Wednesday, December 22, 2010

69% of Crop Residues Utilized

A truck loaded with corn stalks

China has managed to feed a huge number of people on a limited resource base by intensively using its biomass for feeding animals, fertilizing crops, and feeding household cooking stoves and heaters. When rural villages were poor and isolated, people used whatever energy sources they could find nearby and recycled everything--byproducts, manure, and biomass like crop residues--stalks, husks, vines, and leaves.

Crop residues, however, are no longer an attractive source of energy when fossil fuels are available, so a lot of biomass gets burned in the fields. Chinese officials are now trying to simultaneously promote fossil-fuel-powered agriculture by subsidizing agricultural mechanization while also promoting the utilization of biomass for feed, fertilizer and energy.

The government has had a campaign to utilize the residues from crop production at least since the 1990s, and there seems to be a renewed emphasis now that China is grappling with energy issues. Authorities are campaigning to encourage utilization of the energy in crop residues as animal feeds, alternative energy, and raw materials for manufacturing.

As part of this campaign, the Ministry of Agriculture has been carrying out a detailed survey of crop residue utilization over the past year. The results of the crop residue survey were announced last week in a brief article which announced that 69% of crop residues were utilized. The total crop residues available were estimated at 687 million metric tons (mmt) (slightly less than the commonly-cited figure of 700 mmt). Of that total, 265 mmt is corn stalks, 205 mmt rice straw, and 150 mmt wheat stalks. Presumably the balance of 67 mmt includes material from potatoes, cotton, and rapeseed which were also identified as target crops for the survey.

The use of crop residues (see chart) includes feed use 211 mmt (30.69%); energy use 129 mmt (18.72%); 102 mmt fertilizer (14.78%); use as a base for growing mushrooms 15 mmt (2.4%); and use for making paper is 16 mmt (2.37%). The energy use presumably includes use as fuel for cooking and heating in village homes as well as new commercial "alternative" energy projects using biomass.
Chart by dim sums using data from China Ministry of Agriculture

The State Council told the Ministry of Agriculture to formulate standards for crop residues and to carry out the survey in cooperation with local agriculture departments. They apparently have been working on it since 2009. The purpose is to speed up utilization of crop residues in accordance with each region's special characteristics and resourcs. After meeting the needs of livestock feeding, the ambition is to make reasonable use of crop residues for commercial energy production.

This is all part of a massive effort to re-engineer energy use in rural China. The campaign to subsidize agricultural machinery is described as an explicit effort to replace animal and human labor with machines. Thus, the energy for farm work comes from fossil fuels replacing grains and biomass (that fed the workers and animals) produced locally. Water buffalo and other draft animals are probably the main consumers of the 211 mmt of crop residues used for feed, so the reduced number of animals reduces demand for crop residues.

A related campaign promotes conservation tillage--ploughing the residues back into the soil. Another related campaign subsidizes construction of pits to make methane gas from pig manure for cooking and electricity.

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