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Subsoiling improves conservation tillage in cereal production of severely degradedAlfisols under Mediterranean climate
Ingrid G. Martínez a, Christian Prat b, Carlos Ovalle a,⁎, Alejandro del Pozo c, Neal Stolpe d, Erick Zagal d
a Instituto de Investigaciones Agropecuarias INIA, Casilla 426, Chillán, Chileb Institut de Recherche pour le Développement IRD, Laboratoire d'étude des Transferts en Hydrologie et Environnement, BP 53, 38041 Grenoble Cedex 9, Francec Universidad de Talca, Facultad de Agronomía, Av. Vicente Méndez 595, Chillán, Chiled Universidad de Concepción, Facultad de Agronomía, Av. Vicente Méndez 595, Chillán, Chile
Central Chile has a Mediterranean climate with a mean annual precipitation of 695 mm, 80% concentrated inwinter. In this context, water erosion and inappropriate agricultural management along hillslopes are the majorcauses of soil degradation. From 2007 to 2010, different agricultural systems were compared: conservation tillagewith stubble retained: no tillage (Nt), Nt+subsoiling (Nt+Sb), Nt+barrier hedges (Nt+Bh) and Nt+contourplowing (Nt+Cp). All the systemswere compared to conventional tillage (Ct)without crop stubble on the surface.The runoff plots were 50 m×20 m on a hillside with 12.5% slope in an oat–wheat crop rotation. Runoff, sedimentand nutrient losses measured for every rainfall event, occurred during winter months when rainfall energy wasalso the highest of thewhole year. Conservation tillage systemsmitigatewater erosion compared to the Ct system.In heavy rains, conservation tillage systems reduced soil loss by more than 72% compared to Ct. In addition, therunoff coefficient during the rainy period was 70% lower in conservation tillage systems when the crop was at theinitial tillering stage and 90% lower at final tillering. These results show the importance of conservation tillage andcrop stubble to decrease erosion, especially in yearswhen extremeprecipitation presented a high potential for soilerosion. Moreover, cereal production showed higher biomass and grain yield in Nt+Sb. It was concluded that notillage with stubble retained on the surface was the best option to mitigate soil erosion. However, the effects ofsubsoiling decrease over time, making new subsoiling necessary with the implied costs. Due to the strongfluctuations in the prices of the agricultural products, it is impossible to estimate the balance of costs/benefits ofthis system. On other hand, the duration of the experimentmay have been too short tomeasure the real impacts ofno-tillage practices.
Many Alfisols in semi-arid regions are characterized by severeproblems of water erosion, soil compaction and crusting, which reduceinfiltration and increase runoff (Rao et al., 1998; Salako et al., 2006). As aconsequence, runoff not only limits water availability for crops but alsogreatly increases the risk of erosion (Rao et al., 1998). Today soil erosionis a global problem with severe economic and environmental impacts.All predictivemodels indicate an upward trend in the intensity of rainfallwith the increased effects of greenhouse gasses (IPCC, 2007). It has beenfound that a change in the amount and intensity of precipitation has asignificant effect on soil erosion and runoff. Specifically, when precip-itation changes by 1%, it results in a 2.4% change in soil loss and a 2.5%change in runoff (Pruski and Nearing, 2002).
On arable land, tillage erosion induces displacement of surface soilfrom higher to lower parts of the landscape (Adekalu et al., 2006), with
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severe impacts on soil organic matter and nutrients (De Gryze et al.,2008). This impact reduce crop yield due to changes in the physicaland chemical characteristic of the soils (Dexter, 2004). Thus, waterand tillage erosion clearly interact to landscape disturbance increasingerosion rates.
In the Mediterranean climate of central Chile, with a rainfall of690 mm (80% concentrated in winter and autumn), both processesare the major causes of this type of soil degradation (Ovalle et al.,1999). This landscape is dominated by the “espinal” agroecosystemof Acacia caven (Molina), which shows low productivity (Martínezet al., 2010; Ovalle et al., 2006). A recent study, showed that 48.9% ofthe land is affected by some degree of erosion; 19% severely eroded,30% highly eroded, 28% moderately eroded and 23% slightly eroded(CIREN, 2010). As a consequence, soils are highly compacted, withlowwater holding capacity and low crop yields. Therefore, the use ofconservation tillage techniques is necessary to mitigate the erosionprocesses in these highly vulnerable areas (De Gryze et al., 2008;Govers et al., 2006).
