Availability of sparingly soluble phosphorus sources to cotton ('Gossypium hirsutum' L.), wheat ('Triticum aestivum' L.) and white lupin ('Lupinus albus' L.) with different forms of nitrogen as evaluated by a ³²P isotopic dilution technique

Abstract

Background & Aims: Previous studies revealed that cotton plants grown on soils with low available-P were accessing significant non-fertilizer P sources. This suggests that cotton can access stable-P pools from soil. This study examined cotton's ability to utilize sparingly soluble P sources in comparison with wheat and white lupin. Methods: Plants were grown for 45 days in a Vertosol supplied with AlPO4 and hydroxyapatite, and NH4-N or NO3-N. A ³²P dilution technique was used to determine the availability and plant uptake of P from these P sources. Results: Three species differed substantially in P acquisition from the P sources. When averaged over N sources, the proportion of P in shoots sourced from AlPO4 was 89%, 54% and 19% for wheat, cotton and white lupin, respectively. When supplied hydroxyapatite, white lupin sourced 75% from the added P, in contrast to 36% for wheat and 17% for cotton. NH4-N nutrition increased the availability of hydroxyapatite to all the species and AlPO4 to cotton and white lupin. Conclusion: Cotton is inefficient in utilizing sparingly soluble P while wheat is efficient in mobilising AlPO4 and white lupin is efficient in using hydroxyapatite. The superiority of wheat in AlPO4 utilization may be related with its high root length density.