Effects of film mulching and nitrogen fertilization on rhizosphere soil environment, root growth and nutrient uptake of winter oilseed rape in northwest China

The ridge film mulching and furrow planting (RFMF) pattern has been increasingly applied to the production of wheat, maize, and potato in arid and semiarid regions of northwest China because it can significantly improve crop yield. How RFMF affects the productivity and whether it can improve the rhizosphere soil environment of winter oilseed rape (Brassica napus L.) is not clear. The main objective of the present study was to determine whether RFMF can improve rhizosphere soil environment and winter oilseed rape productivity in comparison to the conventional flat planting (FP) pattern in a three-year (2014-2017) field experiment. In combination with each planting pattern, we determined an optimal nitrogen (N) application rate among six levels: 0 (NO), 60 (N60), 120 (N120), 180 (N180), 240 (N240) and 300 (N300) kg N ha(-1). Results showed that the RFMF pattern significantly improved the rhizosphere soil environment by increasing soil moisture by 0.3-5.6% and soil temperature by 0.6-3.0 degrees C. However, soil oxygen concentration decreased by 0.03-5.66% during the flowering stage of winter oilseed rape. In addition, the RFMF pattern markedly improved rhizosphere soil enzyme activity and microorganism abundance and thus promoted root growth, nutrient uptake, and seed yield of winter oilseed rape. The resulting optimal N application rates remarkably improved rhizosphere soil enzyme activity, microorganism abundance, root growth, nutrient uptake, and yield of winter oilseed rape in both RFMF and FP treatments. In the RFMF treatment, N240 obtained significantly greater rhizosphere soil enzyme activity, microorganism abundance, root growth parameters, nutrient uptake, and seed yield than N0, N60, N120, and N180, with no significant differences observed between N240 and N300. In conclusion, the RFMF pattern in combination with the optimal N-application rate of 240 kg ha(-1) has great potential to improve rhizosphere environment and winter oilseed rape productivity in arid and semiarid regions of northwest China.