Erosion studies in Chile have mainly evaluated surface runoff,sediment and nutrient loss. However, these evaluations include no
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tillage management without considering additional practices in order tosolve compactionproblems.Many authors have reported the effects of notillage with subsoiling which improve yield, soil moisture and reducingrunoff (Jin et al., 2008), while others have studied management optionslike contour plowing and barrier hedges which have shown the increaseof soil's ability to store water and improve infiltration (Gebreegziabheret al., 2009; Nyssen et al., 2000; Pansak et al., 2008).
Moreover, local evaluations using the USLE model to determinethe erosion index (Wischmeier and Smith, 1978) were based in plotswith dimensions that range between 40 and 100 m2, with a length lesserthan 20 m (Joel et al., 2002; Peña, 1986; Rodríguez et al., 2000). Thisapproach is not appropriate to our conditions and/or Mediterraneanclimates (Casalí et al., 2008; Gumiere et al., 2009), where the single rainevents and its intensity are most relevant.
Our objectives were to evaluate: (i) surface runoff under fourconservationist systems compared to the traditional tillage system,(ii) to quantify soil and nutrient loss, and (iii) their relationship to cropproductivity. The evaluation was conducted on 1000 m2 plots with asloping length of 50 m.
2. Material and methods
2.1. Study site and field experiment description
The study area is located in a dryland area at the CauquenesExperimental Center of the Agricultural Research Institute (INIA) in thesouth of central Chile (35° 97′S, 72° 24′W),Maule Region. The area has asub-humidMediterranean climatewith an average annual precipitationof 695 mm (80% concentrated in winter), with five months of drought(Del Pozo and Del Canto, 1999). The principal climatic characteristics ofthis area observed during the last 29 years are presented in Fig. 1. Soilsare Alfisols of the Cauquenes type, classified as Ultic Palexeralfs (Stolpe,2006). The soil is made up of materials of granite origin with moderateacidic conditions and low organic carbon (O.C.) (Table 1). Soil-profile
Precipitation Evaporation
Jan Feb Mar AprMay Jun Jul Aug Sep Oct Nov Dec
50
100
150
200
250
(a)
Precipitation Evaporation
Tmax Tmed Tmin
Jan Feb Mar AprMay Jun Jul Aug Sep Oct Nov Dec
5
10
15
20
25
30(b)
Tmax Tmed Tmin
0
0
Fig. 1.Monthly climatic characteristics at Cauquenes research station.Dates observed over29 years. (a) Precipitation and evaporation (mm); (b) Tmax: Temperatures maximum;Tmed: medial; Tmin: minimum (°C).
bulk density is >1.79 Mg m−3 and porosity ranges between 28 and 32%(0–100 cm of depth). Soil clay content is 15% between 0 and 18 cmdeep, below this depth it is higher than 44%.
Five large experimental runoff plots of 1000 m2 (20×50 m) wereestablished andmonitored from 2007 to 2010 on a hillsidewith a 12.5%slope (Fig. 2). Four conservation tillage systems were evaluated: notillage (Nt), Nt with subsoiling (Nt+Sb), which consisted of a subsoilerat 40 cm deep conducted in 2007 before sowing; Nt with a Phalarisaquatica barrier hedge (Nt+Bh) at a distance of 12.5 m; and Nt withcontour plowing (Nt+Cp) every 12.5 m with a 1% slope to removewater from the plot, compared to conventional tillage with animalplowing (Ct). It was considered an oat–wheat crop rotation. The sowingdate was around May 15th of each year. The seed rate for oats was140 kg ha−1 and 200 kg ha−1 for wheat. Fertilization consisted of 110,70 and 80 kg ha−1 of N, P2O5 and K2O, respectively for oats, and 140, 90and 80 kg ha−1 of N, P2O5 and K2O, respectively for wheat. The harvestdate was around December 15th of each year.
