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

• Published in: Plant and soil 2000-01, Vol.222 (1/2), p.1-13
• Main Authors: Shand, C.A., Williams, B.L., Smith, S., Young, M.E.
• Format: Article
• Language: English
• Subjects: Acid soils; Agricultural soils; Agronomy. Soil science and plant productions; Biological and medical sciences; Brown soils; Chemical, physicochemical, biochemical and biological properties; Cuttings; Defoliation; Dissolved organic carbon; Fallowing; Forest soils; Fundamental and applied biological sciences. Psychology; Grasses; Grassland soils; Mineral components. Ionic and exchange properties; Organic nitrogen; Physics, chemistry, biochemistry and biology of agricultural and forest soils; Soil science; Soil solution; Soil treatment; Soil water; Urea; Urine
• ISSN: 0032-079X; 1573-5036
• DOI: 10.1023/a:1004799323646

We have determined the temporal changes in the concentration of dissolved organic carbon (DOC) and P and N components in soil solution following application of synthetic sheep urine (500 kg N ha⁻¹) to a brown forest soil in boxes sown with Agrostis capillaris. Three contrasting defoliation treatments (no cutting, single cut before urine application and regular cutting twice per week) plus a fallow soil were studied. The synthetic urine contained ¹⁵N 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 solution pH, DOC and total dissolved phosphorus (TDP) concentrations. For the regularly 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 those of the control. Concentrations of $NH_4^ + $ and $NO_3^ - $ in the no-urine treatments fluctuated and the greatest treatment differences were between the fallow soil and the soil sown with grass. Adding synthetic urine increased $NH_4^ + $ concentrations during the first week, but $NO_3^ - $ concentrations decreased. This was consistent with the ¹⁵N labelling of the $NO_3^ - $ pool which required 3 weeks to reach that of $^{15}NH_4^ + $. Dissolved organic nitrogen (DON) reached 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 ¹⁵N label indicating that it was derived from sources in the soil. Differences in soil solution composition related to the effect of the other cutting treatments and the fallow treatment were small compared to the effect of synthetic urine addition.