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Farmers’ approaches on rehabilitations of degraded soils in
the Northeast of Thailand

Ruaysoongnern, S.1

Abstract

Soil degradation in the Northeast of Thailand is extremely severe due to both low current commodity prices and general poverty of small farmers that does not allow appropriate inputs for those production systems. Fortunately, some farmer innovators have developed soil rehabilitation technologies for farmers that utilize sandy soils in their production systems. The essence of the technology is based on experiences and observations on the ability of natural habitats to recover after land clearings. The observations have led to attempts by farmers to transform agricultural field into an integrated farming system and agroforestry that reduce soil disturbances with some small organic amendments. The success of this approach is evident since plant ecosystems have emerged that has enabled other higher fertility requiring crops to be grown in an integrated manner with low external inputs. These practices are evident in a diverse array of ecosystems of the Northeast of Thailand on more than 50 farmer fields. As a result productivity and the appearance of previously degraded sandy soils have been reversed to similar levels of the former pristine soil fertility. From soil sampling of those farmer fields and their analysis indicate that most of soil fertility parameters are replenished to a similar level under forest covers. After 5-7 years of agroforestry, soil organic matter could be found as high as 5-7% in the 0-5 cm, or 1% in the 0-10 cm soil depth with crumb structure and evidences of various soil faunal activities. In most cases of integrated farming systems and agroforestry, soil organic matter has increased to at least 0.5%. Cation exchange capacity was also increased in relation to soil organic matter. With the increases in cation exchange capacity, all cations were high, and in most cases higher than fertility status in forest soils. The increases could be attributed to both natural and man-made influences.

Introduction

Soil and land degradation have to a significant degree been driven from different socio-economic pressures that operate at both the macro and micro scales (Matsuo, 2002; Panichapong, 1988). Through this process there have been losses of biodiversity, forest lands and finally agriculture production systems that have not adopted appropriate conserving practices (Figure 1) (Noble et al., 2004b). Various attempts for reversing degradation from different organizations and development agencies have been done with limited successes, due to application of single approaches for systematic issues and constraints (Noble et al., 2004a, Webb, 2003). Chemical fertilizer applications is one example where there is limited improvement in soil fertility, but with improve crop production in most cases (Ragland and Boonpuckdee, 1987). Most practices have eventually resulted in greater soil degradation in most production systems. This degradation has caused losses not only in natural resources but also affected negatively the livelihood and ability of poor farmers to achieve self sufficiency and enhance their incomes (Noble et al., 2001).

Mangement of Tropical Sandy Soil for Sustainable Agriculture

Figure 1. Degraded soils showing signs of surface wash associated with inappropriate management

The dominant strategies to reversing degrada­tion have focused addressing a single issue by importing and recycling external sources without conservation. Some of these practices have resulted in short-term on site advantages, but they may produce degradation off site due to continuous export (Noble et al., 2000). As such the effects of the technologies were only short-term for crop and soil productivity improvement.

The objectives of the current study are as follows:

  1. To survey the successful cases of soil rehabilitation using indigenous technical knowledge.
  2. To document rehabilitation changes associated with the implementation of indigenous technical knowledge on soil properties.
  3. To evaluate potential extension of indigenous technical knowledge within and external to Local Wisdom Networks

Methodology

  1. Planning meeting with Local Wisdom Networks and preliminary survey
  2. site selection and planning for sample collection for laboratory analysis using modified paired sites comparison techniques (Noble et al. 2000) but only using composite top soil samples.
  3. site history collection
  4. data compilation and analysis

Preliminary field surveys

Information on soil rehabilitation has been collected from farmer networks and Local Wisdom Networks, during both meetings and general field surveys. It was found that most of the rehabilitation has been associated with organic amendment and tree planting. An example has been drawn from the case of Mr. Kammee Mungkun of Nakhon Ratchasima (Figure 2).

Mangement of Tropical Sandy Soil for Sustainable Agriculture

Figure 2. Mr. Kammee Mungkun on his farm where he has adopted significant tree planting

He has collected most of available organic materials available from both around his farm and his home site for improvement of his paddy field. Moreover, he also gradually planted numbers of trees on paddy buns within his farm for more than 10 years. As a result productivity of his land has been greatly improved with less and less necessity of soil amendment. Besides, he has observed that trees have different growth rates and degree of soil rehabilitation. In this respect he has observed that larger leaves can cover the soil and rehabilitate the soil ecosystems faster than smaller species due to soil cover.

