Potential analysis on winter oilseed rape production under reducing nitrogen input and increasing its efficiency in China

ObjectivesEvaluation of nitrogen fertilizer saving potential in oilseed rape under the national plan of zero growth in chemical fertilizers would be meaningful for the development of high yield and high efficiency for oilseed rape production.

MethodsThe statistical dataset (2005–2014), literature dataset (after 2000), fertilization dataset (2005–2015) and investigation dataset (2009–2011) were combined in our study for quantifying the oilseed rape yield gap and partial factor productivity of nitrogen (PFP_N) gap in domestic and abroad and determining the nitrogen saving potential of recommended level compared to farmers’ level in the major winter oilseed rape producing provinces. The nitrogen saving potential of winter oilseed rape under the different scenarios in the future was explored using the Quantitative Evaluation of the Fertility of Tropical Soils (QUEFTS) model.

ResultsThe statistical results showed that oilseed rape yield in China was approximate with that in the world (1800 kg/hm²) in the past ten years, and winter oilseed rape yields were mainly from 1500 to 2100 kg/hm², but lower than those in Europe. The national yield increase was at a low level, and appeared to yield stagnation. The investigation results showed that the nitrogen rates at the farmers’ level were generally higher with an average of 188 kg/hm². Combination of the planting area (6238×10³ hm²) and recommended nitrogen rate (162 kg/hm²) for winter oilseed rape, the nitrogen saving potential was calculated, i.e. 16.6×10⁴ t. And the main nitrogen saving provinces were Jiangsu, Hunan, Hubei, and Sichuan. Considering that soil indigenous nitrogen supply (INS) is a critical factor for the yield potential and nitrogen saving potential, the N supply levels were divided into low, middle and high according to the nitrogen uptakes of the nitrogen omission treatments of N 30, 50 and 70 kg/hm² (corresponding yields were about 500, 1000 and 1500 kg/hm²), respectively. On the basis of farmers’ level, the recommendation level was set as the scenario Ⅰ, and PFP_N amounts increased by every 5 units were set as the scenarios Ⅱ (foreign normal level), Ⅲ (foreign medium level), and Ⅳ (foreign high level). The result showed that nitrogen demand was improved by increasing target yield, and the increment was growing bigger. Under the low level of INS and the target yield was more than 2500 kg/hm², nitrogen rate could be saved only when the foreign normal level was reached. Under the middle or high levels of INS, nitrogen saving capacity was sufficient when different target yields were achieved.

ConclusionsCombination of INS, target yield of oilseed rape and other agricultural measures was crucial for accomplishing high yield, high efficiency and nitrogen saving.