Session 1
“Global extent of tropical sandy soils
and their pedogenesis”

Sandy soils of Asia: a new frontier for agricultural development?

Eswaran, H.¹, T. Vearasilp², P. Reich¹, and F. Beinroth³

Keywords: Sandy, skeletal soils, distribution, agricultural limitation.

Introduction

The beginning of the new millennium saw tremendous advances particularly in information technology and with a general enhancement of the quality of life in most countries of the world there was optimism about the immediate future with respect to sustaining the anticipated population increases. Population growth, though viewed as a blessing at the family level, is a great concern at the national level, particularly in Asia. The current trends suggest that population growth rates have decreased slightly but even this is not adequate for many countries in Asia that would negate further significant increases in food production.

In practically every country in Asia, a large proportion of the energy and capital of a nation is used to address concerns of food security. In industrialized countries such as Japan, Singapore, and South Korea or countries that have adequate natural resources such as Malaysia, wealth is accumulated through non-agricultural means and food imports provide for national food needs. Other countries have to enhance the productivity of land and this implies sacrificing biodiversity and utilizing stressed lands. An earlier study of Eswaran et al. (1999) observed that, “Asia is losing its genetic resources at an alarming rate. Human incursions to natural systems are probably initiating an accelerated process of extinction of species greater than the disappearance of dinosaurs. The core problem is of course the addition of millions of humans at decreasing time spans. We must accept that in the threatened and critical zones, technological fixes may no longer be an option. We must not allow the pressures of poverty, greed, and development to destroy the very resources that can offer solutions to the problem. Soil and water protection, preservation, and conservation take on urgency never before felt in the history of Asian society.”

In a recent study, Engelman et al., (2005) suggested that the limit of per capita arable land is about 0.07 hectares. This is the bare minimum land capable of supplying a vegetarian diet for one person under ideal conditions without the use of fertilizers or amendments. They estimate about 420 million people live in countries that have less than 0.07 hectares of cultivated land per person and about 75% of this is in Asia. When per capita arable land is projected to the year 2025 as undertaken by Engelman et al. (2005) the number of countries that reach this benchmark increases as shown in Table 1. Globally, the population belonging to this category is expected to increase to about a thousand million persons.

Table 1. Population and estimates of per capita arable land in selected Asian countries. Data Source: Engelman, R. et al. (2005)

In practically every country of Asia, all suitable land is being used for agriculture and cultivation has also spilled over to marginal lands. With increasing rural populations, agriculture is moving upslope onto steep landscapes with all the negative consequences of erosion, or invading the wetlands with concomitant impacts on hydrology. Other negative effects on the ecosystem and biodiversity have been repeatedly emphasized. In many countries, there are sandy and skeletal soils, which are of inferior quality in comparison to lands that are currently cultivated but probably they are a much better alternative to steep lands or wetlands. These are two distinct groups with respect to management technology needs and land uses, however in this paper they are considered together as they also share similar constraints, particularly for resource-poor farmers.

The purpose of this paper is to report on previous assessments of the extent of sandy and skeletal soils in Asia, evaluate some general constraints for agriculture and then to justify their status as one of the new frontiers for agriculture. Research in the management of these soils has not received the attention they deserve. It is from this perspective of demanding special attention that such systems are considered as the next frontier for soil research.

Land Resource Stresses

The kinds of edaphic constraints to food production are summarized in Table 2. The study of Eswaran et al. (1999) showed that only about 21% of the land in Asia is stress-free land. There are about 58,000 km² of lands with long cold periods, which precludes use of the land for most agricultural purposes. These are mainly in, Mongolia, Northern China and in the high mountains of Pakistan and India. The deserts of Asia are the Thar Desert of India and Pakistan, and the Taklamakan desert of China extending into Mongolia. Moisture availability is restricted unless irrigation is available. With good irrigation, as around Urumchi in China, the deserts are very productive. In the absence of appropriate drainage outlets, as in parts of Pakistan and India, there is a rapid build up of groundwater and salinity. Sustainable agricultural systems can be developed on the deserts if appropriate land management is practiced. Steep sloping land and soils with shallow depths, due mainly to underlying rock, cannot be used for most agriculture without capital-intensive inputs to prevent environ­mental degradation. Most countries of the region have such lands and if the climate is favourable, they are generally under forests. In the semi-arid and arid parts of the region, the steeper terrain and shallow soils are generally used for grazing of small ruminants. These four land resource constraints – continuous moisture stress, continuous low temperatures, steep slopes, and shallow soils – are land use constraints that cannot be corrected easily by technology. Such lands have great difficulties in supporting sustainable agriculture and are singled out here to compare with lands with sandy and skeletal soils. The latter also present constraints specifically for their function of crop production but in contrast to the other four mentioned earlier, many of the constraints can be overcome with appropriate technology.

