South China Degraded Land Issues

BACKGROUND

China’s people historically have relied on their soil not just to support food production but also to provide an on-the-spot supply of building materials.  Ancient methods probably discovered through trial and error allowed soil to be used to build houses and even parts of enormous structures like China’s Great Wall.  Soil probably seemed an endless resource during China’s early history so using it to make adobe bricks, rammed earth walls, and common fired bricks and tiles seemed harmless enough.

Over time, however, as China’s population grew to 1.4 billion, a conflict over soil use for agriculture vs. building materials ultimately led to government intervention.  The government in 2007 established that a “red line” of 120 million hectares (295 million acres) of farmland be maintained to assure that its people have a continuous and adequate source of food crops.   Maintaining this level is difficult because of the many other demands for farmlands — urbanization, sites for new factories, forest plantings, reservoir construction sites, etc. (1 ).  China’s government showed further concern for their country’s soil when in 2006 they conducted a survey to determine how much of their agricultural land was polluted by the uncontrolled development of recent years.   In April, 2014, China’s Ministry of Environmental Protection, and the Ministry of Land Resources released the study which reported 19.4 percent of China’s farmland was too polluted to produce safe crops (2).

Further, the Xinhau News Agency, China’s official press, recently reported on how much soil is lost in one year to brick production alone. In 2001 a professor from China’s State Economic and Trade Commission reported that China’s 120,000 brick factories produced about 700 billion bricks annually and that in the process used about 1.4 billion cubic meters of soil.   He calculated that this use of soil alone resulted in the annual destruction of 80,000 hectares (197,684 acres) of farmland (3).  The same year the government instituted a partial ban on the manufacture of red brick and tile (4).

How much of China’s farmland soil historically was “mined” as a raw material for production of adobe building blocks, rammed-earth structures, and fired brick and tile is not known.  These building materials though have a long history of use in China; all three were used at various times and places in the construction of China’s Great Wall (5 ).

SOIL CONVERSION TO BUILDING MATERIALS

The following general descriptions are of methods used historically to convert soil into three common building materials: adobe, rammed earth, and fired brick and tile.

Adobe:  Soil was mixed thoroughly with water, sand, and straw to form a thick paste or clay mass.  The material was packed into open wooden frames and sun dried.   Once the frames were removed the blocks were dried a few days longer before use.  If a small amount of lime were added to the mixture, the bricks became “stabilized,” i.e. their durability was increased to withstand the rain and wind.  Even parts of China’s Great Wall were built with adobe.

An adobe-block farm building, Wuhua County, Guangdong. (Photo by W.E. Parham, 1998.)

Rammed earth:  A temporary wooden frame was constructed to the thickness of the desired wall and fixed into place.  A layer of 4 to 10 inches of damp soil, sand, and gravel, generally mixed with a small amount of lime to harden or stabilize the mixture, was placed between the frame walls.  The mixture then

 Tan colored rammed-earth wall with a stucco  coating, Zhuhai, Guangdong.  Note layering from the ramming process (Photo by W.E. Parham, 2005).

was rammed and compacted with blunt poles.  The procedure was  repeated many times to increase the wall’s height. Ultimately, the wood frame was removed carefully and the wall allowed to air dry. The lime reacted with the clay minerals in the soil to bond the rammed-earth particles together, a bond that increased in strength over the next several years. In some instances where lime was not added,  a layer of stucco was applied to the wall’s surface to protect the rammed earth from wind and rain.  Rammed earth  was used also to make building foundations.  The first use of rammed earth in China dates to about 5000 – 3000 B.C.E. (6).

Fired brick and tile:  Soil was mixed with enough water to produce a soft, plastic clay mass which was used to fill wooden brick-forms. Once firm by air drying, the bricks were removed from the frames and stacked for additional drying. Workers then piled the bricks into large, three-dimensional

Fired brick in clamp kiln, north of Guangzhou; (Photo by W.E. Parham, 1982).

stacks with space between adjacent bricks.  The stack was built so that wood fires could be maintained beneath it in fire boxes for about a week. The bricks cooled slowly after the fires were extinguished. These three-dimensional brick piles are called “clamp kilns.”  In some cases a clay plaster was used to coat the “clamp kiln” to help contain the heat during firing.  Clay coated clamp kilns are called “scove kilns.”  Early dome shaped kilns also were used and evolved into the “bee-hive” kiln. Much of the common brick and tile produced in this fashion had a red color.  The first use of fired brick in China dates to about 5000 – 3000 years B.C.E. (7)

