Temporal changes in C, P and N concentrations in soil solution following application of synthetic sheep urine to a soil under grass

We have determined the temporal changes in the concentration of dissolved o rganic carbon (DOC) and P and N components in soil solution following appli cation of synthetic sheep urine (500 kg N ha(-1)) to a brown forest soil in boxes sown with Agrostis capillaris. Three contrasting defoliation treatme nts (no cutting, single cut before urine application and regular cutting tw ice per week) plus a fallow soil were studied. The synthetic urine containe d N-15 labelled urea and was P-free. Intact soil cores were taken after 2, 7, 14, 21 and 56 d and centrifuged to obtain soil solution. The urea in the synthetic urine was rapidly hydrolysed in the soil, increasing soil soluti on pH, DOC and total dissolved phosphorus (TDP) concentrations. For the reg ularly defoliated sward, DOC and P reached maximum concentrations (4000 mg DOC L-1 and 59 mg TDP L-1) on day 7. From their peak values, pH and DOC and P concentrations generally decreased with time and at day 56 were near tho se of the control. Concentrations of NH4+ and NO3- in the no-urine treatmen ts fluctuated and the greatest treatment differences were between the fallo w soil and the soil sown with grass. Adding synthetic urine increased NH4concentrations during the first week, but NO3- concentrations decreased. Th is was consistent with the (1)5N labelling of the NO3- pool which required 3 weeks to reach that of (NH4+)-N-15. Dissolved organic nitrogen (DON) reac hed a maximum value at day 7 with a concentration of 409 mg N L-1. The DON in soil solution contained no detectable amounts of N-15 label indicating t hat it was derived from sources in the soil. Differences in soil solution c omposition related to the effect of the other cutting treatments and the fa llow treatment were small compared to the effect of synthetic urine additio n.