Vol.4, No.11 A, 12-18 (2013) Agricultural Sciences
http://dx.doi.org/10.4236/as.2013.411A002
Water infiltration and time to recharge the profile of
three soils Rio Grande do Sul, Brazil
Afranio Almir Righes, Galileo Adeli Buriol, Valduino Estefanel
Environmental and Sanitary Engineering of Franciscan University, Santa Maria, Brazil;
Received 2 September 2013; revised 3 October 2013; accepted 8 November 2013
Copyright © 2013 Afranio Almir Righes et al. This is an open access article distributed under the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
ABSTRACT
The Rio Grande do Sul-RS State, even with av-
erage annual rainfall of 1.721 mm, has shown a
lack of water in the soil for crop production. The
study aimed to determine the variation of an-
nual and seasonal precipitation over the time;
determine the year seasons that can provide the
recharge of water into the soil profile and esti-
mate the time needed to fulfill the soil pore
space with water from effective rainfall with dif-
ferent scenarios of water infiltration. The soil
uses were: oxisol; Red Yellow Podzolic and Pla-
nosolo Hydromorphic Eutrophic respectively in
the North, Centre and South of RS State. We
determined the total variation of annual rainfall,
mean annual potential evapotranspiration and
the time required to refill the soil profile for three
infiltration scenarios: with fractions 1/2, 2/3 and
3/4 of effective rainfall. In the regions of Passo
Fundo, Santa Maria and Santa Vitóriado Palmar,
from 1914 to 2004 there was no reduction in the
annual volume of rainfall. Considering that 50%
of soil volume and water storage are met and
that the fraction 1/2, 2/3 and 3/4 of the effective
rainfall infiltrates into the soil, the recharging
time profile varies from 3.7 to 16.6 years, infil-
trating 2/3 range from 1.8 to 6.6 years and infil-
trating 3/4 of effective precipitation range from
1.2 to 5.1 years, the time required to refill the
entire soil porous space. The recovery of water
storage in the soil profile must occur mainly
during winter, followed by spring and fall.
Keywords: Macro Porosity; Rainfall; Drought; Soil
Water Storage
1. INTRODUCTION
In Rio Grande do Sul (RS) State in Brazil, during the
colder months of the year, all of the territory has excess
water, and in the warmer months, especially in December,
January, and February, droughts occur.
These conditions are more frequent in the southern
area of the state [1]. Normal medium rainfall data indi-
cate that in the southern part of the state, the probability
of potential evapotranspiration is higher than the total
monthly rainfall in the summer months, approximately
70%, but the northern area showed no water deficit [2].
However, despite these results, the deficiencies of soil
water for crops, even in soils more than 8 m deep and
with high water storage capacity, appear to have in-
creased, especially in the northern part of the state. In
this part of the state, at Passo Fundo, the soil type is ox-
isol [3,4]. The soil macroporosity layer of 0.025 m to
0.15 m depth has only 10% of volume in macropores [5].
The mean total annual rainfalls for the north, center,
and south of the state are approximately 2000, 1700, and
1200 mm, respectively [6,7]. The normal values of aver-
age annual potential evapotranspiration range from ap-
proximately 600 mm in Sierra Northeast to 1000 mm in
the Lower Valley of Uruguay [8]. Considering these val-
ues, the areas probably would not have water deficits if
all, or most, of the volume of water precipitated was
stored in the soil and the plant root system could extract
it [9]. Thus, other contributing factors are present, so that
within periods of the same number of days without pre-
cipitation, soil water deficits occur with more intensity.
The intensive soil is mobilized by mechanical equip-
ment, such as plows and harrows, that occurred in the
1970s accelerated the soil structure degradation and in-
creased soil compaction. The intensive soil mobilization
changed its original structure by fractionation of the ag-
gregates into smaller units, reducing the percentage of
organic matter and the percentage of macropores and
increasing the soil bulk density and the volume of mi-
cropores. As a consequence, there is a reduction in the
soil water infiltration rate, resulting in increased runoff
[10-12]. A similar situation has also occurred in areas

