Soil & Tillage Research, 13 (1989) 399-405 399 Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands

The Effect of M a c h i n e r y Traf f ic on the Phys i ca l P r o p e r t i e s of a Sandy Loam Soil and on the Yie ld of S o r g h u m in N o r t h - e a s t e r n N i g e r i a

JOHN O. OHU' and O.A. FOLORUNSO 2

~Department of Agricultural Engineering and 2Department of Soil Science, University of Maiduguri, Maiduguri (Nigeria)

{Accepted for publication 5 September 1988)

ABSTRACT

Ohu, J.O. and Folorunso, O.A., 1989. The effect of machinery traffic on the physical properties of a sandy loam soil and on the yield of sorghum in north-eastern Nigeria. Soil Tillage Res., 13: 399-405.

To assess the damage done to sorghum production by soil compaction from vehicular traffic, a randomized complete block design of field plots was selected to comprise treatments of 0, 5, 10, 15 and 20 passes of a tractor with 31 kPa contact pressure in a sandy loam soil. Agronomical treat- ments were kept the same for all the plots. The soil dry bulk density and penetrometer resistance for each applied load were measured and the yield from each treatment was determined.

Results indicated higher dry bulk density and penetration resistance with increase in the num- ber of tractor passes. Both the head weight and total plant yield of sorghum increased with in- creases in the number of tractor passes up to a point, and then decreased with further increases in the number of passes. Statistical models are used to predict grain yield, plant yield, dry density and penetration resistance in terms of the number of tractor passes and contact pressure.

INTRODUCTION

The effect of excessive soil compaction resulting from tractor wheel passage during seed bed preparation for crop production has produced reductions in crop yield (Phillips and Kirkham, 1962; Feldman and Domier, 1970; Raghavan et al., 1978; Taylor et al., 1981 ). The amount of compaction varies with the soil moisture conditions, the type of soil and the size and type of external loading. Machinery operation and resultant compaction changes the permeability of the soil, and in the worst cases causes a high loss in porosity and may even prohibit penetration of plant roots (Raghavan et al., 1977). Raghavan and Mckyes (1983) reported a decrease in the physical and hydraulic characteris- tics of a clay soil due to heavy traffic, which had earlier been reported to cause excessive reductions in corn yield (Raghavan et al., 1979). Huck et al. (1975)

0167-1987/89/$03.50 © 1989 Elsevier Science Publishers B.V.

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reported reductions in root densities of cotton plants which adversely affected the yield owing to heavy vehicular traffic. Also, wheat yield was reported by Maurya ( 1985 ) to be significantly affected by tillage practices in an irrigated northern Nigerian soil. In spite of the numerous studies available in the liter- ature on the effect of vehicular traffic on crop production, information relating machinery traffic to sorghum production in West Africa is limited.

The objective of this study was to assess the effect of traffic intensity on the dry bulk density, penetration resistance and the yield of sorghum in a sandy loam soil.

MATERIALS AND METHODS

A 20-plot experiment consisting of 5 treatments with 4 replicates was set up at the University of Maiduguri Experimental Farm using a complete random- ized block design in a uniform field of sandy loam soil. The soils of the study area are classified as Typic Ustipsamment (Rayar, 1984), made up of 77% sand, 6% silt and 17% clay particles. The treatments consisted of a zero traffic and 5, 10, 15 and 20 passes of the tractor at 31.0 kPa (the ratio of load to contact area) vehicle contact pressure. These were imposed before seeding. The weight of the standard Massey Ferguson 165D 2-wheel drive tractor with rear tyre dimension 0.43 X 0.71 m used in the treatments was 43.35 kN and the resulting ground pressure over the measured contact area was 31.0 kPa (0.32 kg cm-2). The 20 plots, each of dimensions 10 mX 10 m were worked upon with only 5 m X 5 m area of each plot planted with sorghum. The preparation of the field consisted of dry-season plowing in July 1986 which resulted in an average bulk density of 1.40 Mg m -3 in the top 0.20 m of the soil. The plots were covered completely with tyre paths of the assigned contact pressure and number of passes at an average field moisture content of 8% which is less than the deter- mined optimum moisture content (12.5%) for compacting the soil. The treat- ments were performed on 26 July 1986 followed by seeding which was done manually on 30 July 1986 by placing 4 seeds hole -1 at 0.25 m in the row in 7 rows spaced 0.70 m apart. This was followed by thinning 15 days after emerg- ence to 2 plants hole- 1. Basal levels of fertilizers at the rate of 100 kg N ha- 1 as urea, 30 kg P ha-1 as mono-superphosphate and 30 kg K ha-1 as muriate of potash were applied to each plot at planting. The plots were hand weeded throughout the period of growth.

The soil bulk density and gravimetric water content of each plot were deter- mined in quadruplicate immediately after seeding. Since penetrometer resis- tance has been used by many researchers (Phillips and Kirkham, 1962; Rag- havan et al., 1979; Ohu et al., 1985 ) to evaluate the soil resistance encountered by roots, a standard cone penetrometer (ASAE 1984) with a cone base diam- eter of 15 m and cone angle 30 ° operating at 1829 mm min- 1 penetration speed

401

was used to measure penetration resistance in all the plots immediately after the seeding operation. Four readings were taken randomly on each plot to rep- resent the penetration resistance from the soil surface to the 0.20-m depth.

