Denitrification‐ and Nitrate Leaching‐Losses in an Intensively Cropped Watershed

In continuation of former measurements about gaseous denitrification losses, these losses together with those by nitrate leaching were measured by different methods in a field cropped during two years by wheat. Furthermore, N‐uptake by the plants of fertilizer‐ and soil‐N as well as N‐im‐mobilization in soils during and after the cropping periods was determined by application of highly enriched 15 N‐labeled fertilizer. Denitrification losses determined by the N 2 O release from C 2 H 2 –treated undisturbed soil cores agreed reasonably well with losses obtained by 15 N‐balance measurements. They both amounted during the cropping periods 12–15 and 6–20 kg N ha −1 , respectively. Gaseous N‐losses increased mainly during wet periods when the field was barren. Denitrifying enzyme activities and soil respiration (CO 2 ‐release) was measured throughout one year. Leaching losses of NO 3 from soil‐and fertilizer‐N occurred only during fall until spring. Leached NO 3 − originated mostly from mineralized soil‐N and very little from previously immobilized fertilizer‐N.