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Evolution of Soil Extractable Nitrogen as Affected by Winter Flooding and Straw Burning in Southern Spain Rice Systems

Manuel Aguilar, Jose L Fernández-Ramirez, Teodoro Gonzalez-Pineda and Clemente Ortiz-Romero*

This study tested the effects of straw burning and winter flooding on soil nitrogen (N) dynamics in Southern Spain rice (Oryza sativa L.) systems during two consecutive seasons. Experiments were established in Isla Menor shire, in the Guadalquivir Marshes, with main plot treatments being winter flooding (F) or non-flooding (NF); and two straw management practices (burning before puddling or incorporating the whole harvest remains) as subplot treatments. Fertilizer was applied to the plots at the recommended levels for each site, but within each plot a zero nitrogen microplot was established. Total straw inputs before winter flooding averaged 11,235 kg ha-1 for the non-burn treatments and 3,976 kg ha-1 for the burn treatment (straw N inputs ranged from 24 to 85 kg ha-1). Burning (B) part of the harvest remains reduced the biomass and the N inputs into the soil by approximately 65% with respect to nonburning (NB). Before flooding the field for planting, there was 13% less biomass in winter flooded plots compared to non-flooded plots. Winter flooding of the plots did not influence significantly the total extractable N (Ex N: NO3- + NH4+) availability throughout the season, although the treatment that provided more ExN - and in a faster way - to the crop in both seasons was the F/NB combination. However, there were significant differences between treatments in the content of ExN in the soil at specific moments, almost always resulting higher in F and NB treatments. Grain yield and plant height did not vary significantly among treatments during the two seasons. Both the B/NB and the F/NF treatments presented agro-environmental advantages and disadvantages and the cumulative effect of these practices on ExN and some agrophysiological rice parameters over several years should be studied in Southern Spain in order to optimize the recommended N-fertilizers rate.