Subsoil compaction effects on crops in Punjab, Pakistan:

Soil & Tillage Research 60 (2001) 153–161

Subsoil compaction effects on crops in Punjab, Pakistan: II. Root growth and nutrient uptake of wheat and sorghum M. Ishaqa,*, M. Ibrahima, A. Hassanb, M. Saeedc, R. Lald a

Soil Chemistry Section, Ayub Agricultural Research Institute, Faisalabad, Pakistan b Department of Soil Science, University of Agriculture, Faisalabad, Pakistan c Ali Akbar Group, Agro Division, 97, Street No. 12, Lahore Cantt, Pakistan d School of Natural Resources, The Ohio State University, Columbus, OH 43210, USA Received 9 June 2000; received in revised form 19 January 2001; accepted 2 March 2001

Abstract Crop yields can be reduced by soil compaction due to increased resistance to root growth, and decrease in water and nutrient use efficiencies. A field experiment was conducted during 1997–1998 and 1998–1999 on a sandy clay loam (fine-loamy, mixed, hyperthermic Typic Haplargids, USDA; Luvic Yermosol, FAO) to study subsoil compaction effects on root growth, nutrient uptake and chemical composition of wheat (Triticum aestivum L.) and sorghum (Sorghum bicolor L. Moench). Soil compaction was artificially created once at the start of the study. The 0.00–0.15 m soil was manually removed with a spade. The exposed layer was compacted with a mechanical compactor from 1.65 Mg m
3 (control plot) to a bulk density of 1.93 Mg m
3 (compacted plot). The topsoil was then again replaced above the compacted subsoil and levelled. Both compacted and control plots were hoed manually and levelled. Root length density, measured at flowering stage, decreased markedly with compaction during 1997–1998 but there was little effect during 1998–1999. The reduction in nutrient uptake by wheat due to compaction of the subsoil was 12–35% for N, 17–27% for P and up to 24% for K. The reduction in nutrient uptake in sorghum due to subsoil compaction was 23% for N, 16% for P, and 12% for K. Subsoil compaction increased N content in wheat grains in 1997–1998, but there was no effect on P and K contents of grains and N and P content of wheat straw or sorghum stover. During 1997–1998, K content of wheat straw was statistically higher in control treatment compared with compacted treatment. In 1998, P-content of sorghum leaves was higher in compacted treatment than uncompacted control. Root length density of wheat below 0.15 m depth was significantly reduced and was significantly and negatively correlated with soil bulk density. Therefore, appropriate measures such as periodic chiselling, controlled traffic, conservation tillage, and incorporating of crops with deep tap root system in rotation cycle is necessary to minimize the risks of subsoil compaction. # 2001 Elsevier Science B.V. All rights reserved. Keywords: Leaf analysis; Vehicular traffic; Nitrogen; Phosphorus; Potassium; Subsoil compaction; Pakistan

1. Introduction Subsoil compaction of agricultural soils is a global concern (Lowery and Schuler, 1991; Oussible et al., * Corresponding author. Fax: þ9241653874. E-mail address: [email protected] (M. Ishaq).

1992; Ha˚kansson and Reeder, 1994; Soane and van Ouwerkerk, 1994) due to adverse effects on crop yields and the environment. Root growth into the subsoil can be inhibited by unfavourable soil chemical and/or physical conditions. Physical conditions detrimental to root proliferation in subsoil are frequently related to tillage pans that develop below plough

0167-1987/01/$ – see front matter # 2001 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 - 1 9 8 7 ( 0 1 ) 0 0 1 7 7 - 5

