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in the laboratory for two Trinidadian soils (sandy loam and clay) mixed with three organic materials [peaty farm yard manure (FYM), and filter press mud (FPM)] ...
MAXIMUM BULK DENSITY ACHIEVED DURING SOIL COMPACTION AS AFFECTED BY THE INCORPORATION OF THREE ORGANIC MATERIALS R. J. Stone, E. I. Ekwue MEMBER

MEMBER

ASAE

ASAE

Maximum dry bulk density (MDBD) and the corresponding critical moisture content (CMC) were measured in the laboratory for two Trinidadian soils (sandy loam and clay) mixed with three organic materials [peaty farm yard manure (FYM), and filter press mud (FPM)] each at four levels (0, 4, 8, 72% by mass) and compacted using 5, 75, and 25 standard Proctor hammer blows. The compaction tests on the soils were carried out at different moisture contents determined according to the consistency limits of the soils. While the mean MDBD declined significantly (P < 0.001) from 1.51 to 1.26 Mg m~^y the mean CMC increased from 23.2 to 32.9% as added organic materials increased from 0 to 12%. While the former increased, the CMC decreased with increasing compaction efforts. The effectiveness of the organic materials in terms of reducing MDBD and increasing CMC was in decreasing order: peaty FYMy and FPM. Clay soil achieved lower values of MDBD at higher corresponding CMC than the sandy loam. The significant interaction effects observed between some of the experimental factors were used to describe the effect of incorporation of organic materials on soil compaction. Prediction equations for MDBD and CMC were derived for each of the organic materials and all of them combined. Keywords. Bulk densityy Critical moisturCy Organic material. ABSTRACT.

S

oil compaction is undesirable in agricultural practice since it reduces soil aeration, water availability to plants, and imparts high mechanical impedance to root growth (Thompson et al., 1987). There is, therefore, the need to perform soil compaction tests in order to determine the CMC so that cultivation by farm machines can take place at less than this moisture content. The severity of soil compaction depends on the magnitude and nature of the compacting forces, the soil moisture content, the initial soil compaction, and the soil characteristics like texture and organic matter content (Free etal., 1947). Organic matter reduces soil compaction (De Kimpe et al., 1982; Datta and Hundal, 1984). It does this by increasing the stability of the soil. In addition, the greater amounts of molecules of moisture retained around particles of soils with high organic matter content helps such soils to withstand compaction (Paul, 1974). Organic materials normally incorporated to improve the soil physical properties and reduce soil compaction include peat (Ekwue, 1990; Ohu et al., 1985), FYM (Felton and Ali, 1992), FPM (Paul, 1974), straw (Miller and Aarstad, 1971), and green manure (MacRae and Mehuys, 1985). However, since organic materials have different densities and some are more effective than others in increasing the stability of soils (Ekwue, 1992), it is not clear how effective

each of them will be in reducing soil compaction. Specifically, peat has been found to reduce soil aggregate stability (Greenland et al, 1975; Ekwue, 1990). Since peat also reduces soil compaction (Ohu et al., 1985), the mechanics of its action is therefore not clear. Few studies have compared the effects of different organic materials on soil compaction. This article quantifies the effects of three organic materials: peat, FYM, and FPM on MDBD achieved during soil compaction and the CMC at which the maximum density occurred.

MATERIALS AND METHODS The study involved a factorial laboratory experiment to assess the variations of MDBD and CMC for two soils incorporated with three organic materials, each at four levels and compacted using three levels of compactive effort. Each treatment combination was replicated three times. A completely radomized design was adopted. Two of the major soils in Trinidad, West Indies (table 1), collected from the top 0- to 20-cm depth of soil profile were used in the study. The soils were air-dried and ground to pass through a 2-mm sieve. Particle size distribution was carried out with the hydrometer method (Lambe, 1951). The Piarco soil is of sandy loam texture and is classified as Aquoxic Tropudults. The Talparo soil is Table 1. Organic matter and particle size distribution (%) of the soils

Article was submitted for publication in March 1993; reviewed and approved for publication by the Soil and Water Div. of ASAE in September 1993. Research support by the University of the West Indies, St. Augustine Campus. The authors are Reynold J. Stone, Lecturer in Agricultural Engineering, Faculty of Agriculture, and Edwin I. Ekwue, Lecturer in Agricultural Engineering, Faculty of Engineering, The University of the West Indies, St. Augustine, Trinidad, West Indies.

