Effects of excreta return on properties of a grazed pasture soil

Abstract

The long term impact of excreta return on some chemical and biological properties of a pasture soil fertilised with sulphur and phosphate was studied in a system that had been with or without excreta for 23 years. Excreta free areas that had developed under electric fencelines, and parallel transects in the paddocks, were sampled to provide this comparison. Sampling was to 300 mm depth in 0–75, 75–150 and 150–300 mm sections. Total carbon and nitrogen were 20% higher in the 0–150 mm soil layer of areas receiving excreta but did not differ in the 150–300 mm layer. Carbon:nitrogen ratios were similar in both systems as was mineralisable nitrogen, both absolutely and as a percentage of total in the 0–75 mm layer. Significantly more N was mineralised in the 75–150 mm layers of the areas receiving excreta but this was reversed in the 150–300 mm layer. Nitrification rate was higher in all layers of the excreta areas. Inorganic and organic P fractions did not differ significantly. Total P was significantly higher in the 0–75 mm layer and significantly lower in the 150–300 mm layer of the excreta areas. Exchangeable potassium was much higher throughout the excreta areas while this was offset by calcium. The sum of the cations was similar in both areas. Excreta affected most of the diagnostic soil tests used for fertiliser recommendations. The soil properties measured did not reflect clearly the differences in productivity that were obvious in the two areas. It is concluded that excreta return has a impact resulting in increased organic matter storage. Short-term effects of urine have a greater impact on productivity. The major effect is on the disposition of cations and available P.