Objectives Paddy soil is the largest and most widely distributed type of arable land in China, and rice production accounts for about one-half of the country's total grain output. Clarifying the characteristics of nutrients evolution in paddy soil is of great significance to its quality construction and productivity maintenance. By using data from the 136 national long-term paddy soil monitoring sites, this study explored the evolutionary characteristics of paddy soil fertility and productivity in China, aiming to provide scientific basis and guidance for the rational fertilization management in paddy soil.
Methods The soil fertility data and crop yields under conventional fertilization on paddy soil were collected. The overall variation trends of soil organic matter (SOM), total nitrogen (TN), available phosphorus (AP), readily available potassium (AK), pH and crop yield during different monitoring periods were summarized using time trend analysis combined with mean and median analysis methods. Among the above five fertility factors, the main contribution factors for soil fertility and the main fertility factors affecting crop yield in paddy soil were analyzed using the principal component analysis and redundancy analysis.
Results Compared with the initial monitoring stage, the content of organic matter (31.3‒32.2 g/kg) and total nitrogen (1.88‒1.92 g/kg) in paddy soil were basically stable, and those of soil available P and readily available K were significantly increased. The average content of AP in paddy soil during 2012−2016 was 20.1 mg/kg, which was 32.2% higher than the average value of 15.2 mg/kg at the initial monitoring stage. The average content of AK in paddy soil during 2012−2016 (92.1 mg/kg) was 18.4% higher than the initial level (77.8 mg/kg). The pH of paddy soil was declined by 0.35 units. The principal component analysis results showed that the two determinants of paddy soil fertility were AK and AP. The redundancy analysis results showed that the main fertility factors affecting crop yield were soil AK, AP and SOM.
Conclusions Under the conventional farmer's fertilization in the past 30 years, the soil fertility is slightly improved and the productivity level is significantly increased in paddy soils of China, despite of the trend of acidification. The increment of soil fertility and productivity is mainly owing to the significant increase of soil available P and readily available K contents, while the total nitrogen and organic matter contents are the obstacles. So, more attention should be paid to the input of organic materials and the balanced application of N, P and K fertilizers for stable and sustainable fertility and productivity of paddy soils in the future.
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