| China is a large chemical fertilizer consumer and rich in organic fertilizer resources,but the spatial and temporal distribution of organic fertilizer nutrients and the amount of nutrients returning to farmland as well as the characteristics of input and output of nutrients in farmland haven‘t been clear.Nutrients demand and supply in agricultural production in various regions are undefined.These issues have seriously restricted rational allocation and efficient use of nutrient resources for sustainable development of agriculture.It is crutial to study nutrients input/output and balance in farmland as well as nutrients requirements in agricultural production at regional and national level,and to clearly understand the characteristics of nutrients resources and utilization in different regions for providing strategic countermeasures and basis for scientific management and allocation of nutrients resources.This paper,based official statistical data and existing literature reviews,studied the quantity,regional distribution,and effective returning of nutrients from organic sources such as crop residues,livestock and poultry faeces,as well as human excreta from 1980 to 2016,to analyze temporal and spatial changes and characteristics of nutrients input/output and balance of farmland at provincial level,to estimate the current demand for nutrients in China's agricultural production and fertilizer gaps between fertilizer supply and demand in overall balalnced fertilization scenario.The main results were as follows:1)Based on crop yield,straw/grain ratio,straw returning rate,and straw nutrients content,the average amount of straw and its N,P,K nutrients resources as well as their returning in different provinces were calculated and estimated.Results showed that China's straw and its nutrients resources(N+P+K)increased by 85.77% and 104.00% in 2010 s over 1980 s,respectively,and the increase was great in the Northwest provinces,Tibet and Heilongjiang province,over 2/3 resources was distributed in North China,the Middle and Lower Reaches of Yangtze River region,the Sichuan Basin,and Heilongjiang province.By 2010 s,average straw and NPK nutrients resources annually reached 90585.89×104 and 2502.11×104 t,respectively.Compared with 1980 s,the average amount of straw nutrients returning annually in 2010 s was tripled,and the greatest increase of straw nutrient returning occurred in the Northwest region.The total amount of NPK returning each year in 2010 s was 1783.23×104 t with the returning rate of 71.27%,including 579.14×104,106.27×104 and 1097.87×104 t of N,P and K with the returning ratio of 60.70%,77.34% and 77.83%,respectively.The amount of straw nutrient returning to farmland in Northcentral,the Middle and Lower Reaches of Yangtze River,the Sichuan Basin,and Heilongjiang province accounted for about 70% of the national total.2)Based on the number of livestock and poultry in stock at the end of each year and offtake each year,the feeding period,the excretion coefficient,and the nutrients content of manure and urine,the average amount of livestock and poultry manure and urine resources and their NPK resources as well as their returning annually in each province in different time slots were calculated.Results indicated that in 2010 s,compared with 1980 s,the average amount of national livestock and poultry manure and urine resources and their NPK increased by 53.35% and 62.28%,and reached in 423529.66×104(fresh basis)and 4095.76×104 t,respectively.The largest increase was in the Northeast region.The amount of NPK nutrient returning from livestock and poultry faeces to farmland annually increased from 1132.71×104 t in 1980 s to 1713.33×104 t in 2010 s.The amount of annual NPK nutrient returning to farmland from livestock and poultry faeces in Henan,Sichuan,Inner Mongolia,Shandong,Hebei,Hunan,Xinjiang,Guangxi,Yunnan,and Anhui provinces accounted for approximately 55.02% to 59.66% of the national total returning.The amount of N,P and K returning from animal faeces annually in 2010 s was 617.99×104,297.81×104 and 797.53×104 t with returning ratio of 30.58%,70.75% and 48.22%,respectively.3)The