Three Major Staple Crops Produce Large Amounts of Straw, but Low Utilization Rate Holds Things Back
China is a major agricultural production country with a long history of farming. As the scale of agricultural production has continued to expand, large amounts of concentrated straw have been produced, with annual crop straw output reaching 6.5×108 tons.
According to statistics, the proportion of national straw returned to fields and fed to livestock and returned to fields as manure accounts for about 32% of total output, the amount of straw used as industrial raw material is about 20% of the total, while the amount of straw resources wasted or burned is more than 45%. The incomplete combustion of straw produces large amounts of nitrogen oxides, sulfur dioxide, hydrocarbons and smoke dust, seriously polluting the environment.
In recent years, the Ministry of Agriculture has promoted straw return-to-field projects, which are an important way to continuously improve and fertilize soil fertility. Although their role is widely recognized, in the implementation process they are constrained by factors such as temperature, climate, mechanical equipment and cost, and the pace of promotion is still restricted. How to solve this problem scientifically and reasonably has become an important topic of academic research.
Turning “Waste” into Treasure
According to estimates, if the national amount of straw burning were reduced by 200 million tons each year, carbon dioxide emissions would be reduced by about 214 million tons, and losses such as fires and traffic accidents caused by straw burning would be reduced by more than 50%, thereby reducing economic losses by about 100 billion yuan.
In addition, assuming we industrialize straw at the production site, such as manufacturing biodiesel, straw organic fertilizer, straw biological feed, and straw boards to replace wood, it can not only effectively use China's abundant rural human resources, but also bring substantial income to growers in the planting areas, increasing income by 300-400 yuan per mu.
Data show that China's annual available straw amount is about 680 million tons, and the direct benefit generated each year can reach 340 million yuan, which is a very large income for new rural construction.
In Shuangcheng city of Heilongjiang province, there is a company that uses straw to produce environmentally friendly furniture, environmentally friendly packaging, environmentally friendly building materials, etc., which can both solve the problem of straw resource utilization and increase company income through exports, turning straw resources into an economic advantage; many breeding enterprises in Liaoning and Jilin use biotechnology to make straw into cattle and sheep feed, and test results show that this feed can improve meat quality.
With national policy guidance, most regions of China have already implemented straw biogas and straw power generation technologies, exploring new ways for straw utilization. In recent years, China has also successively built more than a dozen straw biomass power plants.
However, the process details of straw utilization are still not perfect, the cost of deep processing of straw is higher than that of similar products, the straw utilization rate is low, and there is still a lack of strong market operation.
Stones from Other Hills
Looking across some technologically developed countries in Europe and the Americas, their methods for utilizing straw resources are more scientific and effective, significantly improving the utilization rate and value of straw, and are worth learning from.
For example, in Canada, when crops such as corn, rice and wheat mature, farmers use combine harvesters to crush the straw to 3 cm-5 cm while harvesting the crops, and the crushed straw is returned directly to the field to increase the organic matter content in the soil. In the United States, 26 million tons of straw from crops such as corn and rice are used each year to make biological feed; about 9.2 million tons of straw are pressed into blocks for filling house walls; 14 million tons of straw are used as an emerging biomass fuel, that is, ethanol is extracted from straw for reuse, further advancing the comprehensive utilization technology of straw resources.
Comprehensive straw resource utilization projects have also mostly received support from local governments in terms of policy and funding. For example, in Denmark, growers bale straw and sell it to power plants, and the power plants use straw combustion to generate electricity, providing residents with cheap electricity. In other words, farmers use straw to offset part of their electricity bills, and the straw ash produced by straw power plants is then returned directly to fields by farmers, providing nutrients for farmland and realizing an organic cycle between industry and agriculture.
Development Direction
Surveys show that China's straw mainly comes from corn, rice and wheat. The annual available straw amount is 680 million tons. In 2010, the utilized amount was about 500 million tons, and the comprehensive straw utilization rate reached 70.6%, mainly concentrated in feed processing, fuel use, edible fungus substrate and other aspects.
Although comprehensive straw utilization has achieved certain results, such a large resource should have better development prospects.
Fertilizer use: the main utilization method is direct return to the field after crushing or return to the field with added organic material decomposing agent. This method is feasible in southern China and has good effects. However, in northern China, due to the lower temperatures during the fallow period, straw cannot decompose quickly, and microorganisms cannot play a role, so it is not feasible in most areas of northern China. Second, straw reactor technology is mostly used in protected cultivation and cash crops, and the application effect is good, but it has not been widely promoted due to cumbersome operation and high labor requirements. In recent years, the Shenyang Institute of Applied Ecology of the Chinese Academy of Sciences has made straw boards from straw and beneficial microorganisms, which can be laid directly in the working soil, reducing digging depth; beneficial microorganisms can enter the soil and activate nutrient elements in the soil, with obvious application effects. Third, straw can be composted together with livestock and poultry breeding waste for use as organic fertilizer. Fourth, after crushing, straw undergoes microbial decomposition and activation, and the cellulose and other nutrients in it are converted to replace peat and turf resources, making seedling substrates, cultivation substrates and flower nutrient soil, etc., which can reduce the development of peat and turf resources and reduce damage to wetlands and the environment.
Feed use: in 2010, the numbers of livestock and poultry in China's large-scale breeding enterprises were 110 million cattle, 460 million pigs, and 5.35 billion poultry. The proportion of national straw returned to fields and fed to livestock and returned to fields as manure accounts for about 32% of total output, mainly including straw silage and hay storage technology, ammoniation technology, and straw rubbing and puffing technology, etc.
Energy use: data show that China's straw use as fuel is about 122 million tons, accounting for about 17.8% of the total. What China mainly promotes at present are straw fuel blocks, bio-carbonization, biogas and combustion power generation. Among them, straw fuel block technology can be free from scale restrictions and has no requirements for straw sources, so it has good development prospects in solving rural straw pollution in China; straw biogas utilization can produce gases such as methane to provide fuel for urban and rural areas, and can also convert the gas into electricity, and this technology has already been implemented in some areas of China. Direct straw combustion for power generation is theoretically feasible, and some large enterprises in China implemented it years ago, but due to lax raw material quality control, the benefits have been poor, and most enterprises are in a maintenance state.
Material use: as China's urbanization process continues to increase, people's demand for wood is increasing day by day, leading to large-scale logging of trees and supply falling short of demand. However, crop straw contains large amounts of cellulose and lignin, and these resources are not rationally utilized. If straw is made into boards and composite materials, it can reduce logging of forests. In addition, adding an appropriate amount of straw in edible fungus production can also meet the growth needs of edible fungi while reducing the demand for sawdust.