Mineralization of 15N-labelled sheep manure in soils of different texture and water contents

Summary in the original language of the document

In order to investigate the effect of soil moisture and texture on C and N mineralization of applied organic matter, sheep faeces was sandwiched between two halves of intact soil cores and incubated at 20°C. The soils contained 10.8 (L1), 22.4 (L3) and 33.7% (L5) clay, respectively, and were drained to seven different matric potentials in the range –15 to –1500 hPa. Evolution of CO2-C was determined during four weeks of incubation. Contents of NO3-N, 15N and microbial biomass N were determined at the end of the incubation.
The net release of CO2-C from the faeces (estimated as the difference between soils with and without faeces) and the total CO2-C evolution from soils with faeces was not related to soil moisture contents. Most CO2-C evolved from faeces amended soils in the least clayey L1 soil. The faeces caused immobilization of soil NO3-N but the soil matric potential had no major effects on the net NO3-N production. Less than one per cent of the faeces 15N was found as NO3-N at the end of the incubation.
The unamended sandy L1 soil held least N in microbial biomass but showed the largest increases in biomass N when faeces was added to this soil. The content of microbial biomass N in soils with faeces application peaked in the most clayey soil (L5). The recovery of faeces 15N at the end of the incubation ranged from 89 to 102%. The variation in 15N recovery was not related to soil clay content nor to soil matric potential.
The experimental set-up was designed to mimic field conditions where manure is left as a discrete layer surrounded by structurally intact soil. In this situation the soil clay content and the soil moisture level appeared to have little influence on the C and N turnover in the manure layer.