soil management and traffic effects on infiltration of irrigation water applied using sprinklers
TRANSCRIPT
ORIGINAL PAPER
Soil management and traffic effects on infiltration of irrigationwater applied using sprinklers
Hakim Boulal • Luciano Mateos •
Helena Gomez-Macpherson
Received: 1 July 2010 / Accepted: 18 November 2010 / Published online: 11 December 2010
� Springer-Verlag 2010
Abstract Zero tillage and controlled traffic have been
proposed as means for more productive and sustainable
irrigated farming. Both practices affect soil infiltration
characteristics and, therefore, should have effects on
sprinkler irrigation performance. This study compared
water infiltration and runoff in three sprinkler irrigation
tests performed on an alluvial loam soil at different times
during a maize (Zea mays L.)–cotton (Gossypium hirstium
L.) rotation under two soil managements: permanent beds
with crop residue retention (PB: planting beds maintained
unaltered from year to year) and conventional beds with
residues incorporated with tillage (CB: disc and chisel
ploughing followed by rotavator pass and bed forming
every year). Traffic was controlled and two types of fur-
rows were distinguished in both tillage systems: with (?T)
and without (-T) wheel traffic. The irrigation tests were
performed on maize at full cover, on bare soil just before
cotton sowing and on cotton with 50% ground cover.
Infiltration and runoff were affected notably by both traffic
and soil management. The soil under PB infiltrated more
water than under CB, and -T furrows more than ?T
furrows. Considering the combined treatments, -T furrows
in the CB system infiltrated more water than ?T furrows in
the PB system. A sprinkler irrigation model for simulating
water application and soil infiltration and runoff was for-
mulated. The model was used to analyse irrigation per-
formance under infiltration characteristic of the CB and PB
systems in trafficked and non-trafficked furrows. Five
irrigation performance indicators were used to assess the
various combinations of tillage and traffic: Wilkox–Swa-
iles coefficient of uniformity; application efficiency; deep
percolation ratio; tail water ratio; and adequacy. The model
was used to develop operation diagrams and provided
guidelines for making irrigation decisions in the new
controlled traffic/permanent bed system and in a standard
conventional system.
Introduction
Conservation tillage combined with controlled traffic
provides opportunities for more productive and sustain-
able farming (Tullberg et al. 2007). Conservation tillage
may enhance physical and biological soil conditions
(Hulugalle et al. 2007; Verhulst et al. 2010), save energy
by the reduction of soil preparation requirements
(Hernanz et al. 1995), improve irrigation water use
(Tennakoon and Hulugalle 2006) and, in certain envi-
ronments, double cropping is enabled by shortening the
fallow period between crops (Braunack et al. 1995;
Rawson et al. 2007).
Bed or ridge planting is widely used on irrigated land,
especially on levelled soils adapted to furrow irrigation
(Sayre and Moreno 1997). If the field is sprinkler irrigated,
bed planting is less common but sometimes used, as for
low energy precision water application (LEPA systems).
Communicated by T. Trooien.
H. Boulal � L. Mateos (&) � H. Gomez-Macpherson
Instituto de Agricultura Sostenible,
Consejo Superior de Investigaciones Cientıficas,
Alameda del Obispo, 14071 Cordoba, Spain
e-mail: [email protected]
H. Boulal
Departamento de Agronomıa,
Universidad de Cordoba,
Campus Universitario de Rabanales,
14071 Cordoba, Spain
123
Irrig Sci (2011) 29:403–412
DOI 10.1007/s00271-010-0245-1
The advantages of bed or ridge planting include (Unger and
Musick 1990; Sayre and Moreno 1997) the following:
better irrigation efficiency; improved traffic control;
opportunity for precision planting and for planting in moist
soil without placing the seeds too deeply; control of water
logging during germination and emergence; and potential
for decreasing erosion.
In Southern Spain, a combination of sprinkler irriga-
tion and a permanent bed planting system with con-
trolled traffic has been developed successfully at a
commercial farm in the Guadalquivir Valley (Gomez-
Macpherson et al. 2009). In this new system, maize and
cotton crops are rotated on permanent beds, crop resi-
dues are maintained mostly in the bottom of furrows (to
where they are displaced mechanically before planting)
and controlled wheel traffic is followed during all
operations. The aim is maintaining crop residues on the
soil surface and restricting tillage to furrows that are
compacted, i.e., trafficked furrows are deep-ripped when
excessive compaction is observed only, which happens
particularly if cotton harvest takes place when the soil is
wet due to early autumn rains.