2.2. Rainfall erosivity, runoff and sediment evaluations
Precipitation was registered daily with a digital pluviometer bypulses with a resolution of 0.2 mm (Model PV008, GIS Ibérica, Spain),which allowed for precisely calculating the characteristics of pre-cipitations (duration, intensity, energy and erosivity). Surface runoff,soil loss and nutrient loss were determined by placing two tanks on eachtreatment, with capacities of 1 m3. The first tank had 42 runoff orifices,one of them connected to the second tank. The surface runoff of eachrainfall event was evaluated for each tillage system. Then, the runoffcoefficient (Kr) was calculated as the percentage between the surfacerunoff and rainfall per month. Soil loss was determined in the laboratoryfrom a sample of 100 ml of runoff water with suspended sediments,taken after removing thewater from the tank. Nutrient losswas obtainedin the laboratory analyzing a sample of runoff water. Total nitrogen(TN) was quantified by dry combustion with an elemental analyzer(VarioMAX CNS, Elementar Analysensysteme GMBH, Hanau, Germany).N–NH4 and N–NO3 were extracted with KCl 2 mol l−1 (1:10w/w) anddetermined by colorimetry through the reduction of nitrate with Cd/Cuand flux injection segmented with an autoanalyzer (Skalar SA 4000,Skalar Analytical B.V., Breda, The Netherlands). Ca, Mg, Na and Kexchange were extracted with ammonium acetate 1 mol l−1 a pH 7followed by emission spectroscopy and atomic absorption (Unicam900A, Thermo Scientific Elemental, Waltham, Massachusetts, USA)(Sadzawka et al., 2006).
No tillage(Nt)
Nt + contour plowing (Nt+Cp)
Nt + barrier hedges (Nt+Bh)
Nt + subsoiling(Nt+Sb)
Conventionaltillage (Ct)
50
20 m
12.5 m
Tillage direction
slope
Fig. 2. Map of experimental site.
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2.3. Soil compaction and crop measurements
For these evaluations, each tillage system was divided into fourreplicates 20×12.5 m (Fig. 2). Soil compaction as a cone index wasmeasured in April of the second and fourth seasons (2008 and 2010)prior to sowing the crop by pushing a hand-held cone-tipped (12.8 mmdiameter) penetrometer (Field Scout SC900 Soil Compaction Meter;Spectrum Technologies, Inc., Plainfield IL). Soil compaction readingswere recorded in 5.0 cm increments to 20 cm deep, with 20 replicatesin each plot.
Fractional PAR (photosynthetically active radiation) interceptionwas measured during the growing season with a hand held ceptometer(AccuPAR LP-80, DecagonDevices, Inc., Pullman,USA)within 1 h of localsolar noon. In 2007 to 2010, measurements were recorded at tillering(Zadoks stage 23) (Stapper, 2007). For each replicate, ten measure-ments were taken in rapid succession for randomly selected above(Io) and below (I) canopy positions. Thus fwas calculated (O'Connellet al., 2004): f=(1−(I / Io)×100) to estimate ground cover. Above-ground biomass and grain yield were recorded at crop maturity in1 m2 with four replicates. Samples of biomass were oven-dried for48 h at 55 °C.
2007 Season
0
30
60
90
120
150
J F M A M J J A S O N D
Rai
fall
per
even
t (m
m)
2009 Season
0
30
60
90
120
150
J F M A M J J A S O N D
Rai
nfal
l per
eve
nt (
mm
)
Fig. 3. Rainfall distribution by m
2.4. Statistical analysis
An ANOVA (Pb0.05) was applied for soil compacting, percentageof cover in tillering and crop yield (grain+biomass). Means amongtreatments were separated through the Duncan test, using the SASSystem for Windows v8 (SAS Institute, 2002–2003).
3. Results
3.1. Rainfall characteristics during experimental period
Rainfall during the four seasons of the study was variable indistribution and intensity, with annual precipitations of 372, 768, 536and 400 mm for the years 2007, 2008, 2009 and 2010, respectively.During this period 80% of the precipitation events were lower than50mm (Fig. 3). In 2007, three rainfall events were registered (27, 17and 10mm) that caused runoff, reaching energy levels of 3823, 2338and 1290 J m−2 per mm of rain, respectively. In May of 2008 high-intensity rains were registered that accumulated 370 mm, whichrepresents 54% of the rainfall in an average year. Two rainfall eventsof 138 and 45 mm reached energy of 17,738 and 12,477 J m−2 per
2008 Season
0
30
60
90
120
150
J F M A M J J A S O N D
Rai
nfal
l per
eve
nt (
mm
)
2010 Season
J F M A M J J A S O N D0
30
60
90
120
150
Rai
nfal
l per
eve
nt (
mm
)
onth from 2007 to 2010.
