How you compost rice straw changes how much carbon soil locks away
Chen L, Cheng S, Fang H, Guo Y, Shi F
Soil Health
The compost pile or straw mulch you add to garden beds isn't just feeding plants directly, it's feeding soil microbes whose efficiency determines whether that carbon stays locked in the ground or drifts off as CO2.
Scientists buried different forms of rice straw, fresh, decomposed, or turned into biochar, in paddy soil for six months to see how soil microbes handled the carbon. Decomposed straw won by a wide margin: it helped microbes grow more (up to 204% more) while wasting less carbon as respiration, essentially making soil better at banking carbon instead of breathing it away. Whether the soil was kept wet or dry also changed the story, showing that how you manage water and organic inputs together shapes how much carbon soil can hold onto.
Key Findings
All three straw amendments (fresh straw, biochar, decomposed straw) significantly increased microbial carbon use efficiency under both flooded and unflooded conditions over 180 days.
Decomposed straw produced the largest effect, increasing microbial carbon growth by 204% (unflooded) and 172% (flooded) versus untreated soil, while sustaining the highest efficiency and dissolved organic matter diversity.
The drivers of efficiency differed by water regime: nutrient availability and lower microbial specialization mattered most without flooding, while metabolic constraints most limited efficiency under flooded conditions.
chevron_right Technical Summary
Adding decomposed rice straw to paddy soil boosted microbial efficiency at turning carbon into stable soil biomass rather than losing it as CO2, especially when the field wasn't flooded, suggesting straw management could help farmers lock more carbon into rice paddy soils.
Abstract Preview
Original paper
Dissolved organic matter molecular diversity and transformation potential are associated with microbial carbon use efficiency in paddy soils.
Microbial carbon (C) use efficiency (CUE) is a key regulator of soil C sequestration, reflecting how assimilated C is partitioned between biomass production and respiration. In paddy soils, how dis...
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