Phosphorus Concentrations in the Leaves of Cotton in Tropical Australia are Determined by Temperature

ABSTRACT

Previous research on P leaf analysis for detecting deficiencies in cotton (Gossypium hirsutum L.) has not considered temperature as a determining factor. This is despite correlations between leaf P content and temperature being observed in other crops. As part of research into a new cotton farming system for the semi-arid tropics of Australia, we conducted two P fertiliser rate experiments on recently cleared un-cropped (bicarbonate P < 5 mg kg^{− 1}) and previously cropped (bicarbonate P 26 mg kg^{− 1}) soil. They aimed to develop P requirements and more importantly to determine if temperature affects the leaf P concentrations used to diagnose P deficiencies. In 2002, optimal yield on un-cropped, low P soil was achieved with a 60 kg P ha^{− 1} rate. In 2003, residual P from the 40 kg P ha^{− 1} treatment produced optimal yield. On cropped, high P soil there was no yield response to treatments up to 100 kg P ha^{− 1}. On low P soil, a positive correlation was observed between P concentration in the youngest fully-unfurled leaf (YFUL), fertiliser rate, and mean diurnal temperature in the seven days prior to sampling. On high P soil, a positive correlation was observed between the YFUL and mean diurnal temperature however there was no correlation with fertiliser rate. These results show that YFUL analysis can be used to diagnose P deficiencies in cotton, provided the temperature prior to sampling is considered.

Keywords:

• leaf
• phosphorus
• concentration
• northern Australia
• lint yield
• soil
• temperature

ACKNOWLEDGEMENTS

The authors are grateful for the scientific guidance from Stephen Yeates and Colin Martin as well as statistical advice from Mark Hearnden. We appreciated the technical assistance from Sue Willoughby, Vlad Kawaljenko, Jack Wheeler, Nick Hartley and other staff at Katherine Research Station.

Notes

^a Colwell P was below the detectable limit of 5 mg kg^{− 1}.

^a–d Means from the same date that share the same letter are not significantly different (p < 0.05).

^† Day degrees calculated using base 12°C.

^a–c Means from the same date that share the same letter are not significantly different (p < 0.05).

^†Day degrees calculated using base 12°C.

^ns not significant (p > 0.05).

∗significant (p < 0.05).

∗∗very ignificant (p < 0.01).

∗∗∗highly significant (p < 0.001).