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. © 2007 Taylor & Francis.