Assessing Soil Quality for Sustainable Agricultural Systems in Tropical Countries Assessing Soil Quality for Sustainable Agricultural Systems in Tropical Countries Using Spectroscopic MethodsUsing Spectroscopic Methods

B. JintaridthB. Jintaridth11, P.P. Motavalli, P.P. Motavalli11, K.W. Goyne, K.W. Goyne11, and R.J. Kremer, and R.J. Kremer22

11Department of Soil, Environmental and Atmospheric Sciences, University of Missouri, Columbia, MO 65211 USADepartment of Soil, Environmental and Atmospheric Sciences, University of Missouri, Columbia, MO 65211 USA

22USDA-ARS, Columbia, MO 65211 USAUSDA-ARS, Columbia, MO 65211 USA

IntroductionIntroduction

Soil quality assessment is a process by which soil Soil quality assessment is a process by which soil resources are evaluated on the basis of soil function. resources are evaluated on the basis of soil function. The need for an effective, low-cost method to evaluate The need for an effective, low-cost method to evaluate soil quality is important in developing countries soil quality is important in developing countries because soil degradation is a major impediment to because soil degradation is a major impediment to sustainable crop growth. Soil organic matter (SOM) sustainable crop growth. Soil organic matter (SOM) or soil organic C (SOC) is an important indicator of or soil organic C (SOC) is an important indicator of soil quality (Gregorich et al., 1994) because it affects soil quality (Gregorich et al., 1994) because it affects many plant growth factors, including water-holding many plant growth factors, including water-holding capacity and long-term nutrient availability. In capacity and long-term nutrient availability. In general, SOC varies across landscapes, soil types general, SOC varies across landscapes, soil types and climatic zones and is characterized by both labile and climatic zones and is characterized by both labile and recalcitrant or humified forms. and recalcitrant or humified forms.

There are many techniques that measure the size There are many techniques that measure the size and turnover time of SOC pools to evaluate soil and turnover time of SOC pools to evaluate soil quality in the laboratory or the field to help guide quality in the laboratory or the field to help guide sustainability of agricultural management practices. sustainability of agricultural management practices. Among these methods are several spectroscopic Among these methods are several spectroscopic procedures which are rapid and relatively low-cost. procedures which are rapid and relatively low-cost. The KMnO4 method developed by Weil (2003) has The KMnO4 method developed by Weil (2003) has been adapted for field use and measures a labile C been adapted for field use and measures a labile C fraction. Near infrared (NIR) spectroscopy has also fraction. Near infrared (NIR) spectroscopy has also been adapted for field use and could provide a rapid been adapted for field use and could provide a rapid method to measure soil C fractions (method to measure soil C fractions (ShepherdShepherd et al., et al., 2007)2007). Another technique which has been studied is . Another technique which has been studied is the use of diffuse reflectance infrared Fourier-the use of diffuse reflectance infrared Fourier-transformed (DRIFT) mid-infrared spectroscopy which transformed (DRIFT) mid-infrared spectroscopy which can identify labile and recalcitrant C in soil (Ding et can identify labile and recalcitrant C in soil (Ding et al., 2002). However, many of these techniques have al., 2002). However, many of these techniques have not been assessed under a wide range of soil types not been assessed under a wide range of soil types and cropping systems.and cropping systems.

ObjectivesObjectives

1. 1. To determine the use of spectroscopic-based (i.e. To determine the use of spectroscopic-based (i.e. near-infrared, mid-infrared, and visible range) near-infrared, mid-infrared, and visible range) analytical methods to evaluate soil organic matter analytical methods to evaluate soil organic matter fractions and soil quality in degraded and non-fractions and soil quality in degraded and non-degraded soils in a wide range of environments.degraded soils in a wide range of environments.

2.2. This project also has an objective of assessing This project also has an objective of assessing community perceptions of soil quality, but this community perceptions of soil quality, but this information is not presented in this poster.information is not presented in this poster.

I. I. U.S.A (Sanborn Field and Tucker Prairie, Missouri)U.S.A (Sanborn Field and Tucker Prairie, Missouri)

• Soil samples were collected in 2008 from depths of Soil samples were collected in 2008 from depths of 0-10 and 10-20 cm 0-10 and 10-20 cm from two locations near from two locations near Columbia, Missouri, USA. Columbia, Missouri, USA.

