The soil N-turnover after application of easily degradable organic fertilizers does not follow the classical pattern

摘要

In spite of other influencing factors, the turnover of recalcitrant or moderately degradable organic fertilizers in soil is usually described as a function of the soil temperature. In our investigations, we focussed on those materials containing considerable fractions of easily degradable water soluble or structural organic matter, each of which was characterised by a relatively low C/N-ratio. Typical materials were fresh or dried green manure plants, especially legumes, and other plant derived fertilizers such as different leguminous seed meals and castor cake meal. Laboratory incubation studies as well as field experiments were carried out. It could be shown that the turnover of these materials differed considerably from the classical concept of temperature dependency mentioned above. Net N-mineralisation after soil incorporation of these materials was not or only very little temperature sensitive. Strong N-priming effects could be detected for some of the materials even at low temperatures, especially if considering soil microbial biomass N in addition to soil mineral N. It was concluded that low temperatures induce a decrease of the bioavailability of C-rich polymers (e.g. cellulose) and a preferential microbial utilisation of N-rich low molecular substances.