The distribution in soil and plant of 35S from sheep excreta

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Abstract
The utilization of 35S from labelled sheep excreta, applied to pasture swards, was studied in two experiments lasting 384 and 217 days respectively. The possible losses due to volatilization were examined in another experiment. The percentages of sulfur in plant material that were derived from urine and faeces were as high as 94% and 57% respectively. Above-ground plant material took up to 20% of the radioactivity applied in urine and 16 % of that applied in faeces. It was calculated that the excreta from 20 sheep ha-' could provide 20% of the sulfur requirement of the above-ground plant material. The uptake by plants of labelled sulfur from excreta occurred in the surface soil, not from the 'available' soil sulfur present in the 0-5 cm depth. The recovery of radioactivity dropped rapidly, especially when 35S was applied in urine. After 384 days, less than 40 % of the radioactivity applied could be accounted for. The loss of radioactivity from the application site was not due to volatilization, but to a combination of lateral spread and leaching.

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