VOL. 36(6): 1713-1719-NOVEMBER-DECEMBER 1993

Soil Series

Organic Matter Content (%)

Sand (2-0.05) (mm)

Silt (0.05-0.002) (mm)

Clay (< 0.002) (mm)

Piarco

1.65 ±0.1*

64.910.1

17.010.1

18.110.3

Talparo

2.7010.1

25.410.5

28.310.2

46.310.3

* All values are means of three replicates 1 standard deviation.

© 1993 American Society of Agricultural Engineers 0001-23517 93/3606-1713

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of clay texture and is classified as Aquentic Chromuderts. The classification is according to the Soil Taxonomy system (Soil Survey Staff, 1975). Organic matter content of the soils was assessed using the method of Walkey-Black (1934). The organic matter content of the control soils was increased by adding three organic materials (peat, FYM, and FPM) at the rates of 4, 8, and 12%, dry mass basis. Peat moss with fibrosity of 83% and dry density of 0.08 Mg m~^ was used. Fibrosity is expressed as the dry fibre content by weight of the organic material more than 0.1 mm in diameter (Farnham and Finney, 1965). The FYM was collected at the University of the West Indies, Trinidad field station farm, and had a dry density of 0.29 Mg m-3 and a fibrosity of 8 1 % . The FPM is a by-product of sugar cane factories and normally incorporated into soils near the factories. The FPM contains calcium, phosphorous, soil, trash, waxes, bagasse, and other extraneous materials (Paul, 1974). The FPM collected from the Sugar Cane Feeds Center, Trinidad, with a dry density of 0.33 Mg m~^ and fibrosity of 51% was used in this study. Bulk density of the organic materials was determined by measuring their dry weights when loosely packed into cores of known volumes. The MDBD and the corresponding CMC were determined using the standard Proctor method (Lambe, 1951). Compaction for each sample was carried out at different moisture contents (ranging from 5 to 50%) using 5, 15, and 25 blows from a standard Proctor compaction hammer in cylindrical molds with 102-mm diameter and 116-mm height. The moisture contents for compaction were chosen according to the soil consistency limits, which were determined by the method of Lambe (1951). Dry bulk densities were plotted against the corresponding moisture contents to obtain MDBD and CMC. Soil aggregate stability was assessed using the water drop test method (Farres and Cousen, 1985). The total energy of water drops (4-mm diameter) required to fall 1-m distance to destroy 4- to 5-mm diameter soil aggregates placed on a 3-mm sieve were used as an index of aggregate stability. Fifteen replicates were used for this test. RESULTS AND DISCUSSION FACTORS AFFECTING VALUES OF MDBD CMC

AND

OF SOILS

Figure 1 shows the dry bulk density-moisture content plots for the sandy loam soil. For all the plots, dry bulk density increased up to a limit, called the MDBD after which it decreased with further increases in moisture content. This is typical soil compaction behavior. The moisture content at which this maximum density occurs is called 'optimum' in engineering work. This is, however, called 'critical' in this article following the recommendation of Saini et al. (1984) and Ohu et al. (1989). This is because in agricultural practice, soil compaction is an undesirable phenomenon and the moisture content at which its maximum occurs should be called critical not optimum. All the samples tested exhibited a similar behavior to the plots shown in figure 1 except that the values of MDBD and CMC were different. The values of these parameters for the two soils are summarized in table 2. The mean values for the main effects of added organic content, type of organic material, soil type, and compaction levels 1714

O Control Soil 1-8

D Plat (4%) X Peat (8%) A Peat (12%)

1-6 H

'e

c

1-4

1-2 H

O

CD

10

O

0-8 H 10

20

Moisture

30

Content

40

50

(%)

