6. AGRICULTURAL POTENTIAL

6.1 Introduction
6.2 General Suitability for Cropping
6.3 Land Capability and Crop Suitability Evaluation
6.4 Conclusions and Recommendations

6.1 Introduction

Any assessment of potential agricultural use should first focus on several basic issues. Agriculture as considered here encompasses arable use (the growing of the widest possible range of annual crops), horticulture (perennial crops in general, and fruit trees in particular), pastural use (grassland and fodder crops) and silviculture (commercial growing of trees).

An assessment of land use potential should take into account both the characteristics of the peat as a growing medium and the character of the peatswamps as a whole. In peat soils the improvement of drainage is usually the first step toward the creation of good growing conditions for crops. Artificial drainage, however, has several undesirable side-effects of which subsidence of the land surface is but one. These changes affect the physical and economical feasibility of peat reclamation on a sustained basis, and they therefore must be given prime attention in potential use assessment. It is thus necessary to distinguish between use potential for the years immediately after reclamation and the potential under conditions that develop eventually.

A proper evaluation of the suitability of peats for a particular crop under fixed conditions first requires judgement on which characteristics of the peat and the peatswamps should be taken into account. The nature and range of any limitations for a certain use can then be assessed. Because of the dramatic changes that take place with peat wastage it is sensible to evaluate the potential use of the mineral soil beneath the organic materials taking into account the predicted environmental conditions after wastage. These can be markedly different from the original ones.

This chapter deals largely with the process and methodology of evaluating peat soils and peatswamps and their suitability for various uses. Because of the complexity of the technical problems involved in reclamation and related management we have tried to divorce these aspects from the issues directly related to the evaluation of potential use. Technical problems of reclamation is dealt with separately in Chapter 7 and agricultural management is covered in Chapter 8.

6.2 General Suitability for Cropping

There are diverse opinions on the suitability of peat soils for general agricultural use Coulter (1957) at one extreme, suggested that peat in peninsular Malaysia should be disposed of as rapidly as possible by removal, burning or deep drainage with the ultimate aim of using the underlying mineral subsoil for growing wet rice. This view is still heard in some quarters. Preservationists favour keeping most peatswamps in their natural state as nature reserves, because they are unique ecosystems with a specialized but threatened flora and fauna. Andriesse (1974) describing the tropical peats of South East Asia expresses the moderate compromise view that agriculture should only be allowed in areas which can be permanently drained at reasonable cost without endangering the environment. Other, generally deep peat areas are best left in their natural state for the possible development of silviculture.

The reclamation of peatswamps has always been a matter of some controversy. In the past agricultural development has avoided them for various reasons, usually disease risk, particularly malaria which kept the population from settling near the swamps. In the past, the main reason for draining peatswamps was probably to improve communications rather than to increase agricultural productivity. As a result of initial drainage, the land surface subsided and drainage conditions deteriorated. The environment became less healthy for the local populace necessitating rigorous reclamation. The history of the reclamation of the Pontion swamps, now the Agro Pontino in Italy follows this pattern. Development, which started in 312 B.C. with the construction of the Via Appia, was not completed until early this century when it finally became arable land and fit for permanent settlement. Another reason for draining swamps was turf cutting and use of peat as a source of energy. This took place in Europe starting in the Middle Ages becoming an important means of heating in towns until it was replaced by coal and oil during the 19th and 20th centuries. Peat is still used today in many countries but mainly for fuelling electricity power plants. Because of its relative importance as an alternative energy source in some developing countries the use of peat materials for energy is dealt with specially in Chapter 9.

The agricultural use of tropical peat is commonly viewed with great scepticism. Pons and Driessen (1975) summarize the findings and opinions of most research workers in South East Asia. They express the view that the poor chemical and physical properties of oligotrophic lowland peat soils in South East Asia indicate a very low suitability for any agricultural use. Traditional reclamation disturbs the existing equilibrium which leads to rapid chemical exhaustion of the soil and to strongly increased compaction and decomposition of the peat. The deep, oligotrophic lowland peats produce most biomass if left under forest vegetation, and if managed carefully, exploitation of the forests is possible; a view endorsed by Andriesse (1974). They a brogue that modern agriculture is only possible with uneconomical capital inputs. In many countries, however, peat soils are more highly rated than mineral soil as a medium for intensive cropping. This is particularly so for vegetable growing (Cassidy 1968).

