Nutrient availability, soil respiration and microbial biomass after the second residue addition are influenced by the C/N ratio of the first residue added, but not by drying and rewetting between residue amendments

Abstract

It has been shown that the C/N ratio of the first residue amendment influences soil respiration and nutrient availability after the addition of a second residue, which is referred to as legacy effect. However, little is known about the effect of dry-rewet (DRW) cycles on nutrient availability in soil amended with residues differing in C/N ratio and on the legacy effect. A loamy soil was amended twice (days 0 and 32) with plant residues with either high (H) or low (L) C/N ratio to give the treatments low than high (LH) or high then low C/N residue (HL). Between the first and the second residue addition the soil was maintained at 50% WHC or exposed to one, two or four DRW cycles. After the second residue addition all treatments were kept at 50% WHC until day 64. During the first period, N and P availability and microbial biomass C were higher in LH than HL in all moisture treatments. Cumulative respiration (mg CO2-C g soil−1) was higher in LH than HL only in the constantly moist treatment. Available N and P concentration were higher in dry soil than moist soils in 1 DRW and 2 DRW. After the second residue addition, moisture and residue treatments did not differ in available N and P concentration, which confirmed the legacy effect, but indicated that drying only temporarily increased N and P availability and that the previous moisture treatment did not influence the legacy effect.