Figure 1-Density-moisture content relationship for the sandy loam soil at 25 blows compactive effort.

on MDBD and CMC are shown in table 3. It will be observed in tables 2 and 3 that while the values of MDBD decreased, those for the CMC increased with increasing added organic matter levels. The decreasing order of the organic materials in terms of reducing values of MDBD and increasing those of CMC was: peat, FYM, and FPM. The clay soil had lower values of MDBD and greater CMC than the sandy loam soil. The values of MDBD increased while those of CMC decreased with increasing compacting efforts. The analysis of variance showed that the main effects of the study variables and their first, second, and third order interactions were all highly significant (P < 0.001). The analysis showed that the main effect of type of organic material was the highest, followed by those of added organic matter levels and compaction levels. For both MDBD and CMC, the first order interaction between type of organic material and levels of added organic matter was highest followed by those between soil type and type of organic material and between soil type and levels of added organic matter. However, the interaction effects between the other three first order interactions as well as those of the three second and third order interactions were small compared to the main effects and the three mentioned first order interaction effects. Only the latter were examined in the subsequent sections. ADDED ORGANIC MATTER LEVELS AND TYPE OF ORGANIC MATERIALS

Mean values of MDBD decreased while those of CMC increased with increasing added organic matter levels (table 3). This was true irrespective of the type of organic material, soil type, and compactive effort. TTie decline in values of MDBD with organic matter is attributed to the lower density of the organic material and the greater TRANSACTIONS OF THE ASAE

Table 2. Maximum dry bulk density (Mg m-^) and the corresponding critical moisture contents (%) of the soils applied different organic materials and compacted at different levels Compact]ion Level (Blows)

Soil

4% Organic Content Control Soil

Peat

FYM*

FPM*

8% Organic Conteent Peat

FYM

12% Organic Content

FPM

Peat

FYM

FPM

Piarco Sandy Loam 5

MDBDt CMCt

1.60 19.9

1.22 29.3

1.55 22.3

1.57 20.1

1.05 35.3

1.52 23.0

1.49 20.8

0.94 43.3

1.45 26.3

1.46 25.0

15

MDBD CMC

1.71 15.0

1.37 20.8

1.65 16.3

1.65 16.1

1.14 35.0

1.60 18.3

1.60 19.5

1.03 41.0

1.52 22.7

1.55 20.2

25

MDBD CMC

1.75 13.8

1.45 20.5

1.73 15.2

1.73 15.0

1.17 30.0

1.65 18.0

1.62 16.2

1.07 36.3

1.55 22.3

1.57 20.0

5

MDBD CMC

1.25 34.4

1.00 37.5

1.24 34.8

1.21 34.5

0.84 41.0

1.19 38.6

1.19 35.5

0.80 45.0

1.16 40.0

1.18 36.8

15

MDBD CMC

1.35 29.5

1.15 35.0

1.34 32.5

1.36 29.0

1.00 39.5

1.32 32.0

1.32 30.5

0.97 44.5

1.29 33.5

1.31 31.2

25

MDBD CMC

1.42 26.8

1.24 32.0

1.40 28.0

1.41 27.6

1.08 39.3

1.38 30.0

1.39 28.2

1.02 41.3

1.36 31.5

1.35 30.8

Talparo Clay

* FYM and FPM are farm yard manure and filter press mud, respectively. t MDBD and CMC refer to the maximum dry bulk density and tfie corresponding critical moisture content, respectively. Values are means of three replications. The range of standard deviation for MDBD values is from 0.02 to 0.05 while that for CMC is from 0.4 to 3.0%.

moisture content obtained when organic matter was added. This helps such soils to reduce compaction (De Kimpe et al., 1982; Ohu et al., 1985). Since peat had the lowest dry bulk density (0.08 Mg m"^), it produced the lowest values of MDBD in the soil. The dry density of FYM (0.29 Mg m-^) was only slightly lower than that of the FPM (0.33 Mg m-^) and so the mean values of MDBD imparted by the two organic materials were not significantly different at the 5% level (table 3). In addition to soil dilution, organic materials also reduce soil bulk density by increasing the aggregate stability of the soil (MacRae and Mehuys, 1985). Table 4 shows that while the FYM and Table 3. Mean maximum dry density'*' and critical moisture contents of the soils (n =» 216) Factor Level

