Time of fallow (years)

0 10 20 30 40 50

Cu

mu

lati

ve C

O2-C

rel

ease

d (

mg

kg

-1)

0

400

800

1200

1600

2000

Y = 626 + 1.93XR2 = 0.08 NS, n = 42

Y = 1184 + 7.67XR2 = 0.24***, n = 39

Lower communities

Upper communities

EFFECTS OF CHANGES IN FALLOW LENGTH ON SOIL ORGANIC C DUE TO CLIMATE CHANGE AND EFFECTS OF CHANGES IN FALLOW LENGTH ON SOIL ORGANIC C DUE TO CLIMATE CHANGE AND SOCIOECONOMIC FACTORS IN POTATO-BASED CROPPING SYSTEMS IN THE BOLIVIAN HIGHLANDSSOCIOECONOMIC FACTORS IN POTATO-BASED CROPPING SYSTEMS IN THE BOLIVIAN HIGHLANDS

P.P. MotavalliP.P. Motavalli11, J. Aguilera, J. Aguilera22, B. Jintaridth, B. Jintaridth1,1, C. Valdivia C. Valdivia11, M. Gonzales, M. Gonzales2 2 and C. Chambillaand C. Chambilla22

11College of Agriculture, Food and Natural Resources, University of Missouri, Columbia, MO 65211 USACollege of Agriculture, Food and Natural Resources, University of Missouri, Columbia, MO 65211 USA22FundaciFundacióón PROINPA, La Paz, Bolivian PROINPA, La Paz, Bolivia

Figure 1 A-D.Figure 1 A-D. (A-D) location and landscape example of the (A-D) location and landscape example of the study communities and villages in the Altiplano of Bolivia.study communities and villages in the Altiplano of Bolivia.

IntroductionIntroduction The Bolivian highland plateau region (Altiplano) is The Bolivian highland plateau region (Altiplano) is a semi-arid region in the Andes Mountains that a semi-arid region in the Andes Mountains that occupies approximately 27% of the area of Bolivia occupies approximately 27% of the area of Bolivia and has a range in elevation of between 3600 and and has a range in elevation of between 3600 and 4300 m above sea level. The region’s climate is 4300 m above sea level. The region’s climate is characterized by high diurnal temperature variations, characterized by high diurnal temperature variations, frost risks, low and irregular precipitation and high frost risks, low and irregular precipitation and high risks of drought during the growing season (Garcia et risks of drought during the growing season (Garcia et al., 2007).al., 2007). Potato-based cropping systems and Potato-based cropping systems and livestock rearing of cows, sheep and camelids (e.g., livestock rearing of cows, sheep and camelids (e.g., alpaca and lama) are the primary agricultural alpaca and lama) are the primary agricultural activities (Valdivia et al., 2001). Crop rotations are activities (Valdivia et al., 2001). Crop rotations are initiated with potato followed by two to three years of initiated with potato followed by two to three years of cereal crops (e.g., quinoa, barley) and then an cereal crops (e.g., quinoa, barley) and then an extended uncultivated fallow period which can last extended uncultivated fallow period which can last from 1 to over 40 years. This long fallow period from 1 to over 40 years. This long fallow period allows for restoration of soil fertility, control of crop allows for restoration of soil fertility, control of crop disease and pests, grazing of natural vegetation (e.g., disease and pests, grazing of natural vegetation (e.g., “thola”“thola” ( (Parastrephia lepidophylla)Parastrephia lepidophylla)) ) and fuel for and fuel for cooking (Bottner et al., 2006; see Fig. 2 A-D)).cooking (Bottner et al., 2006; see Fig. 2 A-D)). Increasing human population in the Altiplano and Increasing human population in the Altiplano and competing land uses have caused a growing competing land uses have caused a growing reduction in the use and length of fallow (Coûteaux et reduction in the use and length of fallow (Coûteaux et al., 2008). Moreover, practices, such as use of al., 2008). Moreover, practices, such as use of mechanized disc plowing and cutting native mechanized disc plowing and cutting native vegetation for fuel, have reduced the regrowth of vegetation for fuel, have reduced the regrowth of natural vegetation during the fallow period, possibly natural vegetation during the fallow period, possibly diminishing the amount of organic inputs and the rate diminishing the amount of organic inputs and the rate of soil fertility restoration. The impact of fallowing in of soil fertility restoration. The impact of fallowing in this environment on soil properties is unclear. For this environment on soil properties is unclear. For example, Hervé (1994) in a comparison of soils with example, Hervé (1994) in a comparison of soils with up to 20 years of fallow from the Bolivian Altiplano up to 20 years of fallow from the Bolivian Altiplano did not observe any clear improvement in soil did not observe any clear improvement in soil physical (e.g., bulk density) and chemical properties physical (e.g., bulk density) and chemical properties (e.g., soil total organic C) with increasing fallow. (e.g., soil total organic C) with increasing fallow. Cabaneiro et al. (2008) in the Andes in Venezuela Cabaneiro et al. (2008) in the Andes in Venezuela determined that fallowing only increased labile determined that fallowing only increased labile organic C in soils collected from slopes with a organic C in soils collected from slopes with a northeast compared to a southwest aspect, possibly northeast compared to a southwest aspect, possibly due to differences in microclimate.due to differences in microclimate.

