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Soil and Crop Management for Sustainable Slopeland Farming in Indonesia
Djoko Santoso and Sukristiyonubowo
Center for Soil and Agroclimate Research,
JIn Ir. H. Juanda 98,
Borgor 16123, Indonesia, 1994-08-01

Abstract

Upland soils in Indonesia have great potential for the future development of agriculture. However, most of these soils have low inherent fertility and many have become degraded, especially those in sloping areas. A single heavy application of rock phosphate (1 mt/ha) followed by the planting of a fast-growing leguminous cover crop (Mucuna sp.) resulted in improved productivity of Imperata grassland, with significant residual effects that lasted three years. Bench terraces, ridges, and alley cropping systems were effective in controlling erosion and surface runoff. Sustainable upland farming is difficult to achieve using annual crops alone. Introducing perennial and leguminous crops with livestock into slopeland farming systems is expected to increase farmers' incomes and improve sustainability. While technical solutions to sustain slopeland farming are available - terracing, multiple cropping, and agroforestry or alley cropping systems _ the most urgent need is to identify and transfer technology acceptable to farmers. The methods needed for research into sustainable systems differ greatly from the procedures of conventional agricultural research. Sustainability issues require a combination of simulation modeling and reference-site monitoring, and research should be conducted on the scale of the region or watershed.

Abstracts in Other Languages: 中文(1143), 日本語(1158), 한국어(994)

Introduction

Increased production of foodcrops and higher incomes for farmers are two important goals in Indonesian agricultural development. While agricultural development has been very successful in reducing poverty over the past three decades, much of this gain has occurred in lowland areas through large investments into irrigated rice production. Development has, to a large extent, bypassed the rainfed upland areas where the incidence of poverty among smallholders remains high. Furthermore, because of population growth combined with accelerated industrialization and other development, the agricultural use of upland areas is increasing. Land that was once considered unsuitable for agriculture because of the risk of erosion or other hazards, has been cleared, and is being used for cultivation. Consequently, there is increasing soil erosion and other forms of environmental degradation.

Indonesia has a large upland (rainfed) area of about 79 million ha, most of which is distributed in the islands of Sumatera, Kalimantan, Sulawesi, and Irian Jaya. However, a large part of the land available for agricultural expansion has highly weathered soils, dominated by a 1:1 type clay with a low cation exchange capacity and a high oxide content. Most of the soils are Ultisols and Oxisols. They have a low pH (acidic), a low nitrogen, phosphate, potassium, and organic matter content, and generally have undulating to rolling topography. Productivity of these soils remains low. The lack of development and of appropriate farming technology has caused soil degradation, which has generally been worsened by the low economic status of most upland farmers. This paper presents current conservation farming techniques being used in Indonesia, and suggests research needs for future development.

Progress in Conservation Farming Techniques

Every activity in managing farmland has to be harmoniously related to the other activities. For example, the amount and type of fertilizer applied should match the soil, the cropping pattern and the kind of crop. In turn, the cropping pattern has to be adjusted to the availability of water, farm labor, and funds for investment. Therefore, there is no single soil management program that will fit all farms. The best program for a farm depends on the kind of soil, the amount of money available or allocated for farming, the level of risk the farmer is willing to take, and the knowledge and skill of the farmer. This suggests that soil management activities should be matched with crop management to achieve a sustainable integrated farming system. In the following discussion, soil and crop management practices are presented separately, although they are not always mutually exclusive.

Soil Management

Any sound soil management program must provide three conditions:

  • A satisfactory state of soil tilth for the development of crop roots;
  • An adequate amount of the right kinds of plant nutrients needed for good crop production; and
  • Protection against excessive soil loss and water runoff.

In the following section, only fertility management and erosion control techniques will be discussed.

Fertility Management

Most of Indonesia's fertile mineral soils with a high base saturation and/or flat topography are already being used for cultivation. What is left is slopeland (undulating to rolling) with acid soils, mainly Oxisols and Ultisols. Since these acid soils are highly weathered, their inherent fertility is usually very low and fragile. Successful permanent use for agriculture has so far been largely limited to tree crops, mainly rubber and oil palm. Long-term use of these acid soils for annual crops invariably leads to soil degradation, as has occurred in many transmigration schemes where farmland has been abandoned and taken over by Imperata grass.