The bulk density, penetration resistance and moisture content of each plot were also determined 24 h after every major rainfall event throughout the growing period. Similarly at 64 days after harvesting the crop (the peak of the dry hamarttan season ), the penetration resistance and the bulk density of each plot were measured to assess the effect of drying on the physical properties of the soil after compaction.

The pannicle yield (Head weight), the grain yield and the plant yield with- out grain were measured at harvesting. Samples of grain and plant from each plot were taken for moisture content determination. The crop yield parameters and the physical properties of the soil were compared in terms of traffic treatments.

RESULTS AND DISCUSSION

Mean values of dry bulk density and penetration resistance at different moisture contents for each treatment are listed in Table 1. Different predictive models were tried to relate the density and penetration resistance to the traffic treatments characterized as the product of number of passes, n, and contact pressure, p in Mpa. The forms of the models that best described the relation- ships were

p=Bo+BI(np)+B20 (1)

and

Pr =Bo +Blln(np) +B21n(0) (2)

where p and Pr are dry bulk density and penetration resistance in Mg m -:~ and Mpa, respectively; np is the product of the number of passes and contact pres- sure; 0 is gravimetric moisture content ( % ).

The coefficients Bo, B1 and B2 for the dry density and penetration resistance are listed in Table 2. The values of the correlation coefficients and their levels of significance are also indicated in the same table.

It was observed (Table 1 ), that the dry bulk density and penetration resis- tance increased with increasing number of passes. The maximum penetration resistance was obtained at the lowest moisture content of measurement for all the traffic treatments, while the bulk density increased with increasing mois- ture content up to a point and decreased with further increase in moisture content. This observation could be the probable reason why a logarithmic model could not be used to fit the dry bulk density data as used for penetration resis- tance. The predictive models are in line with the ones proposed by Raghavan et al. (1979) in which statistical models were used to express dry density and penetration resistance in terms of soil moisture contents and traffic treatments.

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TABLE 2

Predicted coefficients, correlation coefficients and levels of significance for dry bulk density and penetration resistance in Equations (1) and (2)

Parameter Bo B1 B2 r 2 C (level of significance )

Dry bulk density 1.46 0.43 -4 .17 × 10 -3 0.84 0.01 Penetration resistance 1.99 -0 .15 -0 .07 0.54 0.01

TABLE 3

Mean values of plant moisture, grain moisture, plant yield and grain yield in field plots of sandy loam soil as affected by 5 different traffic treatments in a randomized complete block design

Treatment Plant Grain Plant yield Grain yield moisture moisture (Mg ha -1) (Mg ha 1) (%) (%)

Zero traffic 29.71 4.00 13.511 + 5.06 2.441 _+ 2.16 5t rac tor passes 31.68 4.25 13.71 _+2.64 2.61 ___ 1.59

10 tractor passes 33.17 4.50 13.81 _+ 3.79 2.67 _+ 1.86 15 tractor passes 36.87 4.50 14.75 _ 4.93 2.83 _+ 2.86 20 tractor passes 43.24 4.50 14.46 4- 3.61 2.50 _+ 3.04

1Values are not significantly different between the treatments (P < 0.05 ). Each value is a mean of 4 replicates. Standard errors of the mean plant yield and mean grain yield are indicated.

The results of plant without grain moisture, grain moisture, grain yield and plant yield are shown in Table 3. The plant moisture varied from a minimum of around 30% at lower treatment levels to a maximum of about 43% at higher treatment levels. This is expected from the observed plant diameter at the time of harvesting. The diameter of the plants at higher compaction levels were physically observed to be greater than those at lower compaction levels. This is expected, since the plant in a highly compacted soil will not be able to develop enough roots to store water needed for its growth. Then the only means of water storage for the development of the plant is in the stem. Similar increase in stem diameter of tomato seedling has been reported (Liptay and Geier, 1983 ) which was attributed to variations in the compression of the soil in the vertical profile. This is also in line with the results of Ohu et al. (1985) in a study of the effect of soil compaction and organic matter on the growth of bush beams in which the diameter of the crop in highly-compacted soils was observed to be larger than in moderately and uncompacted soils. However, the grain moisture was not affected by the level of compaction.

A plant yield of 13 710 kg ha - 1 was obtained at moderately compacted plots, whereas a value of 13 510 kg ha - 1 was recorded for the zero-traffic plots. Cor-

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responding values for grain yield were 2612 and 2440 kg ha -1. It will be seen that both the plant yield and grain yield increased with higher compaction levels up to a point and then decreased with a further increase in soil compac- tion. However, the increase in plant and grain yield were not statistically sig- nificant. In a dry area and with a loose sandy soil such as the condition under which this study was carried out, it is evident from the results that a certain amount of machinery traffic can be beneficial for crop production. A similar trend in maize yield was recorded by Raghavan et al. (1979) in a study of vehicular traffic effects on development and yield of maize planted in a Ste. Rosalie clay soil in Quebec, Canada, when the weather condition was abnor- mally dry for the region.

