Relationship between residue quality, decomposition patterns, and soil organic matter accumulation in a tropical sandy soil after 13 years

The objectives of this study were to investigate decomposition patterns and soil organic matter (SOM) accumulation of incorporated residues (10 Mg ha(-1) year(-1)) of different quality, and identify microbiological parameters sensitive to changes in SOM dynamics, in a 13-year-old field experiment on a sandy soil in Northeast Thailand. Mass loss was fastest in groundnut stover (high N), followed by rice straw (high cellulose) and tamarind (intermediate quality), and slowest in dipterocarp (high lignin and polyphenol) following a double exponential pattern. The decomposition rate k (1) (fast pool) was positively correlated with cellulose (r = 0.70*) while k (2) (slow pool) was negatively related to lignin (r = -0.85***) and polyphenol (r = -0.81**) contents of residues. Residue decomposition was sensitive to indigenous soil organic nitrogen (SON), particularly during later stages (R (2) = 0.782**). Thirteen years' addition of tamarind residues led to largest soil organic carbon (SOC) (8.41 Mg ha(-1)) accumulation in topsoil (0-20 cm), while rice straw yielded only 5.54 Mg ha(-1) followed by the control (2.72 Mg ha(-1)). The highest SON (0.78 Mg N ha(-1)) was observed in the groundnut treatment. Increases in SOC were negatively correlated with cellulose content of residues (r = -0.92***) and microbial respiration (CO2-C) losses, while SON was governed by organic N added. During later decomposition stages, there was a high efficiency of C utilization (low qCO(2)) of decomposer communities especially under tamarind with the lowest qCO(2) and CO2-C evolution loss. This study suggests that N-rich residues with low cellulose and moderate lignin and polyphenol contents are best suited to improve SOM content in tropical sandy soils.