An initial evaluation of the new system showed a
tendency for reducing required applied irrigation without
yield penalty (Gomez-Macpherson et al. 2009). Effec-
tively, transformation into a permanent raised bed system
and cumulating crop residues in the furrow bed is
expected to enhance infiltration (Boulal et al. 2008) and
reduce soil evaporation. On the other hand, infiltration in
trafficked furrows would be expected to be less than in
non-trafficked ones, as it has been reported in furrow
irrigation experiments (Kemper et al. 1982; Allen and
Musick 1992; Undersander and Regier 1988). Therefore,
the innovative soil management system described earlier
has implications on irrigation water infiltration and run-
off—and thus on irrigation performance—that must be
examined before providing irrigation advice. Further-
more, the infiltration variability introduced by controlled
traffic (that compacts wheel furrows while non-trafficked
furrows remain unaltered) adds to the natural variability
of the infiltration characteristics of irrigated land
(Oyonarte et al. 2002), which in turn depends on the soil
management system.
The objectives of this research were, firstly, to assess
experimentally the effects of permanent beds versus con-
ventional-till beds, both with controlled traffic, on sprinkler
irrigation infiltration and runoff, and, secondly, to simulate
sprinkler irrigation performance under the soil conditions
derived from the previously compared soil managements.
Complementarily, the paper also provides diagrams for the
operation of irrigation (determination of water depth and
application rate) under conventionally tilled and permanent
raised bed systems, the last under controlled traffic.
Materials and methods
Experimental field, tillage systems and controlled
traffic
The tests were performed at the Alameda del Obispo
experimental farm (latitude 38�N, longitude 5�W, altitude
110 m), Cordoba, Spain. The climate is Mediterranean
with mean annual rainfall of 595 mm. The soil at the
experimental farm was a Typic Xerofluvent (Soil Survey
Staff 2010), with loam texture, and without apparent
restriction for root growth to 3 m depth. Estimated water
content at field capacity was 0.24 cm3 cm-3, and at wilting
point, 0.12 cm3 cm-3. Typical irrigation depth in this soil
is 80 mm. Greater depths lead to significant runoff due to
infiltration restrictions caused by soil surface sealing.
The experimental field (144 9 54 m) was divided into
three 144-m-long, 18-m-wide blocks (replications).
A cotton (Gossypium hirstium L.)–maize (Zea mays L.)–
cotton rotation was followed in an experimental field dur-
ing 2007, 2008 and 2009 with clean fallow periods between
crops. The field was ploughed (a double pass of discs, a
single pass of chisel and a single pass of rotavator) on 20
April 2007, and beds were put in place three days later.
Cotton was sown on 9 May and hand-picked on 27 Sep-
tember of the same year; 4 months after the cotton harvest,
the standing residues were chopped. In February 2008,
each of the three blocks was divided into two plots, each
consisting of ten 0.85-m-spaced furrow/bed sets, and two
tillage treatments, permanent beds system (PB) and con-
ventional beds system (CB), were established using a
randomised block experimental design with three replica-
tions. In the PB system, crop residues were left on the soil
surface after harvest, and the planting beds were main-
tained unaltered from year to year; in the CB system, the
soil was ploughed and crop residues incorporated, and the
beds formed every year. The CB plots were then ploughed
(a double pass of discs followed by a single pass of chisel)
and the beds formed (on 13 February 2008). Maize was
sown on 19 March 2008 and machine harvested on 17
September 2008. In late February 2009, crop residues were
chopped and left on the soil surface in PB while, in CB,
they were incorporated in the soil (a pass of chisel followed
by rotavator) before forming the beds on 16 March 2009. A
second cotton crop was sown on 14 May and hand-picked
on 29 September 2009.
Traffic was controlled. Since the separation between
tractor wheels was 1.70 m, twice the separation between
furrows, furrows with wheel traffic (?T) alternated with
furrows without (-T). In PB, non-traffic furrows (PB-T)
were not travelled by wheels during the whole experi-
mental period. In CB, soil was tilled every year but,
nonetheless, the two types of furrows were demarcated
404 Irrig Sci (2011) 29:403–412
123
after the beds were formed, that is, CB-T furrows were not
travelled during the season until soil preparation the fol-
lowing year.