A. A. Righes et al. / Agricultural Sciences 4 (2013) 12-18 13
used by livestock with a high number of animals per area.
Being trampled by the animals has compacted on the soil
surface, with hydrological results similar to those of
heavily exploited agricultural areas. Intensive traffic of
agricultural machines and animal trampling in areas with
a crop-livestock system have increased soil compaction.
In this system of management, the use of heavy machin-
ery must be prevented and animals must be removed
from the common crop-livestock area when the soil wa-
ter content is over the range of friability [13].
The biggest problems of water erosion, siltation of riv-
ers, and soil loss in the RS occurred in the 1970s. By that
time, different mechanical techniques were used to con-
trol soil erosion, such as terraces, sub-soiling, and scari-
fications. These techniques were not sufficient to control
soil erosion satisfactorily. Finally, the no-tillage system,
ideal for tropical regions, was introduced. However,
when implemented on degraded soils with impediment
layers (compacted layers with a low rate of water infiltra-
tion) located below the mobilized layer in the conven-
tional tillage system, the no-tillage system reduced water
infiltration into the soil.
The effectiveness of no-tillage in controlling soil ero-
sion led the farmers in the northern region of the RS to
almost entirely removing the existing terraces in their
crops and fields, because of the increased operating ca-
pacity of agricultural machinery and even sowing in the
slope direction. However, the farmers have not used crop
rotation in the no-tillage system. The “foot plow” was
not eliminated and remains in use today. Thus, the no-
tillage system has effectively controlled soil loss, but the
water losses by runoff are even higher than in the con-
ventional tillage system. The losses of nutrients and or-
ganic matter in runoff sediment in the no-tillage system
are higher than those in the same soil with conventional
tillage [14]. Low values of infiltration dramatically re-
duce the water storage in the soil and aquifer recharge,
increasing runoff and flooding. In the north regions of
the RS, in the oxisols mapping units Passo Fundo and
Santo Angelo, most wells with depths between 10 and 15
m are dry during drought periods, and even after heavy
rainfall in the summer time, the water levels do not re-
turn to normal. This shortage is evident that the macro-
pores are not filled with water from rainfall and, as a
consequence, there is little free gravity water to feed the
wells, rivers, and strands. Another finding of this effect
can be seen in road cuts in deep soils, that, during heavy
rainy periods, after only a few hours, there is no more
water to be gravity drained from the soil profile.
This study was conducted in three soil-mapping units
in three regions of the RS, with the following objectives:
1) determine the variation of annual and seasonal pre-
cipitation over time, 2) determine which seasons of the
year effective rainfall can refill the soil water profile, and
3) estimate the time required to fill the pore space of the
soil profile with water available from the effective rain-
fall with different scenarios of water infiltration into the
soil.
2. METHODS
The study was conducted in the north of the RSon the
Passo Fundosoil-mapping unit, classified as oxisol;in the
center of the RS on the São Pedro soil-mapping unit,
classified as red-yellow podzolic loam texture; and in the
south of the RS onthe Vacacaí soil-mapping unit, classi-
fied as planosolo hydromorphic eutrophic, used with
flood-irrigated rice [3,4].
The study of temporal rainfall was done using monthly
and annual totals data from three weather stations: Passo
Fundo (latitude 28˚15'39''S, longitude 52˚24'33''W, and
altitude 678 m), Santa Maria (latitude 29˚41'25''S, longi-
tude 53˚48'42''W, and altitude 138 m), and Santa Vitória
do Palmar (latitude 33˚31'14''S, longitude 53˚21'47''W,
and altitude 6 m), located, respectively, in the north, cen-
ter, and south of the RS. Data were obtained from the
Eighth District of Meteorology (8th DISME) of the Na-
tional Institute of Meteorology (INMET), in Porto Alegre.
The observation period of rainfall for the three sites was
1914 to 2004. From the monthly totals, annual and sea-
sonal monthly averages were obtained, taking into con-
sideration the summer months of December, January, and
February; the autumn months of March, April, and May;
the winter months of June, July, and August; and the
spring months of September, October, and November.
Atthe three weather stations, the rainfall was found to
be of type iso-hygro, the rain is distributed similarly over
the 12 months of the year, and the Spearman correlation
coefficient showed that the rainfall is homogeneous [15].
This coefficient shows that the rainfall is homogeneous
for the three stations, not that the system is iso-hygro.
The iso-hygro quality was checked visually. In a prelimi-
nary exploratory analysis, as suggested by the World Me-
teorological Organization [16], scatter diagrams were
plotted, relating the calendar year to the original data and
also to the centered moving average, with a period of 9
years. To verify the existence of abrupt changes in each
weather station, the historical data series was divided
into two periods and the Mann-Whitney test applied,
comparing the averages of these periods. The dividing
point was held year to year from 1918 to 1998, involving
81 test applications. The year in which the test showed a
lower minimum level of significanceMLSwas considered
the date of abrupt change. A year in which no test had p ≤
0.05 was considered a year of no abrupt changes.
The Spearman correlation coefficient and the Mann-
Whitney nonparametric test were used because rainfall
data do not meet all the requirements of parametric