• The sites included Sanborn Field (Fig. 1), a long-The sites included Sanborn Field (Fig. 1), a long-term research site that has been continuously term research site that has been continuously cultivated since 1888.cultivated since 1888.

• Plots sampled in Sanborn Field have been Plots sampled in Sanborn Field have been supporting continuous corn crops (supporting continuous corn crops (Zea mays.Zea mays. L.) L.) and include treatments of: and include treatments of: T1: conventional tillage, full fertilizer treatment T1: conventional tillage, full fertilizer treatment T2: no-till, full fertilizer treatmentT2: no-till, full fertilizer treatmentT3: conventional tillage, no fertilizer treatment T3: conventional tillage, no fertilizer treatment T4: conventional tillage, manure treatmentT4: conventional tillage, manure treatment

• Tucker PrairieTucker Prairie (T5), a native prairie site in Missouri (T5), a native prairie site in Missouri that represents the undisturbed soil found in that represents the undisturbed soil found in Sanborn Field prior to initial cultivation. It is Sanborn Field prior to initial cultivation. It is dominated by bluestem grasses.dominated by bluestem grasses.

II. II. BoliviaBolivia

• Two communities (San Juan Circa and San JosTwo communities (San Juan Circa and San Joséé) in ) in the Umala Municipality (Fig. 2 A-B) of the Central the Umala Municipality (Fig. 2 A-B) of the Central Highland (Altiplano) region of Bolivia (Fig. 3 A-B) Highland (Altiplano) region of Bolivia (Fig. 3 A-B) were selected as study sites in 2006.were selected as study sites in 2006.

• Soil samples were collected from farm fields from Soil samples were collected from farm fields from a depth of 0-20 cm. a depth of 0-20 cm.

• Soil samples were taken from fields with Soil samples were taken from fields with 1, 10, 20, 1, 10, 20, 30 and > 40 years of fallow30 and > 40 years of fallow. .

Materials and MethodsMaterials and Methods Preliminary ResultsPreliminary Results Evaluating SOC with NIR Evaluating SOC with NIR

•The NIR analysis was conducted to The NIR analysis was conducted to develop a comparison between three soil C develop a comparison between three soil C fractions (POM-C, KMnO4 and total C) and fractions (POM-C, KMnO4 and total C) and near infrared spectra results (700-2500 nm). near infrared spectra results (700-2500 nm). •A total of 30 soil samples were collected A total of 30 soil samples were collected from the 0-10 and 10-20 cm depths. The from the 0-10 and 10-20 cm depths. The number of data points was 90. Partial least number of data points was 90. Partial least square analysis was used to build square analysis was used to build prediction models with a calibration data prediction models with a calibration data set of 10 terms for whole soils to produce set of 10 terms for whole soils to produce these predictions.these predictions.•The prediction models for measured POM-The prediction models for measured POM-C had rC had r22 values of 0.88, 0.928 and 0.958 for values of 0.88, 0.928 and 0.958 for POM-C, KMnO4 and total C. respectively POM-C, KMnO4 and total C. respectively (Fig. 8 A-C). (Fig. 8 A-C).

ConclusionsConclusions

Fig. 8 A-C.Fig. 8 A-C. Predicted vs. measured POMC (%) Predicted vs. measured POMC (%) content of 30 soil samples from Sanborn Field.content of 30 soil samples from Sanborn Field.

• The undisturbed prairie soil had the lowest bulk density (Db) The undisturbed prairie soil had the lowest bulk density (Db) (0.74 g(0.74 g..cmcm-3-3) compared to cultivated plots at the 0-10 and 10-20 ) compared to cultivated plots at the 0-10 and 10-20 cm depths (Fig. 5 A). The treatment whose soil contained the cm depths (Fig. 5 A). The treatment whose soil contained the highest Db was conventional tillage and no fertilizer (1.23 ghighest Db was conventional tillage and no fertilizer (1.23 g ..cmcm-3-3) . ) .

