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The dissolved organic matter (DOM), water soluble organic matter derived from sewage sludge was separated into hydrophobic fraction (Ho) and hydrophilic fraction (Hi). The sorption of DOM and its fractions on soils and the effects of DOM sorption on a nonionic pesticide (atrazine (2-chloro-4-ethylamino-6-isopropylamino-1,3,5-trazine)) distribution between soil and water were investigated using a batch equilibrium technique. The total DOM sorption on soils described by the Langmuir equation reached saturation as the DOMconcentration increased. The sorption of Ho fit the Freundlich model. In contrast, a negative retention evidently occurred as adding Hi at higher level in tested soils. The sorption of Ho dominated the total DOM sorption and the release of soil organic matter (SOM). Effects of DOM on the atrazine sorption by soils were DOM-concentration dependent and dominated by the interaction of atrazine, DOM, and soil solids. Generally, the presence of DOM with lower concentration promoted atrazine sorption on soils, namely the apparent partitioning constant (K^*_d) for atrazine sorption in the presence of DOM was larger than the distribution constant (K_d) without DOM; whereas the presence of DOM with higher concentration inhibited atrazine sorption (i. e., K^*_d

Abstract: The interaction effect of two sulfonylurea herbicides, bensulfuron-methyl (B) and metsulfuron-methyl(M), were tested on microbial biomass C, N, N-mineralization and C/N ratio in a loamy sand soil. The herbicides were applied at various levels of: control (B0M0), 0.01 and 0.01 (B1M1), 0.01 and 0.1 (B1M2), and 0.01 and 1.0 (B1M3) micro g/g soil. Determinations of soil microbial biomass-C, N and N-mineralization contents were carried out at 1, 3, 5, 7, 10, 15, 25 and 45 days after herbicides application. The results showed that the soil microbial biomass-C (C[sub mic]) and microbial biomass-N (N[sub mic]) decreased consistently with the increasing rates of herbicides. The results further indicated that B1M1 and B1M2 caused a significant reduction in C[sub mic] and N[sub mic] within first 10 and 7 days of incubation, respectively, as compared with the control. These reductions in C[sub mic] and N[sub mic] were also significant (P = 0.05) with B1M3 application especially within first 15 days of incubation. A significant reduction in N-mineralization (N-min) was observed with high doses (B1M2, B1M3) of herbicides within first 5 days of incubation, while low rate (B1M1) failed to produce any significant effect. An increase in the soil microbial biomass C:N ratio was also noted. [ABSTRACT FROM AUTHOR]