Not all trafficked furrows supported the same number of
tractor wheel passes: all ?T furrows supported soil culti-
vation, sowing, residues chopping and harvesting opera-
tions, while only some were travelled also when spraying
the crop. The number of wheel passes per year in trafficked
furrows was between 5 and 9.
Irrigation tests
Three sprinkler irrigation tests were carried out in the
central block of the experimental field on the following
dates: 6 August 2008 (Test 1), when the maize crop was
close to maturity; 23 April 2009 (Test 2), with bare soil
recently prepared for cotton sowing; and 13 July 2009
(Test 3), when the cotton crop had an average ground cover
of 50%.
The slope of the test block was 0.8%. Three irrigation
laterals were used, two along the borders of the block and
the third down the centre. Laterals were spaced 9 m with
sprinklers at 12 m. The sprinklers (VYR-60) had two
nozzles of 4.36 and 2.38 mm in diameter. The sprinklers
reached 24 m and discharged 1,560 L h-1, at a pressure of
3.45 kg cm-1. The sprinklers in the laterals along the
border were set to operate with an angle of 1808, with the
wet semicircle towards the test block.
Applied depth was measured using 40 catch containers
distributed in five transects across the block. An ane-
mometer installed next to the experimental field automat-
ically recorded wind speed and direction during the
irrigation tests. Application rate varied slightly from test to
test: 0.28, 0.26 and 0.30 mm min-1 in Tests 1, 2 and 3,
respectively. The duration of the three irrigation tests were
as follows: 745 min (Test 1), 300 min (Test 2) and
513 min (Test 3).
Runoff rate was measured periodically using long-
throated flumes of trapezoidal cross-section with sill width
equal to 100 mm (Clemmens et al. 1984). The flumes were
installed near the tail of every furrow (132 m from the
head) except borders, i.e., there were 8 monitored furrows
per treatment, 4 in non-traffic furrows and 4 in traffic
furrows. The replications of CB?T and CB-T that were
located at the eastern side of the experimental block were
discarded in Test 2 due to wind blowing from the east that
reduced precipitation rate on those furrows. In fact, Test 2
lasted 5 h only because of wind persistence.
Cumulative infiltration was obtained from the difference
between water application (obtained from measured aver-
age applied depth and irrigation time) and runoff.
Note that the irrigation tests were performed in the central
block of the experiment. Therefore, the randomised block
design was not applicable to the statistical analysis of infil-
tration and runoff data. However, having 8 controlled fur-
rows (four trafficked and 4 non-trafficked) in the two soil
management plots allowed performing statistical analysis
based on the factorial approach (Snedecor and Cochran
1980), with two factors: soil management (PB or CB) and
furrow traffic (-T or ?T), and four replications (furrows)
per treatment. Pairwise comparison tests of infiltration,
runoff and time to runoff initiation for the soil management
and traffic treatments were performed using the freeware
statistical analysis program Statistix 9 (http://www.statistix.
com/).
Irrigation performance simulation
Several sprinkler irrigation simulation models have been
reported in the literature (e.g., Carrion et al. 2001; Mateos
1998; Andrade and Allen 1999). All of them dealt with
water distribution but not with infiltration once water
reaches the soil, making them unsuitable for the purpose of
this study. Therefore, a new model that simulates sprinkler
irrigation in two steps, (1) application and (2) infiltration,
was developed.
The simulated field application distribution resulted
from overlapping the precipitation patterns of individual
sprinklers in a fixed system. The sprinklers were VYR-60
as those used in the experimental study. The sprinkler
laterals were spaced 11.9 m (14 furrows separated 0.85 m)
and the sprinklers along the laterals, 12 m. The distribution
pattern of single sprinklers was assumed to match shape 3
of Appendix A in Mateos (1998). The application rate was
calculated at 1-m intervals along each furrow in each
simulated field.
The hypothetical field consisted of alternating traffic and
non-traffic furrows. Both permanent and conventional bed
systems were simulated.
