How Comprehensive Utilization of Straw Can Recover the Other Half of Agriculture
The photo shows agricultural machinery being used to bale straw directly in the field for removal. Photo by Liang Baozhong
Editor's note: The autumn grain harvest season has arrived once again, and the issue of banning straw burning has once again drawn attention from all sectors of society. In agriculture's spring blossoming and autumn fruiting, half of the product lies in the grain and half in the straw. Expanding the channels for comprehensive utilization of straw means recovering the other half of agriculture, which is of great significance for solving the difficult problem of agricultural non-point source pollution and promoting sustainable agricultural development.
1. Way out: The utilization pattern of “five-materialization” has basically taken shape
China produces nearly 600 million tons of straw every year, and such a huge figure has come about along with the consecutive annual increases in China's grain output. In the past, straw disposal did not become a follow-up problem in agricultural production as it is today. In traditional farming practices, straw was a precious resource for farmers' production and daily life. After the autumn harvest, farmers would haul all the crop straw home and stack it neatly around their houses. Straw could be used to light fires for cooking, to bed pig, cattle and sheep pens, and as coarse feed for livestock. In households with biogas digesters, it could be used to produce biogas and then be composted into fertilizer. Today, however, with changes in the rural energy structure, straw's function as fuel has been replaced by natural gas, electricity and so on, and with rising rural labor costs, harvesting the already useless straw has even become a burden for farmers.
Even garbage is a resource placed in the wrong spot, so straw certainly cannot be without any use. For straw utilization, the first priority is returning it to the field. It is understood that most straw in developed countries is returned to the field. For example, the United States produces 450 million tons of crop straw annually, and the amount returned to the field accounts for 68% of straw production. Straw itself comes from the land, and returning straw to the field can effectively increase soil organic matter content and improve soil aggregate structure and physicochemical properties.
But returning straw to the field still cannot consume the total amount of straw produced each year. What should be done? Go back to the old trade: use it as fuel, feed, and raw material for biogas. At this point, applying a certain amount of pressure to press it into pellets, blocks, rods and other formed fuels gives it advantages such as high efficiency, cleanliness, easy ignition and zero carbon dioxide emissions. It is a high-quality fuel and is also one of the main development directions of biomass energy at present. As for using straw as feed, it is not fed directly; it must go through the processes of silage and yellow storage, that is, through fermentation to inhibit and kill various microorganisms and produce useful metabolites, giving the feed an aromatic, sour, sweet and other flavors and improving palatability.
Although these are old methods from the past, using industrial thinking and methods to do agriculture has improved the efficiency of straw utilization and opened up more ways to use straw. Most corn straw can be crushed and returned to the field, or made into silage feed, while gramineous straws such as wheat straw and rice straw are among the excellent raw materials for cultivating straw-decomposing fungi. By combining them with nitrogen sources such as cow dung, wheat bran, soybean cake or rice bran, they can be used as a base material for edible mushroom cultivation under suitable environmental conditions.
Making artificial boards from straw is a production technology that has advanced rapidly in recent years. It mainly uses wheat straw, rice straw, corn straw, cotton stalks, sunflower stalks and so on to make particleboard and other artificial boards. Their performance can meet the national standards for wood particleboard, and they do not contain formaldehyde, but the current cost is slightly high.
From being used only as rural domestic energy and livestock feed in the past, straw has now expanded into utilization fields of “five-materialization” including fertilizer, feed, edible mushroom base material, fuel and industrial raw material. It has also gradually formed ecological circular agriculture combining farming and animal husbandry, such as breeding——biogas fermentation——planting——power generation. All of these have opened up space for the comprehensive utilization of straw.
2. Difficulties: High cost of removal from and return to the field, incomplete collection, storage and transportation system
In one agricultural production cycle, both the fruit and the straw are achievements of agricultural production. However, the fruit is the grain that people cherish, while the value of straw as the other half of the achievement is often overlooked. Although we have the means of “five-materialization” utilization, the phenomenon of setting straw on fire still occurs from time to time.
