Abstract:Excessive application of phosphate fertilizer wastes phosphorus resources and induces eutrophication in lakes and rivers. To study the effect of reduction of phosphorus fertilizer on phosphorus fractions in calcareous soil and its relationship with crop phosphorus accumulation, three treatments were set up, i.e., phosphorus application rates of 150 kg∙hm ⁻²(P150), 37.5 kg·hm ⁻²(P37), and 0 kg∙hm ⁻²(P0). After two consecutive years of “winter wheat-summer maize” crops rotation, the changes in the contents of soil phosphorus fractions were studied using Hedley soil phosphorus fractionation method, and the storage contribution rate and output contribution rate of each fraction were also estimated. The relationship between soil phosphorus fractions contents, phosphorus fertilizer application rate, and crop phosphorus uptake amount were explored by using regression analysis, path analysis, and structural equation model. The results showed that compared with P37, P150 led to a significant increase in soil total phosphorus content. The contents of inorganic phosphorus extracted with anion exchangeresin (resin_P _i), with NaHCO ₃(NaHCO ₃_P _i), with NH ₄OAc (NH ₄OAc_P _i) and with NaOH-Na ₂S ₂O ₆(Fe_P _i), and organic phosphorus extracted with NaHCO ₃(NaHCO ₃_P _o) in P150 were significantly higher than those in P37, while the other fractions showed no significant change. P0 did not cause a significant decrease in the contents of soil phosphorus fractions. The storage contribution rates of soil inorganic phosphorus fractions and organic phosphorus fractions were 72.6% and 23.8%, respectively. Among them, the storage contribution rates of inorganic phosphorus extracted with HCl (HCl_P _i), Fe_P _i, NH ₄OAc_P _i, resin_P _i, and organic phosphorus extracted with HCl (HCl_P _o) were 24.45%, 18.1%, 13.62%, 11.15%, and 9.30%, respectively. The output contribution rate of soil inorganic phosphorus fractions was 41.0%, and that of organic phosphorus fractions was 56.4%. Among them, the output contribution rates of HCl_P _o, Fe_P _i, and NH ₄OAc_P _iwere 39.44%, 17.36%, and 13.06%, respectively. The output contribution rates of HCl_P _iand resin_P _iwere only 1.91% and 0.40%, respectively. In the structural equation model, the load factors of phosphorus fertilizer application rate on Fe_P _i, HCl_P _i, NH ₄OAc_P _i, resin_P _i, organic phosphorus extracted with NH ₄F (NH ₄F_P _o), NaHCO ₃_P _i, and NaHCO ₃_P _owere 0.078, 0.077, 0.061, 0.036, 0.018, 0.015, and 0.012, respectively. The load factors of Fe_P _i, NH ₄OAc_P _i, and HCl_P _oon crop phosphorus uptake were 0.355, 0.334, and −0.039, respectively. The above results show that in calcareous soil, Fe_P _i, NH ₄OAc_P _i, and HCl_P _owere the key phosphorus fractions. Among them, Fe_P _iand NH ₄OAc_P _iwere easily consumed when no phosphorus fertilizer was applied, but they can be easily supplemented by phosphorus fertilizer application. However, HCl_P _owas available to the crop but was not easily replenished by phosphorus fertilizer application. The high storage contribution rate and low output contribution rate of HCl_P _ifraction were the important reasons for the low efficiency of phosphate fertilizer in the current season. It is suggested that the choice of phosphorus application rate should be based on the storage contribution rate of the key phosphorus fractions.