Transformations of nitrogen and phosphorus in sheep faeces located in saltbush rangeland and on irrigated pasture

Sheep faeces enclosed in terylene mesh bags were placed in two contrasting microenvironments within a semi-arid rangeland dominated by Atriplex vesicaria Hew ex Benth., and one within an irrigated pasture. Groups of bags were retrieved and their contents analysed at 3-monthly intervals over a total of 20 months. Sheep faeces from semi-arid rangeland and irrigated pastures were used at each site. Irrespective of source, microenvironment, and season, the amount of faecal material remaining on the semi-arid rangeland sites decreased consistently by approximately 2% month−1. The rate of disappearance for faeces placed under irrigated pastures was 2.5% month−1. The retention of N in the faeces was proportionately greater than the retention of faecal material. The presence of faecal pellets increased the mineral and total N of the soil beneath bags in the betweenbush microenvironment, but not the mineral-N content beneath bags placed under bushes of A. vesicaria in semi-arid rangeland. After 20 months, the proportion of total and inorganic P remaining in the faecal material placed under bushes was 50 and 40% respectively, and in faecal material placed between bushes the corresponding figures were 30 and 20% More Truog “available” P accumulated in soil under bags placed between bushes than under bags placed below bushes. The amount of total and inorganic P remaining after 20 months in the faecal pellets on the irrigated pastures was 20 and 10% respectively. The small loss of organic P from the faecal material indicated an absence of mineralization.