total amount of NPK(N+P+K)from organic resources in China was 7779.41×104 t in 2010 s,increased by 67.11% compared with that of 1980 s.The greatest increase of NPK from organic sources occurred in the Northeast region.The amount of organic fertilizer NPK resources in Henan,Shandong,Sichuan,Hebei,Hunan,Inner Mongolia,Hubei,Yunnan,Jiangsu and Anhui provinces was accounted for 55.21% to 57.33% of national total.By 2010 s,the average annual organic fertilizer N,P,and K returning to farmland was 1332.69×104,437.97×104,and 1929.30×104 t,with the returning ratio of 35.00%,61.91%,and 58.78%,respectively.The amount of organic nutrient returning to farmland in Henan,Shandong,Sichuan,Hebei,Inner Mongolia,Hunan,Anhui,Jiangsu,Hubei,and Guangdong provinces was accounted for 55.72% to 60.82% total returning in China.4)Based on economic production of various crops,the amount of nutrients uptake required for producing a unit economic production and the amount of returned nutrients to farmland from straw,the average amount of nutrient removal in crop production in different provinces was estimated.Results showed that the average amount of nutrient removal(N+P2O5+K2O)from farmland increased continually from 1980 to 2016.Compared with 1980 s nutrients removal increased by 75.33% in 2010 s,and the removal of N,P2O5,and K2 O increased by 67.03%,82.59%,and 84.81%,respectively.The greatest increase occurred in Northwest region.The average amount of nutrients removal from farmland annually in 2010 s was 3086.90×104 t including N 1497.07×104 t,P2O5 621.23×104 t,K2 O 968.60×104 t,55.66% to 59.75% was from Henan,Heilongjiang,Hebei,Jiangsu,Sichuan,Jilin,Anhui,Hubei,Hunan and Guangdong provinces.5)By calculation of nutrient input(chemical fertilizer,organic fertilizer)and output(crop removal),the average nutrients apparent balance and partial balance(PNB,nutrient removal/input)in various province in different years were obtained.From 1980 s to 2010 s,the national surplus of total N,P2O5 and K2 O increased by 208.23%,with the largest increase in Northeast region,56.23% to 64.33% nutrients surplus was in Henan,Shandong,Sichuan,Hubei,Hebei,Guangxi,Guangdong,Anhui,Hunan,Jiangsu,and Yunnan provinces.By 2010 s,the average annual nutrients surplus was 5284.42×104 t,including 2220.36×104,2002.27×104 and 1061.79×104 t of N,P2O5 and K2 O,respectively.PNB-NPK,PNB-N,PNB-P2O5,and PNB-K2 O decreased continually,by 2010 s.PNB-N was between 0.13 and 0.85,and above 0.37 in most provinces of Northeast,North China and the Middle and Lower Reaches of the Yangtze River region.PNB-P2O5 was between 0.06 and 0.41,above 0.26 in Northeast region,0.19 to 0.29 in most provinces of North China and the Middle and lower reaches of Yangtze River region,below 0.20 in other provinces.PNB-K2 O ranged from 0.02 to 0.85,above 0.53 in most provinces of Northeast and North China region,and 0.3 to 0.6 in most other provinces.6)According to crop,economic forest,grassland,aquaculture area in 2016 and balanced fertilization rates,the total requirement for N,P2O5 and K2O(N+P2O5+K2O)in China was 8441.80×104t including 3758.13×104 N,2035.96×104 P2O5 and 2647.71×104 t K2 O,respectively,in overall balalnced fertilization scenario.The nutrients requirement by food crops accounted for about 41.53% of the total demand,followed by vegetables/melons of 21.09% and then fruit trees and tea of 13.16%.The regional demand for nutrients was more in the Middle and Lower Reaches of Yangtze River and Northcentral regions than other regions.Nutrient demand in Henan,Sichuan,Shandong,Hunan,Guangxi,Hebei,Yunnan,Hubei,Inner Mongolia and Jiangsu provinces accounted for 52.96% of total requirement in China.The difference between fertilizer consumption and demand in China was 744.52×104 t surplus,where N was 120.61×104 t deficit,P2O5 was 474.78×104 surplus and K2 O was 390.35×104 t surplus.The most overused chemical fertilizer was in Northcentral China,especially in Henan,Shandong and Hebei provinces,while the majority of the provinces in the Northwest and Southwest region had inadequate chemical fertilizers consumption. |
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