Objectives To analysis the changes of fertility and productivity of the black soils in the past 30 years by using 13 national long-term black soil test sites, to provide scientific basis and guidance for improvement of soil quality and fertilizer management of black soils.
Methods The trends of soil nutrients and crop yield under conventional fertilization in black soils were analyzed using time trend analysis and mean and median value analysis methods. The evolution characteristics and overall trends of soil organic matter (SOM), total nitrogen, available phosphorus, readily available potassium, pH, and maize yield in different monitoring periods were summarized. Using principal component analysis and correlation analysis, the five fertility factors and crop yields were analyzed to indentify the major contribution factors for soil fertility and the major fertility factors affecting crop yield.
Results Compared with the initial monitoring stage, the contents of organic matter, total nitrogen, available phosphorus and available potassium in black soils all increased, and the available soil nutrients content increased significantly. The average content of available phosphorus in 2012−2016 was 37.73 mg/kg, which was significantly greater than the average content of the initial monitoring period (17.38 mg/kg). The soil available potassium content also showed a significant increasing trend. The average available potassium content (224.31 mg/kg) in 2012−2016 was increased by 44.9% compared to the initial monitoring period (171.50 mg/kg). The pH of black soils showed a downward trend. After nearly 30 years of long-term fertilization, soil pH decreased by 0.59 units. The principal component analysis showed that the two determinants of soil fertility in the black soil were the soil available potassium and available phosphorus, and the major constraint was the low soil total nitrogen and organic matter content. Correlation analysis showed that the major fertility factors affecting maize yield were soil organic matter and total nitrogen content.
Conclusion Under conventional farmer's fertilization management, the fertility and productivity of the black soil has been increased in the past 30 years, but the effect is not sustainable. Meanwhile, soil pH has been decreased and there is a risk of acidification. The major constraint to the improvement of soil fertility is soil total nitrogen and organic matter content. Therefore, fertility management of the arable land in the black soil region should pay attention to rational application of organic materials on the basis of balanced application of N, P and K fertilizers.
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