When infiltration was supply controlled (i.e., while the
application rate was less than the potential infiltration rate),
cumulative infiltration (I, mm) was calculated as the
application rate (r, mm min-1) times the irrigation time (t,
min). Once the application rate exceeded the potential
infiltration rate (which occurred at time t = tro, being trothe time to runoff initiation), I resulted from adding to the
cumulative infiltration at tro (i.e., r 9 tro) the difference
between cumulative infiltration at the time considered and
cumulative infiltration at tro. Using Horton’s equation,
I was expressed as:
I ¼ rt if t\tro ð1aÞ
Irrig Sci (2011) 29:403–412 405
123
I¼ rtroþ if t� troð Þþ r0 � ifk
e�k tro�t0roð Þ�e�k t�t0roð Þh i
if t� tro
ð1bÞ
where r (mm min-1) is the application rate for a particular
simulation; r0 (mm min-1) is the application rate during the
experimental test used for adjusting the parameters in
Horton’s equation; t0ro (min) is the time at which runoff
started during that experimental test; if (mm min-1) is the
steady-state potential infiltration rate; and k is a dimen-
sionless soil parameter that describes the rate of decrease in
potential infiltration rate.
An infiltration equation was assigned to each 1-m fur-
row segment. Furrow-averaged if was generated randomly
using the Monte Carlo method assuming a normal fre-
quency distribution with mean and standard deviation
obtained in the experimental tests. Furrow segment if was
generated using the same method although entering in the
simulation of random values the previously obtained fur-
row-averaged if and a standard deviation obtained in the
same experimental field by Oyonarte et al. (2002). Since
t0ro presented some correlation with if (Fig. 1), for sim-
plicity, t0ro was calculated from if. Note that data from Test
2 were not used in this relationship because irrigation time
in this test was not long enough for the infiltration rate
achieving steady state. The parameter k was then computed
for each furrow segment as:
k ¼ 1
t0roln
io � if
r0 � ifð2Þ
where io (mm min-1) is the initial potential infiltration rate.
For simplicity, a constant value of io = 1 mm min-1 was
chosen for all furrow types after fitting all experimental
data simultaneously.
Cumulated runoff was calculated over time and for each
simulated furrow by adding, if positive, the difference
between application rate and infiltrability in each furrow
segment.
Five irrigation performance indicators were then com-
puted: Wilkox–Swailes coefficient of uniformity
(WSCU = 1 - CV, with CV the coefficient of variation of
infiltrated depth; Wilcox and Swailes 1947); application
efficiency (AE); deep percolation ratio (DPR); tail water
ratio (TWR); and, adequacy (Ad). AE is defined as the
fraction of applied water stored in the root zone. DPR and
TWR are the fractions of applied water going to percola-
tion and tail water runoff, respectively. Adequacy, Ad, is
the fraction of the root zone that is filled to field capacity
with irrigation water. The numerator of DPR was calcu-
lated by cumulating the values of the positive differences
between the infiltrated depths and the required depth (Dreq).
WSCU was computed for both applied water (WSCUapp)
and infiltrated water (WSCUinf).
AE and Ad are key irrigation performance indicators
that are widely used (e.g., Burt et al. 1997). DPR and TWR
are suitable indicators for determining the fate of water
losses (Walker and Skogerboe 1987). Uniformity is com-
monly expressed as distribution uniformity based on the
low-quarter depth (Burt et al. 1997); however, WSCU was
preferred because it has more statistical meaning than other
uniformity indicators (Mateos 2006).
Operation diagrams were produced by running the
model multiple times, varying application depths and rates,
and computing the five performance indicators. Isolines of
selected values of the performance indicators were gener-
ated by triangulation with linear interpolation, using the
Surfer 9.2 surface mapping software (Golden Software
Inc., Golden, Colorado, US).
Results and discussion
Experimental results
In Test 1, cumulative infiltration increased more rapidly in
furrows with no wheel traffic than with traffic and more
rapidly in PB than in CB. Thus, at the end of the test, the
total cumulative infiltration was highest in PB-T and
lowest in CB?T (Table 1). Comparison assuming a 2 9 2
factorial design showed that the difference between
cumulative infiltration at the end of the test was statistically
significant for both tillage systems (P \ 0.05) and furrow
traffic (P \ 0.01). Interestingly, wheel traffic resulted in
similar infiltration in PB?T, after 2 years of traffic and
leaving crop residues on the soil surface, and in CB?T,
after only 1 year of operations but incorporating residues in
the soil (158 and 149 mm, respectively).