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layers (Maurya, 1988; Gill and Aulakh, 1990). Tillage pans have high bulk densities, few macropores for roots to grow through, and a mechanical impedance great enough to markedly reduce root growth rates (Rafiq, 1990; Hassan and Gregory, 1999). The impact of mechanical impedance on root growth under adverse soil moisture and soil temperature regimes is not well understood. Compaction causes unfavourable changes in soil bulk density, porosity and penetration resistance (Soane et al., 1981). Several researchers (Lal and Tanaka, 1991; Lal, 1996; Flowers and Lal, 1998) have examined the effect of uniform soil surface compaction on crop growth and yield. In an experiment with barley (Hardeum vulgare L.), Willatt (1986) observed that root length density (RLD) in the upper 0.30 m of soil and rooting depth decreased as the number of tractor passes increased from zero to six. Bulk density and soil strength on traffic side of a plant row can be much greater than those in the non-traffic side of the same row (Lal et al., 1989; Kaspar et al., 1991; Voorhees, 1992). This positional variation of soil properties with respect to the crop row can alter root growth distribution. Compaction below the depth of normal tillage operations is generally called subsoil compaction. Adverse effects of compacted soil horizons on plant root growth and concomitant poor plant growth and yields have been recognized for many years (Oussible et al., 1992; Etana and Ha˚ kansson, 1994; Unger and Kaspar, 1994; Jorajuria et al., 1997). Oussible et al. (1992) found that compacting a clay loam soil to a density of 1.52 Mg m
3 below 0.1 m depth significantly reduced the root elongation of wheat by 19– 36% within the compacted layer. A correlation coefficient of
0.93 was obtained between RLD and mechanical impedance. Similar negative correlation between root length and soil strength has been reported by Gerard et al. (1982) and Dexter (1986a). Limited water and nutrient availability to plants due to compaction are major constraints to plant growth and yields in many soils. Lowery and Schuler (1991) studied effects of subsoil compaction on nutrient uptake by maize (Zea mays L.). Soil was compacted with 4.5 (control), 8 and 12.5 Mg axle loads. Uptake of N and K were decreased, while those of Fe and Mn increased with increasing levels of compaction. They also reported that ear-leaf contents for N, P and K were not significantly affected by subsoil compaction treat-

ment. Compaction can result in low water use efficiency (Raghavan et al., 1990; Ishaq et al., 2000), greater losses of plant-available water (Reeves et al., 1990) and less use of fertilizer (Ste˛ pniewski and Przywara, 1992). Losses of N due to denitrification are generally greater on compacted than uncompacted soils (Arah et al., 1991; Douglas and Crawford, 1993). Other researchers (Gameda et al., 1994; Lal, 1996; Ishaq et al., 2000) have also reported that crop yields are reduced by soil compaction due to increased resistance to root growth, and decrease in water and nutrient use efficiencies. In Pakistan, the tillage operations by farmers are generally performed with bullock and tractor-driven cultivator to a depth of 0.10–0.15 m. Repeated use of tractor-driven cultivator creates a hard pan at about 0.15 m depth which hinders the movement of water and air and inhibits growth of plant roots (Rafiq, 1990; Hassan and Gregory, 1999). A little information is available about the soil and crop response to subsoil compaction under local conditions. Thus, it is important to quantify the effects of tillage-induced hard pans on soil properties and crop growth. The effects of subsoil compaction on soil bulk density, penetration resistance, and yields of wheat and sorghum and nutrient and water use efficiencies by these crops have been reported in the companion paper of Ishaq et al. (2000). The adverse effects of subsoil compaction on crop growth and yield may be due to unfavourable physical conditions, and/or due to low nutrient uptake. The information about the effect of subsoil compaction on root growth and nutrient uptake under field conditions in Pakistan is scanty. Therefore, the objectives of this study were to quantify the effect of subsoil compaction on (i) root growth and nutrient uptake by wheat, and (ii) chemical composition of wheat and sorghum crops.

2. Materials and methods 2.1. Site The study was conducted on the research farm of Soil Chemistry Section, Ayub Agricultural Research Institute (AARI), Faisalabad, Pakistan. The soil is sandy clay loam (fine-loamy, mixed, hyperthermic Typic Haplargids, USDA; Luvic Yermosol, FAO)