Mean Maximum Dry Blk Density (Mg m-^)

Mean Critical Moisture Content

Added Organic Contents ts(%) (%) 0 4 8 12

1.51 dt 1.40 c 1.31b 1.26 a

23.2 d 25.9 c 29.5 b 32.9 a

1.20 a 1.45 b 1.46 b

32.8 a 26.0 b 24.9 c

1.51b 1.24 a

22.1b 33.7 a

Sal Type of Organic Material lai

Peat Farm yard manure Filter press mud Soil Type Piarco Sandy Loam Talparo Clay Compaction Blows 5 15 25

1.28 a 1.39 b 1.45 c

31.3 a 27.1b 25.2 c

Mean values for each factor were obtained by averaging the experimental values over the levels of the other three factors. For instance, the mean value of 1.51 for no added organic level is the value of MDBD for this organic content averaged over the levels of the three organic materials, two soil types, and three compaction levels. Values followed by dissimilar letters are significantly different at 0.1 % level. Mean separation was by least significant difference.

VOL. 36(6): 1713-1719-NOVEMBER-DECEMBER 1993

FPM increased soil aggregate stability, peat reduced it. The reduction of soil aggregate stability by peat has been observed in previous research by Greenland et al. (1975) and Ekwue (1990) and is attributed to the low degradability and chemical inertness of the peat material. Therefore, this shows that the mechanics of the reduction of dry bulk density by peat is by diluting the soil matrix with its own less dense material. In addition, on wetting and compacting, soils with peat suffered low levels of soil slaking and breakdown of soil aggregates, giving rise to the lower values of MDBD. Ekwue (1990) observed that although peat reduces soil aggregate stability, it nevertheless reduces slaking, breakdown of soil aggregates, and splash detachment by replacing soil aggregates with its own bulk which is less susceptible to water disruption. As was also obtained by Ekwue (1992), FYM increased soil aggregate stability (table 4) and this in addition to diluting the soil, led to lower values of MDBD than the control soil. The FPM imparted greater stability to both soils than FYM (table 4) but still had slightly higher mean MDBD than the FYM. These results suggest that the reduction of MDBD of the soil during compaction by incorporating organic materials is related more to the density of the organic material than to the aggregate stability imparted to the soil by the material. Future work should examine this finding. The values of CMC for compacting the soils to maximum density increased with increasing added organic matter levels because the organic materials increased the consistency limits of the soils (table 5). The increases in Table 4. Values of aggregate stability* index (mj) of the soils Added Organic Matter Levels by Mass (%) 4 0 8 12

Soil Type

Organic Material

Piarco Sandy Loam

Peat Farm yardmanure Filter press mud

20.9t± 3.4 20.9 ± 3.4 20.9 ± 3.4

15.6 ± 1.7 26.2 ± 4.5 31.7 ± 3.5

14.6 ± 1.2 30.4 ± 4.8 33.5 ± 4.9

Talparo Clay

Peat Farm yard manure Filter press mud

71.7 ± 8.0 71.7 ± 8.0 71.7 ± 8.0

67.8 ± 9.1 73.6 ± 6.4 78.8 ± 8.2

64.6 ± 5.5 34.5 ± 2.9 95.6 ± 7.7 136.1 ± 8.4 97.0 ± 9.1 142.4 ± 9.9

10.1 ± 1.5 31.7 ± 5.2 34.8 ± 3.8

* Aggregate stability index was measured as the total energy of water drops required to destroy individual soil aggregates. t Values are means of 15 replicates ± standard deviation.

