Studies On The Key Technical Parameters Of Oilseed Rape After Wheat Multiple Cropping As Green Manure In Hetao Irrigation District

In Hetao irrigation district,the light and temperature resources of spring wheat planting have the characteristics of"surplus in one season and shortage in two".There is a land idle period of 2-3 months from the harvest of spring wheat to the beginning of winter.We can use the light,temperature,water,and soil resources during this period to plant green manure crops to achieve the purpose of increasing land coverage and fertilizing the soil.Oilseed rape is an important oil crops in China,and it is also a kind of high-quality green manure with wide adaptability.At present,it has been introduced in the Hetao irrigation district,but there are few studies on oilseed rape after wheat multiple cropping as green manure in this area,and the lack of corresponding planting technology in production has affected the application of this mode.In this study,field experiments were carried out to compare the effects of different varieties,sowing dates,sowing rates and fertilizer rates on the biomass,nutrient concentration and nutrient accumulation of green manure oilseed rape,explored the key technical parameters of oilseed rape after wheat multiple cropping as green manure,which provided technical support for oilseed rape after wheat multiple cropping as green manure in Hetao irrigation district.The main results are as follows:（1）There are significant differences in biomass,nutrient concentration and nutrient accumulation among different green manure varieties.The effect of multiple cropping oilseed rape as green manure in the Hetao irrigation district is significantly better than that of traditional green manure crops such as Hairy vetch,Common vetch and Oat.Under the same production conditions,the fresh weight and dry weight of Hairy vetch were 12.32t/hm² and 2.54 t/hm²,respectively,which were significantly lower than those of oilseed rape varieties（except Huahang 901）.After comparative analysis,Huayouza 62,green manure 1617,Huayouza 62-F₂,Siyou 2 and Yangguang 2009 were the best green manure planting in this area.The fresh weight,dry weight,carbon accumulation,nitrogen accumulation,phosphorus accumulation and potassium accumulation of the above varieties reached 26.76-49.35 t/hm²,7.31-8.18 t/hm²,2671-3151 kg/hm²,140.4-177.7 kg/hm²,17.1-23.6 kg/hm²,153.3-257.7 kg/hm²,and the C/N ratio was 15.0-22.4:1.In this study,the price of rapeseed such as Huayouza 62-F₂ and Yangguang 2009 was only 10 yuan/kg,which was much lower than those commercial seeds.Therefore,when considering green manure biomass and seed cost,it is recommended to select those rapeseed of winter oilseed rape such as Huayouza 62-F₂ and Yangguang 2009.（2）The biomass and nutrient accumulation of green manure oilseed rape decreased significantly with the delay of the sowing date.In this study,the fresh weight,dry weight,carbon accumulation,nitrogen accumulation,phosphorus accumulation and potassium accumulation of oilseed rape that sown on July 26 were the highest,which were 71.39 t/hm²,11.33 t/hm²,and 3885 kg/hm²,259.7 kg/hm²,37.2 kg/hm²,and 381.3 kg/hm²,and the treatment that sown on July 31 was 47.7%,50.1%,53.6%,53.1%,42.1%and 43.8%of that on July 26,respectively.Due to the influence of weeds and insufficient light and temperature resources in the later stage,the sowing date treatment on August 5 and later could not grow green manure oilseed rape.The result indicates that the sowing date of green manure oilseed rape after wheat multiple cropping should be as early as possible.（3）The sowing rate has a significant effect on the biomass and nutrient accumulation of green manure oilseed rape.The biomass and nutrient accumulation of Huayouza 62 and Huayouza 62-F₂ increased first and then decreased with the increase of sowing rate,and both reached the highest when the sowing rate was 15.00 kg/hm².When the seeding rate was 15.00 kg/hm²,the fresh weight,dry weight,carbon accumulation,nitrogen accumulation,phosphorus accumulation and potassium accumulation of Huayouza 62 were76.67 t/hm²,13.64 t/hm²,4769 kg/hm²,258.9 kg/hm²,35.8 kg/hm² and 391.7 kg/hm²,and Huayouza 62-F₂ were 52.69 t/hm²,10.3 t/hm²,3885 kg/hm²,199.8 kg/hm²,28.5 kg/hm²,253.1 kg/hm²,respectively.The biomass and nutrient accumulation of 11.25 kg/hm² and18.75 kg/hm² were slightly lower than 15.00 kg/hm²,but there was no significant difference.The biomass and nutrient accumulation of green manure 1617 increased with the increase of sowing rate,but the increase was not significant and tended to be stable when the sowing rate was more than 18.75 kg/hm².When the sowing rate was 22.50 kg/hm²,the fresh weight,dry weight,carbon accumulation,nitrogen accumulation,phosphorus accumulation and potassium accumulation of green manure 1617 were the highest,which were 52.13 t/hm²,14.40 t/hm²,5521 kg/hm²,192.2 kg/hm²,41.9 kg/hm² and 278.1 kg/hm²,respectively.According to the relationship between sowing rate and fresh weight,dry weight,nutrient accumulation,a quadratic equation model with one variable was established,and the result shows that the optimal sowing rate ranges of Huayouza 62,Huayouza 62-F₂ and green manure 1617 were 15.44-16.35 kg/hm²,15.08-15.50 kg/hm² and 22.22-23.33 kg/hm²,respectively.（4）Fertilization significantly increased the biomass and nutrient accumulation of green manure oilseed rape.Compared with no fertilization treatment（CK）,the dry weight of F₁（13.5 kg N/hm²）,F₂（33.75 kg N/hm²）,F₃（13.5 kg N/hm²+34.5 kg P₂O₅/hm²）,F₄（27 kg N/hm²+34.5 kg P₂O₅/hm²）and F₅（27 kg N/hm²+69 kg P₂O₅/hm²）treatments increased by 27.7%-37.2%,64.3%-67.7%,49.5%-62.2%,80.1%-81.3%and 107.3%-121.3%,respectively.When the seeding rate was 7.5 kg/hm² and 15 kg/hm²,F₅ treatment had the highest fresh weight,dry weight,carbon accumulation,nitrogen accumulation,phosphorus accumulation and potassium accumulation,which were 79.26 t/hm²,14.36t/hm²,5329 kg/hm²,259.8 kg/hm²,36.8 kg/hm²,372.6 kg/hm² and 79.44 t/hm²,13.16 t/hm²,4788 kg/hm²,295.3 kg/hm²,36.4 kg/hm²,366.3 kg/hm²,respectively.F₄ treatment followed,but the difference was not obvious.The result shows that the optimal fertilization treatments for green manure oilseed rape in this study are F₄ and F₅,namely 27 kg N/hm²+34.5 kg P₂O₅/hm² and 27 kg N/hm²+69 kg P₂O₅/hm².According to the actual fertilizer supply,the recommended fertilizer rate for multiple green manure oilseed rape after wheat in the Hetao irrigation district is 30 kg urea+75 kg diammonium phosphate or 150 kg diammonium phosphate per hectare.To sum up,several key technical parameters of oilseed rape after wheat multiple cropping as green manure were determined through the study as follows:The recommended green manure oilseed rape variety is the rapeseed of Huayouza 62 and Yangguang 2009;the recommended sowing date is July 26,it should be sown as soon as possible after wheat harvest in the actual planting;the recommended sowing rate range is 15.0-16.5 kg/hm²;and the recommended fertilizer rate is 150 kg diammonium phosphate or 30 kg urea+75 kg diammonium phosphate per hectare.