M. Ishaq et al. / Soil & Tillage Research 60 (2001) 153–161

and the site is in a semiarid region and under flood irrigation with canal water. The areal extent of soil similar to this experiment site is about 21% of the total cultivated area of Punjab province (Anonymous, 1984–1991). Out of 12.3 million ha of total cultivated area in Punjab, about 2.52 million ha is covered by Typic Haplargids and other soils of similar properties. The experiment, involving a wheat–sorghum (fodder) rotation, was conducted during 1997–1998 and 1998– 1999 season. Details of the field layout and experimental techniques are given in another report (Ishaq et al., 2000), but a brief description is given below to make clear understanding of this paper. 2.2. Experimental background In the laboratory, a Proctor density test was conducted to develop a relationship between soil water contents and bulk density. Bulk soil was obtained from 0.15 to 0.30 m depth. Six soil water levels (20, 60, 70, 120, 150 and 190 g kg
1) were created. The moist soils were kept in plastic bags for 48 h for equilibration. Soils were compacted to their maximum compactibility using the modified compacted mould (diameter of 0.15 m and length of 0.12 m with hammer of 4.54 kg fall) (British Standards Institution, 1975). Maximum compaction was attained at 120 g kg
1 of soil water content. In the field, the top soil (0.15 m) was removed manually by using a spade and the exposed soil was compacted at water content of about 50% of the field capacity (120 g kg
1 soil water content). This subsoil compaction protocol was selected to simulate the hard pan created by longterm ploughing of soil with field cultivator. Continual shallow cultivation has been reported to create a hard pan below 0.15 m depth. The bulk density of this plough pan ranges from 1.71 to 1.81 Mg m
3 (Farooq and Amin, 1990; Hassan and Gregory, 1999). Also, plough pan at places affected the soil permeability and consequently crop production (Rafiq, 1990; Razzaq et al., 1990). The subsoil compaction treatments were imposed once at the start of the study 1997–1998. The compaction was achieved by a powered vibratory tamper with a weight of 60 kg, a base area of 0:30 m  0:30 m, a static pressure of 8.4 kPa, and operating at 80 strokes min
1. The bulk density and penetration resistance of exposed compacted soil were determined. Then the topsoil was replaced. Bulk

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density and penetration resistance of the uncompacted control plots from 0.00 to 0.15 and 0.15 to 0.30 m depths were also determined. Both compacted (of bulk density 1.93 Mg m
3) and uncompacted control (of bulk density 1.65 Mg m
3) plots were hoed and levelled. Plots were arranged in a randomized complete block with four replications of each treatment (control and compacted). Plots consisted of 15 rows, each 3 m long and spaced 0.2 m apart. The magnitude of soil compaction was quantified by measuring soil bulk density, penetration resistance, total porosity and air-filled porosity. These soil parameters were determined at the start of the study during 1997– 1998 and after the harvest of three crops during 1998–1999. The bulk density was measured using the core method (Blake and Hartge, 1986). The soil penetration resistance was measured using cone penetrometers (308 cone tip angle, 9:2  10
3 m diameter). At the same time soil samples from the respective depths were taken to determine soil water content. These observations were recorded in between crop rows. Soil cores collected for bulk density measurements were used to determine the gravimetric and volumetric water contents, total porosity and air-filled porosity by following the techniques described by Lowery et al. (1996). 2.3. Soil and plant analyses Composite soil samples from 0.00 to 0.15, 0.15 to 0.30 and 0.30 to 0.60 m depth were analysed for chemical characteristics (Table 1). Three composite soil samples were taken from each depth before sowing the first wheat crop during 1997–1998. Soil samples were analysed for pHs (McLean, 1982), electrical conductivity of saturation paste extract (Rhoades, 1982a), total organic carbon (Nelson and Sommers, 1982), cation exchange capacity (Rhoades, 1982b), total soil nitrogen (Tecator, 1981), 0.5 M NaHCO3–P (Olsen and Sommers, 1982) and 1 N NH4OAc–K (Knudsen et al., 1982). Wheat grain and straw samples collected at maturity, and the whole sorghum plant 60– 65 days after planting, were digested in an acid mixture (HNO3 and HClO4) prior to chemical analysis. Total P was determined using the vanadomolybdophosphoric acid yellow colour method (Yoshida et al., 1976). Plant K contents were measured flame-photometrically (Yoshida et al., 1976). Total

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Table 1 Soil chemical analyses of the profile of the experimental site at AARI, Faisalabad, Pakistana Depth (m)

pHs

ECe (dS m
1)

Kjeldahl-N (g kg
1)

NaHCO3–P (mg kg
1)

NH4OAc–K (mg kg
1)

SOC (g kg
1)

CEC (cmolc kg
1)

0.00–0.15 0.15–0.30 0.30–0.60

8:19  0:02b 8:29  0:019 8:20  0:019

1:33  0:09 1:40  0:08 1:50  0:09

0:43  0:01 0:39  0:01 0:34  0:01

7:06  0:10 2:76  0:20 1:23  0:12

205  4:1 148  5:6 130  3:7

3:63  0:09 2:45  0:04 2:02  0:03

7:10  0:08 6:83  0:03 8:08  0:06

a b

AARI: Ayub Agricultural Research Institute. Mean  standard deviation.

N concentration was determined using the method described by Tecator (1981).

(Duncan, 1955). Simple correlations were used to relate soil and plant parameters.