In the case of Mr. Chantee Pratumpa a Local Wisdom Member of Nakhon Ratchasima (Figure 3), started his garden plot on dugout materials from his farm ponds. He has found that at minimum inputs of small dose cattle manure in vegetable plots and gradual successions of trees, the soil could be improved to similar color of surface forest soil. Mr. Chiang Thaidee of Surin Province has improved his garden with coconut coir and other products of coconut. He also found that the soils could be improved in both there appearances and productivity (Figure 4).

Mangement of Tropical Sandy Soil for Sustainable Agriculture

Figure 3. Mr. Chantee Pratumpa Local Wisdom Member of Nakhon Ratchasima

For Mr. Phai Soisraklang the Local Wisdom Networks leader of Burirum, he has used various kinds of plant materials for soil improvement and found that most of natural plants growing on his land could be used as green manures for vegetable plot improvement (Figure 5). The materials include weedy species, shrubs and tree branches. The practice could be used for rehabilitation of degraded lands.

For Mr. Boontem Chaila, a Local Wisdom Network member of Khon Kaen, has developed an integrated farming systems on his former upper paddy over the past 14 years (Figure 6). The results indicated that soil fertility has been physically improved both by soil structure and color of surface soils to 20 cm, comparing to similar paired sites.

Mangement of Tropical Sandy Soil for Sustainable Agriculture

Figure 4. Garden plots of Mr. Chiang Thaidee at Surin

Mangement of Tropical Sandy Soil for Sustainable Agriculture

Figure 5. Mr. Phai Soisraklang at his experiment on his farm

For Mr. Kamdueang Pasi learning centre, has constructed the platforms for tree planting using subsoils as landfill (Figure 7). After 7 years, soil under Acacia mangium has been greatly improved as shown in the right picture below. The surface soil has changed from pale brown to a black color. When the situation was compared with tree plantation on degraded soil, the depth of soils is found to be 4 inches for the same period of 7 years.

Mangement of Tropical Sandy Soil for Sustainable Agriculture

Figure 6. Mr. Boontem Chaila plots built from landfill materials from his farm ponds 14 years ago

Mangement of Tropical Sandy Soil for Sustainable Agriculture

Figure 7. The plot of 7 years under agroforestry on degraded soil (top) and landfill (bottom), the bottom picture tends to compare landfill and under agroforestry (carried by Mr. Kamdueang’s hands)

For Mr. Suthinan Prachayaprut’s network centre, there are a number of tree and crop systems that have been assessed and implemented (Figure 8). There are improvements of soils compared to the attributes of the degraded soils after more than 20 years. Eucalyptus plantations have demonstrated improvement of soils in most of the systems. Soils are black and fertile, at least from the soil surface to 10 cm.

Mangement of Tropical Sandy Soil for Sustainable Agriculture

Figure 8. Agroforestry systems of Mr. Suthinan’s learning centre (left) and soil improvement techniques for vegetable production

Results of soil sample analysis

Soil analysis for supporting the observations that were made has been undertaken for selected sites according to suggestions of the Local Wisdom Network members. This assessment involved a paired site approach. The results are as followed:

Table 1. Changes of soil properties of Mr. Boontem Chaila network

Name

Depth (cm)

Plots

Soil properties

pH

EC (ms/ cm)

%

CEC (cmol/ kg)

(meg/100 g soil)

ECEC (cmol/ kg)

mg kg-1

water

CaCl2

O.C.

O.M.

K

Ca

Mg

Na

Al+H

ext. P

NH4-N
Boontem 0-10

Control Improvement

6.01 6.78

5.49
6.39
0.05 0.21

0.83 1.66

1.44
2.87
2.84 7.96 0.28 0.55

2.31 6.34

0.76
1.67
0.04 0.03


3.39 8.59

64 103

5.00
35.00

  20-30

Control Improvement

5.33 6.55

4.77
6.18
0.02 0.07

0.41 0.59

0.71
1.02
2.61 5.70 0.15 0.41

1.62 3.75

0.84
1.55
0.05 0.05


2.67 5.76

73 79

2.10
6.90

  50-70

Control Improvement

5.54 6.18

4.65
5.59
0.02 0.03

0.29 0.46

0.50
0.80
2.03 3.86 0.13 0.23

1.34 2.84

0.51
0.77
0.08 0.08


2.06 3.91

29
30 

1.30
3.00

Table 2. Changes of soil properties in farms of Mr. Tas Krayom network

Name

Depth (cm)

Plots

Soil properties

pH

EC (ms/cm)

%

CEC (cmol/kg)

(meg/100 g soil)

ECEC
(cmol/kg)

water

CaCl2

O.C.

