when flooded at 4 WAT. pH and Eh values in both soils decreased rapidly with decreasing rice straw addition.

Key Words:

• anaerobic fermentation
• complexing agents
• soil reduction
• solution pH and Eh

Additional information

Notes on contributors

S.K. De Datta

Former Scholar and Principal Scientist and Head, Agronomy Department, IRRI, Los Baños (mail address: P.O. Box 933, Manila), Philippines.