CROP RESIDUE TYPE AND WETTING AGENTS SHAPE SOIL NUTRIENT TRANSFORMATION AND MICROBIAL FUNCTION DURING DECOMPOSITION

Abstract

A 19-week pot study with unplanted arable topsoil evaluated the decomposition of six incorporated cover crop biomasses such as Egyptian clover, pea, phacelia, sunflower, safflower, and white mustard. The biomasses were pre-rinsed with water (control) or with two non-ionic wetting agents including Mero 33528 (rapeseed fatty acid methyl esters + tridecyl alcohol ethoxylate) and Trend^® 90 (isodecyl alcohol ethoxylate). Mass loss of biomasses was significant, ranging from ~90% (safflower) to ~60% (sunflower, white mustard). Wetting agents did not systematically enhance the decomposition but redirected the microbial functioning. Mero consistently enhanced enzyme activities, increased total soil N, and lowered microbial C-limitation indices. By contrast, Trend^® 90 dampened the enzymatic activity and exerted neutral or negative effects on N cycling and stoichiometric indicators. Both agents reduced bacterial biomass compared to water-rinsed residues, while fungal responses were crop-dependent, consistent with soil C gains observed under Mero. Despite the primary hypothesis, not the wetting agents but the residue quality (C:N ratio) was the primary driver of decomposition efficiency, while wetting agent chemistry modified microbial pathways without materially altering the bulk mass loss.