water infiltration and clod size distribution as influenced by ploughshare type, soil water content...

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Research Paper: SW—Soil and Water

Water infiltration and clod size distribution asinfluenced by ploughshare type, soil water contentand ploughing depth

A. Hemmat�, I. Ahmadi, A. Masoumi

Agricultural Machinery Engineering Department, College of Agriculture, Isfahan University of Technology, Isfahan 84156-83111, Iran

a r t i c l e i n f o

Article history:

Received 18 July 2006

Accepted 22 February 2007

Available online 7 May 2007

nt matter & 2007 IAgrE.temseng.2007.02.010

[email protected] (A.

Soil management techniques, especially tillage, have been linked to the creation of low-

permeability pans that reduce soil infiltrability and increase runoff and soil erosion on

agricultural soils. In Iran, the mouldboard plough is the standard tillage implement used for

primary tillage and that could create a compacted plough pan, especially under wet

conditions. It was hypothesised that serrations on the ploughshare would increase water

infiltration into the soil. A field experiment was conducted in Isfahan (central Iran) on a

silty clay loam soil (Typic Haplargids). The infiltration rate and cumulative infiltration of

water into furrow bottoms after ploughing with a mouldboard plough were measured using

a double-ring infiltrometer. The plough was equipped with five share types (deep-suck

share (control), trapezoidal share with/without sharepoint and serrated share with/without

sharepoint) and ploughing performed under two soil water contents (0.55 and 0.85 plastic

limit, PL), and two ploughing depths (15 and 20 cm). The clod mean weight diameter (MWD)

was determined as an index of soil pulverisation, using dry sieving. The average 90 min

cumulative water infiltration for the serrated share with sharepoint was significantly

greater than for the other share types due to the furrow-bottom soil cracking resulting from

an increase in the thickness of cutting edge of the plough. Ploughing at 0.85 PL significantly

improved cumulative water infiltration compared with ploughing at 0.55 PL. The final

infiltration rate for the serrated share with/without sharepoint was statistically similar to

that of deep-suck share (control). For shallow ploughing at 0.85 PL, the clod MWD for the

trapezoidal share without sharepoint was significantly greater than that of the control. For

the serrated share with sharepoint, the proportion of coarse clods (X40 mm) was

significantly higher under dry condition (0.55 PL), when compared with the moist condition

(0.85 PL), whereas for the rest of ploughshare types, those proportions were statistically

similar. These results indicate that for improving water infiltration and still having similar

soil pulverisation, the deep-suck share could be replaced by the serrated share with

sharepoint in heavy soil (i.e., silty clay loam) with low water infiltration while ploughing at

a moisture content of 0.85 PL.

& 2007 IAgrE. All rights reserved. Published by Elsevier Ltd

All rights reserved. Published by Elsevier LtdHemmat).

dx.doi.org/10.1016/j.biosystemseng.2007.02.010

mailto:[email protected]

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1. Introduction

Water infiltration into soil is one of the most important

processes affecting crop production and the volume, trans-

port route and water quality of agricultural drainage. Except

in regions of timely and/or excessive precipitation, any

practice that increases infiltration and thereby increases

water availability to crops is desirable (Mukhtar et al., 1985).

Low infiltration rate is a major cause of water runoff and

soil erosion. It is also one of the main concerns in sustainable

agriculture for both irrigated and dryland farming systems.

Sakai et al. (1992) reported that low water penetration is a

major problem in the production of crops on over 1 million ha

of irrigated land in California, USA. Reduced infiltration is

also detrimental in dryland farming, especially on steeply

sloping agricultural lands, which are common in many areas

of the Pacific Northwest, USA (Zuzel et al., 1990).