Table 2. Edaphic constraints to food production

Eswaran et al. (2003) developed a procedure to undertake a global assessment of land resources stresses using soil and climate information. They defined 24 broad stress classes for this global exercise. Other stresses may be important locally. These can be represented on national or regional maps. Each of the 24 stresses listed in Table 3 requires a different level of investment to correct for agriculture use. The ability to correct the stress with minimal cost is the over­riding factor employed to prioritize the classes in the list. The cost of correcting the stress varies with the country and the kind of stress (Buol and Eswaran, 1994). For sustainable development, an understanding of the kinds of stresses and the costs involved in correction and maintenance is essential. This approach is used to make an assessment for Asian countries (Table 4). As a priority listing is followed and as multiple stresses are not considered, some of the classes in the beginning of the list may incorporate some stresses listed later. For example, areas designated as ‘continuous moisture stress’, which essentially are the deserts of the region, may have soils with salinity problems and if sandy or skeletal have low water holding capacity. As the assessment is made on a small-scale map, polygons on this map may have inclusions that may not have the depicted stress. This empirical assessment can be improved at national level by the use of detailed maps. However, the present assessment is made to provide regional information only and is reliable for this purpose.

Table 3. Description of major land resource stresses or conditions

From an analysis of the dominant stresses, Eswaran et al. (1999) estimated the land quality (Table 5). It is interesting to note that some countries do not have any Class I land. Afghanistan has also an insignificant amount of Class II land. Classes I to III lands are generally the most productive lands of a country though their ability to withstand mis­management varies. Of the three classes, Class II is least resilient which implies that they are most prone to degradation. It is probably correct to assume that, with the exception of a few countries such as Papua New Guinea, Class I to III lands are mostly under agriculture, unless they were set-aside a few decades ago as national parks or forest reserves. Classes IV to VI are generally more prone to degradation and are lands subjected to an onslaught by the land-less. These are the hilly lands and some of the swamps. Most governments are unable to prevent people from using these lands; the more astute governments try to assist the farmers to implement some kind of conservation technology. Land is a limiting resource in many of the countries. With time, the situation will worsen due to soil degradation which reduces the performance of the soil. Exponential growth of urban centres consumes large areas of prime land as the centres originally developed on land that had the potential to feed the community and road or river links to other centres. Those countries which have opted for large scale irrigation programs to compliment their food producing capacity are generally at risk due to salinization and or alkalization which slowly but surely accompanies irrigation in arid and semi-arid envionments.

Table 4. Land quality classes in Asia. Data from Eswaran et al., 1999

Table 5. Some of the land resource stresses in countries of Southern Asia (Area in km²). Land area of soils composed of sandy or skeletal materials (Class 19) is highlighted

In the drier countries of the world the supply of water may become a limiting factor before the inability of the land to produce food is felt (Postel, 1989, 2000). Waterways traversing nations, or even states as in India, have become areas for conflict when limits of the resource base are reached. Further, the increasing requirements of non-agricultural water use will inflate prices resulting in stringent irrigation policies that will be reflected with gains in efficiencies of production. Inadequacies or inefficiencies of irrigation (Postel, 2000) continuously reduce the effective amount of land that can be used for food production.

A further factor that prevents efficient use of land in many developing countries is the purchasing power of the land users, which is the result of poverty (Swaminathan, 1986). Appropriate technological inputs in many of these countries can double production. However, farmers have no capital to invest in the land or there are no incentives, when they do not own the land. They have fewer facilities and an inadequate knowledge base to implement land management technologies and thus there can be few expectations of managing land degradation. Sustainability and the efficient use of the land can only occur through the appropriate application of modern knowledge. Reincarnating past technologies is not a solution to the challenges of today; it is an excuse for a lack of national will and ineptitude.

Incursions into Stressed Systems

A characteristic feature in most Asian countries is that the farm population is declining much faster than that observed in urban areas. Urban areas, in recent years, have seen dramatic increases in population but this is due to influx from rural areas where job opportunities are few. This is generally also an indication of the limits of land for farming. In practically all countries, land that is reasonably suitable for agriculture is already under agriculture. Protected lands are usually a small proportion of the nation’s land area but even these are prone to illegal land use. Table 5 lists a few constraints relevant to this paper (reader is referred to Eswaran et al., 2003, for the complete table). The three major groups of land, referred to previously, that are generally considered stressed are the steep lands or hilly terrain (classes 23 and 22), the swamps (class 20) and the sandy or skeletal soils (class 19). Unlike the steep lands and the swamps where the farmer can eke out a living by using these landscapes, sandy or skeletal soils present problems beyond the capacity of the resource-poor farmers. Thus intensity of use of sandy and skeletal soils or even incursions into such systems was low to negligible in the past but this situation is rapidly changing.

