Research Of Nitrogen Flow Characteristics And Optimum Management Approaches In Crop-livestock System In Hebei

In recent years,with the acceleration of economic development,urbanization,population growth and improvement of living standards,China's livestock husbandry has also undergone rapid transformation.While developing to intensive and large-scale farming,it has also brought a series of environmental pollution risks,such as low nitrogen use efficiency,ammonia volatilization,water eutrophication and greenhouse gas emissions,which have seriously restricted the sustainability of crop-livestock systems.For further development,it is urgent to explore the optimal management of nitrogen for high yield,high efficiency and environmental protection in crop-livestock system on the basis of clarifying the characteristics of nitrogen flow.In this study,taking the crop-livestock system of Hebei Province as an example,along the whole chain of“feed input-dairy cow production-manure treatment-cropland application”,the characteristics of nitrogen flow and its control strategies were systematically studied from dairy farm,cropland and region scales.On the scale of dairy farm,the relationship between the nitrogen utilization?fate?and the farming scales and the dietary nitrogen levels was discussed through on-site tracking and monitoring and dairy cows feeding experiment;the characteristics of carbon and nitrogen transformation and fate in manure treatment under different composting methods were studied through composting experiment;and the characteristics of nitrogen flow in cropland system after organic manure replacing part of chemical fertilizer were discussed through two-year field experiment.At the regional scale,the NUFER model was used to quantitatively analyze the spatial and temporal characteristics of nitrogen flow in the crop-livestock system of Hebei Province from 1980 to 2015.Through scenario analysis,the strategy of optimizing the management of nitrogen in the whole chain of the crop-livestock system of Hebei Province was discussed.With a view to providing reference for the efficient utilization and sustainable development of nitrogen in the crop-livestock system of China.The main results are as follows:?1?Nitrogen utilization and output at dairy farm scale are closely related to the breeding scale and dietary protein level of lactating cows.The dairy farms were divided into four scales:?100,101-300,301-500 and>500.The tracking and monitoring results showed that,compared with dairy farms with less than 100 cows,the three farms with more than 100 cows had higher average milk yield,milk nitrogen output and average nitrogen use efficiency at dairy farm scale and lactating cow scale,with little difference in average nitrogen input and there was no difference among the three large-scale dairy farms.In terms of nitrogen balance of dairy farm scale standard cattle?body weight is 600kg?,milk nitrogen output of dairy farms with less than 100 cows were significantly lower than that of other three types of dairy farms;manure urea nitrogen output?94.0 kg/head/year?and ammonia volatilization nitrogen loss?26.2 kg/head/year?,which were significantly higher than that of the three kinds of bigger scale dairy farms.There was no significant difference between nitrous oxide emission and water body nitrogen losses.The results of different dietary nitrogen levels experiment showed that compared with high dietary protein level?17.2%?treatment,the low dietary protein level?15.0%?treatment had no significant difference in milk yield and milk nitrogen output,but could significantly improve nitrogen use efficiency?increasing 13.4%?and significantly reduce milk urea nitrogen content.It had no effect on fecal nitrogen content and fecal nitrogen output,and could significantly reduce urine nitrogen content and urine nitrogen output.?2?Nitrogen transformation and fate during manure treatment link of dairy farms vary with different composting methods.The results of four composting methods experiment showed that compared with static treatment?ST?,the turning treatment?TT?,forced aeration treatment?FAT?and forced aeration with acidification treatment?FAAT?can significantly increase the total nitrogen content of compost products and ammonia volatilization rate,and can significantly reduce the ammonium nitrogen content of compost products and nitrous oxide emission rate;compared with ST,the TT and FAT can significantly reduce the nitrate nitrogen content of compost products,and the nitrate nitrogen content of FAAT was basically equal to that of ST?0.170 g/kg?.Except for ST,the TT,FAT and FAAT all reached full maturity.Turning and forced aeration accelerated the composting process,improved the composting efficiency,shortened the harmless time based on plant physiological toxicity?shortened by more than 60.0%?and increased the loss of carbon and nitrogen.Taking forced aeration combined with acidification as the composting method will get the best quality?total nitrogen content 19.7 g/kg?and the lowest GHG value?52.8 kg CO₂-eq/t?.Comprehensively considering the environmental impact,agronomic value,plant toxicity and efficiency index,the composting method of forced aeration combined with acidification is the most suitable production method for the treatment of manure.?3?The nitrogen utilization and balance of wheat-maize rotation system were changed by replacing inorganic fertilizer with organic fertilizer.The results of two-year experiment showed that with the increase of the proportion of organic nitrogen application,the amount of nitrogen uptake,nitrogen use efficiency and soil Nmin decreased gradually,the loss of nitrogen caused by ammonia volatilization decreased significantly and the soil surplus nitrogen increased gradually.Compared with other treatments,inorganic 0.75 treatment?organic fertilizer nitrogen replacing 25%inorganic fertilizer nitrogen?can improve the nitrogen use efficiency in cropland system.Yield of wheat and maize,nitrogen uptake of aboveground crops and nitrogen use efficiency have been improved in varying degrees.The average yield and nitrogen use efficiency of wheat and maize increased by 4.6%and5.1%,respectively.Compared with inorganic treatment,the yield and nitrogen use efficiency of each organic-inorganic fertilizer combination treatment with organic fertilizer substitution ratio more than 25%decreased in varying degrees.?4?The nitrogen input and environmental nitrogen loss?accounting for 44.9%of the total nitrogen input?of the crop-livestock system in Hebei Province increased significantly,but the nitrogen use efficiency of the system was low?31.3%?from 1980 to 2015.In 2015,the cropland system in Hebei Province had the characteristics of large amount of nitrogen input?185.7×10⁴t?,high proportion of chemical fertilizer nitrogen input?about 70.0%?,low nitrogen use efficiency,large regional differences and high environmental risk.In 2015,feed nitrogen input in livestock system of Hebei Province mainly came from the purchase of feed in other provinces?about 75.0%?.At the same time,the input and output of nitrogen in livestock husbandry per unit area between different regions were significantly different.?5?There is great potential to optimize the management of nitrogen in the whole chain of crop-livestock system.Scenario analysis of different nitrogen management strategies showed that nitrogen flow in the whole chain of crop-livestock system showed good effects of low input,high efficiency and low environmental risk under the condition of optimal management.Among them,optimizing composting method and appropriate proportion of organic fertilizer instead of chemical fertilizer are the key factors affecting regional nitrogen flow.Taking 2015 as a benchmark,under the condition of nitrogen optimization of the whole chain,the nitrogen use efficiency and nitrogen output of the main products of the crop-livestock system can be significantly improved,the total nitrogen input of the system decreased by 14.8%,and the total nitrogen loss of water and atmosphere decreased by 31.7%in Hebei Province.In summary,there are serious segregation phenomena in the crop-livestock system.By properly expanding the scale of dairy farms,reducing the feed of dietary protein level,optimizing the treatment types of manure and substituting chemical fertilizer with organic fertilizer,the flow characteristic,utilization and direction of nitrogen in the system can be effectively changed,nitrogen use efficiency can be improved and environmental impaction can be decreased.By optimizing the whole chain of crop-livestock system,the potential of nitrogen optimal management strategies with different links and scales can be more clearly defined,and the methodological basis for realizing the combination of crop-livestock husbandry can be provided.