Abstract: This study was based upon a longterm fertilization experiment at the Fengqiu Agricultural Experiment Station of CAS. Four fertilization treatments including NP (T₁), NK (T₂), PK (T₃) and NPK (T₄), and nonfertilization (CK) were compared to investigate the effects of longterm application of N, P and K on the daily variations of net photosynthesis rate (P_n), transpiration rate (T_r) and water use efficiency (WUE) of wheat(Triticum aestivum) at its heading and filling stages. The results showed that the daily accumulative P_n at the two stages was in the order of T₄>T₁>T₂>T₃>CK, but statistically significant difference only occurred between T₄ and CK. N, P or K deficiency reduced the P_n, with the order of N>P>K. The curves depicting the daily variations of T_r at both stages were all singlehumped and similar in shape, and no significant differences in daily T_r variation were found among all treatments. N, P or K deficiency reduced leaf WUE. At heading stage, T₁ and T₄ had significantly higher daily accumulative WUE than CK, while the daily accumulative WUEin T₁ and T₄ was not significantly differed with CK, indicating that WUE was affected most strongly by N or P deficiency. At filling stage, the daily accumulative WUE in T₄ was significantly higher than that in CK. Different fertilization treatments affected the range, but not the rhythm, of the daily photosynthetic variations of winter wheat. Our results suggested that applying N, P and K in combination could improve the P_n and WUE of wheat more effectively.

Key words: Long-term located experiment, Calcareous soil, Fractionation of soil inorganic phosphorus, Fractionation of organic phosphorus