0
5
10
15
20
25
30
0-2500 2501-5000 5001-10000 10001-20000
Rainfall energy rate (J mm-2 mm)
Freq
uenc
y2007
2008
2009
2010
Fig. 4. Frequency of rainfall energy from 2007 to 2010.
13I.G. Martínez et al. / Geoderma 189–190 (2012) 10–17
mm of rainfall, respectively. Fourteen additional events occurredduring the rest of the year that caused runoff and the energies rangedbetween 993 and 5198 J m−2 per mm of rainfall. In 2009, ten rainfallevents were registered that caused runoff between July and November,with precipitation levels between 8 and 125 mm, whose energy levelsranged between 1194 and 4106 J m−2 per mm of rainfall. The highestlevel in August (66.2 mm) registered an intensity of 7503 J m−2 permm of rainfall. In the last year (2010), 70% of the rainfalls had anintensity of less than 2000 J m−2 permmand only one event registereda precipitation level greater than 22 mm (Fig. 4).
3.2. Runoff coefficient
Surface runoff was negligible in the 2007 and 2010 seasons, owingto the low levels of precipitation and energy levels registered in thoseyears (Fig. 5). It was not possible in 2008 to calculate the Kr in Maybecause the installations to evaluate runoff and sediment had beenremoved when the soil was being prepared for seeding. Subsequently,in June with a monthly precipitation of 103 mm, the Ct treatmentreached a Kr of 52%, in contrast to the conservationist systems,which ranged between 20 and 29%. In July, with a similar monthlyprecipitation (104 mm), the differences between the conventionalsystem and the conservationist systems were even greater, with the
Ct
Nt+Sb
Nt+Bh
Nt+Cp
Nt
Jun Jul Aug Sep0
10
20
30
40
50
60
70
%
59 123 63 31 mm
2007 season
June Jul Aug Sep
10
20
30
40
50
60
70
%
197 61 148 38 mm
2009 season
0
Fig. 5. Percentage of monthly runoff coefficient for conservation and
Ct registering a Kr of 58%while the conservationist systems registered aKr of less than 7%. During the 2009 season, the Ct system registered a Krof 67% and the conservationist systems presented a different behavior:with the Nt+Sb and Nt+Bh the Kr was 50 and 54%, respectively, butwith the Nt+Cp and Nt it was 29 and 15%, respectively.
3.3. Relationship between annual rainfall with runoff and soil losses
The yearswith the highest runoff and sediment loss during the periodof study were 2008 and 2009. The relationship between accumulatedprecipitation and accumulated runoff, indicating that in 2008, with anannual precipitation level of 768 mm, the Ct system reached a runoff of296 mm, while runoff with the conservationist systems ranged between93 and 108 mm (Fig. 6a). In 2009, with an annual precipitation of536 mm, Ct showed an annual runoff of 39 mm, while the conserva-tionist systems ranged between 8 and 32 mm (Fig. 6b).
During 2007, 2009 and 2010, sediment losses were less than100 kg ha−1, these losses being similar in all the tillage systems. In2008, when the highest precipitation levels were registered (768 mm),the Ct system present a soil loss of 638 kg ha−1, higher than that of theconservationist systems, which ranged between 95 and 174 kg ha−1
(Fig. 6c). The highest losses occurred in July, the month in which themost intense precipitation occurred.
3.4. Soil nutrient losses in eroded sediments
The highest losses of total TN, N–NO3, Ca and Mg were registeredduring the 2008 season being the losses in the Ct system the highest(Fig. 7). The conservationist systems presented lower and similar levelof losses. The losses of N–NH4, P, K and Nawereminimal and similar forall the treatments.
3.5. Soil compaction and crop response
Comparing the resistance to penetration in the soil profile in thesecond year of the experiment, all the evaluated tillage systems, withthe exception of Nt+Sb, showed a strongly compacted layer at thedepth of 10 cm (>1300 kPa), which increased to over 2000 kPa between15 and 20 cm deep (Table 2). Nt+Sb showed less compaction, beyond
Jun Jul Aug Sep
10
20
30
40
50
60
70
%
103 104 94 22 mm
2008 season
Jun Jul Aug Sep0
10
20
30
40
50
60
70
%
30 31 31 30 mm2010 season
0
conventional tillage systems during the 2007 to 2010 seasons.
