Five fertilizers, monoammonium orthophosphate (MAP), ammonium polyphosphate (APP), triammonium pyrophosphate (TAPP), urea orthophosphate (UOP), and urea polyphosphate (UPP) were compared in the field and growth chamber using wheat (Triticum aestivum L.) as the test crop. They were tested with and without the nitrification inhibitor 2-chloro-6-(trichloromethyl)-pyridine (N-Serve).
In both the field and growth chamber tests, the use of the nitrification inhibitor, to maintain greater levels of ammonium-N in the soil, with the ammonium and urea phosphates increased the percent P and P-uptake of vegetative wheat plants prior to heading significantly above the levels obtained without the nitrification inhibitor. However, the increased uptake of P during early stages of growth did not affect the yield of grain significantly.
Ammonium polyphosphates (APP and TAPP) and urea phosphates (UOP and UPP) were more effective fertilizers than MAP in both the field and growth chamber. In the field, wheat receiving ammonium polyphosphates and urea phosphates sustained its dry matter production and P-uptake after heading (adding 23% of their dry matter and 22% of their P-uptake between heading and harvest) while wheat with MAP added little to its total dry matter or P-uptake after heading.
Using phosphate fertilizers increased P levels in wheat and depressed Ca, Mn, and Zn concentrations in the herbage. In the case of Zn, TAPP showed less depressive effect on concentration than MAP; the Zn levels were 13.2, 15.7, and 25.9 ppm for MAP, TAPP, and no P, respectively.