O.M.

K

Ca

Mg Na

Al+H

Tas 0-15 Improvement 6.70 6.60 0.26 1.44 2.47 8.74 0.40 13.8  1.93 0.35 0.20

16.64

  0-15 Improvement 6.30 5.40 0.19 0.42 0.72 5.28 0.23 6.24  1.00 0.34 0.50

8.31

  0-15 Control 8.10 6.70 0.31 0.41 0.71 0.24 0.53 3.06 4.44 2.47 0.60

11.10

Table 3. Changes of soil properties in farms of Mr. Phong Katepiboon network

Names

Depth (cm)

Plots

Soil properties

pH

EC (ms/cm)

%

CEC (cmol/kg)

(meg/100 g soil)

ECEC

water

CaCl2

O.C.

O.M.

K

Ca

Mg Na

Al+H

(cmol/kg)

Phong 0-15 Improvement 6.01 5.93 0.15 0.20 0.34 17.16 0.69

2.83

12.65 3.24

19.42

Apichart 0-15 Improvement 7.51 7.25 0.31 0.43 0.74 18.84 1.72

1.28

20.51 1.47

24.99

Tongsa 0-15 Improvement 6.33 6.22 0.17 0.14 0.24 15.97 1.91 2.47 7.19 3.40 0.20

15.17

  0-15 Control 6.49 6.36 0.41 0.41 0.71 9.83 1.89 2.75 6.24 3.16

14.04

Table 4. Changes of soil properties in farms of Mr. Tongbai Tonlo network

Names

Depth (cm)

Plots

Soil properties

pH

EC (ms/cm)

%

CEC (cmol/kg)

(meg/100 g soil)

ECEC

water

CaCl2

O.C.

O.M.

K

Ca

Mg

Na

Al+H

(cmol/kg)

Tongbai 0-15 Control 7.30 6.60

0.47

1.15 1.99

3.55

0.94

21.78

2.42

0.39

0.40

25.93

  0-15 Improvement 7.00 6.50

0.31

0.17 0.28

1.53

0.20

1.40

0.28

0.26

0.20

2.34

Kawin 0-15 Control 7.20 6.80

0.40

0.33 0.56

2.32

0.38

2.82

0.49

0.18

0.40

4.28

  0-15 Improvement 7.40 7.20

0.39

0.05 0.09

2.01

0.14

2.30

0.27

0.23

0.20

3.14

Sawat 0-15 Control 6.80 6.30

0.49

1.57 2.70

18.13

1.30

21.37

4.08

0.59

0.40

27.74

  0-15 Improvement 5.90 5.20

0.33

0.27 0.46

17.74

0.84

20.73

3.37

1.12

0.60

26.66

Chamnong 0-15 Control 5.90 5.20

0.30

0.60 1.03

3.47

0.19

2.84

0.46

0.38

0.40

4.28

  0-15 Improvement 7.20 7.00

0.40

0.16 0.28

2.41

0.54

5.29

1.11

0.31

0.60

7.85

Utis 0-15 Control 5.60 5.30

0.50

1.09 1.88

4.16

0.25

3.45

0.49

1.35

0.60

6.14

  0-15 Improvement 5.60 5.00

0.28

0.51 0.88

3.13

0.44

1.85

0.39

0.43

0.80

3.91

Table 5. Changes of soil properties in farms of Mr. Yu Sunthornthai network

Names

Depth (cm)

Plots

Soil properties

pH

EC (ms/cm)

%

CEC (cmol/kg)

(meg/100 g soil)

ECEC

water

CaCl2

O.C.

O.M.

K

Ca

Mg

Na

Al+H

(cmol/kg)

