Uptake of potassium and nitrogen by pasture from urine-affected soil

Abstract

A field experiment was carried out to determine the depth of soil from which pasture plants growing in urine-affected soil recover urine potassium (K) and nitrogen (N). A comparison of the amounts of K and N taken up by the herbage with the decline in soil K and N levels showed that K and N were absorbed mainly from the 0–12 cm depth of soil. This coincides with the distribution of plant roots within the soil profile, as 86% of the roots in the 0–30 cm depth of soil were found in the top 15 cm. The experiment also showed that immediately after a dairy cow urination event in mid winter (July), up to 59% of the urine K moved preferentially through a network of soil macropores to below a soil depth of 14.5 cm. A simulation of the field trial in the glasshouse confirmed that preferential flow of the urine could result in large losses of urine K. Fortyeight percent of the urine-N was also unaccounted for by soil analysis immediately after the urination event, and is considered to have been lost preferentially with the K. The urine K and N that remained in the 0–14.5 cm soil profile as exchangeable K and potassium chloride-extractable N were absorbed by the pasture plants over the following spring and summer.

Keywords:

• potassium
• nitrogen
• potassium leaching
• nitrogen leaching
• herbage potassium
• herbage nitrogen
• plant uptake
• urine
• K cycle
• N cycle