Infiltration of water into the soil is controlled by the soil

surface and physical conditions of the soil. An aggregated soil

with many large continuous pores to the surface will have a

higher infiltration rate than a consolidated soil surface with

many small continuous pores (Lindstrom et al., 1981). Dense

and compacted layers lead to infiltration problems. These

layers can occur naturally (cemented pan) or can be created

by farming practices (plough pan, compaction) or by irrigation

(surface crusts). Abrupt changes in soil texture between

neighbouring layers can also cause infiltration problems

(Sakai et al., 1992). Infiltration and percolation of rain or

irrigation water into and through the soil profile, respectively,

is affected by surface sealing and the presence of a

compacted ploughsole. The ploughsole prevents further

percolation and drainage of the excess water through the

soil profile. On a sloped field, the water stored in the plough

layer can create a temporary saturated zone in which

subsurface flow can result in overland flow (Oltenfreiter

et al., 2003). Field measurements of saturated hydraulic

conductivity in eastern Oregon, USA, have indicated that

the tillage pan is the most restrictive layer for water flow

(Pikul & Allmaras, 1986). In the Pacific Northwest, USA, and

other areas where frozen soils are a major cause of runoff and

erosion, poor internal drainage because of a tillage pan may

perch water near the surface, resulting in the formation of

impermeable concrete frost during the winter (Molnau et al.,

1987).

When crusts dry, soil aggregates shrink, bend and crack

and, therefore, the dry crusts do not impede water penetra-

tion (Shainberg & Singer, 1985). Allen and Brand (1968)

reported that cracks increased infiltration rate in Sharkey

clay soil. Although cracks swelled shut when the crust got

wet, infiltration rate still remained high.

Effects of soil water content at the time of tillage on the

aggregate size distribution resulting from a tillage operation

have been investigated by several researchers (Gupta &

Larson, 1982; Wagner et al., 1992). Baver (1956) concluded that

there is a water content between the extremes of field

capacity and permanent wilting point at which tillage results

in the formation of finely pulverised soil made up of smaller

clods. When soil is worked at water contents near the lower

plastic limit, it tends to be most friable, large clods fragment

easily into smaller aggregates, and structural damage can be

accelerated (Utomo & Dexter, 1981). Tangie et al. (1990)

performed some field experiments and reported that soil

water content at the time of tillage significantly affected the

resulting aggregate size distribution; maximum aggregate

breakdown occurred when the soil was tilled at water

contents near the optimum water content for compaction

as determined by a standard Proctor test. Several works

(Braunack & Dexter, 1989; Adam & Erbach, 1990) related to

tillage-induced soil aggregate size distribution showed that

large aggregates are formed at both high and low water

contents.

Mouldboard ploughing is the main cultivation operation in

both dryland and irrigated farming systems in Iran. In the

dryland grain-growing regions, the traditional cropping

system during the fallow period comprises grazing of wheat

stubble after harvest, tilling the soil with mouldboard plough

and following it by sweeping in mid-summer of the next year

before autumn wheat planting. For a progressive farmer, in

addition to stubble grazing, fallow is maintained by spring

mouldboard ploughing followed by one or two passes of

sweeping to prevent weeds. However, no seedbed is prepared

before fall planting in either case (Hemmat & Eskandari,

2004). In irrigated farming of Iran, the conventional tillage is

also based on mouldboard plough and disk harrow for

primary and secondary tillage, respectively (Hemmat & Taki,

2001).

In the central parts of Iran, the soils are generally low in

organic matter content but they are intensively tilled.

Consequently, these soils tend to have unstable structure

(Hajabbasi & Hemmat, 2000). Eghbal et al. (1996) studied the

formation of crust after the first irrigation of a soil in the

region. They reported high exchangeable sodium together

with physical deterioration of surface structure due to a long

period of mechanised cultivation on the soil, which created a

suitable condition for crust formation and soil compaction.

Therefore, low water movement into the soil due to farming

practices (plough pan, compaction) or surface irrigation

(surface crusts) is a major problem in most of the farms in

central Iran.

It was hypothesised that by the use of serrated plough-

shares, plough pan formation could be prevented and the low

infiltration rate in mouldboard ploughed fields would be

alleviated. The objective of this study was to evaluate the

effect of five ploughshare types on water infiltration into the

soil of furrow bottoms after ploughing a silty clay loam soil at

two soil water contents and two ploughing depths. The

degree of soil pulverisation after ploughing with the plough-

share types was also measured.

2. Materials and methods

Field experiments were conducted at the Isfahan University

of Technology Research Station Farm (32120 N, 511230 E, 1630 m

above sea level) in central Iran. The soil was silty clay loam

(fine-loamy, mixed, thermic Typic Haplargids; USDA system)

initially low in organic matter and, consequently, with weak

structural stability which is a common attribute of arid soils.