A. A. Righes et al. / Agricultural Sciences 4 (2013) 12-18
14
equivalent tests, particularly the assumption of inde-
pendence of errors [17].
The potential evapotranspiration (PET) was calculated
by the model of Thornthwaite and Mather [18]. For this,
the average monthly temperatures for the period 1931-
1960 were used [7]. The effective rainfall to refill the soil
profile was obtained by the difference between the rain-
fall computed for the period and average PET, the normal
value for the same period.
To estimate the time needed to fill the soil profiles
with water from the effective rainfall, we used precipita-
tion data and mean values of the soil physical parameters
for water and dates from its mapping-unit descriptions.
These values were obtained from the reconnaissance soil
survey of the RS [4] and experiments performed in the
areas under study [5,19]. The total porosity (Tp), in% of
volume was calculated by Equation (1):

100
100 Sd Tp Pd





, (1)
where Sd is the soil bulk density, and Pd is the particle
density.
The maximum storage of water for each mapping unit,
Equation (2), was determined by considering the depth of
the soil profile:

100
Fc Wp
VSd

dS , (2)
where V is the maximum storage of water (m3·ha−1), Fc
is field capacity (% mass), Wp is wilting point (% mass),
Sd is soil bulk density, S is the area (m2), and d is soil
depth (m).
To estimate the time required to refill the pore space of
the soil profile it was assumed that 50% of the maximum
soil water storage capacity (field capacity less wilting
point) was already filled with water. Three scenarios of-
water infiltration into the soil were simulated using 1/2,
2/3, and 3/4 of the normal average effective precipitation.
The volume needed to fill the macropores (Vmacro = pore
space between field capacity and % of soil water satura-
tion) was calculated, using Equation (3):

100
macro
Tp Fc
V

dS , (3)
where Vmacro is the volume of water needed (m3·ha−1) to
fill the soil macropores, Tp is the total porosity (%
volume), Fc is field capacity (% vol.), d is profile depth
(m), and S is area (m2). If the area S is 10,000 m2, to find
the values in depth of water h (mm) the value Vmacro must
be divided by 10.
3. RESULTS AND DISCUSSION
Figure 1 shows the total annual rainfall scatter points
for the counties of Passo Fundo, Santa Maria, and Santa
Vitóriado Palmarduring the period of 1914-2004 and
average normal values for PET. It shows that for Santa
Maria and Passo Fundo, only in 1917 was the average
PET higher than the total annual rainfall. For Santa
Vitóriado Palmar PET was higher than average rainfall in
4 years. The results in Figure 1 indicate that the volume
of water from rainfall is not the limiting factor for the
lack of water in the soil.
When the existence of sudden changes in precipitation
curves for two observation periods were studied, a
change in the volume of precipitation was found in or
near the year 1981.
After 1981, the averages were higher for the three
weather stations: Passo Fundo, 241.5 mm; Santa Maria,
219.7 mm; and Santa Vitóriado Palmar, 129.1 mm (Table
1). From these results, it is evident that in recent years no
reduction in the volume of rainfall occurred in the three
regions of the RS, although the impacts of drought peri-
ods on water shortages have been higher.
The drought effects that occur today are extremely
more impactfulon crop yields and on base flow of the
riversthan formerly occurred because in that time more
water was probably stored in the soil profile. To analyze
this impact, Table 2 presents the average values of physi-
cal parameters of the soil and water in the three soil-
mapping units used in this work, which form the basis to
simulate future scenarios on the time required for the soil
profile to recover the saturated flow to sustain the
streams and rivers.
In Table 2, the high value for total depth of water
needed to saturate the soil profile for the Passo Fun-
dosoil-mapping unit is because of the 8-meter depth and
high percentage of water storage (10%). The data show
that if the water infiltration rate is not the limiting factor,
this soil can store the total amount of one year’s rainfall
at once. However, that is not possible because of low
infiltration. The estimation of the time required to fill the
pore space of the soil profile with water available from
the effective rainfall with different scenarios of water
infiltration into the soil can be found in Table 3.
When PET values were higher than the effective rain-
Table 1. Average total annual rainfall for the three weather
stations in the RS during the periods of 1914-1981 and 1982-
2004.
1914-1981 1982-2004 Difference
Weather Stations
(mm)
Santa Maria 1672.2 1891.9 219.7
Passo Fundo 1697.1 1938.6 241.5
Santa Vitória do Palmar1204.4 1333.5 129.1
Average 1524.8 1721.3 196.7

