Assessing Soil Quality for Sustainable Agricultural Systems in Tropical Countries Using Spectroscopic Methods B. Jintaridth 1, P.P. Motavalli 1, K.W. Goyne 1, and R.J. Kremer 2 1 Department of Soil, Environmental and Atmospheric Sciences, University of Missouri, Columbia, MO USA 2 USDA-ARS, Columbia, MO USA Introduction Soil quality assessment is a process by which soil resources are evaluated on the basis of soil function. The need for an effective, low-cost method to evaluate soil quality is important in developing countries because soil degradation is a major impediment to sustainable crop growth. Soil organic matter (SOM) or soil organic C (SOC) is an important indicator of soil quality (Gregorich et al., 1994) because it affects many plant growth factors, including water-holding capacity and long-term nutrient availability. In general, SOC varies across landscapes, soil types and climatic zones and is characterized by both labile and recalcitrant or humified forms. There are many techniques that measure the size and turnover time of SOC pools to evaluate soil quality in the laboratory or the field to help guide sustainability of agricultural management practices. Among these methods are several spectroscopic procedures which are rapid and relatively low-cost. The KMnO4 method developed by Weil (2003) has been adapted for field use and measures a labile C fraction. Near infrared (NIR) spectroscopy has also been adapted for field use and could provide a rapid method to measure soil C fractions (Shepherd et al., 2007). Another technique which has been studied is the use of diffuse reflectance infrared Fourier- transformed (DRIFT) mid-infrared spectroscopy which can identify labile and recalcitrant C in soil (Ding et al., 2002). However, many of these techniques have not been assessed under a wide range of soil types and cropping systems. There are many techniques that measure the size and turnover time of SOC pools to evaluate soil quality in the laboratory or the field to help guide sustainability of agricultural management practices. Among these methods are several spectroscopic procedures which are rapid and relatively low-cost. The KMnO4 method developed by Weil (2003) has been adapted for field use and measures a labile C fraction. Near infrared (NIR) spectroscopy has also been adapted for field use and could provide a rapid method to measure soil C fractions (Shepherd et al., 2007). Another technique which has been studied is the use of diffuse reflectance infrared Fourier- transformed (DRIFT) mid-infrared spectroscopy which can identify labile and recalcitrant C in soil (Ding et al., 2002). However, many of these techniques have not been assessed under a wide range of soil types and cropping systems. Objectives 1. To determine the use of spectroscopic-based (i.e. near-infrared, mid-infrared, and visible range) analytical methods to evaluate soil organic matter fractions and soil quality in degraded and non- degraded soils in a wide range of environments. 2.This project also has an objective of assessing community perceptions of soil quality, but this information is not presented in this poster. I. U.S.A (Sanborn Field and Tucker Prairie, Missouri) Soil samples were collected in 2008 from depths of 0-10 and cm from two locations near Columbia, Missouri, USA.Soil samples were collected in 2008 from depths of 0-10 and cm from two locations near Columbia, Missouri, USA. The sites included Sanborn Field (Fig. 1), a long- term research site that has been continuously cultivated since 1888.The sites included Sanborn Field (Fig. 1), a long- term research site that has been continuously cultivated since Plots sampled in Sanborn Field have been supporting continuous corn crops (Zea mays. L.) and include treatments of:Plots sampled in Sanborn Field have been supporting continuous corn crops (Zea mays. L.) and include treatments of: T1: conventional tillage, full fertilizer treatment T2: no-till, full fertilizer treatment T3: conventional tillage, no fertilizer treatment T4: conventional tillage, manure treatment Tucker Prairie (T5), a native prairie site in Missouri that represents the undisturbed soil found in Sanborn Field prior to initial cultivation. It is dominated by bluestem grasses.Tucker Prairie (T5), a native prairie site in Missouri that represents the undisturbed soil found in Sanborn Field prior to initial cultivation. It is dominated by bluestem grasses. II. Bolivia Two communities (San Juan Circa and San José) in the Umala Municipality (Fig. 2 A-B) of the Central Highland (Altiplano) region of Bolivia (Fig. 3 A-B) were selected as study sites in 2006.Two communities (San Juan Circa and San José) in the Umala Municipality (Fig. 2 A-B) of the Central Highland (Altiplano) region of Bolivia (Fig. 3 A-B) were selected as study sites in Soil samples were collected from farm fields from a depth of 0-20 cm.Soil samples were collected from farm fields from a depth of 0-20 