Before productive conservation farming systems can be practiced on degraded soils, appropriate rehabilitation techniques are needed. The basic principle of land rehabilitation is to increase the level of soil organic matter and plant nutrients, in order to improve the chemical, physical, and biological properties of the soils. A key component in increasing the fertility status of many upland soils in Indonesia is the application of phosphorus (P). While there is no doubt that the P status of the soil can be increased by P fertilizer, the challenge is to provide farmers with fertilizers at an economic price, and ensure that fertilizers are used as efficiently and effectively as possible. Trials in farmers' fields showed that the application of a high rate of reactive rock phosphate (1 mt/ha -1) followed by the planting of a fast-growing leguminous cover crop ( Mucuna sp.) successfully suppressed the regrowth of Imperata grass on degraded soils in Sumatera. The application of rock phosphate combined with proper organic matter management is a very promising method of rehabilitating degraded land (Sri Adiningsih and Kasno 1994).

Although the application of P fertilizer can overcome the major fertility constraint, the large quantity of P fertilizer involved and its high cost are a major obstacle to farmers. Only those farmers with access to sufficient funds will be able to establish and develop sustainable upland farming systems in areas where poverty would otherwise reign. However, the benefits from productive and sustainable upland farming accrue not only to the farmer, but to the national economy. It is proposed, therefore, that this single heavy application of rock phosphate should be subsidized by the government. This could be considered an investment, equivalent to the irrigation investment supported by the government for lowland farming systems.

The most serious difficulty in farming the highly weathered tropical slopeland soils of Indonesia is that many of these soils are acid clays with low or very low inherent fertility. Nutrient retention is poor, and any organic matter tends to be present only in a few centimeters of top-soil. Soils quickly become depleted of nutrients in the humid tropics. Methods of maintaining nutrient levels as cultivation becomes more intense are of critical importance. Judicious plant nutrient management which avoids nutrient mining is a major key to sustained productivity. Traditional methods of fertility maintenance, which involve the application of farmyard manure and the burning of trees and/or crop residues to allow nutrients to recycle back to farmland, are mostly no longer viable because of the higher rates of nutrient removal by modern crop varieties. While the recycling of organic residues is important, this will not in itself raise the productivity of soils with an initially low inherent nutritional status. There is no escape from having to supply nutrients removed in crops, or lost by leaching and erosion, from other sources - most commonly and cheaply from inorganic fertilizers.

Nutrient balance sheets for seven field experiment sites of the Sloping Land Network have recently been estimated. The study showed that unless high rates of fertilizer were applied, the continuous use of acid soils in tropical Asia for annual crops over four to five years resulted in soil degradation. For the site in Indonesia, the low-fertilizer treatment gave negative balances for potassium (about 0.5 cmol K kg -1) calcium (n 0.27 - 1.23 cmol Ca kg -1), and magnesium (0.14 - 0.21 cmol Mg kg -1). Loss of topsoil from erosion was the largest single factor responsible for the rapid decline in the fertility of the soils in the Network (Santoso et al. 1994b).

Once the level of phosphorus has been built up, and a reasonable organic matter content is being maintained in the soil, further fertility improvement and the prevention of erosion become important. Multiple nutrient deficiencies are often found in the highly weathered tropical soils of Indonesia. Long-term experiments conducted in Jambi Province in collaboration with IBSRAM showed that the application of a moderate rate of phosphorus fertilizer induced potassium and calcium deficiencies, while application of a high rate of phosphorus fertilizer with lime resulted in potassium deficiency (Santoso et al. 1994b). Integrated nutrient management (INM) methods will usually be needed to raise productivity and ensure sustainability. The essential component in an INM strategy is to maximize biological nitrogen fixation in the system. Most of this will be from the inclusion of legumes, whether in crop rotation or as hedgerows.