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Table 5. Plastic and liquid limits (%) of soils applied three organic materials at various rates Soil Type

Organic Material

Piarco Sandy

Peat

Talparo Clay

Added Organic Matter Levels by Mass (%) 0

4

8

12

PL* LLt

20.2 22.8

23.6 24.0

29.0 30.4

38.6 39.0

Farm yard manure

PL LL

20.2 22.8

20.7 23.3

21.0 24.8

24.3 27.7

Filter press mud

PL LL

20.2 22.8

20.3 22.9

22.1 28.3

22.8 29.3

Peat

PL LL

33.9 57.9

40.6 67.5

45.1 72.3

50.5 76.2

Farm yard manure

PL LL

33.9 57.9

34.0 60.0

35.4 61.8

38.7 63.5

Filter press mud

PL LL

33.9 57.9

34.0 58.0

34.3 60.0

34.4 61.2

* PL refers to plastic limits. t LL refers to liquid limits.

consistency limits of soils with organic matter is because the latter makes the first demand for water added to the soil. The control soils and those with lower levels of added organic matter then started behaving like a liquid at lower moisture contents when soils with larger levels of added organic matter were still compactible. This increased the values of CMC for the latter soils. Table 5 shows that peat increased the consistency limits of the two study soils at all levels of organic matter incorporation than FYM and FPM. Soils with peat therefore had significantly higher values of CMC than those for FYM and FPM (tables 2 and 3). Unlike the mean values of MDBD for FYM and FPM, which were very close, the mean value of CMC for FYM was significantly higher than that of the FPM (table 3). (a)

This is because while the two organic materials had very close dry densities, the fibrosity of FYM was 81% while that of tihe FPM was only 51%. This suggests that while MDBD of soils during compaction may be determined by the dry density of the incorporated organic materials, the moisture content at which this maximum occurs is additionally affected by the fibrosity (coarseness) of the organic materials. Hafez (1974) stated that the coarseness of the FYM helps it to impart high moisture content to soils. The interaction between soil type and added organic matter levels (figs. 2a and 3a) shows that as the latter increased, the MDBD declined while CMC increased more rapidly in the sandy loam than in the clay soil. This interaction shows that the incorporation of organic materials to reduce soil compaction is expected to be higher in soils with high rather than low values of sand contents. Also, the magnitude of MDBD and CMC differences among the three organic materials increased with increasing added organic matter levels as shown by the interaction between type of organic material and added organic matter levels (figs. 2b and 3b). The mean values of MDBD for FYM and FPM were very close so were plotted together in figure 2b. Ekwue et al. (1993) made a similar observation that the differences in splash detachment produced by different organic materials increases with increasing organic matter levels. Also, results here showed that the differences in MDBD and CMC values among the three organic materials were higher in the sandy loam than in the clay soil (figs. 2c and 3c). The greater advantage of peat over FYM and FPM in decreasing soil MDBD and increasing CMC during soil compaction is then soil dependent. These results show that at low rates of incorporation to reduce soil compaction, there may be little to choose among the various organic materials. The selective (b)

X Sandy Loam

(C) A Control Soil

A FYM, FPM

• Clay

B

O Peat

LSD(l%) = 0 02

17

FYM, FPM

C Peat

LSD(l%) = OOI

LSD(I%) = 0 0 2 1-5

1-3 H

0-91 4

8

12

Added Organic Matter (%)

0

4

8

12

Added Organic Matter (%)

A B C

Sondy Loam

A B C

Clay

Figure 2-The effect of the interactions between (a) soil type and level of added organic matter, (b) type of organic material and level of added organic matter, and (c) type of organic material and soil type on maximum dry bulk density.

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TRANSACTIONS OF THE AS A E

• Clay

O P»at

50-1

X Sandy Loom

50

A FYM DFPM

C FYM

y ^

40-

40H

X

30-

t 20-

^

^

=

-

8

12

Added Organic Matter (%)

FPM

D Peat

LSD(l7o) = 0 - 4 6

30i

^

=

^

20 H

LSD (17.) = 0 6 4

101

10-

4

A Control Soil B

3

4

8

12

Added Organic Matter (%)

(a)

A B C D

A 8 C D

Sandy Loam

Clay

(c)

(b)

Figure 3-The effect of the interactions between (a) soil type and level of added organic matter, (b) type of organic material and level of added organic matter, and (c) type of organic material and soil type on critical moisture content.

