Responses of vegetable yield and changes of phosphorus fractions in cinnamon soil to long-term excess phosphorus application

ObjectivesThis study explored the vegetable yield responses to long term excess phosphorus (P) applications, fates and changes of P fractions in cinnamon soil.

MethodsA phosphorous fertilization field experiment was consecutively conducted for 11 years, 21 vegetable seasons in total in the Piedmont Plain of Taihang Mountain. The five application rates were P₂O₅ 0, 360, 720, 1080 and 1440 kg/hm², named as CK, P1, P2, P3 and P4. The vegetable yields were investigated, and the contents of different fractions of soil inorganic P were measured.

ResultsComparing with CK, the treatments of P₂O₅ 180, 360, 540 and 720 kg/hm² for annual all had significantly higher vegetable yields. However, no significant differences were observed in vegetable yields among P2, P3 and P4 application rates. With the single vegetable season application rates of P₂O₅ 360, 720, 1080 and 1440 kg/hm², the measured surplus P in soil were as 41.2–478.7 kg/hm², equivalent to 26.2%–76.1% of their application rates. With the increase of P input rates, the soil Olsen-P, total P, inorganic P fractions including Ca₂-P, Ca₈-P, Al-P and Fe-P showed trends of increasing, less change in O-P and Ca₁₀-P contents were observed. The annual P₂O₅ input of 720, 1080 and 1440 kg/hm² had led to annual increase of 2.3, 4.2 and 5.0 mg/kg available P contents, respectively. Linear correlation was found between soil P surplus and soil availabe P content. After calculation, every increase of 100 kg/hm² of total soil P surplus will lead to annual increasing in contents of soil Olsen-P, Ca₂-P, Ca₈-P, Al-P and Fe-P of 1.13, 2.41, 15.27, 4.14 and 1.37 mg/kg, respectively, indicating an accumulation order of Ca₈-P > Al-P > Ca₂-P > Fe-P > Olsen-P. Meanwhile, the proportions of Olsen-P in total P and the proportions of Ca₂-P, Ca₈-P and Al-P in the total inorganic P increased with the elongation of cultivation years.

ConclusionsWhen growing cabbage and kidney bean on cinnamon soil, P fertilization rate at 180 kg/hm² can significantly increase yields but the increase will not be more productive when the P input excess the rate. With the increases of P fertilization rates and cultivation years, the contents of Olsen-P, Ca₂-P, Ca₈-P, Al-P and Fe-P and their proportions in the total inorganic P all showed increasing trends except for O-P and Ca₁₀-P. Based on the yield response and soil P balance, P fertilization rates of P₂O₅ 180 kg/hm² for cabbage and 270 kg/hm² for kidney bean are recommended.