Kaitisak 0-15 Control 6.90 6.10 0.17 0.94 1.62 8.93 0.18 0.55 9.13 0.49 0.20

10.55

  0-15 Improvement 7.10 6.50 0.21 1.28 2.21 7.53 0.22 0.36 22.70 0.87 0.40

24.52

Weerawat 0-15 Control 6.90 6.50 0.17 0.26 0.45 3.16 0.36 0.75 2.45 0.17 0.40

4.12

  0-15 Improvement 7.00 6.50 0.34 3.60 6.21 13.30 1.20 0.59 20.30 5.12 1.00

28.17

Suntanee 0-15 Control 7.70 6.90 0.37 0.26 0.45 6.43 0.26 2.20 5.50 0.46 0.20

8.62

  0-15 Improvement 7.20 6.70 0.25 2.50 4.31 8.38 0.85 0.42 17.60 3.20 0.80

22.89

Somboon 0-15 Control 7.00 6.50 0.15 0.61 1.05 3.61 0.64 0.46 2.17 0.35 0.60

4.22

  0-15 Improvement 6.60 6.40 0.18 0.26 0.45 4.59 0.52 0.38 3.41 0.69 0.20

5.19

Pradab 0-15 Control 6.50 5.50 0.10 0.18 0.31 1.81 0.24 0.46 0.20 0.04 1.00

1.94

  0-15 Improvement 6.40 6.10 0.21 1.18 2.04 5.62 0.53 0.42 6.77 0.83 0.20

8.75

Praderm 0-15 Control 6.70 6.40 0.16 0.53 0.91 4.19 0.31 0.34 2.79 0.47 0.20

4.10

  0-15 Improvement 6.80 6.60 0.25 1.56 2.69 7.38 0.67 0.34 15.90 0.97 0.60

18.54

Supan 0-15 Control 8.80 7.90 0.40 0.11 0.19 5.98 0.25 2.99 10.70 0.07 0.40

14.39

  0-15 Improvement 7.10 6.80 0.14 0.29 0.50 2.20 0.25 0.49 1.45 0.24 0.40

2.84

Sorn 0-15 Control 6.10 4.20 0.07 0.76 1.04 4.54 0.23 0.44 1.89 0.19 4.60

7.36

  0-15 Improvement 6.50 5.50 0.18 0.24 0.41 5.97 0.31 0.44 4.37 0.47 0.20

5.80

Somniam 0-15 Control 6.60 5.70 0.14 0.54 0.94 3.90 0.64 0.65 3.88 0.66 0.20

6.03

  0-15 Improvement 6.90 6.00 0.26 1.55 2.68 6.71 1.29 0.60 7.94 1.11 0.40

11.34

Table 6. Changes of soil properties in farms of Mr. Sanan Parisawong network

Name

Depth (cm)

Plots

Soil properties

pH

EC (ms/cm)

%

CEC (cmol/kg)

(meg/100 g soil)

ECEC

water

CaCl2

O.C.

O.M.

K

Ca

Mg Na

Al+H

(cmol/kg)

Sanan 0-15 Control 6.30 5.60 0.20 2.20 3.80 20.80 1.40

30.40

11.30 3.00 0.20

46.20

  0-15 Improvement 6.50 5.70 0.30 1.40 2.40 44.50 1.20

30.50

10.10 3.30 0.20

45.20

Table 7. Changes of soil properties in farms of Mr. Chiang Thaidee network

Names

Depth (cm)

Plots

Soil properties

pH

EC (ms/cm)

%

CEC (cmol/kg)

(meg/100 g soil)

ECEC

water

CaCl2

O.C.

O.M.

K

Ca

Mg

Na

Al+H

(cmol/kg)

Chaing 0-15 Control

6.30

5.50

0.12

0.17 0.29

2.50

0.65

0.84

1.51

0.17

0.60

3.78

  0-15 Improvement

6.70

5.90

0.20

0.84 1.45

4.23

0.47

0.69

11.60

0.69

0.40

13.82

  0-15 Improvement

6.90

6.10

0.26

2.27 3.91

9.20

0.98

0.59

22.80

1.95

0.60

26.90

Chaluay 0-15 Improvement

5.60

4.90

0.30

0.47 0.81

2.79

0.18

2.56

0.31

0.30

0.60

3.93

Dan 0-15 Improvement

7.20

6.80

0.43

0.20 0.35

5.64

0.45

9.22

0.83

0.79

0.40

11.69

  0-15 Control

5.70

4.70

0.27

0.28 0.49

1.80

0.41

0.80

0.16

0.30

0.60

2.26

Table 8. Changes of soil properties in farms of Mr. Chalee network

Names

Depth (cm)

Plots

Soil properties

pH

EC (ms/cm)

%

CEC (cmol/kg)

(meg/100 g soil)

ECEC

water

CaCl2

O.C.

O.M.