Although there are no statistically significant differences between the yield parameters from one treatment to the other, there is about 0.22 Mg ha -1 dif- ference in head weights between the zero traffic and 5 tractor passes. This increases further to about 0.45 Mg ha- 1 difference between the zero traffic and 15 tractor passes which consequently reduced to about 0.10 Mg ha-1 between the zero traffic and 20 tractor passes. Correspondingly for the plant yield, a difference of about 0.20 Mg ha- 1 was recorded between the zero traffic and 5 tractor passes which increased to 1.24 Mg ha-1 for the 15 tractor passes and 1.16 Mg ha-1 between the zero traffic and 20 tractor passes. A second degree equation in the machinery traffic variable, np (number of passes, n and contact pressure, p) described the variation of head yield and plant yield in the form

Yhead=3.38+2.26(np)--3.16(rip) 2 (r2=0.84) (3)

Yp,a,t = 13.45+ 1.68(np) +0.75(np) 2 (r2=0.85) (4)

where Yhead is head weight yield (Mg ha- 1 ); Yplant is plant yield (Mg ha- 1 ); n is number of tractor passes; p is the contact pressure (Mpa).

Equations (3) and (4) are similar to Vomicil's (1955) parabolic formula relating plant yield to soil bulk density.

CONCLUSION

The average dry bulk density and penetration resistance values measured during the season in a sandy loam field varied with moisture content depending on the severity of the treatment. It can be said from the results that during the growing season the soil moisture affected the dry bulk density and penetration resistance that resulted from the initial traffic treatments.

The plant moisture content varied from a minimum of about 30% at lower traffic treatment levels to a maximum of about 43 % at higher treatment levels, while grain moisture was not affected significantly by the level of compaction. Even though there is no real yield differences between the treatments in this experiment, it is evident from the results obtained that soil compaction affects

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the p r o d u c t i o n of so rghum. T h e r e f o r e it c an be conc luded t h a t in a d ry envi- r o n m e n t or when the wea t he r condi t ions are a b n o r m a l l y dry, especial ly in loose soils, a ce r t a in a m o u n t of m a c h i n e r y t raf f ic on the field can be benef ic ia l to c rop p roduc t ion . T h e need for a carefu l choice of m a c h i n e weight , t y re size and t raf f ic t i m i n g p r o g r a m m e for agr icu l tu ra l p r o d u c t i o n eff ic iency a n d prof i tab i l - i ty is ind ica ted f r o m the resu l t s ob ta ined .

REFERENCES

ASAE, 1984. Am. Soc. Agric. Eng. Standards 1986, St. Joseph, MI, 534 pp. Feldman, M. and Domier, K.W., 1970. Wheel traffic effects on soil compaction and growth of

wheat. Can. Agric. Eng., 12: 8-11. Huck, M.G., Browning, V.D. and Young, R.E., 1975. Leaf water potential and moisture balance

field data. ASAE Paper No. 75, 2582, ASAE, St. Joseph, M149085. Liptay, A. and Geier, T., 1983. Mechanism of emergence of tomato (Lycopersicon esculentum L. )

seedlings through surface crusted or compressed soil. Ann. Bot., 51: 409-412. Maurya, P.R., 1985. Effect of tillage and residue management on crop yield and physical properties

of an irrigated soil in Northern Nigeria. Paper presented at 10th Conference of International Soil Tillage Research Organization, University of Guelph, Guelph, Canada.

Ohu, J.O., Raghavan, G.S.V., Mckyes, E., Stewart, K.A. and Fanous, M.A., 1985. The effects of soil compaction and organic matter on the growth of bush beans. Trans. ASAE, 28: 1056-1061.

Phillips, R.E. and Kirkham, D., 1962. Soil compaction in the field and corn growth. Agron. J., 54: 29-34.

Raghavan, G.S.V. and Mckyes, E., 1983. Physical and hydraulic characteristics in compacted clay soils. J. Terramech., 19: 235-242.

Raghavan, G.S.V., Mckyes, E., Stemshorn, E., Gray, A. and Beaulieu, B., 1977. Vehicle compac- tion patterns in clay soil. Trans. ASAE, 201: 218, 219, 220, 225.

Raghavan, G.S.V., Mckyes, E., Gendron, G., Borhlum, B.K. and Le, H.H., 1978. Effects of tyre contact pressure on corn yield. Can. Agric. Eng., 20: 34-37.

Raghavan, G.S.V., Mckyes, E., Baxter, R. and Gendron, G., 1979. Traffic-soil-plant (maize) relations. J. Terramech., 16: 181-189.

Rayar, A.J., 1984. University of Maiduguri Farm Development Planning Report for Faculty of Agriculture, Annex A, Soil Survey Details.

Taylor, F., Raghavan, G.S.V., Mckyes, E., Negi, S., Vigier, B. and Stemshorn, E., 1981. Soil struc- ture and cory yields. Trans. ASAE, 24: 1408-1411.

Vomicil, J.A., 1955. Ph.D. Thesis, Rutgers State University of New Jersey, New Brunswick, NJ.