ObjectivesCritical soil P levels are important basis for guiding phosphate fertilizer rate and obtaining the best economic benefits for different crops, however, critical soil P values may vary among different crops because of different areas, farming systems, soil types, pH, temperature and humidity conditions. Critical values of soil Olsen-P between maize and wheat in a wheat-maize rotation system in typical fluvo-aquic soil area were determined and analyzed in this studay.
MethodsThis study was based on a 25 year fertilization experiment on " National Long-term Monitoring Station of Fluvo-aquic Soil Fertility and Fertilizer Effects”. Five fertilization treatments were investigated: NK, NPK, NPK plus farmyard manure (NPKM), 1.5 times of application rates of N, P, K plus farmyard manure (1.5NPKM) and N, P, K plus maize straw (NPKS). The critical values of soil Olsen-P for crop yields were calculated using the Mitscherlich exponential model, and the absorption and utilization characteristics of phosphorus in two crops under different soil phosphorus levels were compared.
ResultsCorrespond to 95% of the maximum predicted relative yields, the critical value of Olsen-P was 13.1 mg/kg for wheat and 7.5 mg/kg for maize. The critical value of Olsen-P for maize was lower than that for wheat, and the reasons were: 1) When the soil phosphorus level was low, wheat was more sensitive to the phosphorus deficiency, while maize could maintain a relatively strong ability to absorb phosphorus. Total phosphorus absorption for maize was 1.4 times of wheat in no P fertilization treatment for 25 years. 2) When the content of soil Olsen-P reached the critical value for maize and did not reach the critical value for wheat, the requirement of phosphorus for maize grain, maize straw and wheat grain could be ensured, but the P concentration of wheat straw could only reach 68.9% of the relative maximum P concentration, which seriously affected the normal growth and high yield formation of wheat. When the soil Olsen-P content was increased to the wheat critical value, the P concentration of wheat straw increased to 80.5% of the relative maximum P concentration, and the high yield of wheat could be ensured. 3) When there was adequate soil phosphorus nutrient, the amount of phosphorus absorbed by wheat was higher than that of maize, mainly because with the increase of soil Olsen-P content, the wheat straw P concentration and P uptake amount were greatly increased.
ConclusionsThe critical values of Olsen-P for wheat and maize were 13.1 and 7.5 mg/kg respectively in the typical fluvo-aquic soil. Wheat was relatively less efficient than maize in the absorption and utilization of soil P. Wheat straw needed higher P concentration to maintain normal growth, and needed stronger soil phosphorus supply accordingly for high yield.
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