| China is one of the world's biggest straw producers. In today's society, the development and utilization of straw resources is closely related to the high-efficient transformation of materials and the high-efficient cycle of energies in the agricultural system, the sustainable development issues like soil fertility, environmental safety and high-efficient utilization of renewable resources in the whole agricultural ecosystem, as well as energy use and environmental cleanness in the daily life of farmers, and as a result, it has gradually become an essential element of the sustainable agriculture , circular agriculture and low-carbon economy.There are three major ways to estimate the quantity of straw resources: the first one is to calculate the ratio of straw to grain; the second one is to calculate the ratio of byproduct; the third one is to calculate the harvest index (HI). Based on a lot of experimental study documents on growing crops, the thesis makes use of the basic data provided in these documents such as biomass of different parts of crops, harvest indexes (economic coefficients) and ratios of straw to grain, takes the measurement results of actual ratios of straw to grain in reality into considerations, conducts thorough textual researches on the ratios of straw to grain of various crops, and sets up a more systematic and more accurate straw-to-grain ratio system. And on the basis of the newly established straw-to-grain ratio system, it refers to the statistics of crops production over the years, makes an all-round and systematic estimation of straw output of different crops in our country over the years since 1952 and straw output of different crops in different provinces in 2008, and then summarizes the gross straw output of whole China from 1952 to 2008 and the gross straw output of different provinces in 2008. The results show: (1) the straw output of the country amounted to 842,194,100 tons in 2008, with a net growth of 288% in comparison with that of 1952(216,906,200 tons); (2) China is the world's biggest straw producer; (3) Straw is a biomass resource with the biggest annual growth among terrestrial vegetations in our country, respectively 1.36 times the annual growth of forest biomass, 2.56 times the annual gross grass output of grasslands and 7.75 times the annual growth of garden biomass of the country; (4) the total straw output of rice, wheat and corn accounts for about 2/3 of the gross straw output of the country; (5) nearly half of the country's straw resources are separately located in about 10 percent of the country's land.During the harvesting of agricultural products, many crops needed to be harvested with stubbles; in the growth process of crops, especially during harvesting, most crops will have a certain amount of branches and leaves falling off their stems and residing in field; there will also be partial loss of straws during transportation. Therefore, not all the straws can be gathered. Through investigations and collections of data on different crops'height, stubble height, ratio of leaf biomass, fall-off rate of branches and leaves and loss rate during collection and storage, the thesis establishes the collectable and usable coefficients of straws of different crops in our country, and on the basis estimates the collectable and usable volumes of straws of different crops of our country. Calculation results show: the gross volume of collectable and usable straws was 65,102,100 tons in 2008, and the average collectable coefficient was 0.77.Straws mainly can be used in five ways: the first one is as fuel; the second one is as feed; the third one is as fertilizer; the fourth one is as industrial raw materials; and the fifth one is as raw materials of edible fungi. Based on the natural features of straws such as shape, quality, density, constituents of matter, nutrient content and heat value, etc., the thesis makes categorized and comprehensive evaluations of the natural suitability for straw use. The results of categorized evaluation on the gross volume of collectable and usable straws in 2008 show that: (1) the straws most suitable and suitable to be used as fuel account for above 1/2 of the total; (2) the straws suitable and sub-suitable for gasification, liquefaction, solidification and power account for 95% of the total; (3) the straws most suitable and suitable for biogas production account for about 90% of the total; (4) the straws suitable and sub-suitable to be directly fed to herbivorous livestock account for nearly 80% of the total; the straws to be processed and then fed to herbivorous livestock account for above 90% of the total, and the straws suitable to be directly fed to or processed and then fed to pigs and poultry account for over 1/5 of the total; and (5) the straws suitable for industrial processing and edible fungi growing account for over 90% of the total. The results of comprehensive evaluation on the gross volume of collectable and usable straws in 2008 straws that: Grass Straw and Wood Straw respectively account for about 1/5 of the total while Neutral Straw accounts for about 3/5 of the total.Excessive consumption of straws as fuel directly and inadequate use of straws as feed, newly renewable energy and industrial material are the prominent problems of straw utilization in our country. Of the gross volume of collectable and usable straws in 2008, 210 million tons of straws were used directly as fuel, accounting for 32.26%; 7.2 million tons were used as newly renewable energy, accounting for 1.11%; 176.6 million tons were used as feed, accounting for 27.13%; 43 million tons were used in industrial processing, accounting for 6.61%; 13 million tons were used to grow edible fungi, accounting for 2.00%; 92 million tons were directly returned to the soil, accounting for 14.13%; and 109.22 million tons were discarded or burned, accounting for 16.78%. At present, the total of straws directly returned to field and residing in soil is over 280 million tons, accounting for 1/3 of the gross output of straw resources, and 2.33 tons of straws are returned to each hectare of farming land on average.According to the internal relations between comprehensive utilization of straw resources and"agriculture, rural areas and farmers", the utilization type of straw resources can be divided into three groups: the first one is the recycling utilization of straw resources within the agricultural production system; the second one is the utilization of straw resources within the social economic system in rural areas; the third one is the utilization of straw resources outside the social economic system in rural areas. At present, of the gross volume of utilized straws in our country, the first type accounts for approximately 52%; the second type accounts for approximately 39%; and the third type accounts for approximately 9%.The general trend of our country's exploitation and utilization of straws is specifically embodied by"four increases","two decreases"and"one substitute". The"four increases"refer to increase of use of straws in the new energy development; increase of use of straws as feed; increase of use of straws in industrial processing and utilization; and increase of use of straws in edible fungi planting. The"two decreases"refer to decrease of discarded or burned straws until such practices are completely stopped; and decrease of direct use of straws as fuel."One substitute"refers to that direct returning of straws to field will be gradually replaced by returning of animal manure and biogas fertilizer from respectively raising domestic animals and biogas production using straws.
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