Effect of co-application of phosphorus and potassium fertilisers on phosphorus uptake by Mungbeans

Deep placement of phosphorus (P) has been shown to increase the effectiveness of fertiliser application in soils with a long cropping history. This cropping history has also often depleted potassium (K) reserves. Research on co-application of phosphorus and potassium has produces variable results. Factors contributing to these variable results such as placement, pH, and K source have been investigated in a glasshouse trial. ³²P labelled P fertiliser was applied alone or mixed with four K sources (nitrate, chloride, sulfate, potassium phosphate) to test if the anion associated with K affected P and K uptake by mungbeans [Vigna radiata (L.) Wilczek]. There was no significant difference between treatments in fertiliser P recovery with either surface or deep placement. The only significant effect was higher shoot and root yield and higher fertiliser P and K recovery in most treatments compared with the zero K treatment with the highest values in the P+K₂SO₄ surface treatment. This increased uptake was not attributable to increased root growth in the fertiliser band or to a difference in band or rhizosphere pH as these were not significantly different in this treatment from the other K source treatments.