EFFECT OF TEMPERATURE AND PHOSPHORUS FERTILIZATION ON PHOSPHORUS AND NITROGEN UPTAKE BY SORGHUM

Temperature (T) and phosphorus (P) supply affect each of the mechanism s involved in P and nitrogen (N) uptake by grain sorghum [Sorghum bico lor (L.) Moench]. This study was conducted to assess the extent to whi ch air temperature and P fertilizer influenced P and N uptake and part itioning in sorghum plant parts. Research was conducted in a climatic chamber, where plants (Venturoli Aralba hybrid sorghum) were grown in pots under a 14-h day/night photoperiod regime, Temperature regimes we re kept constant for the entire life cycle at 21, 24, 27, and 30 degre es C, The P fertilization rate was 0 and 150 mg P pot(-1) as triple mi neral perphosphate. Temperature and P supply controlled P and N concen tration and content in all sorghum plant parts during the biological c ycle. Whole plant, leaf, stem, and root P and N contents were highest at 27 degrees C in growth Stages 3, 6, and 9 for both P-fertilized and unfertilized plants. Increased P supply resulted in greater P and N c ontent in leaves and stems in all three stages and at all temperatures , while root P and N contents were unaffected. Panicle P and N content s were highest at 21 to 27 degrees C in Stage 6 and at 24 degrees C in Stage 9. The effect of T on increasing plant P and N contents was att ributable primarily to higher P and N uptake rate per unit of root rat her than to higher rate of root growth, Results do not support the vie w that poor growth at suboptimal temperatures is caused primarily by r estricted P uptake, but that T and P supply limit growth independently , with additive responses.