Stephens (1969), reviewing the drainage problems of peats in Florida, explains the apparent contradiction of very low suitability on the one hand versus high suitability on the other as follows: “this peat, when drained, properly fertilized, and augmented by minor elements, breaks down into an excellent soil. Today, these soils, together with the mucks, make up one of the richest agricultural regions on earth”. This indicates that after various conditions have been met peat can become an excellent medium for plant growth. The difficulties arise in the realization of the conditions required. Improvement of drainage appears feasible at first sight, but once oxidation and subsidence have started, keeping drainage at satisfactory levels to match the rate of subsidence can become a technical and financial nightmare. For this reason many peat researchers take the view that before starting to drain, think twice.

Nevertheless, in many countries peatswamps form a substantial land resource to which politicians and development planners alike are attracted because of several positive aspects, for example; the location, often along major rivers or in deltas; the flat nature of the land, presenting no erosion hazard; the feasibility of irrigation; and the low population density. Pressure is greatest where population growth leads to demands to open up new agricultural land. In such areas interest is often directed to the vast tracts of swampy lands, hitherto untouched. If they are near large population centres offering a ready market for vegetables and fruit, the reclamation of peaty swamps is a lucrative alternative to hauling truck crops from remote areas. These latter areas may have better and more sustained conditions for the growing of the crops, but they are economically less attractive. When assessing agricultural suitability the sustainable economic feasibility should be taken fully into account.

Land evaluations based on economic considerations are by nature short-lived because the conditions influencing commodity prices and the farmer’s costs can change rapidly. The latter can be to some degree unpredictable if sustained reclamation costs have to be covered by farmers. There are, however, conditions which would make the agricultural use and reclamation of peatswamps unavoidable and sometimes even desirable. Full understanding of the limitations can help to limit unrealistic expectations. In this way failure can possibly be avoided. The following sections outline procedures for assessing the agricultural potential of peats.

6.3 Land Capability and Crop Suitability Evaluation

6.3.1 Introduction
6.3.2 The initial survey

6.3.1 Introduction

A proper initial survey is the only sound base from which the future use of a peatswamp can be evaluated. Data supplied by such a survey should give indications on the immediate limitations for the proposed agricultural use. These can then be checked against crop requirements. Any proposals for improvement should be the considered outcome of such a matching procedure. Thereafter, the socio-economic consequences and feasibility of the intended use, with or without improvements, can be properly assessed. This procedure is more or less the same as outlined in an FAO Bulletin (FAO 1983). Both parallel and two-stage approaches can be used. In the first the initial survey covers simultaneously the physical conditions of peat and peatswamp and relevant socio-economic factors. In the second approach the physical landscape features are studied initially followed by socio-economic studies in a subsequent phase. The first approach has the advantage of integration of effort and gives feedback from an interchange of information between the various disciplines involved. It is, however, costly and difficult to organize, so in many cases it is probably more efficient to evaluate the physical situation first and thereafter consider the various technical alternatives which can then be evaluated in their socio-economic context. The suggestion is made that an initial rapid appraisal is made before deciding to proceed with more detailed studies.

6.3.2 The initial survey

A clear distinction must be made between the agricultural value of the organic materials, and the suitability or potential of the peatswamp for agricultural development. Severe wetness is commonly the first serious limitation to cropping in swampland, and drainage is a prerequisite for most agricultural developments. Appraisal of the potential for the provision of adequate drainage is a priority. In this connection the term Reclamation Potential is introduced to parallel the term Agricultural Potential which is used in the restricted sense of the agricultural suitability of the peat materials only. The initial survey should, as far as possible, assess both potentials. The following survey procedures are suggested.

Organization

The area to be studied should firstly be reconnoitered using a scale between 1:50 000 and 1:100 000 depending on its size. Figure 18 illustrates how such a quick survey can be accomplished along transects. The position of the transects depends on the configuration and type of the peatswamps. Satellite images or air-photographs, if available, give important clues to configuration, vegetation and risk of flooding. The extent of the latter may vary with the season. Surveying is helped by easy access so the best season should be chosen for swamp investigations. The end of the driest season is usually the best time. It is always worth checking the extent of flooding of the peat at the rainy season when the highest local floods are expected. If it is not possible to visit the area at this time indicators or signs of flooding should be used later. Vegetation can be a great help, by the distinct marks left on trees (Plate 2) indicating the highest water levels during the wet season. These often remain clearly visible during the following dry season. If air-photographs are not available contoured maps are needed to supply the basic topographic information for the survey.

