Resumen de Soil amendment with high and low C/N residue -influence of low soil water content between first and second residue addition on soil respiration, microbial biomass and nutrient availability

Yanchen Zhang, Petra Marschner

• Soil water content is a major factor influencing organic matter decomposition. In our previous study, we showed that microbial biomass and nutrient availability after the second residue addition is influenced by the C/N ratio of both the first and the second residue (referred to as legacy effect). Different constant soil water content between the first and second residue addition may influence soil respiration, microbial biomass and nutrient availability and also the legacy effect. A loamy soil was unamended (C), or amended with plant residues with either high (mature wheat straw, H) or low C/N ratio (young faba bean, L) on day (d) 0 and d10, giving treatments CH, CL, HH, HL, LL and LH. Between d0 and d10, the soil was maintained at 10, 30 or 50% of water holding capacity (WHC), on d10, before residue addition, soil water content was adjusted to 50% WHC and maintained at this water content until d20. Cumulative respiration from d1 to d10, MBC and MBN on d1 and available N and P on both d1 and d10 were lower at 10% than at 50% WHC. When L was added on d10, cumulative respiration from d11 to d20, microbial biomass C and N on d11 and available N on d20 were higher in soil kept at 10% WHC in the first 10 days than in that maintained at 50% WHC. The previous water content had little effect on respiration and nutrient availability when H was added on d10. Differences in MBC, MBN, MBP and available N on d11 between HL and LL and between LH and HH were greater when the water content in the first period was 10% WHC compared to 50% WHC. It can be concluded that water content between residue additions influences soil respiration and nutrient availability not only directly, but also after rewetting and residue addition.