K

Ca

Mg

Na

Al+H

(cmol/kg)

Supee 0-15 Improvement 4.60 4.10 0.35 2.28 3.94 8.87 0.52 5.00 1.10

0.32

2.20

9.14

Pannya 0-15 Control 5.30 4.50 0.27 0.72 1.25 5.07 0.42 2.76 1.21

0.42

1.20

6.02

  0-15 Improvement 4.60 3.90 0.33 0.27 0.46 5.52 0.43 1.41 0.93

0.30

4.00

7.06

Manee 0-15 Improvement 6.40 6.10 0.19 1.31 2.26 3.53 0.33 0.51 5.54

1.01

0.40

7.78

  0-15 Control 6.70 5.80 0.11 0.67 1.15 2.98 0.73 0.48 1.73

0.74

0.60

4.27

  0-15 Improvement 5.00 3.70 0.04 1.37 2.36 13.25 0.67 6.75 1.07

0.81

4.30

13.60

Nikom 0-15 Improvement 6.40 6.10 0.19 1.31 2.26 3.53 0.33 0.51 5.54

1.01

0.40

7.78

  0-15 Control 6.70 5.80 0.11 0.67 1.15 2.98 0.73 0.48 1.73

0.74

0.60

4.27

Weerachai 0-15 Improvement 6.10 4.20 0.11 0.14 0.24 5.55 0.42 0.86 0.55

0.61

1.60

4.03

  0-15 Control 6.00 4.70 0.14 0.87 1.50 3.10 0.38 1.06 0.64

0.30

0.61

2.98

Chalee 0-15 Improvement 5.70 4.30 0.10 0.40 0.68 4.33 0.24 1.05 0.34

0.38

1.80

3.81

  0-15 Control 6.00 4.80 0.13 0.85 1.46 3.18 0.46 1.38 0.59

0.34

0.60

3.36

Boonmee 0-15 Improvement 5.50 4.30 0.12 0.48 0.84 4.19 0.24 1.07 0.36

0.31

2.00

3.98

  0-15 Control 6.30 5.00 0.14 0.32 0.55 3.65 0.46 0.63 0.19

0.57

0.60

2.45

Discussion

From the land use history of each paired plots for improvement comparisons, most of them have been gradually transformed from natural forests to monocrop production systems. Primary production systems were upland rice and upland crops. Thereafter, when lands were sufficiently cleared there was a move towards lowland rice production. The practices of such production systems were cultivation without or with little soil cover. These practices have become the norm for hard working farmers. As such soils are vulnerable to sunlight and direct raindrop impact. Moreover, when there is infiltration of rainwater into the soil, this often results in leaching losses of soluble cations from the soil due to low ability of these soils in retaining these nutrients in an exchangeable form. These leaching losses are a degradation process that is common to sandy soils in semi-arid to humid environments. Often there is the perception that if farmers leave their lands under tree/vegetation cover other than cropping, that these farmers are easy-going or even lazy farmers.

In many cases, farm pond construction has transformed land and soil ecosystems for both on site and off site. The off site effects includes filling up the land with dugout materials from farm pond preparation. In some cases the dugout materials could be problematic due to lateritic materials or can have some physical limitations that could even exacerbate the effects of soil degradation.

From the primary evaluation of rehabilitation potentials, it was found that physical appearances has been greatly improved after a period of 3-5 years under trees or integration farming systems. Dark black color developed after 5-7 years. Actual rehabilitation was observed with the growth and forming of root mats in the surface soils. Rehabilitation potential from an example of using Eupatorium odoratum for 2 years also shows good soil physical appearances.

Most of the agricultural systems that the farmer network expressed as good practices for soil rehabilitation are integrated farming systems that comprised of diversified crop and plant production systems. Despite general low inputs during the production processes, there is general rehabilitation evidence in the soil systems. The essence of the practices seems to be derived from less or undisturbed natural environment and soil habitats. Only from the second year after the implementation of these integrated management systems was it found that both soil fertility and productivity have been reversed towards rehabilitation trends. Another indigenous practice on soil productivity rehabilitation is the utilization of soil materials from termite mounds and dredged lake sediment. Even though the quality could be low, it has been compensated by being a low cost management improvement strategy. Farmers usually compared amount of nutrients in the sediment to fertilizer bags and found that it could be more beneficial to use lake sediment than chemical fertilizers for the similar cost and productivity. Conclusion of the surveys and observation suggested that rehabilitation processes were primarily from top layers and gradually extending down the profile with times. Primary signs of improvement included soil color and later soil structure. For the productivity, there were improve­ments of growths of plants that are requiring good soils.