Plate 2. Flood levels from the wet season remain visible on the tree trunks during the dry season, South Irian Barat (Indonesia)

Figure 18. Location of observation lines in initial field surveys of peatswamps

Survey parameters

The initial survey should concentrate on the following aspects:

Nature of peat

a. Fibric, mesic or sapric (decomposition stage).
b. Woody or non-woody.
c. Mineral soil component (quantity, layered, non-layered or dispersed).

This is best recorded using locally decided depth classes. These, for example, could be 0-50 cm (very shallow), 50-100 cm (shallow), 100-150 cm (moderately deep), 150-200 cm (deep), >200 cm (very deep). Initial subsidence after reclamation might be as much as 50 cm, leaving in the case of shallow peat only a few centimetres of peat after initial drainage. The quantity of the mineral component also influences the thickness of the peat soil after subsidence.

Nature of underlying materials

Texture (clays, loams or sands) and character (fertile, infertile, marine with shells).

Presence of sulphidic materials

a. In the organic deposits.
b. In the underlying mineral soil (potential acid sulphate conditions).

Levels of conductivity measured with a normal electric conductivity meter.

Depth of groundwater

Date of measurement should be carefully noted, because of seasonal fluctuation.

Sampling

Samples of the organic and mineral materials should be taken at various selected depths and at various distances from the main drainage channels or the coast. They should be taken at field moisture content in air-tight containers or plastic bags for subsequent laboratory analysis.

The range of possible analyses is large (Table 5) but for an initial appraisal of fertility the following should suffice:

- loss on ignition,

- pH,

- texture (organic and mineral component),

- test on presence of pyrite (drying/wetting method on field moist samples or chemical methods such as total oxidizable sulphur),

- nitrogen content percent,

- carbon content percent,

- bulk density (field condition, undisturbed),

- cation exchange capacity (CEC),

- exchangeable cations Ca, Mg, K, Na, H and Al,

- available phosphorus.

The topographic data to be collected along the transects in the initial survey are as follows:

Levels of surface configuration

These should be related to a benchmark. They can then be correlated with known flood and mean water levels in the main drainage channels, and in some circumstances with mean sea level.

Data on hydraulic conductivity

Vertical and horizontal hydraulic conductivities are useful determinations but they are not often readily available. Crude information can be obtained relatively easily by installing a drain and measuring the water-table depth at increasing distances (piezometer method).

Subsidence

Where possible any information should be obtained from local inhabitants on the rate of subsidence after the installation of drains, however rudimentary.

Flooding and inundations

Settlers near the swamps are often a good source of information on incidence, size and persistence of flooding.

Agricultural suitability rating

The results of the initial survey can be used to evaluate the potential suitability of the land for various agricultural uses. In this process it is first necessary to rate the various soil characteristics or limitations recognized in the district. Favourable and unfavourable characteristics and qualities are evaluated by either a scoring or point system (the quantitative approach) or by the use of descriptive terms such as good, moderate, bad and serious (the qualitative approach).

Many countries have developed such land capability rating systems mostly for mineral soils. Most systems are based on the presence or absence, severity and number of limitations on the husbandry of selected crops. Some suitability ratings also take into account the type of management and farming skills, whether, for example, traditional, improved traditional or with input of modern technology.

Soil limitations can also be grouped as permanent or non-permanent depending whether they can be removed or overcome by management. Fertility and wetness are examples of non-permanent limitations; soil depth or texture of permanent ones.

Because of the specific characteristics of organic soils they need specially designed capability or suitability systems. Table 18 outlines such a system developed for the oligotrophic lowland peats of Sarawak which can be regarded as being representative of peat soils in South East Asia. The capability classes in Table 18a are based on the number and severity of soil limitations for general cropping purposes (Table 18b). The ratings shown in this table are based on local experience and are expressed in qualitative terms (minor to very serious). The system serves as an example of how to recognize and interpret the various limitations of organic materials and how to use these assessments to arrive at a proper rating system for a selection of crops.

