Effects of planting patterns and nitrogen application rates on yield, water and nitrogen use efficiencies of winter oilseed rape (Brassica napus L.)

Abstract: Poor soil conditions and drought stress are 2 main factors restricting the agriculture production in arid and semiarid areas of northwest China. The ridge film mulching and furrow planting (RFMF) cultivation pattern, which employs ridges mulched with plastic film to serve as the runoff area and furrows used as the planting area, has been shown to have the ability of improving soil water availability, yield and water use efficiency (WUE) of maize, wheat and potato. However, the RFMF planting pattern has rarely been tested in oilseed rape (Brassica napus L.) for yield improvements in areas where soil evaporation is high. A 3-year (2014-2017) field experiment was conducted to determine whether the RFMF cultivation pattern has the potential of improving winter oilseed rape productivity. The optimal nitrogen (N) application rate for the maximum yield of winter oilseed rape under the RFMF cultivation pattern was also determined. Winter oilseed rape was planted in RFMF and flat planting (FP) patterns, both with 6 nitrogen (N) application rates: 0, 60, 120, 180, 240 and 300 kg/hm2, named N0, N60, N120, N180, N240 and N300, respectively. The results showed that compared to FP, RFMF significantly increased aboveground dry matter (ADM) by 14.2%-61.5%, nitrogen accumulation amount by 17.4%-61.3%, seed yield by 15.5%-43.5%, water use efficiency (WUE) by 25.5%-69.6%, nitrogen partial factor productivity (NPFP) by 15.4%-43.0%, and significantly reduced evapotranspiration (ET) by 3.3%-9.9%. It was manifested by linear fitting that seed yield and WUE were much higher in RFMF than in FP cultivation condition when the plants of winter rapeseed consumed same amount of water. ADM, nitrogen accumulation amount, seed yield, and WUE of winter oilseed rape were significantly increased with the increase of N application rates (in the range of 0-240 kg/hm2) under RFMF cultivation condition. The ADM and nitrogen accumulation amount did not vary significantly, while ET increased significantly, and seed yield and WUE reduced significantly when N application rates exceeded 240 kg/hm2. Under both RFMF and FP cultivation conditions, N agronomic efficiency (NAE), N physiological efficiency (NPE) and N recovery efficiency (NRE) of the winter oilseed rape were all firstly increased and then decreased with the increase of N application rates, and reached the maximum at N180; while the NPFP was consistently decreased with the increase of N application rates. No significant differences of NAE, NPE, NRE and NPFP were found between N240 and N180 under RFMF cultivation condition (P>0.05). The highest yield and net benefits of winter oilseed rape under RFMF and FP cultivation conditions were found in N240 and N180, with the average seed yield of 3 002 and 2 291 kg/hm2, and average net benefits of 9 538 and 7 498 yuan/hm2 across the 3 years, respectively. The highest yield and net benefit in RFMF was improved by 31.0% and 27.2% in comparison to FP. Present study indicated that RFMF cultivation pattern has the potential of improving winter oilseed rape productivity in arid and semiarid regions of northwest China, with the optimal N application rate of 240 kg/hm2.