The experimental site was cropped with corn (Zea mays L.) in

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Fig. 1 – Ploughshare types: (a) deep-suck share;

(b) trapezoidal share without sharepoint; (c) trapezoidal

share with sharepoint; (d) serrated share without

sharepoint; and (e) serrated share with sharepoint.

Side view

Top view

L0=105cm

L1=27cm

Ws=32.5cm

�p=25deg

�t=47deg�s=50deg

�v=10deg

Fig. 2 – Schematic of the plough bottom showing the

geometric variables used to characterise the implement.

Ws, width of cut; Lo, length of plough body; Ll, length of

landside; hp, share cutting angle; hs, share wing angle; hv,

B I O S YS TE M S E N G I N E E R I N G 97 (2007) 257– 266 259

2003. After harvest, the soil was tilled to a depth of 10 cm with

a rigid shank cultivator to level out the ridges and was

fallowed for 10 months. The tests were conducted during the

August of 2004. Table 1 lists the textural data, Atterberg limits

and shear strength parameters of the soil.

The experimental design consisted of a split–split plot

arrangement of a randomised complete block with three

replications. Two soil water contents were main plots, five

ploughshare types were subplots, and two ploughing depths

were sub-subplots. The two soil water contents were 0.85 (17%

db; moist) and 0.55 (11% db; dry) of plastic limit (PL). The five

ploughshare types were deep-suck share (control), trapezoidal

share without/with sharepoint and serrated share without/

with sharepoint (Fig. 1). The two ploughing depths were 15 and

20 cm. Each sub-subplot was 45�2 m. The main plots were

flood irrigated, and mouldboard ploughed performed at

selected soil water content as the plots dried naturally.

A mounted plough with three bottoms was used for all the

tests. The mouldboard form was short and cylindrical. The

bottom spacing was 35 cm. Schematic of the plough bottom

showing the geometric variables used to characterise the

implement is provided Fig. 2. The geometrical characteristics

of the shares are given in Table 2. The cutting edge of the

sharepoint had width of 6 cm and height of 6 mm. The

serrated share was obtained by cutting grooves in the surface

of the trapezoidal share. A gauge wheel was attached to the

plough frame to set the ploughing depth. The average travel

speed of tractor during the ploughing was 4.1 km h�1.

Water infiltration into the soil was measured by a double-

ring (shielded) infiltrometer. The inner ring was 300 mm in

diameter and the outer ring was 600 mm in diameter. The

height of both rings was 400 mm. After pushing aside the soil

in the ploughed strip, the rings were driven gently into the

soil of the furrow bottom to a depth of 10 cm. A ruler was

mounted vertically to the internal wall of the inner ring to

measure the infiltration. The water level in both the inner and

outer rings was kept to a depth of 5 cm over the infiltration

time. The water height in the inner ring was measured at 2, 4,

6, 9, 12, 16, 20, 25, 30, 40, 50, 70 and 90 min after adding water

to the rings. There were one-week and one-day delays

between ploughing and infiltration measurements for moist

(0.85 PL) and low (0.55 PL) water content treatments,

respectively. Due to high air temperature in August, the soil

water content of the furrow bottoms for both treatments was

reduced to 10% w/w at the time of infiltration measurement.

Philip’s two-term infiltration equation sometimes fails to

describe field results precisely (Ghosh, 1983). Though physi-

cally less appropriate, the Lewis–Kostiakov equation is

Table 1 – Some physical and mechanical properties of the soil

Primary particles, g kg�1 Atterberg Limits, kg kg�1

Clay Silt Sand SL PL LL

400 420 180 0.10 0.20 0.30

SL, shrinkage limit; PL, plastic limit; LL, liquid limit.

advantageous in that it can accommodate varieties of field

results (Ghosh, 1983). It was reported that Kostiakov’s

equation was accurately fitted to field data from unstable

soils to which Philip’s two-term equation could not be fitted

(Dixon, 1976). Therefore, to determine the time trends for

both cumulative infiltration and the infiltration rate of this

soil with low structural stability, measured values of cumu-

lative infiltration were fitted using Kostiakov’s equation

(Singh & Yu, 1990):

D ¼ atb, (1)

used in this study

Cohesion (c), kPa Angle of internal friction (Ø), deg

0.55 PL 0.85 PL 0.55 PL 0.85 PL

8.75 5.80 31.4 24

mouldboard shin angle; ht, mouldboard tail angle.