ObjectivesObjectives1.1.To determine the effects of cropping, fallowTo determine the effects of cropping, fallow periods and landscape position on soil total periods and landscape position on soil total organic C and soil organic C fractions. organic C and soil organic C fractions.

2.2.To compare different analytical techniques toTo compare different analytical techniques toevaluate changes in soil organic C fractions. evaluate changes in soil organic C fractions.

ConclusionsConclusions• The decreasing length of the fallow period and The decreasing length of the fallow period and

reduction in native vegetation caused by competing reduction in native vegetation caused by competing uses and mechanized tillage, may be removing an uses and mechanized tillage, may be removing an important mechanism by which total and active soil important mechanism by which total and active soil organic C is restored in potato-based cropping organic C is restored in potato-based cropping systems in this region.systems in this region.

• The impact of fallowing appears to be greater in The impact of fallowing appears to be greater in soils collected at higher elevations which may reflect soils collected at higher elevations which may reflect differences in climate and management practices differences in climate and management practices with elevation in this region. with elevation in this region.

• Several analytical methods for detecting changes in Several analytical methods for detecting changes in soil active organic C fractions were used in this soil active organic C fractions were used in this study and they were sensitive to the effects of study and they were sensitive to the effects of fallowing. Additional development of low-cost and fallowing. Additional development of low-cost and rapid field methods for detecting changes in soil C rapid field methods for detecting changes in soil C fractions would be useful for developing and fractions would be useful for developing and monitoring sustainable agricultural practices. monitoring sustainable agricultural practices.

Materials and MethodsMaterials and Methods• Four small communities in Umala in the central Four small communities in Umala in the central

Altiplano of Bolivia (Fig. 1 A-D)Altiplano of Bolivia (Fig. 1 A-D) were selected as were selected as study sites in 2006 to represent typical Aymara study sites in 2006 to represent typical Aymara farming communities at different relative farming communities at different relative elevations (Table 1). elevations (Table 1).

• Replicate soil samples were collected to a 20 cmReplicate soil samples were collected to a 20 cmdepth from agricultural fields of the samedepth from agricultural fields of the samecropping system and sandy loam soil type (locallycropping system and sandy loam soil type (locallyclassified as “cha’lla” soil)classified as “cha’lla” soil) to determine changes to determine changes in soil C due to cropping and fallow length. in soil C due to cropping and fallow length.

Results and DiscussionResults and Discussion

• Increases in soil total organic C due to fallowing Increases in soil total organic C due to fallowing were more rapid in soils collected from were more rapid in soils collected from communities at higher elevations compared to the communities at higher elevations compared to the lower elevation soils and generally a maximum lower elevation soils and generally a maximum accumulation was reached at higher elevations after accumulation was reached at higher elevations after approximately 20 to 30 years of fallow (Fig. 3A). approximately 20 to 30 years of fallow (Fig. 3A).