A. A. Righes et al. / Agricultural Sciences 4 (2013) 12-18 15
Years
Figure 1. Scatter plots of the total annual rainfall and average annual PET from the meteo-
rological stations of Passo Fundo, Santa Maria, and Santa Vitóriado Palmar.
fall, it was assumed that there was no water storage in
the soil. The recharge of ground water throughout the
year occurs during the winter, followed by spring and
autumn, with reversing spring through autumn in the
Passo Fundo region because of higher values of normal
annual rainfall.
The number of years required to saturate the soil pro-
file can be seen in Figure 2. In the Passo Fundosoil-
mapping unit, considering a scenario in which 1/2 of the
effective rainfall infiltrates the soil, it would take 16.6
years to fill the pores with water. This observation proba-
bly explains why the current droughts have a greater im-
pact on the availability of water in rivers and on slopes
compared with the droughts that occurred before the
1940s. The soil macroporesunder current conditions are
practically empty.
In periods of drought, reducing recharge of macro-
pores has a direct impact on water availability in rivers

A. A. Righes et al. / Agricultural Sciences 4 (2013) 12-18
16
Table 2. Average values of soil physics and hydric parameters of soil-mapping units of Passo Fundo oxisols, Vacacaí planosolo
hydromorphic eutrophic, and São Pedro podzólico hapludox.
County region
Physical parameters1 Passo Fundo Santa Vitória do Palmar Santa Maria
Soil-mapping unit Passo Fundo Vacacaí São Pedro
Depth of soil profile (m) 8.00 1.00 3.00
Field capacity (% mass) 24.00 15.00 19.00
Wilting point (% mass) 14.00 7.00 8.00
Soil bulk density 1.24 1.52 1.41
Particle density 2.69 2.61 2.63
Total porosity (% vol.) 53.90 41.76 46.39
Microporosity (% vol.) 29.76 22.80 26.79
Macroporosity at field capacity (% vol.) 24.14 18.96 19.60
Maximum storage in the soil profile (mm) 992.00 121.60 465.30
Depth of water (50%); maximum storage (mm) 496.00 60.80 232.65
Depth of water to fulfill the soil macroporosity (mm) 1931.47 189.62 587.93
Total depth of water to saturate the soil profile (mm) 2427.47 250.42 820.58
1Source: The values of soil physical parameters used are the average results from published research papers [5,8,19].
Table 3 . Water storage in the soil, normal and effective rainfall, PET, and net storage of water in the soil for the seasons, with three
scenarios and estimation of infiltration recharge of the pore space for the Passo Fundo (oxisols), São Pedro (podzolic hapludox) and
Vacacaí (eutrophic planosolo hydromorphic) mapping units.
Seasons of the Year
Simulated
Scenarios Mapping Unit/Parameters
Spring Summer Autumn Winter
Total
Annual
Passo Fundo Soil (mm)
Total depth of water to saturate the soil profile (mm)*- - - - 2427.5
Normal rainfall (mm) 489.2 439.9 392.8 433.6 1755.5
PET (mm) 213.4 325.3 191.6 107.0 837.3
1/2 Rainfall (mm) 244.6 219.9 196.4 216.8
Net storage in the soil (mm) 31.2 0.0 4.8 109.8 145.8
1/2 of the
precipitation
infiltrates
Time to saturate the soil profile (years) 16.6 years
2/3 Rainfall (mm) 326.1 293.3 261.9 289.1 1,170.4
Net storage in the soil (mm) 112.7 0.0 70.3 182.1 335.0
2/3 of the
precipitation
infiltrates
Time to saturate the soil profile (years) 6.6 years
3/4 Rainfall (mm) 366.9 329.9 294.6 325.2
Net storage in the soil (mm) 153.5 4.7 103.0 218.2 479.4
3/4 of the
precipitation
infiltrates
Time to saturate the soil profile (years) 5.1 years
São Pedro Soil
Total depth of water to saturate the soil profile (mm)*- - - - 820.6
Normal rainfall (mm) 428.8 416.1 430.3 426.8 1702.0

