Microbial growth and sulphur immobilization following the incorporation of plant residues into soil

Wu-O, Jess; O'Donnell, A.G.; Syers, J.K.

Microbial growth and sulphur immobilization following the incorporation of plant residues into soil

1993

Wu-O, Jess | O'Donnell, A.G. | Syers, J.K.

The interaction between microbial growth and S immobilization was investigated in an arable soil amended with oil-seed rape (young leaves) and barley straw (1% w/w). Initially, the rape decomposed more rapidly (40 vs 10% by day 5) and produced a larger microbial biomass (990 microgram C g(-1) soil) than the straw (710 microgram C g(-1) soil). The biomass in both of the amended soils then decreased to amounts 30-50% higher than those in the unamended soil by day 35 and was maintained at levels throughout the 195 day incubation. Most of the rape-S (>80%) and straw-S (>60%) added to the soil was released as SO4(2-)-S or converted to biomass-S in 5 days. By this time, the amount of S assimilated by the biomass in the rape-amended soil was three times that found using straw. Biomass-S in both soils then decreased but remained twice as high in the rape-amended soil over the period of 15-195 days. The biomass in the straw amended soil had a similar C:S (85-120:1) to that of the unamended soil but was narrower (40-50:1) in the rape-amended soil. By day 5, SO4-S in both of the amended soils had increased significantly. The increase in SO4(2-)-S in the rape-amended soil was maintained over the 195 day incubation, suggesting that this S was available for plant uptake. However, by day 15, a net immobilization of soil S by the biomass (25% of soil inorganic S) was found using straw. This immobilized S was retained by the biomass throughout the 195 day incubation and was, therefore, unavailable for plant growth. This suggests that the incorporation of plant residues such as straw which contain low amounts of S may decrease the plant availability of soil S.

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