Fig. 6. Relationship between a), b) accumulative rainfall with accumulative runoff for seasons 2008 (768 mm) and 2009 (536 mm), and relationship between c), d) accumulativerainfall with accumulative soil loss for seasons 2008 and 2009.
14 I.G. Martínez et al. / Geoderma 189–190 (2012) 10–17
20 cmbelow the threshold of 2000 kPa, defined by several authors as thecritical threshold for radicular growth (Chan et al., 2006; Letey, 1985). Inthe fourth year of the study (2010), the results showed an increase incompaction with all the treatments. Although Nt+Sb showed lowercompaction than the other treatments, it exceeded the threshold at15 cm deep (Table 2).
The ground cover at tillering was significantly higher (Pb0.05) inNt+Sb in 2007 and 2008 (Table 3). Also, Nt+Sb was superior to
2007 2008 2009Year
0.0
0.5
1.0
1.5
2.0
2.5
kg h
a-1
TN(a)
CtNtNt+BhNt+CpNt+Sb
2007 2008 2009Year
0.0
1.0
2.0
3.0
4.0
kg h
a-1
Ca (c)
Fig. 7. Annual losses of total nitrogen (TN), nitrate (N–N
conventional tillage (Pb0.05) in the 2007 and subsequent seasons.The total biomass production (grain+shoot) was in general higher inthe Nt+Sb system compared to the other conservationist systems,but statistically similar to the Ct system (Table 4). The accumulatedbiomass in the four years (2007–2010) of the study was also superiorin the Nt+Sb system (45.2 Mg ha−1; Table 4). Finally, grain yieldwas significantly higher (Pb0.05) in Nt+Sb than Nt in 2007 and2010, and higher than Nt in 2007 and 2008 (Table 4).
2007 2008 2009Year
0.0
0.5
1.0
1.5
2.0
2.5
kg h
a-1
N-NO3(b)
2007 2008 2009Year
0.0
0.3
0.6
0.9
1.2
1.5
kg h
a-1
Mg(d)
O3), calcium (Ca) and magnesium (Mg) in runoff.
Table 2Penetrometer resistance profile to measure as the penetration depth cone index (KPa),in five tillage systems and in two growing seasons.
Soil depth (cm)Treatments 2008
5 10 15 20
Nt 1425 a 2214 ba 2996 a 3743 aNt+Sb 1078 ba 1513 c 1325 b 1631 bNt+Bh 1373 a 2358 a 2779 a 3122 aNt+Cp 1438 a 1646 bc 2687 a 3648 aCt 737 b 1333 c 2555 a 3507 a
2010Nt 1673 a 2876 a 3610 a 4000 aNt+Sb 1809 a 1977 c 2243 b 2983 bNt+Bh 1639 a 2721 ab 3526 a 3881 aNt+Cp 1442 a 2365 bc 3292 a 3778 aCt 273 b 661 d 2258 b 3588 a
The mean values in each column followed by the same letter are not significant (Pb0.05).Ct: conventional tillage; Nt: no tillage, Nt+Sb: no tillage+subsoiling; Nt+Bh: notillage+barrier hedges; Nt+Cp: no tillage+contour plowing.
Table 4Total accumulative and yearly biomass (grain yield+shoots) production of oat–wheatcrop rotation from 2007 to 2010.
Treatments Total biomass Total2007–2010
2007 2008 2009 2010
Ct 8.52 ab 13.58 ab 10.3 a 9.01 ab 41.41 abNt+Sb 10.76 a 14.28 a 9.56 a 10.61 a 45.21 aNt+Bh 7.78 ab 11.88 bc 9.64 a 9.39 ab 38.69 bNt+Cp 5.5 b 11.1 cd 9.03 ab 9.4 ab 35.03 bcNt 5.25 b 9.28 d 7.46 b 8.77 b 30.76 c
Treatments Grain yield
2007 2008 2009 2010
Ct 1.42 b 4.66 a 3.97 a 2.64 bNt+Sb 2.22 a 4.28 ab 3.70 a 3.44 aNt+Bh 1.39 bc 3.71 bc 3.53 a 2.85 abNt+Cp 0.97 ab 3.96 ab 3.33 a 3.12 abNt 1.06 bc 2.93 c 3.00 a 2.99 a
Themean values in each column followed by the same letter are not significant (Pb0.05).Ct: conventional tillage; Nt: no tillage, Nt+Sb: no tillage+subsoiling; Nt+Bh: notillage+barrier hedges; Nt+Cp: no tillage+contour plowing.