• Labile C, or active C pools, (using the KMnOLabile C, or active C pools, (using the KMnO44 or water-soluble C or water-soluble C

methods) showed the highest results in Tucker Prairie compared methods) showed the highest results in Tucker Prairie compared to conventional tillage and no-till in Sanborn Field. to conventional tillage and no-till in Sanborn Field.

• TheThe no-till treatment on Sanborn Field had more labile C (or no-till treatment on Sanborn Field had more labile C (or active C) than the conventional tillage treatments including both active C) than the conventional tillage treatments including both fertilized and manured plots (Fig. 5 B-C). fertilized and manured plots (Fig. 5 B-C).

• The Tucker Prairie soil had total organic C levels (3.84 %) three The Tucker Prairie soil had total organic C levels (3.84 %) three times greater than that of the conventional tillage-full fertilizer times greater than that of the conventional tillage-full fertilizer plot in Sanborn Field, (1.39%). Similarly, POM-C in Tucker Prairie, plot in Sanborn Field, (1.39%). Similarly, POM-C in Tucker Prairie, was 1.5 times greater that the POM-C value in Sanborn Field was 1.5 times greater that the POM-C value in Sanborn Field (24.73 and 17.23%, respectively) (Fig. 5 D-E). (24.73 and 17.23%, respectively) (Fig. 5 D-E).

• In every treatment, all SOC pools are higher in the topsoil (0-10 In every treatment, all SOC pools are higher in the topsoil (0-10 cm) than the subsoil (10-20 cm.) (Fig. 5F). cm) than the subsoil (10-20 cm.) (Fig. 5F).

• Changes in soil and crop management Changes in soil and crop management have an effect onhave an effect on soil organic carbon soil organic carbon pools in a wide range of environments.pools in a wide range of environments.

• Labile carbon, and POM-C are sensitive Labile carbon, and POM-C are sensitive indicators of changes in management indicators of changes in management practices and are relatively rapid and practices and are relatively rapid and inexpensive tests of soil quality and inexpensive tests of soil quality and degradation.degradation.

• Near infrared spectroscopy (NIR) is a Near infrared spectroscopy (NIR) is a rapid and nondestructive field method rapid and nondestructive field method for evaluating changes in soil C for evaluating changes in soil C fractions, but its cost may make it less fractions, but its cost may make it less favorable for developing countries.favorable for developing countries.

• This research will be comparing the This research will be comparing the effectiveness of these soil quality effectiveness of these soil quality methods for additional sites in Latin methods for additional sites in Latin America, Africa and Asia. America, Africa and Asia.

Fig. 1.Fig. 1. Sanborn Field Sanborn Field (Columbia, MO USA) (Columbia, MO USA)

• All samples were analyzed using spectroscopic All samples were analyzed using spectroscopic methods in the field and in the lab.methods in the field and in the lab.

• Visible range Visible range spectroscopy (VIS), using pspectroscopy (VIS), using potassium otassium

permanganate (KMnOpermanganate (KMnO44), was utilized with a ), was utilized with a

portable field spectrometer (550 nm) and field portable field spectrometer (550 nm) and field chart chart to analyze lto analyze labile C (Fig. 4 A-C).abile C (Fig. 4 A-C).

• Near infrared rangeNear infrared range spectroscopyspectroscopy (NIR) was (NIR) was conducted using conducted using a portable field NIR spectrometer a portable field NIR spectrometer (Fig. 4 D-E). (Fig. 4 D-E).

• Diffuse Reflectance Fourier Transform Infrared Diffuse Reflectance Fourier Transform Infrared Analysis (DRIFT) was conducted using mid-Analysis (DRIFT) was conducted using mid-infrared spectroscopy (Fig. 4 F).infrared spectroscopy (Fig. 4 F).

