Assessment of soil aggregation properties after conversion from rice to greenhouse organic cultivation on SOC controlling mechanism

Abstract

Organic manure is beneficial for macro-aggregate formation and soil organic carbon (SOC), but how SOC change in aggregate fractions in time-series is still uncertain. Moreover, greenhouse systems converted from cereal fields quickly faced soil degradation. Thus, the role of organic manure here should be discussed. The main objectives of this study were to determine the change of SOC fractions in bulk soil and aggregation level affected by long-term organic manure application. Using 13C solid-state nuclear magnetic resonance (NMR) spectroscopy, we investigated the SOC and its fraction changes within bulk soil and aggregate fractions under 1-year, 9-year, and 14-year organic greenhouse vegetable cultivation, and we also analysed the soil properties of rice-wheat rotation (RWR) fields as the control. Soil aggregate samples were wet sieved into large macro-aggregates (> 2 mm), small macro-aggregates (2–0.25 mm), micro-aggregates (0.053–0.25 mm), and silt and clay particles (<0.053 mm). The proportion of large macro-aggregates increased significantly (P ≤ 0.05) from 1.68 to 7.76% during the 14-year organic cultivation period. Similar trends could also be found in SOC and its fractions. Specifically, the O-alkyl C increased fastest by 14.5 g kg−1 over these years, but its proportion decreased. The change in aggregate associated C was concentrated on large macro-aggregates and micro-aggregates. Pearson’s correlation suggested that there was a non-significant relation between SOC and soil aggregation, while the soil aggregate associated C had a significantly positive relationship with SOC and its fraction amounts. However, the proportion of O-alkyl C was less; the aggregation associated C was higher. This study has shown the different effects of SOC fractions on soil aggregation and aggregate associated C in organic greenhouse vegetable fields. The stable C fractions might show contribution in soil aggregate associated C than active C fractions. It might improve our knowledge about how organic manure may influence soil aggregation by increasing SOC after a long-term greenhouse vegetable plantation.