Effect of plant residue and water management practices on soil redox chemistry, methane emission, and rice productivity

Approximately 5 % of rice growing area in Louisiana experience poor seedling or stand development attributed to anaerobic decomposition of excess plant residue, which create strongly reducing or toxic soil conditions. This study investigated plant residue and flooding regime effects on soil properties as related to rice growth and seedling development. Field experiments were conducted at several commercial farms in Southwest Louisiana (which have experienced problem with rice stand development) to relate observed restricted rice growth to soil redox chemistry and other chemical and physical properties. Field experiments were also conducted at the Crowley Rice Research Station in which various rates of rice straw amendment were added to replicate field plots to determine effect on rice growth and methane emission. The study also include greenhouse experiments on plant residue effect on soil chemical properties as related to rice seedling development and growth including effect of plant residues sources (rice straw or alligator weed on rice seedling germination). These studies showed source and quantity of plant residue significantly affected rice seedling development and germination rates of various commercial rice varieties. Alternating flooded and drained cycles significantly increased growth and grain yield of rice as compared with continuous flooded treatments containing high level of soil plant residue. High rates of plant residue addition increased methane emission (7,350 kg/ha/season) as compared with treatment receiving no added plant residue (370 kg/ha/season). Alternating flooded and drained cycles as compared with continuously flooded resulted in a 50 % reduction in methane emission and increased grain yield by 30 % in treatment receiving 24 t/ha plant residue added. Alligator weed plant residue source had greater effect on rice seedling development as compared with rice straw. Adoption of alternately flooded and drained water management practice, which improves soil chemical properties, can substantially increase rice growth and yield as well as reduces atmosphere methane emission from Louisiana rice soils