Solución KMnO4 después de agitarlo con el suelo

Tabla de campo sobre Calidad de Suelos

Escala del Indice de Calidad de Suelos

>0 – 0.25 >0.25 – 0.50 >0.50 – 0.75 >0.75 – 1.0

Pobre Regular Bueno Excelente

Fig. 4 A-F. Fig. 4 A-F. (A) KMnO4, (A) KMnO4, (B) Portable field spectrometer (B) Portable field spectrometer (550 nm), (C) Field chart, (D-E) (550 nm), (C) Field chart, (D-E) Portable field spectrometer (NIR), Portable field spectrometer (NIR), (F) MIR spectrometer(F) MIR spectrometer

II. BoliviaII. Bolivia

Fig. 5 A-E.Fig. 5 A-E. Mean values for bulk Mean values for bulk density (gdensity (g..cmcm33), KMnO), KMnO44 (mg (mg..kgkg-1-1), ),

water soluble C (mgwater soluble C (mg..LL-1-1), particulate ), particulate OC (%), and total C (%). The same OC (%), and total C (%). The same lower-case letter (0-10 cm.) and the lower-case letter (0-10 cm.) and the same upper-case letter (10-20 cm.) same upper-case letter (10-20 cm.) do not differ significantly by LSD (p do not differ significantly by LSD (p ≤ 0.05).≤ 0.05).

Fig. 6 A-DFig. 6 A-D Determination of Determination of soil organic carbon soil organic carbon fractions [ A) water soluble C (mgfractions [ A) water soluble C (mg..LL-1-1), B) KMnO), B) KMnO4 4

(mg(mg..kgkg-1-1), C) POM-C (%) and D) total C (%)] in two ), C) POM-C (%) and D) total C (%)] in two Bolivian communities in the Central Altiplano.Bolivian communities in the Central Altiplano.

• The results for the soil organic C fractionThe results for the soil organic C fraction for the soils from Bolivia (Fig. 6 A-D) show for the soils from Bolivia (Fig. 6 A-D) show

that:that:

Soil organic C increased with increasing Soil organic C increased with increasing fallow length or was higher in the uncropped fallow length or was higher in the uncropped land (Fig 6D).land (Fig 6D).

Labile C, water soluble C, and total C in San Labile C, water soluble C, and total C in San

Juan Circa were higher than in San JosJuan Circa were higher than in San Joséé. . These results suggest that other factors such These results suggest that other factors such as fallow vegetation, or soil properties affect as fallow vegetation, or soil properties affect SOC during the fallow period.SOC during the fallow period.

Effects of fallow vegetation may be important Effects of fallow vegetation may be important for restoration of soil fertility during the fallow for restoration of soil fertility during the fallow period.period.

I. Sanborn FieldI. Sanborn Field

A. B.

D.C.

E.

A.

C.

B.

D.

C.B.A.

A.A.

F.F.

E.E.D.D.

C.C.

Based on farmer surveys in the Bolivian Based on farmer surveys in the Bolivian communities, the major soils-related constraints to communities, the major soils-related constraints to plant growth are:plant growth are:• Low soil quality and soil fertility (low soil nutrient Low soil quality and soil fertility (low soil nutrient content, high clay content and stoniness)content, high clay content and stoniness)• Excessive water and wind-induced soil erosionExcessive water and wind-induced soil erosion• Insufficient soil moisture due to lower rainfallInsufficient soil moisture due to lower rainfall• Inadequate soil management practices (In Inadequate soil management practices (In appropriate tractor tillage practices, lack of a appropriate tractor tillage practices, lack of a suitable crop, rotation strategy, insufficient soil suitable crop, rotation strategy, insufficient soil fertility inputs, and overgrazing by sheep).fertility inputs, and overgrazing by sheep).

B.B.

AltiplanoAltiplano

San Juan CercaSan Juan Cerca

San JosSan Joséé de Llanga de Llanga

Fig. 3 A-B. Location of the study communities and villages Fig. 3 A-B. Location of the study communities and villages in the Altiplano of Bolivia.in the Altiplano of Bolivia.

Fig. 2 A-B.Fig. 2 A-B. Fallow vegetation has an important role in Fallow vegetation has an important role in (A) grazing for sheep, and (B) a source of fuel for (A) grazing for sheep, and (B) a source of fuel for cookingcooking

A.A. B.B.

A B

Fig. 7 A-B. Fig. 7 A-B. Farmers of the Bolvian Altiplano collecting Farmers of the Bolvian Altiplano collecting soil samples from a fallow field. soil samples from a fallow field.

A. B.