Spatiotemporal Emergy Analysis Of The Blue And Green Water Resources In Major Grain Crop Production Systems In China

Using emergy analysis method to measure the true value and quantitative relationship of different types of energy with the solar energy value of the same objective standard could define the intrinsic contribution and utilization efficiency of different types of water resources in crop production system.It is the basis of implementing water resource management.The sources of water consumption for grain production are blue water（surface water and underground water）and green water（effective precipitation）,and the contributions of these two water resources to yield are different.However,the distinction and quantitative of blue and green water in traditional crop production system emergy analysis is not clear.In this study,four major grain crop production systems（rice,wheat,maize and soybean）in provinces of China from 2001 to 2016 were taken as case studies.Based on the quantitative of blue and green water footprints（WF）and theory of marginal,the blue and green water resources and their contributions were distinguished,and the evaluation index system of water resource emergy of crop production system was established and quantified,including water resource emergy input（WEI）,water resource emergy contribution ratio（WECR）and water resource emergy use efficiency（WEUE）.The water resource emergy analysis of crop production system distinguished blue and green water is scientifically realized.The main results are as follows:（1）The annual total WF of major grain crops in mainland China was 5.04×10¹¹m³/a from 2001 to 2006,with an increase of 22.63%.Green WF accounted for 64.64%,with an increase of 34.27%,while blue WF increased only 4.27%.The annual green WF of all crops was higher than that of blue WF,accounting for more than 50%of the total WF.The proportion of blue water in rice and green water in maize was the largest among all crops.There are significant differences in blue and green WFs among provinces.In 2016,Henan and Heilongjiang got the maximum blue and green WFs,116.07 times and 393.07 times of Tibet with the minimum WFs.（2）Renewable emergy flow（the total emergy of renewable resources invested in the system）accounted for only 26.96%of the total annual input emergy(4.91×10²³sej)of China’s major grain crop production systems,and water resources accounted for 62.70%of the total input emergy.From the perspective of local resource types,purchased resources accounted for 71.89%of total emergy input,and chemical fertilizers（nitrogen,phosphorus,potassium and compound fertilizers）accounted for more than 50%of purchased resources.In different provinces,the proportions of renewable emergy flow input in major grain crop production system are larger in western such as Tibet,Xinjiang,Qinghai and Inner Mongolia（all more than 30%）,but smaller in Zhejiang and Fujian.（3）During the study period,the total WEI in China grain production system increased by 16.61%,reaching 9.21×10²²sej in 2016.The proportion of green WEI was 47.36%,and the increase rate（34.27%）was much higher than that of blue WEI（4.27%）.Among all crop production systems,maize surpassed rice in 2011 and became the biggest crop with the fastest growth rate（63.28%）,among which the growth rate of green WEI was 100.25%.In2016,Heilongjiang got the largest value and increase of total WEI(1.04×10²²sej and94.81%,respectively),Henan and Heilongjiang had the largest value of blue and green WEI（11.48%and 12.90%,respectively）.（4）The increase rate of total WECR was only 3.79%,and the blue WECR was higher than that of green WECR,but the difference between them had narrowed from 3.73%to0.81%（the value）.In each crop production system,the green WECR of soybean was much higher than that of other crops in past years,reaching 12.45%in 2016.The increase rate of blue WECR and green WECR of rice（26.25%and 7.02%）was higher than that of other crops.In 2016,Tibet had the maximum total WECR of different crops,and Fujian had the minimum WECR.Xinjiang had the maximum blue and green WECR of major grain crops.（5）The total WEUE increased by 36.72%during the study period,and the green WEUE was much higher than the blue WEUE over the years,with an annual mean difference of7.72 times,and an obvious growth trend（27.28%）.The total WEUE of maize was higher than that of other crops for many years,with an annual average of 7.64.From the perspective of provinces in China,the annual average total WECR of 10 provinces was higher than the national average,but the total WEUE was lower than the national average,among which 4provinces were distributed in the arid northwest region.Meanwhile,for the water-deficient region,the high WECR but low WEUE meant that the degree of water resources shortage was aggravated.Considering the regional climate and crop growth characteristics,to improve the local water resources use efficiency,crop production system can be adjusted by changing crop planting structure,choosing crop varieties with high yield and good quality,increasing the degree of agricultural modernization,making full use of renewable resources,improving the system capacity.In addition,water shortage areas can also invest limited water resources into crops with greater productivity to increase famer’s income,and alleviate the pressure of local water shortage through inter-provincial food trade,to improve the utilization efficiency of local agricultural water resources and save local agricultural water resources.In conclusion,the major grain crop production system could not only clarify the internal relationship and variation rule between crop production and water consumption,but also improve the evaluation study of water resources emergy in agricultural production system,enrich the research system of agricultural water resources,and provide methods and data reference for efficient utilization and rational allocation of regional agricultural water use.