Denitrification in grassland soils in The Netherlands in relation to irrigation, N-application rate, soil water content and soil temperature

Denitrification rates in agricultural grassland systems are variable, mainly due to soil type, management and weather conditions. The soil water status in such systems was often found to be the most important factor controlling denitrification. The individual and combined effects of irrigation, N-application rate and temperature on denitrification were studied in a field-experiment on a sandy grassland soil in The Netherlands. The relationship between denitrification and soil water status was studied in a laboratory experiment using sand, loam and peat soil, in which four soil water contents were established. Denitrification rates were measured in soil cores kept in a C2H2-enriched atmosphere (10% v/v). The results of the field experiment showed that: (1) denitrification rates in the soil under study were primarily affected by soil water conditions; (2) the effect of temperature on denitrification rate was stronger in non-irrigated plots; and (3) N-application rate had no effect on denitrification rates because NO3− was not limiting. The results of the laboratory experiment indicated that denitrification rates were very low when the soil water-filled porosity had decreased below a threshold value, which varied with soil texture. However, when this threshold value was expressed as soil water tension, the threshold for all soil types was pF 2, or field capacity.