Erosion Control

Water erosion is widespread and serious in Indonesia, and is a major reason for the lack of sustainability in slopeland farming. However, erosion is a secondary rather than a primary factor, the primary cause often being inadequate land management practices. The cultivation of sloping lands without soil conservation practices can result in high rates of soil erosion and water runoff. A variety of soil conservation practices have been investigated, some of which are used on small farms throughout the country. Some of the most common practices include: bench terraces, contour plowing, minimum tillage, the use of cover crops and mulches, and the planting of grasses or leguminous shrubs along contours.

Terracing is a form of mechanical soil conservation, intended to control erosion and surface runoff. Flat bench terraces, sloping bench terraces, and ridge terraces can all keep erosion at tolerable levels. To test the effectiveness of different kinds of terrace, a field trial was carried out in the Brantas watershed in East Java Province. The flat bench terrace was most effective in controlling erosion, followed by the sloping bench terrace, alley cropping, and ridge terraces, in that order ( Table 1(1048)). For shallow or unstable soils, however, alley cropping and grass strips were more effective than bench terraces in controlling erosion (Fagi et al. 1988; Suwardjo and Saefuddin 1988).

Considerable research has been devoted to studying the effectiveness of vegetative conservation measures. For example, alley cropping systems using leguminous crops such as Flemingia sp ., Calliandra sp . and Tephrosia sp. as hedgerows have been found to be effective in reducing soil erosion and runoff ( Table 2(966)). Flemingia sp. gave the best results. Interestingly, a combination of standing grasses and creeping grasses reduced runoff better than standing grasses with a creeping legume. An alley cropping system with hedgerows of Flemingia congesta can build natural terraces about 25 cm high within one year after establishment (Rachman et al. 1990).

Vegetative soil conservation techniques are generally preferred to mechanical conservation methods (e.g. bench terraces) because of their lower cost and labor requirement. However there is a frequently mentioned obstacle to following an alley cropping system, namely the reduction in effective land area (although the construction of bench terraces can also result in reduced crop yields). Solutions to this problem are an important part of research into sustainability. Results from further research showed that there are some productive hedgerow crops available which have been used successfully. Grass and fruit trees or other woody trees are planted systematically along the hedgerows. This opens the new possibility of increased fodder production, which is very much needed to foster livestock development. The growing of fruit trees, or multipurpose trees which provide not only fruit but also firewood, roofing material, fodder, and mulch, are often of compelling interest to farmers.

The experiment in Jambi Province showed that with the same levels of fertilizer, the alley cropping system resulted in lower soil loss and runoff than the other treatments tested. A combination of the alley cropping system and a high rate of fertilizer gave the best results, due to better crop growth and hence better ground cover ( Table 3(1085)).

Crop Management

To maintain the fertility of sloping lands, especially under upland rainfed farming systems, it is important to mimic natural forest conditions as much as possible. The aim is to keep the soil surface covered for as long as possible, by a canopy of crops and by dead or living mulch (von Uexkull 1985). Different crop management systems for maintaining soil fertility have been investigated, some of which have been adopted by farmers. For the past two decades, it has been known that multiple cropping systems can be very useful in upland farming. While only two or at the most three crops can be planted in a year under monoculture, five to six crops can be planted in a multiple cropping system. The intercropping of upland rice, corn, mungbean bean, sorghum, and cassava, for example, has shown the following multiple benefits:

  • Higher crop productivity per land area;
  • An increase and better distribution through the year of farmers' incomes, with several harvests each year instead of a single one;
  • Maintaining soil fertility by reducing soil loss and water runoff by more prolonged soil cover; and
  • Reduced risk of crop failure (Ardjasa et al. 1984).

As noted earlier, various alley cropping systems, in which annual crops are cultivated side by side with fast-growing perennial hedgerow crops, have recently been widely tested, and some have been effective in controlling erosion. Hedgerows can be established around 5 m apart, depending on the steepness of the slope. However, the potential of alley cropping systems should not be over-emphasized. Many different agro-ecological conditions exist, with other types of soil and varying gradients. The developments of farming systems appropriate for local conditions deserves more attention. It should be kept in mind that as a rule of thumb, annual crops can be planted on land with slopes up to 25%, a combination of annual crops and perennial crops can be planted on land with slopes between 25 and 40%, and perennial crops only should be planted as permanent cover on land with slopes of more than 40%.