In Test 2, when irrigation was applied on bare soil just
before cotton sowing, the effect of the tillage system was
t' ro (min) = 2533.3 i f (mm min-1
) - 117.37
r2 = 0.6062
0
100
200
300
400
500
600
700
0.05 0.10 0.15 0.20 0.25
Final infiltration rate (mm min-1)
Ru
no
ff in
itia
tio
n t
ime
(min
)
Test 1
Test 3
Fig. 1 Relationship between the time to runoff initiation and the
steady-state potential infiltration rate during Test 1 and Test 3
406 Irrig Sci (2011) 29:403–412
123
evident in trafficked furrows but inappreciable in non-
trafficked ones: CB?T produced considerable runoff,
while CB-T did not produce any runoff; PB?T produced
little runoff and PB-T did not produce any runoff
(Table 1). Irrigation duration in Test 2 was only 5 h, the
shortest of the three tests (Table 1), due to excessive wind.
It is likely that longer irrigation duration would have pro-
duced some runoff in non-trafficked furrows also. Despite
its short duration, however, the test was capable of
detecting statistically significant infiltration increases as a
consequence of either having permanent beds or preventing
wheel traffic (P \ 0.05 and P \ 0.01, respectively).
In Test 3, where crop cover was 50%, the infiltration rate
was smaller and runoff initiation began earlier than in Test
1 (Table 1). Otherwise, the four tillage–traffic combina-
tions were similar in both tests. At the end of Test 3
(duration 513 min), the trafficked furrows had accumulated
25 and 33% less infiltration than the non-trafficked furrows
in PB and CB, respectively (differences significant at
P \ 0.01); and the CB system had cumulated 21 and 12%
less infiltration than the PB system in ?T and -T,
respectively (differences significantly different with
P \ 0.01).
It is important to note that in none of the three tests was
a tillage system/furrow traffic interaction detected.
Runoff starting time varied from test to test (Table 1). If
we look first at the tests performed in the presence of a crop
(Tests 1 and 3), runoff started later under the maize crop
than under the cotton (Table 1). Application rate was
slightly greater during Test 3, which may explain at least
part of this difference. However, final infiltration rate was
greater in Test 1 than in Test 3 in all treatments except
PB-T, and therefore, factors other than application rate
differentiated these two tests.
Residues in the furrows should retard water runoff and
facilitate infiltration (Green et al. 2003). In our case, the
amount of residues on the PB furrows was greater during
Test 3 than during Test 1 (maize produced more residues
than cotton) but its benefits might have been cancelled by
reduced infiltration with surface compaction in PB?T.
Because of their dissimilar architecture, one could
expect that maize plants would concentrate on the plant
bed more precipitation than cotton plants (Bui and Box
1992; Dekker and Ritsema 1997; Levia and Frost 2003). If
infiltration rate on the plant bed was greater than on the
furrow bottom (Paltineanu and Starr, 2000), then infiltra-
tion under maize would be greater than under cotton,
explaining differences between Tests 1 and 3.
Additionally, soil conditions were likely different in
Tests 1 and 3. Untouched furrows (PB-T) maintained their
final infiltration rate; but final infiltration rate decreased in
PB?T and CB from Tests 1–3. Tillage and wheel traffic
history must have affected final infiltration rate in PB?T
and CB, but our data were insufficient to discern the par-
ticular physical mechanisms that operated in the soil in
these treatments.
Irrigation performance simulation results
Simulations were run for the soil conditions in Test 3.
Simulated cumulated infiltrations for the four tillage/traffic
combinations were 121, 153, 99 and 129 mm in PB?T,
PB-T, CB?T and CB-T, respectively. The similarity of
these values with the corresponding measured values
(Table 1) gave confidence for using the model to simulate
alternative irrigation conditions.