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4. Discussion
The purpose of using large plots (1000 m2) to study the effects oftillage systems on erosion (Hashim et al., 1995; Martínez et al., 2011)is to improve the estimation of surface runoff and sedimentation inrelation to classic studies on small plots (Wischmeier and Smith,1978). This implies incorporating the effect of the slope length on thestudy of erosive processes, simulating a better representation of thenatural functioning of the agro-ecosystem. In effect, the extrapolation ofdata obtained in small plots, in most cases, results in an overestimationof erosion when they are applied to the scale of basins or hillsides(Boix-Fayos et al., 2006; Poesen et al., 2003). As well, the large plotsbetter simulate the real situation that occurs at the level of the fieldgiven that they allows for using conventional machinery, in theparticular case of this study: machinery for zero tillage seeding,subsoiling, construction of physical and biological barriers to mitigateerosion. Wendt et al. (1986) found that although the main factors thataffect runoff and soil loss are homogenous, there can be considerablevariation of measured erosion that is difficult to attribute to only onefactor such as: difference in erosionability of the soil among plots,spatial variations in infiltration, replicate number, and temporalvariability of intense rains (Langhans et al., 2011), variations in thesoil owing to tillage, as well as variations in vegetal cover and soiltexture. This can result in strong differences in the evaluated variablesamong replicates owing the high level of experimental error that isgenerated in the aforementioned variables (Boix-Fayos et al., 2006;Fitzjohn et al., 2002).
4.1. Rainfall intensity, runoff and soil and nutrient losses
In Mediterranean and semi-arid environments, the most importantsoil losses are attributed to intense and infrequent rainfall events
Table 3Ground cover in five tillage systems of oat–wheat crop rotation from 2007 to 2010.
Ground cover at tillering (%)Treatments 2007 2008 2009 2010
Ct 46.95 b 66.78 ab 72.73 a 44.40 aNt+Sb 73.66 a 72.93 a 68.97 a 43.18 aNt+Bh 30.01 c 50.00 c 67.94 a 35.20 abNt+Cp 17.77 d 56.80 bc 66.42 a 32.33 abNt 14.83 d 31.03 d 66.36 a 28.53 b
The mean values in each column followed by the same letter are not significant (Pb0.05).Ct: conventional tillage; Nt: no tillage, Nt+Sb: no tillage+subsoiling; Nt+Bh: notillage+barrier hedges; Nt+Cp: no tillage+contour plowing.
(Angulo-Martínez and Beguería, 2009; Diodato and Bellocchi, 2010;Martínez-Casasnovas et al., 2002; Nyakatawa et al., 2006). Our resultsindicate that soil lossesmay occurwhen the energy of rainfalls is greaterthan 2000 J m−2 per mm (Figs. 4 and 6). Nevertheless, only 15% of therainfalls during the four years of the study exceeded this intensity.Despite these results, it was observed that in intense rains, as occurredin 2008, soil loss in the conservationist systems were 72 to 85% lowerthan conventional tillage (Fig. 6). This loss occurred in a rainfall with anintensity of more 12,000 J m−2 per mm. However, the low loss ofsediments and nutrients can be explained by the conditions of the soilrather than the erosivity of the rain. The landscape of this area is oftenheavily eroded (CIREN, 2010), where a major part of horizon A hasalready disappeared as a result of a conventional tillage system that hasprevailed among agriculturalists over several generations.
Together with these high intensity low frequency events, otherswere registered that were of lower intensity, but much more frequent,which caused considerable levels of runoff in the conventional system,especially in years with annual precipitation rates of 536 mmor higher.In the 2008 season, when the crop was at the beginning of tillering, theconservationist systems reduced the surface runoff by 70%, and wereover 90% lower when the crop was at the end of tillering. During the2009 season, this decrease fluctuated between 46 and 85% when thecrop was at the end of tillering (Fig. 5). According to De Noni et al.(2000) more than 10% of water loss by runoff is considered high for anannual rainfall level of 600 mm−1. Smith et al. (1992) identified a 17%surface runoff rate in zero tillage for soils with a 2% slope and an annualprecipitation rate of 400 mm in Alfisol soils. The high rates of runoffwith the Ct systemare ofmajor economic and environmental importanceif we consider the studies by Pruski and Nearing (2002) and Zhang andNearing (2005). These authors indicate that the potential impact ofclimatic change in the futurewill be attributable not only to the variabilityofmonthly precipitation, but also to increase in the intensity and durationof storms.