2.4. Root length measurements 3. Results and discussion The root length of wheat was measured from soil samples collected at anthesis (flowering) in between the rows, using a sampling core (0.15 m long and 0.08 m in diameter). Root samples were taken at 0.00– 0.15 to 0.15–0.30 m depth from both sides of the row. Roots were separated from the soil and other residue by gentle washing under a flow of swirling water. Root length was measured following the techniques of Tennant (1975). The RLD (mm cm
3) was calculated by dividing the root length (mm) with the volume (cm3) of sampling core.

Subsoil compaction effects on soil physical properties (Ishaq et al., 2000) showed that compaction increased soil bulk density by 16%, and decreased total porosity from 0.37 to 0.27 m3 m
3 and air-filled porosity from 0.16 to 0.06 m3 m
3. The soil penetration resistance of the compacted zone increased from 1.0 to 4.83 MPa. Consequently, grain yield of wheat decreased by 37% in 1997–1998 and 8% in 1998– 1999. The fodder yield of sorghum also decreased by 22% in 1998 and 14% in 1999.

2.5. Nutrient uptake and statistical analyses

3.1. Chemical composition of wheat and sorghum

Nutrient uptake by wheat and sorghum was computed for each plot (concentration in percent  yield in kg ha
1 ¼ uptake in kg ha
1). Data were statistically analysed for the analysis of variance (Gomez and Gomez, 1984). The comparisons among the treatment means were made by Duncan’s Multiple Range Test

The effects of subsoil compaction on the chemical composition of wheat and sorghum crops are presented in Tables 2 and 3, respectively. During 1997–1998, compaction significantly increased the wheat grain concentration of N from 23.16 to 23.34 g kg
1 and significantly decreased the K content of wheat straw

Table 2 Chemical composition of grain and straw of wheat as affected by subsoil compaction Year

Treatment

Grain composition (g kg
1)

Straw composition (g kg
1)

N

P

K

N

P

K

1997–1998

Compacted Control LSD (0.05)

23.34 23.16 0.17

3.17 3.04 0.38

4.51 4.63 0.74

4.20 4.60 2.50

0.58 0.60 0.32

15.21 17.83 1.87

1998–1999

Compacted Control LSD (0.05)

21.84 21.94 1.00

2.75 2.65 0.23

4.74 4.68 0.07

3.46 4.53 1.20

0.29 0.31 0.04

29.29 29.87 4.00

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Table 3 Chemical composition and nutrient uptake of sorghum fodder as affected by subsoil compaction Treatment

Compacted Control LSD (0.05)

Concentration (g kg
1)

Uptake (kg ha
1)

N

P

K

N

P

K

20.30 19.80 3.70

1.88 1.66 0.16

35.25 33.25 1.45

85.2 110.7 21.7

7.5 8.9 2.70

150.9 170.5 25.4

from 17.80 to 15.20 g kg
1 (Table 2). Nitrogen and P contents of straw, and P and K contents of grains were not affected by the compaction treatment during 1997–1998. In the second year, subsoil compaction had no effect on the chemical composition of either the grain or straw. Rather, it was observed that the crops in compacted soils had higher, but nonsignificant, N, P and K content of grain compared with that of the control plots. However, trends in nutrient contents of straw were opposite to that in the grain. Table 3 shows that subsoil compaction significantly increased the P content (1.90 g kg
1) of sorghum leaves compared with that of control (1.70 g kg
1). However, N and K contents were not affected by the compaction treatment. Lowery and Schuler (1991) studied subsoil compaction effects on ear-leaf analysis of maize and reported that leaf N content increased from 20.60 g kg
1 in the control to 22.10 g kg
1 in the 12.5-Mg compaction treatment. Similarly P content increased from 2.70 g kg
1 in the control to 2.90 g kg
1 in the 12.5-Mg compaction treatment. But contrary to our results, K-contents decreased from 21.60 to 20.80 g kg
1 in control and compacted plots. Furthermore, overall, N, P and K content of maize remained unaffected by subsoil compaction. When compared with the sufficiency levels of N (35–40 g kg
1), P (3–6 g kg
1) and K (30–45 g kg
1) contents of sorghum leaves (Lockman, 1972), it is obvious that N and P contents were below the sufficiency range, but the K content was in the sufficiency range. In the field, there were no visible deficiency symptoms of these nutrients. The lower values may be due to the sampling procedure of plant part at different physiological stage (Jones et al., 1991). In this study the whole plants were analysed 60–65 days after planting, in contrast Lockman (1972) analysed leaves 23–39 days after planting.

