Effects of phosphorus application rates on spring rape yield and soil phosphorus balance.

Excessive application of phosphorus fertilizer leads to high soil available phosphorus content but low phosphorus use efficiency in the main production areas of spring rape in eastern Qinghai. Understanding the effects of phosphorous application rates on the growth, phosphorus absorption, soil phosphorus balance in the field of spring rape could improve nutrient management of spring rape, and benefit for the sustainable development of agriculture in Qinghai-Tibet Plateau. A field experiment was carried out in Huzhu County of Qinghai Province from 2017 to 2018. We mea-sured seed yield, phosphorus uptake and oil content of spring rape under five phosphorous fertilizer rates (0, 30, 60, 90 and 120 kg PO·hm). In 2017, the seed yield and oil production of spring rape with the rate of 60 kg·hm were significantly higher than that of no phosphorus fertilizer treatment. In contrast, seed yield and oil production did not increase when the phosphorus rate exceeded 60 kg·hm in 2017. Phosphorus rate did not affect seed yield, phosphorus accumulation, and oil production of spring rape in 2018. The phosphorus use efficiency was low in both years, with a mean value of 6.7%. Phosphorus fertilizer application caused phosphorus surplus in soils, which was low when the application rate was less than 60 kg·hm. Our results suggest that the rate of 60 kg·hm is suitable for spring rape production in the eastern Qinghai Province.