Technology Transfer and Research Needs

In managing slopeland, we are concerned not merely with a soil-crop system, but with the human beings who depend on it for their livelihood. Thus the rationale for developing sustainable slopeland farming involves many considerations, including the capability of the farmer to undertake the task, and the availability of funds. Much is known about the causes of unsustainability in slopeland farming, while suitable technology to overcome these constraints is now available. However, the rate of adoption of such technology by farmers is low, and many upland farms remain unproductive and degraded. This provides a new avenue for research in the quest for sustainability: Why are farmers so slow to adopt these innovations?

While more applied research on conservation farming is still needed, it is finding techniques acceptable to farmers which is of primary importance. The reluctance of farmers to adopt terracing and alley cropping as erosion control measures, because of the cost in labor and land, reflects the need for more involvement by farmers in the research process. The key to sustainable slopeland farming is income generation, and to a lesser extent, reduction in risk. These two factors are a prerequisite for sustainability. If farmers are to adopt new technology, their concerns about income generation and risk aversion must be addressed when research is planned. Every attempt should be made to ensure full farmer participation in each phase of the research process: planning, technology development, and dissemination.

To assess the relative significance of various soil and crop factors related to sustainability, it is essential to have a series of long-term experiments in different agroecological zones, some of which are conducted on a catchment basis. Though it is easier to study components of problems, a holistic approach on a watershed basis has considerable benefits, in terms of showing the relative importance of the various individual factors and their interactions with other factors.

Lastly, with the rapid increase in coal mining activities in Indonesia, there is an urgent need to develop technology to rehabilitate degraded land in coal mining areas, where erosion and soil degradation are severe. The erosion occurs because there are a number of chemical and/or physical constraints to vegetative establishment. Here, the cause and effect of erosion is complex, and a discussion based on only a few factors may be misleading. Addressing erosion is only part of the solution: the wider cause must be understood and rectified.

References

  • Ardjasa, W.S., I.G. Ismail, S. Effendi and A. Djauhari. 1984. Results of farming systems research in Batumarta Transmigration Area. In: Proceedings of the Technical Meeting on Farming System Research to Support Transmigration, Nataatmadja, H., M. Bekti, M. Ismunadji, Suwardjo, S. Effendi and P. Sitorus (Eds.). Cisarua, Bogor, Indonesia, February 27-29, 1984, pp. 130-151. (In Bahasa Indonesia).
  • Fagi, A.M., I.G. Ismail, U. Kusnadi, Suwardjo and A.S. Bagyo. 1988. Research on the farming systems of watersheds. Proceedings of the Workshop on Upland Farming Systems and Conservation of Watersheds. Upland Agriculture Conservation Project (UACP). Salatiga, Indonesia, March 14, 1988, pp. 1-23. (In Bahasa Indonesia).
  • Rachman, A., A. Abdurachman and S. Sukmana. 1990. The effects of several soil conservation practices on soil erosion, surface runoff and crop yield on a Typic Eutropept Ungaran. In: Proceedings of a Meeting on the Results of Upland Farming and Soil Conservation Research. Upland Agriculture Conservation Project-Farming System Research, Agency for Agricultural Research and Development, Bogor, January 11-13, 1990, pp. 41-62. (In Bahasa Indonesia).
  • Rachman, A., R.L. Watung and U. Haryati. 1989. The role of cover crops in erosion control on bench terrace risers on a Latosol Ungaran. Proceedings of a Meeting on Upland Farming and Soil Conservation Research in Watershed Area. Agency for Agricultural Research and Development, Malang, Indonesia, March 1-3, 1989, pp. 3-10. (In Bahasa Indonesia).
  • Santoso, D., S. Karama, Sri Adiningsih, I G.P. Wigena, J. Purnomo and S. Widodo. 1994a. The management of sloping lands for sustainable agriculture in Indonesia. In: Reports and Papers on the Management of Sloping Lands in Asia (IBSRAM/ASIALAND), A. Sajjapongse, (Ed.). Network Document No. 8. The International Board for Soil Research and Management (IBSRAM), Bangkok, Thailand, pp. 89-121.
  • Santoso, D., I G. P. Wigena, Z. Eusof and X. Chen. (In Press). Nutrient balance study on sloping lands. Proceedings of the International Workshop on the Management of Sloping Land for Sustainable Agriculture: Challenges and Prospects. Manila, Philippines, November 1994. PCARR, IBSRAM. (In Press).
  • Sri Adiningsih, J. and A. Kasno. 1994. Integrated farming system for sustainable slopeland agriculture in Indonesia. Paper presented at the International Symposium on the Development of Slopeland Agriculture, Takamatsu-City, Japan. October 17-22, 1994. 27pp. (Unpub. mimeograph).
  • Suwardjo and A. Saefuddin. 1988. Some soil and water conservation problems at the Jratunseluna and Brantas Watersheds. Proceedings of the Workshop on Upland Farming Systems and Conservation of Watersheds. Upland Agriculture Con-servation Project (UACP), Salatiga, Indonesia, March 14, 1988, pp. 25-36. (In Bahasa Indonesia).
  • Thamrin, M., H. Sembiring, G. Kartono and S. Sukmana. 1990. The effects of several terrace types in controlling soil erosion on a Tropudalf in Srimulyo, Malang. Proceedings of a Meeting on Upland Farming and Soil Conservation Research. Upland Agriculture Con-servation Project - Farming Systems Research. Agency for Agricultural Research and Development, Bogor, Indonesia, January 11-13, 1990, pp. 9-17. (In Bahasa Indonesia).
  • von Uexkull, H.R. 1985. Improvement and maintenance of soil fertility in tropical upland farming systems. Potassium in the Agricultural Systems of the Humid Tropics. International Potash Institute, pp. 233-250.

