Effect of nitrogen and phosphorus addition on soil aggregation and its associated organic carbon

Abstract

ABSTRACT Although the response of plant productivity and soil biogeochemical processes to nutrient addition has been widely investigated, little is known about the effects of N and P addition on soil aggregate fractions, an important indicator of soil organic C stability. We investigated the effects of exogenous N and P inputs on soil aggregates and their associated organic C in a 6-year fertilisation experiment in a subtropical Chinese fir (Cunninghamia lanceolata) plantation. A wet sieving method was used to determine the aggregate size distribution. Our results showed that the most abundant aggregate was the macroaggregate, ranging between 59% and 74%. The least abundant fraction was the smallest (silt and clay), ranging between 10% and 15%. Neither the soil aggregate fractions nor their associated organic C differed significantly after 6 years of N and P addition at the 0.05 level. In contrast, the oxalate-extractable iron Fe and pyrophosphate-extractable Fe of 0–10 cm soil were significantly decreased by P addition; this may alter aggregate formation over longer periods. Thus, future studies should examine the effects of nutrient addition on aggregates over a longer period. In particular, more attention should be paid to the effects of P addition in subtropical forests.