incorporation of organic materials may only be necessary if large applications are involved. Moreover, the relative effects of incorporated organic materials on soil compaction may depend on soil texture. SOIL TYPE

The MDBD of the sandy loam soil was significantly higher (P < 0.001) and CMC was lower than the clay soil. This result is expected and is a result of the higher degree of aggregation in clay (Ayers and Perumpral, 1982; Ohu et al., 1989). The clay soil in this research had greater aggregate stability than the sandy loam soil for all organic materials and levels of organic contents (table 4). The differences in MDBD and CMC between the two soils decreased with increasing added organic matter contents (figs. 2a and 3a). This was indicated by the interaction between added organic matter levels and soil type. Though soil texture may affect soil compaction greatly (Ohu et al., 1989), the effect of texture diminishes with increasing organic matter content.

where MDBD is the maximum bulk density (Mg m-^) and CMC is the corresponding critical moisture content (%). The highly significant relationship (P < 0.001) obtained between the parameters is similar to those obtained by De Kimpe et al. (1982) and Rowlands et al. (1984). The values of the regression constant (2.189) and the regression coefficient (-0.033) obtained by the former authors for 21 Canadian soils are in close agreement to the ones obtained in this study. Also close are the constant and regression coefficient values of 2.244 and - 0 . 0 3 3 , respectively, obtained by Rowlands et al. (1984) for some soils from central Iran. The values of MDBD and the CMC for all the tested samples were used to generate linear multiple regression equations that can be used to predict these study parameters for each organic material and all of them combined for given soil textures, compaction levels, and added organic matter levels. The 5, 15, and 25 Proctor compaction blows used in this study were converted to 175, 404, and 618 kPa static pressures using the equation derived by Raghavan and Ohu (1985). The equations were of this general form:

COMPACTION LEVELS

The increases of values of MDBD with increasing compaction levels is expected. The mean values of CMC decreased significantly with increasing compaction effort and this has been found in previous research by Free et al. (1947) and Ohu etal. (1989). MDBD AND CMC A regression equation was developed to relate values of MDBD to the corresponding values of CMC. This relationship was of the form:

REGRESSION EQUATIONS INVOLVING

MDBD = 2.061 - 0.025 CMC , r = - 0.955, N = 72

VOL. 36(6): 1713-1719-NOVEMBER-DECEMBER 1993

(1)

MDBD = a + b. St - c. M + d. Pc + e. Dm

(2)

CMC = a + b. Ct + c. M - d. Pc - e. Dm

(3)

and

where MDBD and CMC = (defined in equation 1 above) St = sand content (%) Ct = clay content (%) M = added organic matter level (%) Pc = compactive effort (kPa) 1717

Table 6. Values of coefficients in multiple regression equations 2 and 3 in text relating maximum bulk density and critical moisture content to sand content, St (%); clay content, Ct (%); added organic level, M (%); compactive effort, Pc (kPa) and dry density of organic material. Dm (Mg m~^) Organic Materials

R^^

Maximum Bulk Density (MgAn~^ Peat Farm yard manure Filter press mud FYMandFPM All organic materials

1.069t 1.034 1.033 1.034 0.781

0.0050 0.0076 0.0075 0.0075 0.0067

0.045 0.011 0.011 0.010 0.022

0.00043 0.00036 0.00037 0.00036 0.00038

0.349 0.468 0.453 0.423

1.743 0.506 0.343 0.864

0.016 0.015 0.014 0.015

1.133

0.912 0.976 0.972 0.965 0.843

. 29.544

0.876 0.973 0.974 0.832

Critical Moisture Content (%) Peat Farm yard manure Filter press mud All organic materials

17.078 13.985 13.689 21.811

* Values of coefficient of determination, R , were all significant at 0.1%. t Values of all regression coefficients were significantly different from zero at 0.1%.