The reported adequate values of total N, P and K for wheat grain are >20, >3 and >4 g kg
1, respectively (Reuter, 1986). In both years, subsoil compaction had no adverse effect on total N, P and K content of wheat grains. In general, subsoil compaction did not reduce the nutrient concentration but did apparently affect yield (Lowery and Schuler, 1991; Ishaq et al., 2000). 3.2. Nutrient uptake by wheat and sorghum The compaction treatment significantly decreased the uptake of N, P, and K by the wheat crop compared with the control (Table 4). In 1997–1998 the reduction in uptake due to compaction was about 35% for N, 27% for P and 24% for K compared with the control treatment. In the second year the effects of compaction were less pronounced compared with the first year due to the reduction in soil bulk density from 1.93 Mg m
3 during 1997–1998 to 1.78 Mg m
3 in 1998–1999. The uptake of N decreased by 12%, of P by 17%, and that of K by 5% due to subsoil compaction. Subsoil compaction significantly decreased the N and K uptake by sorghum fodder but there was no effect on P uptake (Table 3). The effects of mechanical impedance on water and nutrient uptake are related to the volume of soil explored by the roots and to anatomical and morphological changes in the root systems (Castillo et al., 1982). The effect of subsoil compaction on root growth may be directly related to high soil strength and/or indirectly to soil O2 and nutrient availability plus soil water status (Mackay and Barber, 1985; Oussible et al., 1992; Panayiotopoulos et al., 1994; Coelho et al., 2000). The reported values of air-filled porosity that limits root growth range from 0.08 to 0.15 m3 m
3 (Smucker and Erickson, 1989). Ishaq et al. (2000) reported that the subsoil compaction treatment significantly decreased the airfilled porosity from 0.16 m3 m
3 in the uncompacted

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Table 4 Nutrient uptake by wheat as affected by subsoil compaction Year

Treatment

Uptake (kg ha
1) Grain

Total ðgrain þ strawÞ

Straw

N

P

K

N

P

K

N

P

K

1997–1998

Compacted Control LSD (0.05)

54.8 87.9 10.1

7.4 11.5 2.5

10.6 16.9 2.4

22.9 31.1 3.1

3.2 3.9 0.5

85.4 109.3 12.2

77.7 119.0 10.5

10.6 15.4 2.4

96.0 126.2 9.9

1998–1999

Compacted Control LSD (0.05)

68.7 75.4 3.9

8.6 9.1 0.4

14.9 16.1 0.5

16.0 21.5 5.2

1.4 1.5 0.2

135.4 142.1 26.6

84.7 96.9 9.0

10.0 10.6 0.5

150.3 158.2 27

control plots to 0.06 m3 m
3 in compacted treatments, and this decreased the yields of wheat grain by 38% and sorghum fodder by 22%. 3.3. Root length density of wheat During 1997–1998, subsurface compaction significantly decreased the RLD of wheat compared with that of the control plots (Table 5). RLD in the compacted layer was 0.52 mm cm
3 compared with 0.86 mm cm
3 for that of the control plants. At the initiation of the experiment, soil penetration resistance (4 MPa) was more than the critical value of 3 MPa (Coelho et al., 2000) which would be expected to adversely affect the RLD. Logsdon et al. (1987) reported that increased mechanical impedance was associated with a decline in maize root length. During 1998–1999, subsurface compaction did not significantly affect the root length. In the uncompacted zone (0.00–0.15 m depth) almost equal root length was recorded for compacted and uncompacted treatments. However, in the compacted zone, the compacTable 5 RLD of wheat as affected by subsoil compaction Depth (m)

Treatment

Root length density (mm cm
3) 1997–1998

1998–1999

0.00–0.15

Compacted Control LSD (0.05)

4.05 3.85 0.45

5.19 5.22 0.31

0.15–0.30

Compacted Control LSD (0.05)

