Abstract
<p>Farmers in tidal swamplands annually added organic matter (OM) onto the raised beds to maintain organic matter contents and thereby maintain soil productivity of the raised beds. This experiment aimed to study the influence of the types and the amounts of OM on the stabilization of organic matter in the raised-bed soils. Four types of OM: rice straw, eceng gondok (<em>Eichornia crassipes</em>), purun tikus (<em>Eleocharis dulcis</em>) and mixed rice straw-eceng gondok were added to a 27-year raised bed soil with 4 different rates: 0, 0.5, 1.0 and 2.0 of maximum sorption capacity (Q<sub>max</sub>), and the OM stabilization was quantified after 10 weeks of OM addition. Results of this study showed with the exception of rice straw, OM addition to soil resulted in increases in the mineralization of soil OM thereby inducing priming effect. Addition of rice straw at rate of 0.5 of Q<sub>max</sub> resulted in stabilization of 46% added OM, while only 30% and 37% of added OM was stabilized when OM was added to soils at rates of 1.0 and 2.0 Q<sub>max</sub>, respectively. This study showed that the stabilization of OM in raised bed soils were influenced by the chemical composition of OM and the amount of added OM.</p>
Highlights
Farmers of tidal swamplands generally halved their land; some areas of the land were left in flooded condition and planted with rice, while other part of the land were elevated through the deposition of muddy siltclay minerals from surrounding areas
Based the types of organic matter (OM), carbon mineralization increased in the order of rice straw < mixed rice straw-eceng gondok < eceng gondok < purun tikus (Fig. 1)
The lowest carbon mineralization was observed with rice straw application was attributed to the fact that rice straw had the highest lignin content compared to other OM (Table 1)
Summary
Farmers of tidal swamplands generally halved their land; some areas of the land were left in flooded condition and planted with rice, while other part of the land were elevated through the deposition of muddy siltclay minerals from surrounding areas. Crop productivity in the raised beds varies with the age raised beds. Reduction in the crop productivity may due to changing organic matter contents in the raised-beds with increasing the age of raised-beds. Study conducted by Rasmadi (2003) showed that the Farmers annually deposed organic matter that has decayed and mixed with muddy siltclay minerals from sunken-beds and piled them onto the raised-bed. The purpose of mixed silt-clay-OM deposition onto the raised-bed is to elevate raised-bed surface. This process may improve the stabilization of organic matter through the interaction between iron and aluminium oxides that may be contained in the silt-clay minerals and organic carbon present in soils. Lignin,with its aromatic ring structures, is recognised to be more resistant to decomposition than carbohydrates, and together with alkyl carbon areconsidered to account for a biochemically stable component
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