Impacts of soil tillage with added rice straw on organic-rice yield and global warming potential

Abstract

Thailand is a world top country in exporting organic rice, although the average production is verylow, 287 kg rai-1. It is well known that addition of rice straw, tillage and soil submergence creates greenhouse gases(CO2 and CH4) and emits to atmosphere. The present experiment focused on impact of soil tillage with rice strawaddition on organic-rice yield and its global warming potential (GWP). Field experiment was conducted in secondrice cropping, 2008, in a paddy field where 5-consecutive-year organic rice was already grown. It is irrigated arealocates in Ban Nongtoom, Tambol Nongtoom, Ampor Muang, Khon Kaen. Soil texture is sandy loam, Re soil series,Paleustults. Factorial treatments in Completely Randomized Design was set up. Factor 1 as 1) no rice straw (RS)and 2) with rice straw of 4 t rai-1. The rice straw used was not fresh with C:N ratio 42. Factor 2 as 3 types of soiltillage: 1) no tillage, 2) incorporation of rice stubble, and 3) incorporation of rice stubble, harrowing and thenpuddling; this type of tillage in short was called puddling. The total treatments were 6 with 3 replications, carried outon 18 plots. Rice stubble residue left from previous crop was 1,242 kg rai-1. Wet seeding of Chinat 1 rice variety at therate of 10 kg rai-1 was cultivated. Results found that addition of rice straw, 4 t rai-1 with puddling gave highest organicrice yield, 653 kg rai-1, as puddling helped accelerating organic matter decomposition and also releasing plantnutrients. However, this treatment emitted seasonal methane 102 gCH4 m-2 (163 kg CH4 rai-1) and released 250 gCH4kg-1grain with global warming potential (GWP) of 1.57 kg Ceq kg-1grain. On the contrary, adding rice straw and thenincorporating it in moist soil (not in submerged soil like in puddling case) 18 days before wet seeding could reducetotal methane emission. It emitted merely 45 gCH4 m-2 which was considerably lower than that with pudding ricestraw by 56%, but it gave lower grain yield by 18.7%. The results indicated that managing agricultural practice tomitigate the impact on global warming potential can be made at the expense of losing some rice production.