Table 2 presents the selected performance indicators
computed for four irrigation conditions: relatively low and
high application rates (0.15 and 0.4 mm min-1) combined
with two applied depths (D, mm). The depths were D = 76
and D = 137 mm, the first being close to the required
depth (80 mm) and the second 70% higher than the
Table 1 Irrigation duration,
time to runoff initiation (t0ro),
total runoff, total infiltration and
steady-state potential infiltration
rate (if) in the four combination
of tillage (permanent bed, PB,
and conventional bed, CB,
systems) and furrow wheel
traffic (with traffic, ?T, and
without traffic, -T) tested
Values are average; standard
errors are in brackets
Test Duration
(min)
Treatment t0ro(min)
Runoff
(mm)
Infiltration
(mm)
if(mm min-1)
Test 1 745 PB?T 188 (24) 53 (8) 158 (8) 0.20 (0.02)
PB-T 608 (108) 8 (3) 202 (3) 0.23 (0.01)
CB?T 241 (30) 61 (14) 149 (14) 0.13 (0.03)
CB-T 433 (98) 23 (13) 182 (13) 0.19 (0.02)
Test 2 300 PB?T 113 (1) 4 (1) 72 (1) 0.24 (0.02)
PB-T – – 77 (0) –
CB?T 112 (15) 19 (8) 58 (8) 0.14 (0.03)
CB-T – – 77 (0) –
Test 3 513 PB?T 189 (35) 46 (21) 110 (21) 0.13 (0.08)
PB-T 412 (46) 13 (9) 147 (10) 0.23 (0.07)
CB?T 120 (8) 69 (24) 87 (24) 0.10 (0.07)
CB-T 290 (54) 26 (7) 130 (7) 0.14 (0.04)
Irrig Sci (2011) 29:403–412 407
123
required depth. Simulations were run for these four irri-
gation conditions and the four possible tillage/traffic
combinations as well as alternating furrows-type combi-
nations (PB-T?T and CB-T?T).
Simulated WSCUapp was 0.957, a constant value for the
sprinkler type and layout used. WSCUapp was equal to
WSCUinf only in PB-T, the treatment where infiltration was
most favoured, and in CB-T with D = 76 mm. With low r,
low applied depth and high soil infiltration capacity, infil-
tration tends to be supply controlled, and therefore, infiltra-
tion uniformity is basically determined by the application
distribution uniformity. At the extreme, infiltration unifor-
mity equals application distribution uniformity.
Conversely, infiltration is soil controlled with high r,
high D and low soil infiltration capacity. Under these
irrigation conditions, infiltration uniformity is determined
by the variability of soil hydraulic properties, the shape of
the potential infiltration rate curve, and the application
distribution uniformity. [Note that for homogeneous water
application, high or relatively high r (thus r [ if) and long
irrigation duration, infiltration variability would tend to
equal the variability of if.] Therefore, in these circum-
stances, irrigation infiltration uniformity is the result of the
combined effects of irrigation and soil management.
Moreover, controlled traffic introduces further variation.
In consequence, the lowest WSCUinf of the four irrigation
conditions compared in Table 2 occurred in CB-T?T with
r = 0.40 mm min-1 and D = 137 mm (WSCUinf =
0.837). Observe that this uniformity was lower than the
uniformity for the same planting system and irrigation con-
ditions with either all trafficked (CB?T) or non-trafficked
furrows (CB-T).
