Objectives Altitude, parent material, climate, crop cultivar, tillage system and fertilization rate have strong impacts on fertility of cropland. This survey has clarified the current contents of soil nutrients in spring rapeseed planting area of Qinghai Province, which will be helpful to establish proper fertilization strategy for high yield and quality rapeseed production and sustainable development of agriculture.
Methods There are three major counties for spring rapeseed production, i.e. Huangzhong, Datong and Huzhu counties of eastern Qinghai Province. In total, 103 soil samples were collected from the plough layers of farmlands for spring rapeseed production in 2015, and the primary soil nutrient contents were determined. In conjunction with ArcGIS and Kriging interpolation, the current soil fertility of spring rapeseed planting fields and its spatial distribution characteristics were studied.
Results The average contents and levels of soil nutrients were: soil organic matter 26.81 g/kg (moderate), total N 1.97 g/kg (rich), available P 19.03 mg/kg (moderate), available K 164.27 mg/kg (rich), available Fe 12.02 mg/kg (rich), available Mn 6.43 mg/kg (moderate), available Cu 0.70 mg/kg (moderate), available Zn 1.81 mg/kg (moderate) and available B 0.27 mg/kg (deficient). Among the three counties, 94% of soil total N and 91% of soil available P contents were above the moderate levels. The available K and Zn contents were greatly different from each other. 23.0% of the soil was deficient in available K, and the K deficient soil was mainly distributed in Huangzhong and Huzhu. Zn deficient area was 36.9%, which was mainly distributed in Huzhu. As high as 93.2% of the soil was deficient in B and mainly distributed in Huzhu and Datong.
Conclusions The spring rapeseed fields were generally high in soil N, P and K contents, indicating potential for the reduction of NPK fertilizers. In details, nitrogen fertilizer rate should be reduced properly in Datong and Huzhu, and phosphorus fertilizer rates should be reduced in Huangzhong and Datong. Potassium fertilizers should be applied in low K fields in Huangzhong and Huzhu. As the large areas of severe B deficiency in the three counties and the deficiency of available Zn in Huzhu County, B and Zn fertilizers should be applied properly to avoid the decrease of crop yield and quality due to the short supply of important plant nutrients. The balanced supply of nutrients will help to improve the fertilization efficiency and realize the goal of sustainable development of the spring rapeseed industry.
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