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where D is the cumulative infiltration in cm; t is time after

onset of the infiltration process in h; and a and b are

coefficients empirically determined by regression analysis.

Eq. (1) was differentiated with respect to time and used to

determine the infiltration rate:

I ¼ AtB, (2)

where I is the infiltration rate in cm h�1; and A and B are

coefficients related to a and b (A ¼ a�b and B ¼ b�1).

Coefficient A represents the initial infiltration rate depending

on the physical properties of surface soil at the beginning of

the infiltration process. Coefficient B shows the rate of

decrease in infiltration during the infiltration process and

depends mainly on changes of soil structure during water

percolation into the soil. Final infiltration rate after 90 min

was used for the statistical analysis.

After ploughing, rectangular soil samples were taken from

each sub-subplot. A 0.5�0.5 m frame was used to surround

the soil sample; then the soil was removed to the depth of

work by hand, to prevent soil clod break-up. All the soil

samples were oven dried prior to sieving. A set of sieves of

125, 75, 50, 40, 20 and 10 mm mesh openings was used. The

soil sample was passed through the set of sieves, and the soil

retained on each sieve was weighed. The soil that passed

Table 2 – The geometrical characteristics of the shares used fo

Ploughsharetype

Cutting edge width,mm

Cutting edgeheight, mm

Deep-suck

share

520 4

Trapezoidal

sharea

420 6

Serrated sharea 420 6–11

ys, share wing angle; yp, share cutting angle; Ws, share cutting width pera When sharepoint was attached on the share, the down suction was in

Table 3 – Cumulative infiltration, final infiltration rate and clodwith mouldboard plough equipped with five share types unde

Treatment 90 min cumulative infiltra

Soil water content

0.11 kg kg�1 (0.55 PL) 7.4b

0.17 kg kg�1 (0.85 PL) 10.8a

Ploughshare type

Deep-suck share 9.7b

Trapezoidal share without sharepoint 5.3c

Trapezoidal share with sharepoint 8.5b

Serrated share without sharepoint 9.1b

Serrated share with sharepoint 12.7a

Ploughing depth

15 cm 8.5a

20 cm 9.6 a

*In each column, within treatment (soil water content, share type or plou

different at probability Po0.05 according to least-significant difference (

PL, plastic limit.

through the sieve with the smallest aperture was also

weighed. The clod mean weight diameter (MWD) for each

soil sample was calculated using the following equation

(Adam & Erbach, 1992):

dMW ¼X

Xi Wi (3)

where dMW is the clod mean weight diameter in mm; Xi is

average clod diameter in a particular sieve in mm; and Wi the

weight of clods in the size range i, as a proportion of total dry

weight of sample analysed.

Treatment effects were analysed using analysis of variance

by the procedure of SAS (SAS Institute, 1990). When the

analysis of variance was significant at the probability of 0.05,

treatment means were separated by least-significant differ-

ence (LSD0.05) test.

3. Results and discussion

3.1. Cumulative infiltration after 90 min

The serrated ploughshare with sharepoint had the highest and

trapezoidal share without sharepoint had the lowest cumula-

tive infiltration among the treatments (Table 3). The serrated

r the study

ys,deg

yp,deg

Ws,mm

Down suction,mm

Side suction,mm

40 25 398 10 25

40 25 321 6 30

40 25 321 6 30

pendicular to direction of travel.

creased to 13 mm.

mean weight diameter (MWD) as affected by ploughingr two soil water contents and two ploughing depths*

tion, cm Final infiltration rate, cm h�1 Clod MWD, mm

4.7a 31a

5.2a 25a

6.1a 23b

2.3c 32a

3.7bc 20b

5.4ab 33a

7.4a 33a

4.1b 27a

5.9a 29a

ghing depth), means followed by the same letter are not significantly

LSD).