• Cumulative COCumulative CO22-C mineralized during incubation -C mineralized during incubation

provides a relative measure of active organic C and provides a relative measure of active organic C and results from this analysis showed similar results from this analysis showed similar differences between the lower and upper elevation differences between the lower and upper elevation communities as was observed for total organic C communities as was observed for total organic C except this form of organic C continued to except this form of organic C continued to accumulate in the upper communities over 40 years accumulate in the upper communities over 40 years of fallow (Fig 3B). Others have observed in the of fallow (Fig 3B). Others have observed in the Andes in Venezuala that the maximum level of Andes in Venezuala that the maximum level of active C occurred after 8 years of fallow (Cabaneiro active C occurred after 8 years of fallow (Cabaneiro et al., 2008).et al., 2008).

• Additional measurements of soil C fractions Additional measurements of soil C fractions showed a general increase with fallowing in KMnO4 showed a general increase with fallowing in KMnO4 active C and POM C in all communities with active C and POM C in all communities with fallowing except for San José de Llanga (Table 2). fallowing except for San José de Llanga (Table 2).

• Ongoing analysis using MIR-DRIFT has shown Ongoing analysis using MIR-DRIFT has shown some sensitivity in detecting changes in the ratio of some sensitivity in detecting changes in the ratio of labile to recalcitrant C (O/R ratio) with fallowing labile to recalcitrant C (O/R ratio) with fallowing (Fig. 4).(Fig. 4).

• Portable NIR units may allow for rapid Portable NIR units may allow for rapid determination of soil C fractions due to determination of soil C fractions due to management practices, such as fallowing. Fig. 5 management practices, such as fallowing. Fig. 5 shows the results of developing a predictive model shows the results of developing a predictive model for KMnOfor KMnO44 active C using NIR spectra and how it active C using NIR spectra and how it

significantly compared to measured KMnOsignificantly compared to measured KMnO44 active active

C. Development of a low-cost NIR field unit may C. Development of a low-cost NIR field unit may facilitate these type of measurements in locations, facilitate these type of measurements in locations, such as the Altiplano, where laboratory facilities are such as the Altiplano, where laboratory facilities are difficult and costly to access.difficult and costly to access.

•Soils were air-dried and passed through a 2-mmSoils were air-dried and passed through a 2-mmsieve and analyzed for soil total organic C usingsieve and analyzed for soil total organic C using a LECO C/N analyzer. a LECO C/N analyzer. •Active C was determined using a dilute 0.02 Active C was determined using a dilute 0.02 MMKMnOKMnO44 oxidation procedure described by Weil oxidation procedure described by Weil

et al. (2003).et al. (2003).•Particulate organic matter C (POM-C) was Particulate organic matter C (POM-C) was

determined using the wet sieving proceduredetermined using the wet sieving proceduredescribed by Cambardella and Elliot (1994).described by Cambardella and Elliot (1994).•Near infrared (NIR) spectra of the soils wereNear infrared (NIR) spectra of the soils weredetermined using a portable field spectrometer determined using a portable field spectrometer Fieldspec Pro FR (Analytical Spectral Devices, Fieldspec Pro FR (Analytical Spectral Devices, Inc, Boulder, CO) based on methods detailed inInc, Boulder, CO) based on methods detailed inSudduth and Hummel (1993).Sudduth and Hummel (1993).•Ratios of labile (O containing) and recalcitrantRatios of labile (O containing) and recalcitrant(R) C functional groups were determined by(R) C functional groups were determined byMIR-DRIFT analysis of HF-treated humic acidMIR-DRIFT analysis of HF-treated humic acidfractions separated from the samples (Ding et fractions separated from the samples (Ding et al., 2002). al., 2002). •Soils were also incubated for 84 days in 150 mLSoils were also incubated for 84 days in 150 mLFalcon filter units at -47 kPa soil moistureFalcon filter units at -47 kPa soil moisturetension and a constant temperature of 25 ºC.tension and a constant temperature of 25 ºC.Samples were periodically placed in sealed Samples were periodically placed in sealed mason jars and the headspace swept with COmason jars and the headspace swept with CO22--

free air. Changes in head space COfree air. Changes in head space CO22

concentration in the head space due to soil COconcentration in the head space due to soil CO22

evolution was then determined using evolution was then determined using a gasa gaschromatograph (GC) (Buck Scientific Inc., Eastchromatograph (GC) (Buck Scientific Inc., East

Norwalk, CT, USA) fitted with a thermalNorwalk, CT, USA) fitted with a thermalconductivity detector (TCD).conductivity detector (TCD).