To a large extent, sandy deposits are characteristic of deserts and in the assessment these are considered as areas with continuous moisture stress (class 25) and keyed out earlier in Table 5. The sandy, gravelly and skeletal soils (class 19) are mainly in the areas of rain-fed agriculture. There is about 86,000 km² of such lands in Asia. The sandy soils are grouped with the skeletal soils (soils with high amounts of stones or lateritic gravel) because the land use problems are similar resulting in similar management constraints. The constraints are also a function of technology and this distinguishes this fragile ecosystem from the others.

Management Related Properties

As most of the papers in this Conference will deal with management of these soils, the purpose here is to highlight the major kinds of sandy or skeletal soils and important properties with respect to management. In Soil Taxonomy (Soil Survey Staff, 1999), dunes and shifting sands are considered as non-soils. The typical sandy soils are the Psamments, which are deep deposits of sand of alluvial or aeolian origin. Table 6 summarizes some selected properties of soils from Thailand having sandy textures. The Hua Hin Series represents the typical sandy soil, a deep sandy Entisol. The sand is composed of quartz, and there is less than 1% clay; organic matter is also extremely low. The code “WRD” on the second last column of Table 6 refers to Water Retention Difference. WRD is a measure of the water holding capacity and the very low values highlight the most constraining property of such soils. The low clay content points to the low nutrient holding capacity; any nutrients held are generally by the organic matter in such soils. When the soils have high amounts of gravel as in the Muak Lek Series, the effective volume of the active (clay) fraction is reduced. In skeletal soils, despite a relative high clay content, the soils behave like sands. The Ban Thon and Narathiwat Series show other kinds of soils on such deposits. Some of the pedological properties vary but the basic management related constraints are similar. This is also the case of Ultisols and Alfisols formed on sandy materials.

Table 6. Properties of some soils with sandy or sandy skeletal particle size classes

Sandy or skeletal soils have a high proportion of drainage pores. Water and dissolved substances are rapidly lost to deeper layers in the soil or translocated to groundwater. These soils have been referred to as droughty soils and also nutrient deficient. From a productivity point of view, the soils are least attractive even to the ‘illiterate’ farmer. Other kinds of problems arise, when more intensive agriculture is initiated. Agricultural activities such as pesticide-mixing and tank rinsing, and storage of manure, fertilizer and fuels may pose many risks on sandy soils. Handling agrichemicals requires extra precautions on such soils due to their rapid contamination of groundwater and aquifers. Even wells on such soils must be a significant distance away from contaminant sources.

Higher doses of fertilizers are sometimes recommended to counteract the low fertility and the inability of the soils to retain nutrients. Over-fertilization with nitrogen frequently leads to contamination of the groundwater; high concentrations of nitrate in drinking water is a health hazard particularly to the very young and the very old. A nutrient-management plan, based on leaching losses and retention ability of the soil, should be adhered to. Sandy soils have poor structure and in semi-arid environments, it is extremely difficult to maintain a reasonable ground cover. Wind erosion will result and blown particles may carry applied fertilizers to water bodies. It is hence important to have residue enhancing crop rotations, cover cropping, reduced tillage, shelter belts, and even grassed waterways.

It is long been recognized that enhancing the organic matter content is key to alleviating the soil moisture and nutrient retention problems. Conventional agronomic practices have not been successful or the systems have not been sustainable and this presents one of the greatest and immediate research challenges for the use of these soils. One option is to test species of grasses that are drought prone and have the capacity to produce high amounts of above and below-ground biomass. Miscanthus giganteus is one such species and produces about 40-60 tonnes/ha of biomass. Its palatability to animals is not high but can be used as a component in other highly digestible fodders. A number of ornamental varieties of miscanthus are also known to exist under various common names. Miscanthus can be harvested every year with a sugar cane harvester and is normally grown in cool climates. However, it would be an interesting grass to be tested in the tropics. Like other bioenergy crops, the harvested stems of miscanthus may be used as fuel for the production of heat and electric power, or for conversion to other useful products such as ethanol. If miscanthus can be grown on sandy soils and the biomass is used for bioenergy, it would be one of the most efficient uses of such soils.

As suggested several times, water stress is the most important problem for crop production and the temptation of farmers is to apply as much water as possible. Irrigating sandy soils requires increases in fertilizer and pesticides for most crops to produce a maximum economic (profitable) yield. Nitrogen fertilizer and certain pesticides when applied to sandy soils have the potential to move downward (leach) in the soil profile, possibly into the groundwater. This is one of the reasons that the timing and amount of irrigation water applied are crucial decisions for each operator. Applying too much water means increased pumping costs, reduced water efficiency, and increased potential for nitrates’ and pesticides’ leaching below the rooting zone and into the groundwater. Delaying irrigation until plant stress is evident can result in economic yield loss and, consequently, poor use of some agrichemicals. Some under utilized chemicals are then subject to even greater leaching potential after the growing season when the greatest soil recharge events from rainfall usually occur.

