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1 Contribution from Radio Tracer Laboratory, Andhra Pradesh Agricultural Univesrity, Rajendranagar, Hyderabad-500030
Application of 30 kg P205/ha alongwith physical or chemical weeding gave almost as much grain and straw yields of sorghum as application of 60 kg P2Os/ha without weeding. Phosphorus uptake, per cent P derived from fertilizer (% Pdff) and fertilizer P uptake increased with increasing levels of phosphorus application both in sorghum and weeds. With an increase in the dose of P application from 30 to 60 kg P205/ha there was a decrease in %P utilization by sorghum but an increase in %P utilization by weeds. Applied phosphorus was better utilized by sorghum when weed control was done by hand weeding, by using cultivator or by applying atrazine (1 kg/ha) than the plots were left unweeded.