AltiplanoAltiplano

A.A.B.B.

C. UmalaC. Umala

LakeLakeTiticacaTiticaca

UmalaUmala

KellhuiriKellhuiri

San JosSan Joséé de Llanga de Llanga

San Juan CercaSan Juan Cerca

Vinto CoopaniVinto Coopani

La PazLa Paz

• Based on community surveys, fallow land Based on community surveys, fallow land represents between 68 to 82% of cultivated lands represents between 68 to 82% of cultivated lands among both lower and upper elevation among both lower and upper elevation communities (Table 1). Average time of fallow communities (Table 1). Average time of fallow varied between 3.5 to 7.4 years among the varied between 3.5 to 7.4 years among the communities and community members communities and community members perceived that the duration of fallow has perceived that the duration of fallow has generally decreased over the last 10 years due to generally decreased over the last 10 years due to increased human population and increased increased human population and increased forage production. forage production.

• Soil total organic C was significantly lower in Soil total organic C was significantly lower in soils collected from farm fields in the lower soils collected from farm fields in the lower elevation communities compared to the upper elevation communities compared to the upper elevation communities (Table 2). This difference elevation communities (Table 2). This difference was probably due to the generally higher sand was probably due to the generally higher sand content of the soils in the lower communities content of the soils in the lower communities and possibly due to the more intensive and possibly due to the more intensive mechanized tillage used in those communities mechanized tillage used in those communities compared to animal-based tillage in the upper compared to animal-based tillage in the upper communities.communities.

Figure 2 A-D.Figure 2 A-D. Fallow and native vegetation growing during Fallow and native vegetation growing during the fallow period has an important role in (A) grazing for the fallow period has an important role in (A) grazing for sheep, (B & C)) a source of fuel for cooking and (D) soil sheep, (B & C)) a source of fuel for cooking and (D) soil fertility restoration.fertility restoration.

A.A.

B.B.

C.C.

D.D.

D. Umala landscapeD. Umala landscape

Table 1.Table 1. S Selected characteristics of the lower and upperelected characteristics of the lower and uppercommunities in Umala in 2006/2007communities in Umala in 2006/2007..

CCoommmmuunniittyy

AAllttiittuuddee

NNoo.. ooff HHoouusseehhoollddss

PPlloowweedd ffiieellddss ppeerr

hhoouusseehhoolldd**

FFaallllooww ffiieellddss ppeerr

hhoouusseehhoolldd

AAvveerraaggee ttiimmee iinn ffaallllooww

-- mmaassll -- ------ hhaa ------ ------ hhaa ------ -- yyeeaarrss -- LLoowweerr eelleevvaattiioonn SSaann JJoosséé ddee LLllaannggaa 33,,775577 9966 11..8844 33..9966 33..55 SSaann JJuuaann CCeerrccaa 33,,778811 3311 22..5555 77..3377 77..44 AAvveerraaggee 33,,776699 6644 22..2200 55..6666 55..44 UUppppeerr eelleevvaattiioonn VViinnttoo CCooooppaannii 33,,998866 2299 00..8855 33..9966 55..11 KKeelllliihhuuiirrii 44,,007711 2255 11..1177 44..7777 66..33 AAvveerraaggee 44,,002288 2277 22..0000 44..3366 55..77 **FFiieellddss aarreeaass iinn 22000066//22000077 ****NNuummbbeerr ooff ccaattttllee pplluuss sshheeeepp

Table 2.Table 2. Effects of changes in length of fallow period Effects of changes in length of fallow period on soil total organic C and soil C fractions in Umala. on soil total organic C and soil C fractions in Umala.

