Evolution Characteristics Of Soil Phosphorus Pool And Efficiency Of Phosphorus Fertilizer In Typical Cropland Of China Under Long-term Fertilization

Phosphorus is the essential element for plant growth, but easily fixed in the soil. Hence, phosphorus use efficiency was an important issue for sustainable agricultural production in China. Sixteen long-term field experiments were conducted from China to evaluate soil available phosphorus, crop uptake, phosphorus balance (i.e., application rate minus uptake rate), phosphorus recovery efficiency (PRE), phosphorus use efficiency (PUE), phosphorus agriculture efficiency (PAE), and phosphorus physiology efficiency (PPE). There were nine treatments: non-fertilization (CK), nitrogen fertilization (N), nitrogen-potassium fertilization (NK), nitrogen-phosphorus fertilization (NP), phosphorus-potassium fertilization (PK), nitrogen-phosphorus-potassium fertilization (NPK), manure with NPK fertilization (NPKM), straw return with inorganic fertilizer (NPKS), high rates of manure and NPK fertilization (NPKM+) with upland, rice-wheat, and rice-rice cropping systems. The key findings are given as follows:The phosphorus balance showed little changes over the entire studying period across all the sites. There were significant differences in the averaged phosphorus balance among different treatments, with an order of CK,N,NK< PK,NP,NPK,NPKS < NPKM,NPKM+. For the NPK treatment that was applied to all the sites, the averaged phosphorus balance (26 kg/hm~2/yr -149 kg/hm~2/yr) showed a significantly positive relationship (p < 0.01) with phosphorus application rate.Soil total P contents with phosphorus treatments (NP, PK, NPK, NPKM, NPKM+, and NPKS) were higher than those of non-phosphorus treatments (CK, N, and NK). Total P decreased under the CK treatment, but maintained the same levels under the NPK treatment at the Urumqi, Nanchang, and Wangcheng sites. For the NPK treatment, averaged total P was 0.81 g/kg, 0.70 g/kg, and 0.89 g/kg at the three sites, respectively. Total P was unchanged under the CK (0.45 g/kg - 1.11g/kg) and NPK (0.58 g/kg - 1.33 g/kg) treatments at the other sites. The results indicated that phosphorus fertilizer was the important factor to improve soil total P.Soil available P contents increased when the rate of soil phosphorus surplus increased. The change rate of soil available P contents is related with the main fractions of soil phosphorus at the sixteen sites. The soil available P contents change rates at sites where main fraction of soil phosphorus of organic-P (Harbin, 8.77 mg/kg) and occluded-P (Qiyang, 4.03 mg/kg) were higher than those with the main fraction of Ca-P(1.38 mg/kg-2.96 mg/kg).Crop phosphorus uptake increased when the soil available P improved. The relationship between soil available P and phosphorus uptake by crop can be modeled by rectangular hyperbolic model ( ). Crop phosphorus uptake never increased when soil available P attained threshold. The threshold in the rectangular hyperbolic model was parameter"a", called the maximum phosphorus uptake rate (P uptake max). The P uptake max was difference among different regions. The P uptake max at Gongzhuling with single cropping system was 184 kg/hm~2, apparantly higher than the other regions. However, the other single cropping system, such as at Urumqi and Pingliang, the P uptake max were 38 kg/hm~2 and 16 kg/hm~2, lower than that of the double cropping systems (wheat-maize and rice-rice double cropping system).Characteristics of crop (wheat, maize, and rice) phosphorus use efficiency accorded with reward descending rule. Crop PRE, PUE, and PAE at sites with high rate of phosphorus application (chemical phosphorus application rate was 135kg/hm~2-225 kg/hm~2) including Changping, Zhengzhou, Chongqing, Suining, and Fuzhou sites were higher than those with the low rate of phosphorus application (chemical phosphorus application rate was 60 kg/hm~2-90 kg/hm~2) included Harbin, Urumqi, Pingliang, Jinxian (upland), Jinxian (paddy), Yangling, Qiyang, Wuchang, and Nanchang sites. The rates of PRE, PUE, and PAE on Ca-P rich soils were higher than that of the main fraction of soil phosphorus of organic-P and occluded-P sites when the phosphorus application rate was similar. In the NPK treatment, wheat PUE increased 1.0-1.6 point per year at sites where main phosphorus form was Ca-P. Whereas the value was 0.3 point at Harbin whose main phosphorus form was organic-P, wheat PUE unchanged at Qiyang whose main phosphorus form was occluded-P, averaged PUE was 10%. Furthermore, crop PRE, PUE, and PAE were difference among different cropping systems. In the NPK treatment, averaged maize PUE was 11% at Urumqi site with single cropping system lower than 43% at Yangling site of double cropping system. The results showed that phosphorus efficency were influced by application rate, soil phosphorus formation, and cropping system.Soil total P, available P, and phosphorus balance rate increased under long term phosphorus fertilization. The change rate of soil available phosphorus contents is related with the main fractions of soil phosphorus. The relationship between soil available phosphorus and phosphorus uptake can be modeled by rectangular hyperbolic model. The P uptake max in single cropping system was lower than that in the double cropping systems. Phosphorus application rate, soil phosphorus formation, and cropping system were important influnce factors of phosphorus efficency. The results provided academic basis of fertilization at various regions.