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Fig. 3 – Photographs of furrow bottom after pushing aside the soil in the ploughed strip for ploughing with (a) serrated share

equipped with sharepoint and (b) trapezoidal share without sharepoint.


share formed cracks in the soil of the furrow bottom, whereas

the trapezoidal share without sharepoint smeared the soil as

the cutting edge passed (Fig. 3). These observations are in

agreement with those made by Fielke (1996). During experi-

mental sweep tests in the glass-sided soil bin, Fielke (1996)

observed that the blunter cutting edges often induced cracking

in the soil below the tillage depth, while a small angle of

interference (negative clearance between the underside of the

tool and the soil) smeared the soil. Therefore, induced cracks

by serrated ploughshare and smearing by trapezoidal share

without sharepoint in the soil of the furrow bottom signifi-

cantly increased and decreased water infiltration into the soil

of furrow bottom, respectively (Table 3). The 90 min cumulative

infiltration for the serrated share without sharepoint treat-

ment was not statistically different from that of deep-suck

share and trapezoidal share with sharepoint treatments (Table

3). This similarity is attributed to reduced smearing in furrow

bottom soil resulting from using a separate sharepoint or using

a share with high down-suction. Therefore, using deep-suck

share or equipping the trapezoidal share with sharepoint or

cutting part of the share surface increases water infiltration

when compared with the simple trapezoidal share.

Ploughing at low soil water content (i.e., 0.55 PL) signifi-

cantly reduced the 90 min cumulative infiltration by 31%

when compared with ploughing at moist soil water content

(i.e., 0.85 PL) (Table 3). Ploughing at moist water content (0.85

PL) induced more cracks in the soil of furrow bottom and as

the soil dried, the cracks became more stable.

Under moist soil condition (0.85 PL), ploughing with the

serrated share equipped with sharepoint had the highest

value of cumulative infiltration; whereas the trapezoidal

share without sharepoint had the lowest value. The other

ploughshare types had intermediate values [Figs 4(a) and (b)].

Table 4 lists the results of LSD test on the coefficients of

Kostiakov equation for cumulative infiltration (i.e., a and b)

and infiltration rate (i.e., A and B). The soil water content�

ploughshare-type interaction for coefficient a is shown

in Table 5. The results indicate that under moist condition

(0.85 PL), ploughing with a share having a sharepoint yields

significantly higher value of coefficient a compared to the

other ploughshare types. The effect of two-way interactions

between ploughshare type and ploughing depth on coefficient

a is given in Table 6. The coefficient a was statistically similar

for shallow (15 cm) and normal (20 cm) ploughing depth for all

ploughshare-type treatments, except for trapezoidal share

equipped with sharepoint, in which the value of coefficient a

for shallow depth was significantly higher than that for

normal depth. The coefficient b for ploughing under moist

condition (0.85 PL) had significantly lower value when

compared with ploughing under dry condition (0.55 PL). The

results showed that the coefficient b for the serrated shares

had significantly higher values compared with the trapezoidal

share without sharepoint (Table 4). This could be explained by

the fact that crack formation in the soil of furrow bottoms by

the serrated ploughshares increased water infiltration into

the soil. The values of the coefficient b for ploughshares with

sharepoint were statistically similar. This similarity may be

attributed to the increased downward movement of water

into the soil resulting from less soil smearing. The higher

value of coefficient b for normal ploughing depth (20 cm),

compared to shallow ploughing (15 cm), was due to formation

of cracks in the soil of the previous plough pan layer.

3.2. Final infiltration rate

The serrated share with sharepoint and trapezoidal share

without sharepoint had the highest and lowest infiltration

rates, respectively (Table 3). Thus, by cutting part of the share

surface and cutting edge (by 10% and 50%, respectively) and

using sharepoint, the final infiltration rate was tripled. This

was probably due to the prevention of levelling of the soil

(smearing) at the tillage depth and crack formation in the soil

of the furrow bottom [Fig. 3a]. The presence of these cracks

explains the increased infiltration below the depth of tillage

(furrow bottom). Cutting part of the share edge increased the

cutting edge height. As observed by Fielke (1996) in the soil

bin, an increase in cutting edge height increases the forward

soil movement followed by soil rotation behind the cutting

edge. This increased soil movement results in cracks in the

soil below the depth of tillage. The reduction observed in the

infiltration rate for trapezoidal share without sharepoint was

due to levelling of the soil (smearing) at the tillage depth

[Fig. 3(b)]. It was reported (Fielke, 1996) that increased soil

compaction below the depth of tillage resulting from a blunt

cutting edge could be explained by work hardening of the soil

by the forward soil movement and smearing.

