Effect of weed residue application on rice-straw decomposition and soil fungi-to-bacteria ratios

Authors

• Jin-Feng Lin * ¹
• Yoshitaka Uchida ²

1. Graduate School of Agriculture,The Special Postgraduate Program in Biosphere Sustainability Science, Hokkaido University, Sapporo, JAPAN
2. Global Center for Food, Land and Water Resources, Research Faculty of Agriculture, Hokkaido University, Sapporo, JAPAN

Abstract

Purpose Undecomposed rice straw incorporated into the soil can negatively impact rice growth, but it is also an important source of soil carbon. The objective of this study was to evaluate whether the addition of weeds that naturally grow in rice paddy ecosystems could accelerate the decomposition rate of rice straw. The microbes that contribute to the decomposition process were also investigated.
Method Trifolium pratense (clover) and Rumex obtusifolius (bitter dock) both alone and in combination were decomposed along with rice-straw litterbags in rice paddy soils. The rice-straw decomposition rate was measured using the weight changes of the litterbags. The rice-straw carbon-to-nitrogen ratio and microbial abundance (fungi and bacteria) were also measured, as well as the soil respiration rate every seven days.
Results The addition of weed residues increased the soil respiration rates, but it did not influence the rice-straw decomposition rate. However, the carbon-to-nitrogen ratio of the remaining rice-straw and the fungi-to-bacteria ratio in the soil were both affected by the presence of the weeds, and the magnitudes of the effects were dependent on the carbon-to-nitrogen ratio of the added weeds.
Conclusion Given that the addition of weeds altered the quality of the remaining rice straw and the soil microbial community composition, longer term studies are required to determine whether the addition of weed residues primes the rice straw for the later stage of decomposition.

Highlights

• The quality of the remaining rice straw residues (i.e., C:N ratio) and the microbial composition involved in the decomposition (i.e., F:B ratio) were influenced by the added weed residues.
• Microbial biomass‒C was not influenced by the added weed residues, indicating that they were mostly used as a source of respired-C.

Keywords

• Rice-straw decomposition
• Weed residues
• Carbon to nitrogen ratio
• CO2-C respiration
• Fungi-to-bacteria ratio