Discussion

Dr. Djoko was asked about the cost of the phosphorus application, since this would have a big effect on the readiness of farmers to accept the technology. Dr. Djoko replied that at the current time (September 1995), the cost of triple super phosphate was very high, at around US$ 0.50/kg. However, evidence is accumulating that rock phosphate is quite suitable for upland fields as well as for plantation crops. He recommended that the Indonesian government provide a subsidy for Indonesian upland farmers in the form of rock phosphate, in much the same way that it had in the past helped lowland rice farmers with irrigation facilities. He pointed out that without an injection of resources from outside, it is difficult for upland farms to develop economically.

One participant asked whether, instead of expensive chemical fertilizer, a cheaper organic source of nutrients such as compost could be used. Perhaps the soil organic matter content could be increased in a natural way. Dr. Djoko replied that while he felt that organic recycling and the application of additional organic matter is important, it is not enough in itself to make the soil productive. If farmers are to obtain reasonable rice yields of e.g. 2 mt/ha, they have to apply phosphorus. If they do not, they cannot get good yields. Although forest growth in the tropics tends to be very luxurious, once forest cleared the phosphorus levels in the soil are low and cannot support good crops. One participant suggested that if farmers try to pursue the highest possible output, they cannot have sustainability for very long.

Dr. Huang of Taiwan commented that rock phosphate in Taiwan is not of good quality. Dr. Djoko suggested that more attention generally should be paid to the characteristics of rock phosphate, since it is highly variable. In particular, it should be analyzed to find whether it is reactive. If it is, it is suitable for use as fertilizer.

Index of Images

Table 1 The Effect of Different Types of Terrace on Soil Loss in the Brantas Watershed, East Java

Table 1 The Effect of Different Types of Terrace on Soil Loss in the Brantas Watershed, East Java

Table 2 Reduction in Soil Loss and Runoff with the Use of Leguminous Hedgerow Crops in the Rainy Season 1988/89 at Ungarah, Central Java

Table 2 Reduction in Soil Loss and Runoff with the Use of Leguminous Hedgerow Crops in the Rainy Season 1988/89 at Ungarah, Central Java

Table 3 Total Soil Loss and Runoff between July 1992 and June 1993 under Different Soil-Crop Management Treatments, Kuamang Kuning Unit Xix Site, Jambi Province, Indonesia

Table 3 Total Soil Loss and Runoff between July 1992 and June 1993 under Different Soil-Crop Management Treatments, Kuamang Kuning Unit Xix Site, Jambi Province, Indonesia

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