0.52 0.86 0.07

2.24 2.40 0.35

tion treatment slightly decreased the RLD (2.24 mm cm
3) compared to the control (2.40 mm cm
3), but the effect was statistically non-significant. This may be due to reduction in soil bulk density during the second year (Ishaq et al., 2000) and perhaps the root channels and fissures created by the previous crop facilitated more efficient root penetration in the compacted layer (Coelho et al., 2000). 3.4. Correlation analyses Table 6 shows correlations between RLD, bulk density and grain yield of wheat. The values of bulk density used for correlation analyses were 1.65 Mg m
3 for 0.00–0.15 m and 1.93 Mg m
3 for 0.15–0.30 m depths during the first year (1997–1998). Similarly the corresponding values were 1.68 and 1.78 Mg m
3 for the second year (1998–1999). A highly significant ðp < 0:01Þ negative correlation ðr ¼
0:961Þ was obtained between RLD and bulk density in the first year and a negative ðr ¼
0:460Þ but non-significant correlation was obtained in the second year for the compacted layer. Oussible et al. (1992) found a correlation coefficient of
0.93 between RLD of wheat and soil mechanical impedance. Studies with several crops have reported reduced root elongation and similar negative correlations between root length and soil strength (Gerard et al., 1982; Dexter, 1986a,b). The correlation between RLD and soil bulk density was not significant in the second year due to the reduction in soil bulk density (1.78 Mg m
3) compared to bulk density (1.93 Mg m
3) of first year. The correlation coefficient between RLD and grain yield for compacted

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159

Table 6 Relationships between RLD, bulk density and grain yield of wheata Year

Depth (m)

Parameters

Correlation coefficient (r)

1997–1998

0.00–0.15

RLD RLD RLD RLD

vs vs vs vs

grain bulk density grain bulk density


0.460 NSb
0.185 NS 0.968**
0.961**

RLD RLD RLD RLD

vs vs vs vs

grain bulk density grain bulk density


0.065 NS 0.759* 0.184 NS
0.460 NS

0.15–0.30 1998–1999

0.00–0.15 0.15–0.30

a

RLD: root length density. Non-significant. * Significant at the 5% level. ** Significant at the 1% level. b

layer was 0.968 and was highly significant at p < 0:01 during 1997–1998. In the second year, correlation was non-significant. These correlations are in accord with the results reported earlier by Ishaq et al. (2000). The correlations between RLD and nutrient contents of grain and straw of wheat were not significant except for the K content of straw grown on the compacted treatment during 1997–1998 (data not reported). For compacted layers there existed a negative but non-significant correlation between RLD and N and P contents of grain during 1997–1998. Similarly, in the second year, negative but non-significant correlations were obtained between RLD and N, P and K contents of grains. On the other hand, correlations between RLD and straw contents of N, P and K were positive but not significant for all depths and years. These correlations are in accord with the results reported in Table 2. No definite cause–effect relationship between RLD and grain concentration in compacted layer could be established. But for wheat straw, a relationship was developed indicating that with increasing RLD a corresponding increase in nutrient content occurred.

4. Conclusions An increase in bulk density (from 1.65 to 1.93 Mg m
3) and penetration resistance (from 1.00 to 4.83 MPa) due to subsoil compaction decreased the nutrient uptake by wheat and sorghum and RLD of wheat. The reduction in nutrient uptake by wheat was

12–35% for N, 17–27% for P and up to 24% for K. The corresponding values were 23, 16 and 12% for sorghum fodder. RLD of wheat significantly decreased during the first year but the effect was not evident in the second year. Soil compaction had no effect on N, P and K contents of wheat grains and leaves of sorghum fodder. However, during 1997–1998, K content of wheat straw was higher and P contents of sorghum leaves were lower for the control compared with those of the compacted plot. Although the severity of subsoil compaction artificially created in this experiment may not occur in traditional small-scale farming practices, the potential of severe subsoil compaction in alluvial soils exists with progressive increase in mechanization of farm operations in Punjab and elsewhere in South Asia. Therefore, appropriate measures such as periodic chiselling, controlled traffic, conservation tillage, and incorporating of crops with deep tap root system in rotation cycle are necessary to minimize the risks of subsoil compaction.

References Anonymous, 1984-1991. Reconnaissance soil survey reports of Punjab areas. Soil Survey of Pakistan, Lahore. Arah, J.R.M., Smith, K.A., Crighton, I.J., Li, H.S., 1991. Nitrous oxide production and denitrification in Scottish arable soils. J. Soil Sci. 42, 351–367. Blake, G.R., Hartge, K.H., 1986. Bulk density. In: Klute, A. (Ed.), Methods of Soil Analysis. Part 1. Physical and Mineralogical Methods. Agronomy Monograph No. 9, 2nd Edition. SSSA, Madison, WI, pp. 363–375.

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