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

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.