Contribution of silicate fertilizer application to reducing CH4 emission and increasing productivity in Korean rice paddies

Context

Iron slag-based silicate fertilizer, a byproduct of the iron production process, has been applied as a soil amendment in Korean and Japanese rice paddies for over 50 years. Silicate fertilizer application is known to improve rice productivity and decrease methane (CH₄) emissions. In Korea, CH₄ emissions from rice paddy have dropped by around 50 % from 1990 to 2020, which might be attributed to the declining cropping area. In estimating the national CH₄ flux inventory from the rice paddies, the emission factor (i.e., EF_baseline x EF_{organic matter} x EF_{water regime}) and activity data (i.e., area and cultivation period) are considered. However, the silicate fertilizer application effect on CH₄ flux has not been considered.

Objective

To estimate the national-based emission factor of silicate fertilizer application on CH₄ reduction, different levels (0–2.5 %) of Fe oxide (>99 %, Fe₂O₃) were added to silicate fertilizer and applied (1.5 Mg ha⁻¹) to rice paddy fields at three different sites for three years.

Results

Silicate fertilizer application significantly decreased CH₄ emission by around 18 % over the control. In comparison, the Fe-enriched silicate fertilizer suppressed CH₄ by around 29 % over control. The addition of silicate fertilizer increased rice grain yield by approximately 7 % over control but by 18 % for Fe-enriched silicate fertilizer. Application of silicate fertilizer decreased CH₄ flux intensity (seasonal CH₄ flux per grain yield) by 25 % over control and by 38 % for Fe-enriched silicate fertilizer. Its application also improved chemical properties related to soil productivity, increasing soil pH, organic matter content, exchangeable cations, available Si, and extractable Fe concentrations. The enhanced available SiO₂ and extractable Fe concentrations positively correlated with the grain yield. The CH₄ emission factor for silicate fertilizer application is around 3.3 kg ha⁻¹ day⁻¹, which means that around 1.2 Mg CH₄ ha⁻¹ year⁻¹ is emitted.

Conclusion

Silicate fertilizer application as a soil amendment can decrease CH₄ emissions and increase rice productivity. However, the Fe-enriched silicate fertilizer is more efficient than the conventional silicate fertilizer.