Increased ploughing depth significantly enhanced the final

infiltration rate by 44% (Table 3). This could be explained by

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Table 4 – Coefficients of Kostiakov equation for cumulative infiltration (a and b) and final infiltration rate (A and B) asaffected by ploughing with mouldboard plough equipped with five share types under two soil water contents and twoploughing depths

Treatment Infiltration coefficients*

a b A B

Soil water content

0.11 kg kg�1 (0.55 PL) 0.14b 0.92a 0.12b�0.08a

0.17 kg kg�1 (0.85 PL) 0.26a 0.83b 0.21a�0.16b

Ploughshare type

Deep-suck share 0.19abc 0.90ab 0.16ab�0.10ab

Trapezoidal share without sharepoint 0.12c 0.83ab 0.10ab�0.16ab

Trapezoidal share with sharepoint 0.29a 0.80b 0.22a�0.19ab

Serrated share without sharepoint 0.16bc 0.93a 0.14ab�0.072a

Serrated share with sharepoint 0.25ab 0.92a 0.22a�0.075a

Ploughing depth

15 cm 0.21a 0.83b 0.17a�0.17b

20 cm 0.18a 0.92a 0.16a�0.075a

*In each column, within treatment (soil moisture content, share type or ploughing depth), means followed by the same letter are not

significantly different at probability Po0.05 according to least-significant difference (LSD).

PL, plastic limit.

0

2

4

6

8

10

12

14

16

18

0 20 40 60 80 100

0 20 40 60 80 100 0 20 40 60 80 100

0 20 40 60 80 100

Cum

ulat

ive

infi

ltrat

ion,

cm

Cum

ulat

ive

infi

ltrat

ion,

cm

Cum

ulat

ive

infi

ltrat

ion,

cm

Cum

ulat

ive

infi

ltrat

ion,

cm

0

2

4

6

8

10

12

14

16

18

0

2

4

6

8

10

12

0

2

4

6

8

10

12

(a) (b)

(d)(c)

Time, min Time, min

Time, minTime, min

Fig. 4 – Cumulative infiltration as a function of time for ploughing: (a) 15 cm deep at 0.85 plastic limit (PL); (b) 20 cm deep at

0.85 PL; (c) 15 cm deep at 0.55 PL; (d) 20 cm deep at 0.55 PL; , serrated share with sharepoint; , serrated share without

sharepoint; , deep-suck share; , trapezoidal share with sharepoint; , trapezoidal share without sharepoint.


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Table 5 – Soil water content�ploughshare interactioneffect on coefficient a of Kostiakov equation for cumula-tive infiltration

Ploughshare type Coefficient a*

Soil water content

0.11 kg kg�1(0.55PL)

0.17 kg kg�1(0.85PL)

Deep-suck share 0.12cd 0.26abc

Trapezoidal share

without sharepoint

0.10d 0.13cd

Trapezoidal share

with sharepoint

0.26abc 0.32ab

Serrated share

without sharepoint

0.12cd 0.19bcd

Serrated share with

sharepoint

0.11cd 0.40a

*Means followed by the same letter are not significantly different at

probability Po0.05 according to least-significant difference (LSD).

Table 6 – Ploughing depth�ploughshare type interactioneffect on coefficient a of Kostiakov equation for cumula-tive infiltration

Ploughshare type Coefficient a*

Ploughing depth

15 cm 20 cm

Deep-suck share 0.15bc 0.23bc

Trapezoidal share without sharepoint 0.10c 0.13bc

Trapezoidal share with sharepoint 0.42a 0.16bc

Serrated share without sharepoint 0.18bc 0.13bc

Serrated share with sharepoint 0.23bc 0.27b



Table 7 – Ploughing depth � soil water content interac-tion effect on clod mean weight diameter (MWD)

Soil water content Clod mean weight diameter*, mm

Ploughing depth

15 cm 20 cm

0.11 kg kg�1 (0.55 PL) 27ab 35a

0.17 kg kg�1 (0.85 PL) 26ab 24b



PL, plastic limit.

