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Effect of Temperature and Phosphorus Fertilization on Phosphorus and Nitrogen Uptake by Sorhgum

Scuola Superiore de Studi Universitari e di Perfezionamento S. Anna, via Carducci, 40 - 56100 Pisa, Italy
Dip. di Agronomia e Gestione dell'Agro-Ecosistema Univ. of Pisa via S. Michelle degli Scalzi, 2-56100 Pisa, Italy
Dip. di Scienze Agronomiche e Genetica Vegetable, Univ. of Napoli Federico II, via Università, 100- 80055 Portici (NA), Italy

^* Corresponding author.

Temperature (T) and phosphorus (P) supply affect each of the mechanisms involved in P and nitrogen (N) uptake by grain sorghum [Sorghum bicolor (L.) Moench]. This study was conducted to assess the extent to which air temperature and P fertilizer influenced P and N uptake and partitioning 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 were kept constant for the entire life cycle at 21, 24, 27, and 30°C. The P fertilization rate was 0 and 150 mg P pot^–1 as triple mineral perphosphate. Temperature and P supply controlled P and N concentration and content in all sorghum plant parts during the biological cycle. Whole plant, leaf, stem, and root P and N contents were highest at 27°C in growth Stages 3, 6, and 9 for both P-fertilized and unfertilized plants. Increased P supply resulted in greater P and N content in leaves and stems in all three stages and at all temperatures, while root P and N contents were unaffected. Panicle P and N contents were highest at 21 to 27°C in Stage 6 and at 24°C in Stage 9. The effect of T on increasing plant P and N contents was attributable primarily to higher P and N uptake rate per unit of root rather than to higher rate of root growth. Results do not support the view that poor growth at suboptimal temperatures is caused primarily by restricted P uptake, but that T and P supply limit growth independently, with additive responses.

Received for publication February 3, 1995.