A general assessment of capability classes for agricultural purposes is not sufficiently detailed for individual crops or a range of crops. For this, it is necessary to match the capability class assigned to each soil type to the specific soil requirements of the particular crop or range of crops to be established. The specific soil conditions taken into account should be those necessary to give a satisfactory and sustained yield performance. Appendix 3 gives tables indicating soil requirements for a wide range of common crops in South East Asia and in Sarawak in particular.

The matching or correlation of soil capability class with the indicated specific requirements gives a number of suitability ratings for relevant crops or ranges of crops as shown in Table 19. Land is either unsuitable (U), conditionally suitable (C - conditions are given), marginally suitable (M) or suitable (S). The reason for placing soils in the recognized suitability classes is indicated by letter symbols which are also used for the capability subclasses (see Table 18b).

Table 18 ASSESSMENT OF CAPABILITY CLASSES FOR ORGANIC SOILS BASED ON LIMITATIONS TO CROP SUITABILITY AS USED IN SARAWAK (MALAYSIA) (source Maas et al. 1979)

a - Number and severity of limitations for each capability class

Class	Number of limitations
	Minor	Moderate	Serious	Very serious
1	0-1	0	0	0
2	2-3	1 or its equivalent	0	0
3	>4	2-3 or their equivalent	1 or its equivalent	0
4	-	4	2-3 or their equivalent	1
5	-	-	>4	>1

b - Limitations to crop suitability on organic soils

Symbol	Type of limitation		Degree of limitation
			None	Minor	Moderate	Serious	Very serious
a	Depth to sulphidic layer1 (cm)		>100	75-100	50-75	-	-
f	Fertility of the organic layer		Medium (loamy 2 muck)	-	-	Very low (peat or sandy muck)	-
g	Depth to groundwater-table (cm)	natural	-	-	30-60	0-30	-
		drained	60-100	-	30-60	>100	-
h	Degree of decomposition		Hemic-sapric	-	-	Fibric	-
i	Inundation hazard (frequency and duration)		None	Infrequent, short	Frequent, short	Infrequent, long	Frequent and long or submerged
n	Nature (texture) of mineral subsoil at 50-100 cm depth		Fine loamy to clayey			Sandy to coarse loamy	-
o	Depth of organic layer (cm)		-	-	50-100	>100	-
s	Salinity of groundwater (mhos/cm)		<1 000	-	-	1 000-4 000	>4000

¹ Depth after reclamation; allow 25 cm more for subsidence of virgin organic soils.
² The clay content of the mineral component must be greater than 18%.

Table 19 LAND AND CROP SUITABILITY CORRELATION AS USED FOR PEAT SOILS IN SARAWAK (MALAYSIA) (source Maas et al. 1979)

1.	=	Wetland rice	8.	=	Sugar cane	15.	=	Coffee
2.	=	Upland rice	9.	=	Fodder crops	16.	=	Fruit trees
3.	=	Maize, sorghum	10.	=	Forage crops	17.	=	Coconut
4.	=	Soya bean, vegetables	11.	=	Pineapple	18.	=	Cashew
5.	=	Groundnut, tapioca	12.	=	Cocoa	19.	=	Sago
6.	=	Watermelon	13.	=	Oil palm	20.	=	Rubber
7.	=	Banana	14.	=	Pepper, papaya

*	Letters refer to type of limitations (subclass) given in Table 18.
**	S	- Suitable (minor and major soil conservation measures are required for slopes of 12-25° and 25-33° respectively).
	(S)	- Suitable for small-holder and subsistence farming only.
	M	- Marginally suitable (this is mainly deemed to reflect the low nutrient availability thereby restricting productive agriculture).
	C	- Conditional on:	1. non-flood season (e.g. annual on flood-prone areas);
			2. feasibility of flood irrigation;
			3. tolerant or suitable cultivars (e.g. padi on weakly saline soils);
			4. slightly improved drainage (e.g. shallow rooting crops on shallow peats); or
			5. permanently saturated condition (e.g. wetland rice on sulphidic soils).
	C4M	- Conditionally marginal, the number in the centre stipulates the condition (see C).
	U	- Unsuitable. differences being mainly in the rating of those limitations.