Table 8 – Ploughing depth�ploughshare type interactioneffect on clod mean weight diameter (MWD)

Ploughshare type Clod mean weightdiameter*, mm

Ploughing depth

15 cm 20 cm

Deep-suck share 28abc 17c

Trapezoidal share without sharepoint 29abc 34ab

Trapezoidal share with sharepoint 17c 23bc

Serrated share without sharepoint 30abc 35ab

Serrated share with sharepoint 28abc 38a




the fact that ploughing 20 cm deep induced cracks in the soil

of the previous plough pan when compared with 15 cm deep

ploughing. The initial infiltration rate (coefficient A) for the

serrated share with sharepoint was significantly higher for

ploughing under moist condition (0.85 PL) than under dry

condition (0.55 PL) (Table 4). This was due to the formation of

wider cracks in the soil of furrow bottom.

3.3. Clod mean weight diameter

The trend in clod MWD showed that a 35% decrease in soil

water content increased the clod MWD by 24% (Table 3).

Ploughing 20 cm deep formed clods significantly smaller in

MWD under moist soil condition (0.85 PL) than under dry soil

condition (0.55 PL) (Table 7). This is in accordance with

Arvidsson et al. (2004) who found that for a heavy soil, the

smallest proportion of coarse clods occurred under moist

conditions, close to the PL. However, for shallow ploughing

(15 cm), similar clod MWD values were produced for both soil

water contents. The shallow soil layer had less hard clods and

was more affected by weathering process than the deeper

layers.

Ploughing with both deep-suck share and trapezoidal share

with sharepoint formed significantly smaller clod MWD when

compared with the serrated shares (Table 3). By serrating the

cutting edge of the plough, the cutting edge height of the

share was increased and that caused large clod formation.

Similarly, Natsis et al. (1999) reported that the size of the soil

clods increased as the thickness of the cutting edge of the

plough increased.

The effect of ploughing depth on clod MWD was not

significant (Table 8). Similar results were observed by other

researchers (Loghavi & Behnam, 1999) when a clay loam soil

was ploughed with a disk plough. However, increasing

ploughing depth tends to decrease clod MWD for all

ploughshare types, except for deep-suck share, in which

the clod MWD tends to increase with increasing ploughing

depth. In 20 cm deep ploughing with the serrated share

equipped with sharepoint, the clod MWD significantly

increased when compared with ploughing with other shares

having sharepoints (deep-suck and trapezoidal shares)

(Table 8). Removing part of the share surface increased the

cutting edge height of the serrated share. This could change

the failure mechanism from shear to tensile. Tensile failure

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Table 10 – Soil water content�ploughshare type inter-action effect on clod sizes X40 mm

Ploughshare type Clod sizesX 40 mm (%, w/w)*

Soil water content

0.11 kg kg�1

(0.55 PL)0.17 kg kg�1

(0.85 PL)

Deep-suck share 21b 20b

Trapezoidal share without

sharepoint

38ab 30ab

Trapezoidal share with

sharepoint

20b 21b

Serrated share without

sharepoint

33ab 22b

Serrated share with

sharepoint

43a 17b




causes less deformation of the soil than shear failure (Aluko &

Seig, 2000).

The soil water content� share type�ploughing depth

interactions were significant (Po0.01) for soil pulverisation.

Under dry conditions (0.55 PL), shallow tilling (15 cm) of the

soil with the serrated-share plough formed significantly

larger clod MWD than the other ploughshare-type treatments

(Table 9). Under moist conditions (0.85 PL), ploughing at

greater depth (20 cm) with the serrated-share plough pro-

duced clod MWD statistically similar to the rest of plough-

share-type treatments. For the serrated share with/without

sharepoint, the smallest clod MWD occurred under moist

conditions for both ploughing depths, while, for the rest of

share types, the MWD for each ploughing depth was

statistically similar under both soil water contents (Table 9).

