Sterility in Rice Cultivars as Influenced by MSMA Rate and Water Management 1

In recent years an expansion of rice ( Oryza sativa L.) acreage in Arkansas has resulted in rice being produced on soils with a history of cotton production. Most of these cotton soils have had repeated applications of monosodium methanearsonate (MSMA) as a herbicide. There is some evidence that arsenical residues in the soil can lead to sterility in rice. In an effort to answer this question, we conducted a field experiment on a Crowley silt loam soil (Typic Albaqualf) in 1975 to evaluate the influence of MSMA on plant growth and yield of rice. Treatments included two water management regimes (continuous flood vs. one drain and dry), three levels of MSMA [0, 1.1, and 11.2 kg/ha of arsenic (As)] and 15 rice cultivars and experimental strains differing in susceptibility to straighthead disease (abnormally developed or sterile flowers resulting in reduced grain yields). Soil samples taken 65 days after arsenic application showed that As remained in the rice root zone. Vegetative growth prior to panicle initiation was not affected by any of the treatments; however, visual observations made near maturity showed that where MSMA had induced sterility, the plants were dark green suggestive of straighthead. Reproductive growth as shown by panicle weights and sterility ratings was affected most by high MSMA rates and continuous flooding. Under continuous flood, panicle weights were reduced and sterility ratings increased as MSMA rate increased. This effect was more pronounced in cultivars most susceptible to straighthead and was minimized by draining the flood and drying the soil. This data suggests that the MSMA residues induced straighthead. A significant and similar relationship was found between panicle weights and sterility ratings at maturity for both water management regimes.