“Directly returning straw to the field requires the coordination of several conditions: first, the straw must be crushed, plowed under and mixed into the field; second, rational irrigation; third, increased nitrogen fertilizer.” said Bi Yuyun, a researcher at the Institute of Agricultural Resources and Regional Planning of the Chinese Academy of Agricultural Sciences. If straw is not crushed, or not thoroughly crushed, and is directly returned to the field, the straw will accumulate on the soil surface and affect the growth of the next crop. At present, straw crushing is mainly carried out through agricultural machinery operations, and this will increase the fuel consumption of the combine harvester, and the comprehensive operating cost per mu will also increase, which instead becomes a burden for farmers. According to a survey by the Ministry of Agriculture, the subsidy standards in some provinces and cities that have already issued subsidy policies are obviously too low. For example, in some provinces and regions, the pilot subsidy standard for returning straw to the field is only 10-20 yuan per mu, equivalent to about 1/3 of the actual cost of returning it to the field, and farmers have to bear 2/3 of the cost themselves.
In fact, the incomplete collection, storage and transportation system for straw, which leads to the relatively high cost of removing straw from the field, is also an important factor affecting the comprehensive utilization of straw. According to a survey and calculation by the Ministry of Agriculture in the Beijing-Tianjin-Hebei region and surrounding areas as well as eight provinces (municipalities and autonomous regions) including Heilongjiang and Jilin, the cost of returning straw to the field is about 9%-15% of the net income of a single-season crop, and the cost of removing it from the field is about 15%-30%. This has resulted in farmers' weak willingness and low enthusiasm to return straw to the field or remove it from the field. Rural labor is now lacking, and although straw has great value, it is cheap. The straw a laborer can handle in one day may sell for only a dozen yuan, while the daily wage for one day's work is as much as over 100 yuan, so the comparative benefit is indeed not high. Some farmers in Northeast China say helplessly: “If the straw is not burned, the field cannot be planted; if the straw is hauled away, farming is done for nothing; if the straw is taken away, it brings no money.” And using balers for the operation also means increased costs.
In recent years, the Beijing-Tianjin-Hebei region has gradually intensified air governance, and smog has accelerated the adjustment of the energy structure in North China. Biomass fuel has thus shown its environmentally friendly advantages, which has given opportunities for the development of the biomass fuel and supporting combustion equipment industries. Moreover, with the gradual maturation of technology, the thermal efficiency of biomass stoves has generally increased from the original 60% to more than 70%, with the highest reaching 80%. As a product for rural cooking and heating, it is very suitable. However, as coal prices have fallen year after year, the position of biomass fuel has become awkward. Last year, China's coal price already fell below 500 yuan/ton, and this year it may fall below 400 yuan/ton, while the delivered price of raw material for biomass formed fuel is 250-350 yuan per ton, and after processing and forming, the ex-factory price of formed fuel is about 800-1,000 yuan per ton. This has led some users to leave.
The high cost of removing straw from and returning it to the field, the incomplete collection, storage and transportation system, and the lack of price advantage for biomass fuel are all bottleneck problems currently facing whether straw can be effectively utilized.
3. Outlook: Make good use of both the government and the market
On October 10 this year, the National Conference on Comprehensive Utilization of Crop Straw was held in Shijiazhuang, Hebei Province. Participants generally said that comprehensive straw utilization is a cause with broad prospects that benefits the country and the people, and governments at all levels are trying to take action.
Beijing has comprehensively adjusted its planting structure. For plots in mountainous and semi-mountainous areas where machinery cannot operate, it has since this year in an orderly manner reduced grain crop planting, solving from the source the difficult problem of straw utilization in mountainous and semi-mountainous areas. Hebei Province has given play to the role of pilot demonstrations and, in Luquan District, required township governments to organize uniformly the collection, storage and transportation of scattered straw. Each village sets up a collection and storage point, and the village committee is responsible for collecting and storing scattered straw, baling it and transporting it to processing plants to produce compressed straw blocks. For every 1 ton of straw collected, the district finance subsidizes the village committee 50 yuan, and the processing plant bears the transport cost of 20-30 yuan per ton. In response to the situation that government-subsidized straw briquetting still has no price advantage, new mechanisms for commissioned fuel processing and exchange purchases are being actively explored. That is, farmers provide straw raw materials themselves, and after commissioned processing, the enterprise charges a processing fee of 100 yuan per ton; or farmers pay 2 tons of straw to the briquetting station, and the briquetting station provides farmers free of charge with 1 ton of straw briquettes, while about 0.8 tons of briquettes processed from the remaining straw is recovered by the enterprise and supplied for commercial use. In this way, farmers, the government and enterprises are linked together and become a community of shared interests, and straw also forms a virtuous cycle from collection to processing to use.