ifoam'96 Book of Abstracts 11th IFOAM Scientific Conference 11-15 August 1996, Copenhagen, Denmark

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Posters

Effects of dung and urine on N2 fixation in pasture. P2; 35

Plant Nutrition Programme, Environmental Science and Technology Department, Risø National Laboratory, P.O. Box. 49, 4000 Roskilde, Denmark

In a grazed pasture large amounts of N is returned to the soil in animal excreta. Dung and urine may have great effects on N2 fixation in legumes and the competition between pasture species. High concentrations of inorganic N are known to reduce N2 fixation in white clover, and inorganic N released from dung and urine patches can potentially reduce the amount of N fixed in white clover plants adjacent to the patches. The aims of this study were to determine the effect of dung and urine on N2 fixation and accumulation of dung and urine N in grass/clover mixtures using 15N-cross-labelling techniques.
White clover (Trifolium repens L.) and perennial ryegrass (Lolium perenne L.) were grown in mixtures in microplots (0.071 m2) in the field and in containers (11 x 24 x 40 cm) in a growth chamber. After the plants were established in the growth chamber, sheep faeces was prepared to simulate cattle dung and then applied to the soil. The use of sheep faeces is justified by the fact that the chemical composition of sheep and cattle faeces is almost identical. The field grown grass/clover mixtures received urea in rates equivalent to 0, 320 and 640 kg N/ha. Deposition up to 1000 kg N/ha is commonly found in urine patches. Urea was used to simulate cattle urine. By use of 15N-cross-labelling techniques it was possible to estimate N2 fixation in the clover and uptake of dung and urine N in grass and clover. The preliminary results show that dung patches has no effect on the N2 fixation during the first 4 weeks after deposition, whereas application of urea equivalent to 640 kg N/ha reduces the proportion of N2 fixation in the crop from 94 to 64% after 2 months and from 86 to 43% after 3.5 months. The release of N from dung was slow, and after 4 weeks only 1.7% of the N was recovered in the harvested clover and grass. The uptake of N from urea was much more pronounced. About 14-23% of the urea N was recovered in plant tops after 3.5 months.

Haynes, R.J. & Williams, P.H. (1993): Nutrient cycling and soil fertility in the grazed pasture ecosystem. Advances in Agronomy, 49, 119-199.

Ledgard, S.F. and Steele, K.W. (1992): Biological nitrogen fixation in mixed legume/grass pastures. Plant and Soil, 141, 137-153.