Dm = dry density of organic material (Mg m~^) a, b, c, d, e = empirically determined coefficients The values of regression coefficients for equations 2 and 3 are given in table 6 for various organic materials and all of them combined. Considering the tedious and timeconsuming nature of standard compaction tests, the equations above could be used for quick estimation of the values of MDBD and the corresponding CMC at which the maximum density occurs at any compaction effort applied to the soil, knowing the sand, clay, type of organic material, and the percentage-added organic levels. There may, however, be the need to derive values of the regression coefficients for individual soils. The values of the organic matter regression coefficient was highest for peat followed by FYM and FPM. The value of this coefficient for FYM and FPM was almost the same for the MDBD parameter, suggesting that a single equation given in table 6 could be used to estimate this parameter for these two organic materials. However, the value of this coefficient for FYM (0.506) was significantly (P < 0.001) higher than that of the FPM (0.343) for the CMC. This agrees with the findings in the analysis of variance. For all organic materials, the use of dry density to characterize each organic material produced very good relationships for predicting MDBD and CMC for all test samples (table 6). Equations 2 and 3 are improvements to the ones presented by Ohu et al. (1989) and Ahmed (1990). The former authors utilized only sand and clay contents to predict MDBD and CMC. Ahmed (1990) working with six Nigerian soils, incorporated groundnut haulms organic material and obtained the following equation: MDBD = 1.20 + 0.0058 St - 0.076 M + 0.00058 Pc (4) where the parameters are as defined above. The major difference between equation 4 and those obtained in this study is that the absolute value of the regression coefficient for organic matter (0.076) obtained by Ahmed (1990) is higher than those (0.010 - 0.045) obtained in the present research. This suggests that the use of groundnut haulms may even be better than peat in reducing soil compaction. Ekwue et al. (1993) found that in addition to diluting the soil matrix, unlike peat, groundnut haulms increase the aggregate stability of the soil.

1718

CONCLUSIONS Farm machines are at times used in soil moisture conditions that are very wet and encourage soil compaction. This research has demonstrated the initial effects of incorporating three organic materials into the soil before cultivation to reduce soil compaction problem. Since peat decomposes very slowly (Johnston and Brookes, 1979), the effect of peat described in this article is likely to remain long after the normal application has ceased. As the FYM and FPM decompose in the soil, the stabilizing substances produced are expected to further help the soils to withstand soil compaction. Specifically, the following conclusions can be made from the results of this study: • Peat produced the lower values of MDBD and higher values of CMC than FYM and FPM. The relative effects of these organic materials on MDBD and CMC depend on the level of incorporation and soil type. • The values of the coefficients of the multiple regression equations relating MDBD and CMC are affected by the type of organic material. • While the dry density of the organic material affects the MDBD achievable on compaction, the moisture content at which this highest density occurs (CMC) is additionally affected by the fibrosity (coarseness) of the organic material. • Values of MDBD decrease while those for the CMC increase with increasing added organic matter levels. The effect of organic matter on these parameters was higher in sandy loam than in clay soil. • Values of MDBD increase while those of CMC decrease with increasing compaction effort. Clay soil has lower values of MDBD and higher values of CMC than the sandy loam soil. The differences between values of these parameters for clay and sandy loam diminish with increasing organic matter levels. The authors are very grateful to the University of the West Indies, St. Augustine, Trinidad, for sponsoring the research and to Mr. C. Christian of the Civil Engineering Department for assisting with the laboratory work. ACKNOWLEDGMENTS.

REFERENCES Ahmed, U. 1.1990. The influence of groundnut haulms on the compactibility and hydraulic properties of some agricultural soils in Homo State, Nigeria. M.S. thesis, Univ. of Maiduguri, Nigeria. Ayers, P. D and J. V. Perumpral. 1982. Moisture and density effect on cone index. Transactions of the ASAE 25(5): 1169-1172. Datta, S. K. and S. S. Hundal. 1984. Effects of organic matter management on land preparation and stmctural regeneration in rice-based cropping systems. In Organic Matter and Rice, 399416. Manila, Phillipines: International Rice Research Institute. De Kimpe, C. R., M. Bemier-Cardou and P. Jolicoeur, 1982. Compaction and settling of Quebec soils in relation to their soil-water properties. Canadian J. of Soil Science 62(1): 165175. Ekwue, E . I. 1990. Effect of organic matter on splash detachment and the processes involved. Earth Surface Processes 15(2): 175-181.

