The hay powder was obtained from a dried grass specially cultivated on a selected and well prepared soil (granitic and gneissic origin) sprayed with herbicides and fertilised with P, K and high amounts of nitrates (approx. 100 kg.ha-l . treatment-'). The grass was cut by hand with carbon steel sheep shears in fine weather, 5 cm above the soil. Any contact between grass and soil was avoided. The grass consisted entirely of leaf material without heading. It was dried immediately after harvesting in a ventilated oven at about 40 "C. Then it was sent to the Central Bureau for Nuclear Measurements of Geel (B) in polythene bags for the final preparation. The material was dried at 100 "C with pulsed hot air in a stainless steel container and ground in a tungsten carbide grinder to pass apertures of 120 µm. The resulting material was homogenised in a special PTFE-lined drum for 30 min. Portions of about 25 g were transfered into clean brown glass bottles provided with a screw cap and a plastic insert. After filling 40 bottles the contents of the drum were re-mixed for 15 minutes. Then the filling of another 40 bottles was done. Out of every batch of 40 bottles one was set aside for homogeneity studies. keywords: environmental material , biological material , plant material, animal feedstuff , nutrients , trace elements
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