Wheat (Triticum aestivum L.) response to combined organic and inorganic phosphorus fertilizers application under saline conditions

Abstract

Phytoavailability of inorganic phosphorus (Pi) reduces within a few hours of application while continuous application of organic phosphorus (Po) has gained the attention of environmentalists. Therefore, continuous application of either Pi or Po would not be a desirable approach. In addition, the ameliorative effect of phosphorus (P) on plant growth under a saline environment has broadened the scope of this hazard. However, our knowledge about P release from amended soils and plant uptake under Cl or SO₄ salt saturated soils is very limited. Therefore, the current study was designed with two objectives: 1) to evaluate the effect of Cl and SO₄ salts on inorganic P release/uptake; 2) to evaluate wheat response to a new combined application of Po + Pi sources under a saline environment. In a greenhouse study, soil was salinized by adding NaCl and Na₂SO₄ salts and P was amended at the rate of 100 kg ha⁻¹ in the form of composted livestock manure (Po), KH₂PO₄ (Pi) and Po (50 kg ha⁻¹) + Pi (50 kg ha⁻¹) (Pc) along with a control. Irrespective of salt types, application of P sources enhanced plant growth and P uptake compared to the control. Combined P sources (Pc) gave higher shoot and root dry matter than P source applied alone. Chloride salt suppressed shoot and root dry matter more severely than SO₄ salt. Phosphorus uptake and recovery (%) increased in pots amended with Pc. Chloride salt was also more toxic for plant P uptake and recovery than SO₄ salt. In the laboratory experiment, soils were amended with the same P sources. After first extraction with NaCl and Na₂SO₄, biologically available P (extracted with NaHCO3), Fe- and Al- bound P (extracted with NaOH) and stable Ca-bound P (extracted with HCl) fractions were measured. It was observed that SO₄ salt released higher amounts of labile P fractions (salt and NaHCO₃ extracted P) than Cl. This study clearly showed that Cl is more toxic for plant growth and P uptake, while SO₄ has higher P desorption capacity. It is suggested that Pc would not only best meet wheat P requirements under saline conditions, but will also help to reduce the load of waste application on agricultural soils.

Keywords:

• Chloride-salinity
• phosphorus source
• phosphorus recovery
• phosphorus uptake
• P fractions
• P release
• sulphate salinity

Acknowledgements

The author expresses thanks to A.E. Eneji, T. Endo and Shin Abe for their encouragement and help throughout the study. Thanks are also due to the Ministry of Education, Science, Sports and Culture-Japan for financial support during the research work.