A. A. Righes et al. / Agricultural Sciences 4 (2013) 12-18 17
Continued
PET (mm) 221.9 385.0 216.3 111.0 934.2
1/2 Rainfall (mm) 214.4 208.1 215.2 213.4
Net storage in the soil (mm) 0.0 0.0 0.0 102.4 102.4
1/2 of the
precipitation
infiltrates Time to saturate the soil profile (years) 8.0 years
2/3 Rainfall (mm) 285.9 277.4 286.9 284.5
Net storage in the soil (mm) 64.0 0.0 70.6 173.5 308.1
2/3 of the
precipitation
infiltrates Time to saturate the soil profile (years) 2.7 years
3/4 Rainfall (mm) 321.6 312.1 322.8 320.1
Net storage in the soil (mm) 99.7 0.0 106.4 209.1 415.2
3/4 of the
precipitation
infiltrates Time to saturate the soil profile (years) 2.0 years
Vacacaí Soil
Total depth of water to saturate the soil profile (mm)*- - - - 250.4
Normal rainfall (mm) 280.6 290.3 326.4 324.0 1221.3
PET (mm) 190.0 325.0 204.0 94.0 813.0
1/2 Rainfall (mm) 140.3 145.1 163.2 162.0
Net storage in the soil (mm) 0.0 0.0 0.0 68.0 68.0
1/2 of the
precipitation
infiltrates
Time to saturate the soil profile (years) 3.7 years
2/3 Rainfall (mm) 187.1 193.5 217.6 216.0
Net storage in the soil (mm) 0.0 0.0 13.6 122.0 135.6
2/3 of the
precipitation
infiltrates
Time to saturate the soil profile (years) 1.8 years
3/4 Rainfall (mm) 210.5 217.7 244.8 243.0
Net storage in the soil (mm) 20.5 0.0 40.8 149.0 210.3
3/4 of the
precipitation
infiltrates
Time to saturate the soil profile (years) 1.2 years
*Data taken from Table 2.
Figure 2. Number of years with normal rainfall necessary to
saturate the soil profile of the Passo Fundo, São Pedro, and
Vacacaí mapping units for three scenarios of infiltration, 1/2,
2/3, and 3/4 of the effective rainfall.
and reservoirs. Limited recharging incapacitates these
environments, making them unable to resist the climatic
oscillations that were evaluated by analysis of the time
series of rainfall. The storage capacity depends on soil
water infiltration, pore space, and the depth of the soil
profile. Thus, the stability of the flow in rivers in sum-
mertime depends more on storage in deep soils (oxisols)
than in lowland soils (planosols).
4. CONCLUSIONS
1) In the north, center, and south regions of Rio
Grande do Sul State, based on the data of normal rainfall
in Passo Fundo, Santa Maria, and Santa Vitória do Pal-
mar between 1914 and 2004, there is no reduction in the
annual volume of rainfall.
2) During the summer, the three simulated conditions
showed that there is not enough recharge of soil macro-
pores. The recovery of water storage in the soil profile
must occur mainly in winter, followed by the spring and
fall seasons.
3) In the simulation scenario, infiltrating 1/2, 2/3, and

A. A. Righes et al. / Agricultural Sciences 4 (2013) 12-18
18
3/4 of effective rainfall shows that the time needed to
refill the porous spaces is 16.6, 6.6, and 5.1 years in
Passo Fundo soil, is 8.0, 2.7, and 2.0 years in São Pedro
soil, is 3.7, 1.8, and 1.2 years in Vacacaí soil, respec-
tively.
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