TRANSACTIONS OF THE ASAE

. 1992. Effect of organic and fertilizer treatments on soil physical properties and erodibility. Soil Tillage Res. 22(34): 199-209. Ekwue, E. I., J. O. Ohu and I. H Wakawa. 1993. Effects of incorporating two organic materials at varying levels on splash detachment. Earth Surface Processes 18 (5):399-406. Famham, R. S. and H. R. Finney. 1965. Classification and properties of organic soils. Advances in Agronomy 17(1): 115162. Farres, P. J. and S. M. Cousen. 1985. An improved method of aggregate stability measurement. Earth Surface Processes 10(4):321-329. Felton, G. K. and M. Ali. 1992. Hydraulic parameter response to incorporated organic matter in the B-horizon. Transactions of theASAE35{4):n53-n60. Free, G. R., J. Lamb and E. A. Carleton. 1947. Compactibility of certain soils as related to organic matter and erosion. J. of American Society ofAgronomy 39(12): 1068-1076. Greenland, D. J., D. Rimmer and D. Payne. 1975. Determination of the structural stability class of English and Welsh soils. J. of Soil Science 26(3): 294-303. Hafez, A. A. A. 1974. Comparative changes in soil physical properties induced by admixtures of manures from various domestic animals. Soil Science 118(l):53-59. Johnston, A. E. and P. C. Brookes. 1979. Yields of and P, K and Ca, Mg uptakes by, crops grown in an experiment testing the effect of adding peat to a sandy loam soil at Wobum. Rothamsted Experimental Station Report 1978, Part 2, 83-98. Lambe, T. W. 1951. Soil Testing for Engineers, 165. New York: John Wiley. MacRae, R. J. and G. R. Mehuys. 1985. The effect of green manuring on the physical properties of temperate-area soils. In Advances in Soil Science, ed. B. A. Stewart, 71-94. New-York: Springer.

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Miller, D. E. and J. S. Aarstad. 1971. Furrow infiltration rates as affected by incorporation of straw. Soil Science Society of America Proceeding 35(3): 492-495. Ohu, J. O., O. A. Folorunso, F. A. Adeniji and G. S. V. Raghavan. 1989. Critical moisture content as an index of compactibility of agricultural soils in Bomo State of Nigeria. Soil Technology 2(2):211-219. Ohu, J. O., G. S. V. Raghavan and E. Mckyes. 1985. Peatmoss effect on the physical and hydraulic characteristics of compacted soils. Transactions oftheASAE 28(5):420-424. Paul, C. L. 1974. Effects offilter-pressmud on the soil physical conditions in a sandy soil. Tropical Agriculture (Trinidad) 51(2):288-292. Raghavan, G. S. V. and J. O. Ohu. 1985. Prediction of static equivalent pressure of Proctor compaction blows. Transactions of the ASAE 28(5): 1398-1400. Rowlands, G. O., R. Delpak and E. Ghaem-Maghami. 1984. The engineering properties of the saline soils of the Great Kavir in Central Iran. In Proc. 8th. Annual Soil Mechanics and Foundation Engineering for Africa Conference, eds. J. R. Boyce, W. R. Mackechnie and K. Schwartz, 337-341. Harare: Balkema. Saini, G. R., T. L. Chow and I. Ghanem. 1984. Compactibility indexes of some agricultural soils of New Brunswick, Canada. Soil Science 137(l):33-38. Soil Survey Staff. 1975. Soil taxonomy: A basic system for making and interpreting soil surveys. USDA-SCS Agric. Handbook 436. Washington, DC: GPO. Thompson, P. J., I. J. Jansen and C. L. Hooks. 1987. Penetrometer resistance and bulk density as parameters for predicting root system performance in mine soils. Soil Science Society of America Journal 51 (5): 1288-1293. Walkley, A. and I. A. Black. 1934. An examination of the effect of the degtjareff method for determining soil organic matter and a proposed modification of the chromic acid titration method. Soil Science 37(l):29-38.

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