Although precipitation was variable in quantity and intensity, theconservationist systems that maintained stubble on the soil presentedsimilar levels of surface runoff and soil and nutrient loss, demonstratingthe effectiveness of stubble cover to mitigate erosion compared toconventional tillage (Pieri et al., 2009; Tapia-Vargas et al., 2001; Thomaset al., 2007). The major differences were for surface runoff, which couldbe affected by surface crusting given the high clay content and low O.C.level (Table 1). Crusting increases the adhesion of particles of soil,reducing their detachment and loss in erosive events (Sharaiha andZiadat, 2008), as well as reducing the infiltration rate (Adekalu et al.,
16 I.G. Martínez et al. / Geoderma 189–190 (2012) 10–17
2006; Knapen et al., 2007). This explains the lower loss of sedimentsand high rates of runoff, especially with the Ct treatment.
Our results indicate that compacted soils are protected from theimpact of the rain and of erosion when: (i) the tillage system does notdisturb the soil, and (ii) the stubble protects the surface (Gebreegziabheret al., 2009;Huang et al., 2008;McHugh et al., 2008). The beneficial effectsof stubble decreases as the residues decompose (Knapen et al., 2007). Thesubsequent new crop can compensate for the decomposition of residues,but needs to be managed in function of climate, soil type and tillagesystem to be considered as a soilmanagement system(Guérif et al., 2001)
Subsoiling improves grain yield and reduces erosion by increasinginfiltration (Sojka et al., 1993). However, our results did not reflectlower runoff with Nt+Sb compared to the other conservationistsystems (Figs. 5 and 6). The most significant effect was to reduce theresistance of the soil to radicular penetration (Jin et al., 2008; Lal,2001; Nyakatawa et al., 2006), obtaining greater crop developmentduring the first stages of development and reaching higher biomassproduction and grain yield at the end of the season (Tables 3 and 4).The physical condition of compacted soil (porosity of 28.4% and bulkdensity of 1.79 Mg m−3) was improved by subsoiling (Nt+Sb), andthe positive effects were observable by the second year after the workwas done (2008). Subsoiling resulted in a lower level of compactionover the following four years, with 49% higher yield in the year withthe lowest pluviometry (2007), and 35% higher yield in the year withthe highest pluviometry (2008), compared to yields with Nt. Whatremains unknown is the effectiveness of subsoiling after four seasonsand whether it is necessary to repeat this technique every four to fiveyears, or longer.
5. Conclusions
Conservationist systems reducewater erosion hillsides compared tothe effect of conventional tillage. In intense rains, sediment loss withconservationist systems was around 85% lower than with conventiontillage, while in rainy years loss by surface runoff could be 70% lesswhen the crop had low coverage and stubble was maintained on thesoil; and 90% lower at the end of tillering. Although these results showthat conservationist systems in dry zones mitigate erosion, strongsoil compacting is the major limiting factor to increase production ofbiomass and grain yield compared to the conventional system. Nt+Sb was the only conservationist system that resulted in improvedproduction in an oat–wheat rotation system, maintaining this effectfor four years after the original subsoiling. In this manner, the zerotillage system with subsoiling is an effective conservation techniquein hillsides for Alfisol soils in the Mediterranean climate of centralChile.
Acknowledgments
This study was funded by the DESIRE Project (037046) of theEuropean Union, under the title: “Desertification mitigation andland remediation — a global approach for local solutions”, togetherwith the research agreement about conservationist practices be-tween the Servicio Agrícola and Ganadero (SAG) and the Instituto deInvestigaciones Agropecuarias (INIA).
We are grateful to Dr. Hamil Uribe for his support in the design ofrunoff tanks, and to Alvaro Arias, research assistant at INIA-Quilamapu,for his selfless work in the field, and work team at INIA-Cauquenes,composed of the Agronomist Fernando Fernández, the technicianTeresa Aravena and the research assistant María Elena Díaz.
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