Changes in soil solution composition and pH in urine‐affected areas of pasture

Abstract

New Zealand S U M M A R YChanges in soil solution composition and concentrations of exchangeable cations and mineral N in undisturbed cores of pasture soil were investigated in two experiments following applications of sheep urine to the cores. The major cations applied in the urine were K+ and Na+, and the major anions were HCO; and C1-. Addition of urine increased concentrations of exchangeable K+, Na+ and NH and measured ionic strength of the soil solution throughout the surface 15cm of soil, demonstrating that the urine moved through the core by macropore flow immediately following addition. Immediately following urine application the ionic strength in soil solution in the surface 2.5cm of soil increased from 4-6 mM to 24-41 mM.Hydrolysis of urine-urea was extremely rapid, and in less than 1 d high concentrations of NHI-N (i.e. 270-370 mg N kg-') had accumulated in the surface 0-2.5 cm of the urine patch, and soil pH had risen by over one unit. Nitrification then proceeded and, after approximately 15 d, NO; became the dominant form ofmineral N present. During nitrification, soil pH declined and the ionic strength of the soil solution increased substantially with NO; becoming the dominant anion present in solution. There were concomitant increases in the concentrations of Ca2+ and, to a lesser extent, Mg2+ in the soil solution as NO; concentrations increased. After approximately 30 d, concentrations of exchangeable NO; had risen to 250-330 mg N kg-', soil solution NO; concentrations had increased to about 80 mmol, dm-3, and ionic strength in the soil solution had increased to 130-140 mM. These results demonstrate the dominating effect of N transformations in causing large fluctuations in the pH, ionic composition and ionic strength of the soil solution in the urine patch. It was concluded that nutrient availability in the patch was affected directly by nutrient addition in urine, and also probably indirectly through the fluctuations in soil solution pH and ionic strength that occur.

Spatial variability and hotspots of soil N<sub>2</sub>O fluxes from intensively grazed grassland

“…This relationship has also been observed in other studies (e.g. Haynes and Williams, 1992). Organic matter in the soils (total C and N) also correlated with NH + 4 concentrations in the soils (See Table 2).…”

Humic Haplustox under different land uses in a high altitude environment in the Agreste region of Pernambuco, Brazil

“…However, this study also found that the pH may decrease or remain unaffected, depending on the chemical functional group, rate of addition, decomposition, and the initial soil pH. The increase in pH in the pasture soil was also previously attributed to animal excreta (Haynes &Williams, 1992;Shand & Coutts, 2006;Brunetto et al, 2012).…”

Dynamics of a Pasture Soil Microbial Community after Deposition of Cattle Urine Amended with [ 13 C]Urea

“…Scorching of the vegetation is known to occur, depending on deposition rate and urea concentration (42), and it is a result of osmotic stress, NH 3 toxicity, or a combination of both (18,31,42). Plants and microbes respond similarly to hyperosmotic conditions (11), and adverse effects on microbial populations can therefore also occur.…”

“…Excess N in the diet of cattle is mainly excreted as urea in the urine (23), and understanding the regulation of urea turnover in urine patches is therefore of particular interest. Urea typically disappears from the soil solution within 24 to 48 h and is replaced by high concentrations of NH 4 ϩ (18,36). The accompanying increase in osmotic pressure and free NH 3 concentrations can lead to N 2 O emissions and other microbial stress reactions (12,40).…”