SOIL USE AND POPULATION CHANGE

Once farmland soils were used as raw material for construction they were essentially lost for agriculture.  New soil forms extremely slowly and depends on many complex factors such as parent material, topography, climate, and the plants and animals inhabiting the site; soil scientists estimate that it may take from 500 up to thousands of years to form one inch of new soil (8). China’s Great Wall as well as those walls surrounding ancient cities were built with one or more of the three soil derived building materials.  Historically, the older structures were built with rammed earth and the more recent with fired brick; those of intermediate ages used combinations of the two.  (Stone, wood, and plant materials also were used to construct some walls but will not be discussed here.)  Obviously, the large amount of soil consumed  had adverse effects on the local farmland.  Construction of China’s Great Wall, for example, begun in about 200 B.C. and completed some 1700 years later, reached a length of 6000 miles (9).  Ancient city walls were a few tens of miles in length.  Add to these were the multitude of village walls of shorter length. The volume of such walls alone had to consume significant amounts of soil.

Figure 1 illustrates China’s population growth and expected growth from year A.D 1 to 2050. China’s population historically has been rural and even in 1990 it was 73.6 percent rural (China-Profile).  However, China’s recent population shift to urban areas is projected to grow to 60 percent by 2018.

China’s population from A.D. 0 to 2050 (after G.K. Heilig (10).

During  historic periods of increased food production (Song, and Ming Dynasties, e.g.) human populations increased as well.  It seems likely that these periods would also be times of increased building activity.  Soil “mining” probably had  adverse effects on farmlands then just as it would today. Because human populations normally are distributed unevenly, the effects of soil “mining” probably were uneven as well.  Soil today is considered a renewable resource but in retrospect the use of soil to provide building materials takes on the characteristics of  a non-renewable resource   Population growth in the Song and Ming dynasties probably began a process of urban sprawl which in turn buried additional farmland soil.  The Qing Dynasty population grew rapidly to 500 million and the amount of mined farmland soil increased as well as the soil lost to sprawl.

From 1950 to today has been a period of massive population growth for China. During much of that time the population was concentrated in rural areas.  China’s uncontrolled development accelerated damage to all of its renewable resources.  It was this development that led to today’s recognized loss of 20 percent of China’s farmland soil from pollution alone. The spread of villages, towns, and cities in turn buried additional soil beneath their sprawl.

CONCLUSION

Today, techniques have improved to describe various soils, their rates of loss from erosion, etc., and their levels of natural and man-made contamination. Renewed interest in rammed earth for construction, for instance, has led to new research on its ideal particle-size distribution, its mineral composition, and its tolerance for organic matter.  Rammed-earth construction in China has waned but China’s interest in maintaining its soil resources in productive condition for its expanding population has grown.

Even though soil used for building materials has a long history in China, it seems that there has been little investigation on the magnitude of its overall effect on food production.  To determine where soil “mining” took place historically and how much was used probably would require, at a minimum, the cooperative efforts of China historians, soil scientists, and remote-sensing specialists. Such research might make it possible to approximate the amount of soil lost, the estimated time expected  for the land’s recovery, and an estimate of the impact of such changes on China’s future food production.

Walter E. Parham, Ph.D., July 26, 2016

References cited:

(1) “Beijing vows to keep ‘security’ farmland,” So. China Morn. Post, Dec. 29, 2008, http://www.scmp.com/article/665192/beijing-vows-keep-security-farmland.

(2) “One-fifth of China’s farmland is polluted, State study finds, NY Times, April 17, 2014,  http://nyti.ms/1nsGvdM.

(3) “170 Chinese cities to adopt hollow bricks,”  http://news.xinhuanet.com/english/20010511/406938.htm

(4) “Red brick ban to save land,” So. China Morn. Post, July 17, 2001. http://www.scmp.com/article/352545/red-brick-ban-save-land.

(5) Construction materials of the Great Wall, https://www.travelchinaguide.com/china_great_wall/construction/material.htm

(6) https://en.wikipedia.org/wiki/Rammed_earth#History

(7) “Archaeological discovery adds up to 2,000 years onto Chinese brick-making history,” Xinhua News, Feb. 20, 2010, http://news.xinhuanet.com/english2010/china/2010-02/20/c_13181292.htm

(8) https://soilsmatter.wordpress.com/2013/08/29/soil-formation/

(9) “Clay walls of the Ming and Qing Dynasties,” http://www.unesco.org/en/tentativelists/5324.

(10) Heilig, G.K., China-Profile, China-Population A.D. 0-2050, Analyses: Tables, figures & maps, http://www.china-profile.com/data/fig_pop_0-2050.htm.