It should again be emphasized that the examples given deal only with the agricultural potential or suitability of the peat as a growing medium in field conditions. They do not cover socio-economic factors, nor do they pay attention to possible weed and soil-borne pest problems. It is assumed in the examples that drainage can be provided. The Sarawak system, in particular, is far from being an evaluation on which the economic feasibility of crop production can be assessed. The USA system being based on long-term experience and quantitative analysis of crop production on the various types of peats, could serve a useful purpose locally elsewhere. There are often, however, big differences in conditions in most developing countries so only the broad outlines of the system can be copied. The detailed ratings should be thoroughly adapted to local conditions.

Table 20 MANAGEMENT SUITABILITY FOR SPECIFIC CROPS ON ORGANIC SOILS IN THE LAKE STATES OF NORTH-EAST, USA (source Lucas 1982)

Physical feature		Penalty rating for extended use
		Corn	Pasture	Cool season carrots, celery beets, onions	Short season lettuce, radish, cabbage, spinach	Sod
Growing Degree days above 50° F.
	Above 3 000	0	0	0	0	0
	2200-3000	20	10	10	10	10
	Below 2 200	50	20	20	20	20
Thickness of organic material
	Above 130 cm	0	0	0	0	0
	90-130 cm	5	5	10	10	10
	40-90 cm	10	10	25	25	25
Underlying material 40-127 cm depth
	Loamy	0	0	0	0	0
	Clayey	5	5	5	5	10
	Sandy	10	10	10	10	10
	Coprogenous	20	20	20	20	20
	Marly	30	15	15	15	15
	Rock	50	30	50	50	50
Surface texture 0-40 cm depth
	Muck, mucky peat	0	0	0	0	0
	Peat	20	20	20	20	30
	Marl	40	40	40	40	40
Flooding during growing season
	None	0	0	0	0	0
	Slight	20	5	20	15	15
	Frequent	70	20	70	50	50
Wood fragments >10 cm in diameter within 127 cm depth
	0-1%	0	0	0	0	0
	1-10%	5	0	10	10	20
	10-25%	10	5	10	20	50
	Above 25%	25	10	40	40	100
Soil reaction (pH) in 0.01 M CaCl2 (0-40 cm depth)
	Below 4.0	20	20	20	20	20
	4.0-5.0	10	10	10	10	10
	5.0-7.0	0	0	0	0	0
	Above 7.0	10	5	10	10	10
Acid sulphate below pH 3.5		75	75	75	75	75
Salinity (mmhos/cm)
	0-4	0	0	0	0	0
	4-8	20	20	20	20	20
	8-16	50	50	50	50	50
	Above 16	75	75	75	75	75

Total penalty	score and suitability group
0-15	No limitations
20-30	Minor limitations
35-45	Moderate limitations
50-60	Severe limitations (high reclamation costs)
65-80	Severe limitations (forage only)
85-120	Indigenous crops only
Above 120	Not advisable for agriculture

It is probable that the greatest obstacle to the economic evaluation of peat reclamation for cropping is the correct assessment of the feasibility of drainage on a sustainable basis. In the developed countries the reasons for draining swampland have often been multipurpose and reclamation has been a long historical process of learning and adjustment. Mistakes were made and lessons learnt.

In the developing countries the decision-making process is frequently geared by different motives. Here rapid changes in socio-economic conditions have resulted in a demand for land and have needed quick action. Much of the drainage of peatlands in the developed countries would never have been attempted if the consequences could have been predicted. Reclamation of similar areas in the developing world can therefore learn much from their experience accumulated over the centuries.

An assessment of the Reclamation Potential, which for historical reasons has not played much of a role in the developed countries except during the last 50 years, should play an important role in developing countries if mistakes are to be avoided. As indicated reclamation potential should be assessed separately, and be based on different parameters from those used for the assessment of the Agricultural Potential.

Reclamation Potential

An assessment of the reclamation potential should try to answer the following questions:

a. Is it possible to drain the swamp by gravity? If so, what will be the maximum depth at which adequate drainage can be provided without having to resort to costly pumping?

