Change of soil fertility and productivity of purple soil in Western China in recent 30 years

Objectives  Purple soil is widely distributed in China with an area of about 1889 × 10⁴ hm². In this study, the fertility changes of purple soils under the long-term conventional fertilization management were analyzed, to provide scientific guidance for soil nutrient management and sustainable utilization.

Methods  The 29 years’ data of soil organic matter (SOM), total nitrogen (TN), available phosphorus (AP), available potassium (AK), pH, C/N and yields of wheat, maize, and sweet potato were collected from the 8 purple soil long-term monitoring sites. The variations were analyzed using methods of descriptive statistics analysis and median analysis. Principal component analysis and Redundancy analysis were used to explore the main contribution factors to soil fertility in the purple soil and the main factors influencing the crop yield.

Results  After 29 years of conventional fertilization, the contents of organic matter and total N in the purple soil were generally kept stable, while the content of available P and K were increased to various degrees. During 2011−2016, the average AP (15.34 mg/kg) was significantly increased by 151.4% than initial stage (6.10 mg/kg), and the average AK content was increased by 17.23 mg/kg or 23.07% higher than that during 1988−1992. Soil pH was significantly decreased by 0.24 unit compared with the initials. The two determinants of soil fertility in purple soil were AP and AK, and the main limiting factors were low TN and SOM content. The redundancy analysis result showed that the main factors affecting crop yield in purple soil were soil pH, AP and SOM content. The redundancy analysis result showed that the most influential factors for yield of wheat, maize and sweet potato were soil pH, AP and AK in turn.

Conclusions  After 29 years’ conventional fertilization management, yield of corn and sweet potato increased with the improvement of AP and AK, but it led to the imbalance of nutrients. The soil N and pH had been declining as the lack input of organic materials and unbalanced application of P and K fertilizers, and the wheat yield start to decline as the decreased soil pH. The limiting factors of purple soil fertility are lower soil total nitrogen and organic matter content. Therefore, cultivation of purple soil should pay more attention to increase application of organic fertilizers and maintain the soil fertility by applying crop residues.