Concluding Observations

Exploitation of stressed ecosystems for arable cropping will increase with increasing population and the concomitant demand for food. From this perspective, it is important that sandy soils be considered as the next frontier for agriculture and a research agenda developed to use the soils in a sustainable manner. The challenge, particularly on a global scale, can be viewed as being of sufficient importance in terms of land area involved globally and the proportion of people who will be impacted that it can be articulated as one of the main agriculture issues to be addressed in the Millennium Project of the United Nations. At the end of March 2005, the World Bank released on their website a preliminary report of the “Millennium Ecosystem Assessment Report” and reported that humans have changed ecosystems more rapidly and extensively in the last 50 years than in any other period. They do recognize that in some sectors there have been net gains in human well-being but in general economic development has been at the expense of degradation of other services. They stress that degradation of ecosystem services could grow significantly worse during this new Century.

Recommendation 5 of the 10 Key Recom­mendations in the Millennium Project reads, “Developed and developing countries should jointly launch, in 2005, a group of Quick Win actions to save and improve millions of lives and to promote economic growth. They should also launch a massive effort to build expertise at the community level.” Several Quick Win efforts have been identified and one is, “A massive replenishment of soil nutrients for smallholder farmers on lands with nutrient-depleted soils, through free or subsidized distribution of chemical fertilizers and Agroforestry, by no later than the year 2006.” Recommendation #9 is also relevant to this new frontier, “International donors should mobilize support for global scientific research and development to address special needs of the poor in areas of health, agriculture, natural resource and environment management, energy, and climate.”

The sustainable development of sandy and skeletal soils has never received any serious attention in the past for various reasons, including the fact that sustaining the productivity in other ecosystems also presented several challenges. If sandy and skeletal soils are presented as the next frontier for agricultural development, the time may be opportune to mount a concerted research and development effort. In practically all countries of Asia, there is a constant pressure to expand the area of land under arable cropping. All countries also have fragile ecosystems and so the challenge is one of reducing ecological risk. Compared to other groups of soils, the sandy and skeletal soils pose minimum level of risk to the environment. Economically, they present immense problems for sustaining the livelihood of the resource poor farmers. Economic viability of agriculture on these soils is the challenge that research and development must address if these are to become the next frontier for agriculture development. With all the advances in technology, our ability to address this group of problem soils may be better today than ever before.

References

Buol, S.W. and H. Eswaran. 1994. Assessment and conquest of poor soils. In (Ed. Maranville, J.W. et al.) “Adaptation of plants to soil stresses”. INTSORMIL Publication 94-2, Univ. of Nebraska, Lincoln, NE. 17-27.

Engelman, R., R.P. Cincotta, B. Dye, T. Gardner-Outlaw, and J. Wisnewski. 2005. People in the Balance. Publ. Population Action International, Washington, DC. 31 pp.

Eswaran H., F.H. Beinroth, and P.F. Reich. 2003. A global assessment of land quality. In. (Ed.) K. Wiebe, Land Quality, Agricultural Productivity, and Food Security: Biophysical processes and economic choices at local, regional, and global levels. 111-132. Publ. Edward Elgar. Northampton, Ma. USA.

Eswaran, H., P.F. Reich, F.H. Beinroth, and E. Padmanabhan. 1999. Major land resource stresses in relation to sustainable agriculture in Asia. Publ. Food and Fert. Tech. Center. Asia. And Pacific. Extension Bulletin 474. 12 pp. Taiwan.

Postel, S. 1989. Water for agriculture: facing the limit. Worldwatch Paper No. 93, Worldwatch Institute, Washington DC.

Postel, S. 2000. Redesigning irrigated agriculture. State of the World 2000. A Worldwatch Institute Report. W.W. Norton Co. New York. 39-58.

Soil Survey Staff. 1999. Soil Taxonomy: A Basic System of Soil Classification for Making and Interpreting Soil Surveys. 2^nd edition. US Dept. Agric. Handbook 436. Govt. Printing Office. 869 pp.

Swaminathan, M.S. 1986. Building national and global nutrition security systems. In: M.S. Swaminathan and S.K. Sinha (Eds.) Global Aspects of Food Production. Tycooly Int., Oxford, England. 417-449.

¹ USDA Natural Resources Conservation Service, P.O. Box 2890, Washington, DC 20013, USA,
² Land Development Department, Chatuchak, Bangkok 10900, Thailand, and
³ Department of Agronomy, University of Puerto Rico, Mayaguez, Puerto Rico.