The sustainability of adequate drainage is strongly related to the present elevation of the land (peat) surface, the rate of subsidence of the surface after drainage, and the elevation of the underlying mineral deposits or rocks. The data collected on these levels in the initial survey should provide sufficient insight. In the case where the level of the underlying mineral material is above the level of the main drainage outlet, it is possible to drain the peatswamp beyond the stage where the peat has completely disappeared. In cases where the mineral subsoil lies below the level of the main drainage outlet, gravity drainage must eventually be replaced by pumping or the land must be abandoned (Fig. 8).

b. What is the expected life time of agricultural land in the reclaimed area?

Life expectancy of the agricultural use of the reclaimed peat depends on the nature of the peat (including the proportion of mineral material) and its likely rate of oxidation and subsidence. These factors are in turn related to climate (temperature) and depth of drainage. For example, much of the present area of organic soils in the upper Everglades of Florida (USA) will have become too shallow, as a result of subsidence, to support profitable agriculture by the turn of the century. This will come about approximately 75 years after drainage to an original depth of about 3 metres. The overriding problem of subsidence is discussed in detail in Chapter 7. In the assessment of reclamation potential the rate of subsidence features strongly as a negative factor.

c. What is the danger of infiltration by saline water in surface and groundwater?

The possibility of infiltration of saline water is an important factor in assessment of coastal freshwater peatswamps. Here, where the main drainage outlets are tidal, artificial drainage and accompanying subsidence are a hazard.

d. What are the prospects of continuing agricultural production on the non-peaty subsoils once the peat cover has disappeared?

To answer this question the nature of the underlying material must be known and taken into account and it should also be assessed to what extent agricultural production can continue. Conditions may have changed so much by then that gravity drainage, for example, might no longer be possible and will have to be replaced by a polder system.

e. What is the incidence, magnitude and nature of flooding in the area to be reclaimed?

The risks of flooding are best assessed when the nearby rivers are in spate. This could result from high rainfall upstream, from local rainfall or from a combination of the two. Sustained drainage of swamps is not possible without the installation of dykes where the flood levels of main drainage outlets are frequently high. The economic evaluation of measures to be taken depends greatly on the frequency and size of the floods. The author has noted in several schemes a disproportion between the effort spent on draining peatland and the attention given to flood control. This is in many cases so because a swampy area can be partly drained by private enterprise but flood control measures are beyond the scope of individual farmers.

6.4 Conclusions and Recommendations

There are many limitations to the agricultural use of peat soils. Added to these are the problems caused by reclamation of which the subsidence initiated by drainage, a prerequisite for most agricultural enterprises, is perhaps the most serious.

Each peatswamp should be carefully surveyed to collect basic data for a land use evaluation. Because of the complexity of the reclamation problems and the ever-changing characteristics of the peat after reclamation, an economic evaluation of reclamation for agriculture is difficult. Much depends on the scale of the proposed operation, its size, location and the specific nature of the swamp. Each project needs an individual approach. Some broad general guidelines can be given.

i. No peatswamp should be artificially drained before a careful assessment is made of the benefits and disadvantages based on a well planned initial investigation.

ii. Piece-meal development of large peatswamps should be avoided if possible. Spontaneous settlement followed by unorganized reclamation and drainage often results in greater future problems than solved in the short term by reclamation.

iii. The main options for potential use should be studied carefully. These could be:

- To retain the present natural conditions which might be primary forest. Forest products could be exploited on a small scale with a policy of silvicultural measures to ensure sustained production.

- Use for agricultural purposes after improvement involving drainage, and possibly flood control. There are various possibilities for agriculture including shallow drainage with an adapted cropping system and choice of crops (annual and perennial), moderate drainage to allow a wider range of crops, and rigorous deep drainage. Shallow drainage avoids the risk of rapid subsidence and enhances the life span of agricultural use, moderate drainage gives more kinds of use choices but faster subsidence. It costs more to maintain drainage and agricultural life expectancy is shorter. Deep drainage leads to rapid peat wastage and is only recommended if the underlying soil is of very high quality.

It should be carefully considered when making decisions that peat soils reclaimed at high costs will ultimately disappear leaving a changed landscape. The changes can be drastic, sometimes forming lakes.

Once the decision is made to proceed with development many potential problems can be forestalled and prevented by adopting correct management procedures in both reclamation and in the subsequent agricultural enterprises. Management aspects are discussed in the following chapters.