When infiltration is predominantly supply controlled, a
great part of the applied water infiltrates and little runoff is
produced. DPR becomes important when D is high, and
even more when combined with low r as in the case of
r = 0.15 mm min-1 and D = 137 mm in Table 2. In these
conditions, the soil basically did not intervene in the
Table 2 Infiltration Wilkox–Swailes coefficient of uniformity
(WSCUinf); application efficiency (AE); deep percolation ratio
(DPR); tail water ratio (TWR); and adequacy (Ad) for the four
irrigation conditions resulting from combining application rates 0.15
and 0.4 mm min-1 and applied depths 76 and 137 mm, and two soil
managements (permanent, PB, and conventional beds, CB) either
with only one type of furrow wheel traffic (?T) or without (-T) or
with both types (?T-T)
WSCUinf AE
0.15,76 0.15,137 0.40,76 0.40,137 0.15,76 0.15,137 0.40,76 0.40,137
PB-T 0.957 0.957 0.957 0.958 0.995 0.585 0.995 0.585
PB?T 0.937 0.912 0.930 0.882 0.971 0.584 0.957 0.582
PB-T?T 0.943 0.920 0.937 0.871 0.983 0.585 0.976 0.584
CB-T 0.957 0.944 0.957 0.922 0.990 0.585 0.982 0.585
CB?T 0.910 0.895 0.902 0.865 0.895 0.584 0.869 0.573
CB-T?T 0.913 0.878 0.903 0.837 0.942 0.584 0.926 0.579
DPR Ad
0.15,76 0.15,137 0.40,76 0.40,137 0.15,76 0.15,137 0.40,76 0.40,137
PB-T 0.005 0.415 0.005 0.395 0.946 1.000 0.946 1.000
PB?T 0.002 0.341 0.001 0.223 0.922 1.000 0.910 0.996
PB-T?T 0.004 0.378 0.003 0.309 0.934 1.000 0.928 0.998
CB-T 0.003 0.381 0.002 0.270 0.940 1.000 0.933 1.000
CB?T 0.000 0.219 0.000 0.092 0.850 0.999 0.826 0.981
CB-T?T 0.002 0.300 0.001 0.181 0.895 1.000 0.880 0.990
TWR
0.15,76 0.15,137 0.40,76 0.40,137
PB-T 0.000 0.000 0.000 0.020
PB?T 0.027 0.075 0.042 0.195
PB-T?T 0.013 0.037 0.021 0.107
CB-T 0.007 0.034 0.016 0.145
CB?T 0.105 0.197 0.131 0.335
CB-T?T 0.056 0.116 0.073 0.240
408 Irrig Sci (2011) 29:403–412
123
control of infiltration in the treatment where infiltration was
most favoured (PB-T). On the contrary, under predomi-
nantly soil-controlled infiltration, high D and r will
increase runoff. TWR was insignificant in PB-T and
highest in CB?T with r = 0.40 mm min-1 and
D = 137 mm. In the controlled traffic systems (-T?T),
TWR took intermediate values between the corresponding
hypothetical systems with all furrows either trafficked
(?T) or non-trafficked (-T) (Table 2).
As expected, the two irrigation variables (r and D) pri-
marily affected AE. AE took high values when D = 76 mm
and a low but constant value when D = 137 mm but,
interestingly, AE was little affected by soil management. In
the soil management treatments in which deep percolation
was important, runoff was insignificant, and vice versa, when
runoff was important deep percolation was insignificant,
resulting therefore in similar AE (Table 2).
Globally, Ad was high (Table 2). Only the CB?T and
CB-T?T treatments with D = 76 mm resulted in
Ad \ 0.9. Given the infiltration limitation due to the soil
surface conditions, an applied depth of 76 mm was insuf-
ficient to fill the soil profile up to field capacity.
The simulation results discussed earlier helped to under-
stand the interaction between soil and irrigation management
but were restricted to very specific conditions. More practical
simple calculations (done using common computer spread-
sheets) can be used to develop operation diagrams for irri-
gation management under different soil management
systems. Example diagrams are presented in Figs. 2, 3 and 4
for the new permanent bed/controlled traffic system
(PB?T-T) and for the extended conventional bed system
(CB?T). The soil conditions were the same as in the
experimental field and the sprinkler spacing as in the previ-
ous simulations. The operation diagrams were developed for
practical ranges of application rate and applied depth and for
a required depth equal to 80 mm. This depth is appropriate
for the deep loamy soils of the Guadalquivir valley and
practical for summer crops in this climate since it results in
irrigation intervals between 10 and 15 days and in irrigation
durations typically between 6 and 8 h. The diagrams present
isolines for WSCUinf, TWR and DPR (Figs. 2, 3 and 4,
respectively). Grey colour indicates the region in the dia-
grams where adequacy is less than 0.95 and, therefore, the
combinations of operation variables that should be avoided if
deficit irrigation is not desired. The un-shaded area repre-
sents the conditions of adequate irrigation.
An example of how the diagrams may be used follows. In
either PB?T-T or CB?T, maximum uniformity may be
achieved with low application rate only (Fig. 2). In addition,
adequate irrigation in CB?T may be achieved with values of
D close to the required depth only if r is small (Fig. 2b).
