Soil and plant minerals associated with rice straighthead disorder induced by arsenic

Application of As as monosodium methanearsonate (MSMA) to soil has become the common practice for rice (Oryza Sativa L.) straighthead evaluation, a physiological disorder. So far, no study has reported on soil mineral availability and plant mineral uptake as affected by MSMA. Understanding how MSMA influences the availability and uptake should help reveal the causal factors of straighthead. Six cultivars rated as resistant (3), susceptible (2), and moderately susceptible (1) to straighthead were studied in soils receiving 0 and 6.7 kg MSMA ha^-1 in 2004 and 2005. Soil, flag leaves, and heading panicles were sampled and analyzed. Straighthead induced by MSMA was so severe that the susceptible cultivars yielded no grain, which validated the study. MSMA incorporation decreased soil pH, P, Mg, and Ca, increased As, S, and Mn, but had no influence on soil EC, Na, K, Zn, Cu, Fe, and organic matter. Decreased soil pH resulting from the MSMA was associated with less Ca, Mg, and P but more S, Mn, and As in the soil. MSMA increased As, Cu, Mn, Fe, S, and K but decreased B contents in the flag leaves, and increased As, Mn, S, K, and P but decreased Zn and Ca contents in the panicles. Straighthead reduced grain yield and was associated with decreased Ca, Mn, and S, but not with As in flag leaves. Comparisons between reported naturally occurring straighthead and the artificially induced one from this study indicate plant and soil nutrients may behave differently when MSMA is applied.