For the serrated share with sharepoint, the proportion of

coarse clods (X40 mm) was significantly higher under dry

conditions, compared with moist conditions, whereas for the

rest of ploughshare-type treatments, the percentage of coarse

clods was statistically similar for both soil water contents

(Table 10). Lyles and Woodruff (1962) found that a greater

percentage of large clods (438 mm) was produced when a

silty clay loam soil was tilled at 8% compared with 25% (dry

basis) soil water content.

3.4. Possible applications of the results of this experiment

The problems of plough pan formation and reduction in water

infiltration in dryland areas can be alleviated by semi-

ploughing with a plough without mouldboard and replacing

trapezoidal shares with the serrated ones. The serrated

ploughshare offers the potential to increase water infiltration,

and if ploughing is performed under dry conditions, simulta-

neously increases clod size. This in turn leads to reduction of

soil erosion in fallowed lands.

Table 9 – Soil water content � ploughshare type � ploughing(MWD)

Ploughshare type Ploughing depth

Deep-suck share 15

20

Trapezoidal share without sharepoint 15

20

Trapezoidal share with sharepoint 15

20

Serrated share without sharepoint 15

20

Serrated share with sharepoint 15

20

*Means followed by the same letter are not significantly different at prob

PL, plastic limit.

Spoor et al. (2003) stated that the cultivation pans, when

present, play a particularly important role in helping to

protect the subsoil from compaction, and recommended that

these pans or compacted layers should only be disturbed if

they are significantly impeding root development, aeration or

drainage. One alternative solution for not disturbing the

plough pan is by inducing cracks in the soil of the furrow

bottom by ploughing the irrigated farms with the serrated

shares under moist conditions and then letting the cracks be

stabilised by soil drying before secondary tillage operations.

But further studies by measuring water infiltration into the

soil after secondary tillage operations in different soils need

PL, plastic limit.

depth interaction effect on clod mean weight diameter

, cm Clod mean weight diameter*, mm

Soil water content

0.11 kg kg�1 (0.55 PL) 0.17 kg kg�1 (0.85 PL)

17fg 17fg

30cdefg 26cdefg

33bcde 34bcd

31cdef 27cdefg

21defg 25cdefg

19efg 16g

47ab 24cdefg

38bc 23defg

57a 18fg

39bc 16g

ability Po0.05 according to least-significant difference (LSD).

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to be performed to quantify the potential of this measure as

an effective way to increase infiltration.

4. Conclusions

In Iran, the mouldboard plough is usually used to embed

weeds and organic fertilisers, facilitate the seed-bed prepara-

tion and to improve the physical soil condition. The mould-

board plough creates a compacted plough pan, especially

under wet conditions, which reduces water infiltration into

the soil. It was hypothesised that serrations on the plough-

share would increase water infiltration into the soil. The

objective of this study was to assess the effect of serrated and

non-serrated ploughshare types with/without sharepoint on

water infiltration into the soil at two soil water contents and

two ploughing depths. The degree of soil fragmentation after

ploughing with the ploughshare types was also considered.

Based on the presented results, the following conclusions

were drawn:

(1)
The cumulative infiltrations were 12.7 and 5.3 cm per
90 min for serrated share with sharepoint and trapezoidal

share without sharepoint, respectively. The differences in

cumulative infiltration between the serrated share with

sharepoint and the non-serrated shares were attributed

mainly to soil cracking of the furrow bottom.

(2)
The final infiltration rates were 7.4 and 2.3 cm h�1 for
serrated share with sharepoint and trapezoidal share

without sharepoint, respectively. By cutting part of the

trapezoidal share surface and using a sharepoint, the final

infiltration rate was tripled. This increased soil water

infiltration rate was no doubt due to the prevention of

levelling of the soil (smearing) at the tillage depth and

crack formation in the soil of the furrow bottom.

(3)
The increased soil water infiltration into soil ploughed by
the serrated share with sharepoint is useful to reduce the

runoff and erosion hazard.

(4)
Ploughing with the serrated ploughshare at 0.85 of lower
plastic limit gave the largest proportion of small clods,

whereas ploughing with other ploughshare types gave

similar proportions at both dry (0.55 PL) and moist (0.85 PL)

conditions.

Acknowledgments

The authors would like to express gratitude to Vice Chancel-

lor for Research and Research Council of Isfahan University of

Technology for funding this project (No. #1AGD811).

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