From soil sampling and analysis, suggested that most of the farmer observations are confirmed by laboratory results. Clear increases in soil fertility and productivity were clearly demonstrated after 5-7 years after most of the practices, despite observations revealed earlier productivity rehabilitation in the 2nd year and soil rehabilitation appearances in the 3rd year. The minimal disturbance of soil ecosystems seemed to be the key factor leading to natural soil and ecosystem rehabilitation and rehabilitation processes could be observed within 2-3 years for degraded soils and 3-5 years for land-filled subsoil.

Organic matter in top (0-10 cm) soil is generally higher than the nearby paired site regardless of period from the initiation of the improvement phase. However, with longer periods of the improvement phases from 5 years onwards, increases in organic matter in the top soils were at least double that at the start, from less than 1% to 2, 3, 5 or even 6% in some cases. Clear evidence of reversing soil degradation with respect to increased soil organic matter are presented in Figure 9.

Soil pHs in improved systems were generally higher than the control paired sites (Figure 10). The improvements were found when the paired site show low pH ranges of 4-5. However, when the paired site pHs were relatively high, there were no changes or even decreases in soil pH as shown in Figure 10. Most of EC values of the soils were not considered to be within the problematic ranges for salinity, as such the increases of EC could be more beneficial to the soil fertility and soil productivity (Figure 11). There were mostly increases in EC over the control paired sites as shown in Figure 11. Cation exchange capacities of the soils were slightly improved in most cases. The biggest increase was found with long term improvement as shown in Figure 12. The small changes could be associated with transformation of organic materials from plant debris and litter that were not directly associated with the increases of organic matter in the soils. Effective CEC is the indicator of nutrient accumulation in the soil profile. It was found that the accumulation was increasingly higher with times as shown in Figure 13.

Mangement of Tropical Sandy Soil for Sustainable Agriculture

Figure 9. Summary of organic matter improvement varying periods under integrated farming systems and agroforestry

Mangement of Tropical Sandy Soil for Sustainable Agriculture

Figure 10. Summary of soil pH (0.01 M CaCl2) improve­ment after periods of integration farming systems and agroforestry

When the data is compared to the baseline northeast forest soil data, it is suggested that the rehabilitation potential of the farmer practices are very close to forest improvement potentials, especially when the soil and land were managed in similar ways to natural forest systems. The potential rehabilitations are even faster with degraded soils than the landfill systems. The most likely rehabilitation processes could be the tree effects on the natural soil and forest ecosystems.

Mangement of Tropical Sandy Soil for Sustainable Agriculture

Figure 11. Summary of EC (ms/cm) improvement after periods of integration farming systems and agroforestry

Mangement of Tropical Sandy Soil for Sustainable Agriculture

Figure 12. Summary of CEC (cmoles/kg) improvement after periods of integration farming systems and agro-forestry

Mangement of Tropical Sandy Soil for Sustainable Agriculture

Figure 13. Summary of ECEC (cmoles/kg) improvement after periods of integration farming systems and agro-forestry

Summary

The results of the study indicated that changes in productivities were clearly observed by land owners long before the observed changes in soil properties. The observed changes in soil productivity by land owners were even over the effects of conventional chemical fertilizer application. In most cases, farmers have confirmed through memory that the productivity has improved. The changes of soil properties were clearly visibly observed on the soil surface and from topsoil to depths. Organic matter was found increased with associated EC and CEC, and finally ECEC which are indicators of nutrient accumulations.

Therefore it could be concluded that indigenous improvement systems could be used to rehabilitate degraded soils. Successes have derived from less disturbed ecosystems with minimal inputs. Results of this study could be used for both actual practices for reversing soil degradation and policy making for low input management of sandy soils. The essences of the practices are less disturbed and reduced application of toxic materials to the soil and environment. This would allow natural soil processes to revive the soil systems and resulting in holistic soil improvement as shown in this study.

References

Matsuo, K. 2002. Development of upland cropping systems for Crop-Animal integrated farming systems in Northeast Thailand. September 2002. Japan International Research Center for Agricultural Sciences (JIRCAS), Department of Agriculture (DOA) and Khon Kaen University (KKU), Thailand.

Noble, A.D., Gillman, G.P., and Ruaysoongnern, S. 2000. A cation exchange index for assessing degradation of acid soil by further acidification under permanent agriculture in the tropics. European Journal of Soil Science 51, 233-243.

Noble, A.D., Gillman, G.P., Nath, S., and Srivastava, R.J. 2001. Changes in the surface charge characteristics of degraded soils in the tropics through the addition of beneficiated bentonite. Australian Journal of Soil Research 39: 991-1001.

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1 Faculty of Agriculture, Khon Kaen University, Thailand

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