CCoommmmuunniittyy

FFaallllooww lleennggtthh

TToottaall oorrggaanniicc CC

KKMMnnOO44 aaccttiivvee CC**

PPOOMM CC****

-- yyeeaarrss -- ------ %% ------ -- mmgg kkgg--11-- -- %% ooff TTOOCC -- LLoowweerr eelleevvaattiioonn SSaann JJoosséé ddee LLllaannggaa 11 00..4444 ±± 00..0011 116622 ±± 1155 3377..22 ±± 33..99 44 00..4466 ±± 00..0011 117711 ±± 66 3377..66 ±± 11..44 1100 00..4466 ±± 00..0022 117700 ±± 77 3388..00 ±± 00..22 2200 00..5500 ±± 00..0022 118866 ±± 1144 3388..00 ±± 00..99 UUnnccrrooppppeedd 00..5522 ±± 00..0088 220099 ±± 77 3377..55 ±± 00..44 SSaann JJuuaann CCeerrccaa 11 00..5566 ±± 00..0022 116633 ±± 1111 2288..00 ±± 33..33 1100 00..5577 ±± 00..0044 117788 ±± 44 3322..99 ±± 11..66 2200 00..5577 ±± 00..0044 118822 ±± 88 3333..11 ±± 00..66 3300 00..6622 ±± 00..0022 222222 ±± 3300 3355..55 ±± 22..44 4400 00..7777 ±± 00..1155 330077 ±± 4433 4477..77 ±± 1100..22 UUnnccrrooppppeedd 00..8833 ±± 00..0011 335588 ±± 1111 4444..33 ±± 1122..55 UUppppeerr eelleevvaattiioonn VViinnttoo CCooooppaannii 11 00..7755 ±± 00..1166 335522 ±± 1133 3333..99 ±± 22..33 1177 11..0000 ±± 00..1177 336666 ±± 66 3388..22 ±± 00..99 2255 11..0044 ±± 00..1144 337744 ±± 55 3388..33 ±± 00..55 UUnnccrrooppppeedd 00..9922 ±± 00..0044 225500 ±± 1122 2288..55 ±± 00..00 KKeelllliihhuuiirrii 11 11..1100 ±± 00..1122 333377 ±± 5500 3322..66 ±± 00..77 66 11..0066 ±± 00..1199 336611 ±± 3322 3399..99 ±± 77..66 88 11..2222 ±± 00..1166 444444 ±± 44 4411..66 ±± 00..44 **AAvveerraaggee ±± ssttaannddaarrdd ddeevviiaattiioonn ****PPaarrttiiccuullaattee oorrggaanniicc mmaatttteerr CC

Figure 3.Figure 3. Changes in A) soil total organic C and B) cumulative Changes in A) soil total organic C and B) cumulative COCO22-C after 84 days of incubation of soils with different times of -C after 84 days of incubation of soils with different times of

cropping and fallow. Regression lines show relationship for cropping and fallow. Regression lines show relationship for lower and upper elevation communities. lower and upper elevation communities.

Figure 4.Figure 4. MIR-DRIFT MIR-DRIFT scans and O/R scans and O/R ratios of soils ratios of soils with A) 1 year with A) 1 year of fallow and of fallow and B) 40 years of B) 40 years of fallow from fallow from Umala.Umala.

A.

B.

Measured KMnO4 active C

(mg kg-1)

100 200 300 400 500

Pre

dic

ted

KM

nO

4 ac

tive

C

(mg

kg

-1)

100

200

300

400

500

Y = 0.820X + 48.8R2 = 0.82**, n = 49

O/R ratio = 0.69

O/R ratio = 0.79

Figure 5.Figure 5. Predicted KMnO Predicted KMnO44 active C of soils from active C of soils from

Umala using NIR spectra versus measured values. Umala using NIR spectra versus measured values.

So

il to

tal o

rgan

ic C

(%

)

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

Upper communities

Lower communities

Y = 0.91 + 0.0157X - 0.000226X2

R2 = 0.37***, n = 39

Y = 0.52 + 0.00255XR2 = 0.15 *, n = 42

San Jose de LlangaSan Juan CercaVinto CoopaniKellihuiri

Y = 0.52 + 0.00255XR2 = 0.15*, n = 42

A.

B.