However, farmers prefer application rates that allow com-
pleting the irrigation in a short time. For instance, applying
90 mm at a rate of 0.15 mm min-1 would take 10 h but the
same depth applied at 0.25 mm min-1 would take 6 h only
(points marked with 9 in Figs. 2, 3, 4). In CB?T, the
reduction of irrigation time would be at the cost of increasing
TWR from 0.13 to 0.19 and entering into the grey region
where irrigation is inadequate (Fig. 3b); on the other hand,
deep percolation would be slightly reduced, from 0.03 to
about 0.02 (Fig. 4b). The farmer would then need to take
environmental considerations in the decision: First, will the
Fig. 2 Isolines of the Wilkox–Swailes coefficient of uniformity for
infiltrated water (WSCUinf) in the applied depth-application rate plan
for a the controlled traffic and permanent bed system (PB-T?T) and
b the conventional bed system (CB?T). Grey area indicates the
region where adequacy is less than 0.95, assuming required depth is
80 mm. Sprinklers spacing: 11.9 9 12 m; sprinkler type: VYR-60
Irrig Sci (2011) 29:403–412 409
123
runoff rate cause erosion if r = 0.25 mm min-1? Second, is
preserving groundwater more important than preserving
surface water?
The answer to the first question would be positive more
likely under CB?T than under PB?T-T. Moreover, the
same combination of r and D in PB?T-T would result in
lower TWR and higher DPR than in CB?T. Given that
PB?T-T should cause less erosion than CB?T, r could be
further increased because for D & 90 mm DPR is rather
insensitive to r, and it will take a constant value of about
0.09 (Fig. 4a). By increasing r, TWR would increase
slightly (Fig. 3a), but irrigation duration would reduce
proportionally to the increase in r while WSCUinf would
stay in the interval 0.92–0.93 (Fig. 2a).
Although r may be varied within certain limits by modi-
fying working pressure or substituting sprinkler nozzles, the
Fig. 3 Isolines of the tail water ratio (TWR) in the applied depth-
application rate plan for a the controlled traffic and permanent bed
system (PB-T?T) and b the conventional bed system (CB?T). Greyarea indicates the region where adequacy is less than 0.95, assuming
required depth is 80 mm. The two 9 marks in each figure indicate the
location of the points discussed in the text. Sprinklers spacing:
11.9 9 12 m; sprinkler type: VYR-60
Fig. 4 Isolines of the deep percolation ratio (DPR) in the applied
depth-application rate plan for a the controlled traffic and permanent
bed system (PB-T?T) and b the conventional bed system (CB?T).
Grey area indicates the region where adequacy is less than 0.95,
assuming required depth equal to 80 mm. The two 9 marks in each
figure indicate the location of the points discussed in the text.
Sprinklers spacing: 11.9 9 12 m; sprinkler type: VYR-60
410 Irrig Sci (2011) 29:403–412
123
range of variation is narrow unless sprinkler spacing is
modified. But if so, the application distribution pattern would
change. We acknowledge that the r-D region represented in
the operation diagrams goes beyond what in reality may be
achieved without modifying the sprinkler spacing.
Conclusions
Infiltration and runoff were affected notably by traffic and
soil management. More water infiltrated the soil in per-
manent than in conventionally tilled beds that are reformed
each year. Regardless of tillage system, water infiltration
was reduced by traffic.
Therefore, irrigation management practices that have
been identified as appropriate for a soil management that
does not introduce soil infiltration variation across the field
should not be applied under this new system of permanent
beds with controlled traffic. Controlled traffic is an addi-
tional source of infiltration variability that complicates
identifying the best irrigation management practice for
given soil management conditions.
Farmers have to evaluate sprinkler irrigation conditions
(namely application rate and duration) that lead to irriga-
tion adequacy and application efficiency. Moreover, simi-
lar application efficiency may be achieved either by
minimising deep percolation or tail water runoff. And,
therefore, the decision has to balance the environmental
effects of each scenario. The operation diagrams developed
as part of this study provide technically sound guidelines
for making such decisions for both conventionally tilled
and permanent raised bed systems with controlled traffic.
Acknowledgments This research was funded by a grant from the
Spanish Ministry of Education and Science, project AGL2005-05767.
H. Boulal received a grant from the Spanish Agency of International
Cooperation and Development (AECID). We thank I. Carmona, M.
Salmoral, R. Luque, A. Cornejo and O. Medina for field assistance.
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