cm. Soil samples were taken from fields with 1, 10, 20, 30 and > 40 years of fallow.Soil samples were taken from fields with 1, 10, 20, 30 and > 40 years of fallow. Materials and Methods Preliminary Results Evaluating SOC with NIR The NIR analysis was conducted to develop a comparison between three soil C fractions (POM-C, KMnO4 and total C) and near infrared spectra results ( nm).The NIR analysis was conducted to develop a comparison between three soil C fractions (POM-C, KMnO4 and total C) and near infrared spectra results ( nm). A total of 30 soil samples were collected from the 0-10 and cm depths. The number of data points was 90. Partial least square analysis was used to build prediction models with a calibration data set of 10 terms for whole soils to produce these predictions.A total of 30 soil samples were collected from the 0-10 and cm depths. The number of data points was 90. Partial least square analysis was used to build prediction models with a calibration data set of 10 terms for whole soils to produce these predictions. The prediction models for measured POM-C had r 2 values of 0.88, and for POM-C, KMnO4 and total C. respectively (Fig. 8 A-C).The prediction models for measured POM-C had r 2 values of 0.88, and for POM-C, KMnO4 and total C. respectively (Fig. 8 A-C). Conclusions Fig. 8 A-C. Predicted vs. measured POMC (%) content of 30 soil samples from Sanborn Field. The undisturbed prairie soil had the lowest bulk density (Db) (0.74 g. cm -3 ) compared to cultivated plots at the 0-10 and cm depths (Fig. 5 A). The treatment whose soil contained the highest Db was conventional tillage and no fertilizer (1.23 g. cm -3 ).The undisturbed prairie soil had the lowest bulk density (Db) (0.74 g. cm -3 ) compared to cultivated plots at the 0-10 and cm depths (Fig. 5 A). The treatment whose soil contained the highest Db was conventional tillage and no fertilizer (1.23 g. cm -3 ). Labile C, or active C pools, (using the KMnO 4 or water-soluble C methods) showed the highest results in Tucker Prairie compared to conventional tillage and no-till in Sanborn Field. Labile C, or active C pools, (using the KMnO 4 or water-soluble C methods) showed the highest results in Tucker Prairie compared to conventional tillage and no-till in Sanborn Field. The no-till treatment on Sanborn Field had more labile C (or active C) than the conventional tillage treatments including both fertilized and manured plots (Fig. 5 B-C).The no-till treatment on Sanborn Field had more labile C (or active C) than the conventional tillage treatments including both fertilized and manured plots (Fig. 5 B-C). The Tucker Prairie soil had total organic C levels (3.84 %) three times greater than that of the conventional tillage-full fertilizer 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 (24.73 and 17.23%, respectively) (Fig. 5 D-E). The Tucker Prairie soil had total organic C levels (3.84 %) three times greater than that of the conventional tillage-full fertilizer 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 (24.73 and 17.23%, respectively) (Fig. 5 D-E). In every treatment, all SOC pools are higher in the topsoil (0-10 cm) than the subsoil (10-20 cm.) (Fig. 5F).In every treatment, all SOC pools are higher in the topsoil (0-10 cm) than the subsoil (10-20 cm.) (Fig. 5F). v Changes in soil and crop management have an effect on soil organic carbon pools in a wide range of environments.Changes in soil and crop management have an effect on soil organic carbon pools in a wide range of environments. Labile carbon, and POM-C are sensitive indicators of changes in management practices and are relatively rapid and inexpensive tests of soil quality and degradation.Labile carbon, and POM-C are sensitive indicators of changes in management practices and are relatively rapid and inexpensive tests of soil quality and degradation. Near infrared spectroscopy (NIR) is a rapid and nondestructive field method for evaluating changes in soil C fractions, but its cost may make it less favorable for developing countries.Near infrared spectroscopy (NIR) is a rapid and nondestructive field method for evaluating changes in soil C fractions, but its cost may make it less favorable for developing countries. This research will be comparing the effectiveness of these soil quality methods for additional sites in Latin America, Africa and Asia.This research will be comparing the effectiveness of these soil quality methods for additional sites in Latin America, Africa and Asia. Fig. 1. Sanborn Field (Columbia, MO USA) All samples were analyzed using spectroscopic methods in the field and in the lab.All samples were analyzed using spectroscopic methods in the field and in the lab. Visible range spectroscopy (VIS), using potassiumVisible range spectroscopy (VIS), using potassium permanganate (KMnO 4 ), was utilized with a portable field spectrometer (550 nm) and field chart to analyze labile C (Fig. 4 A-C). permanganate (KMnO 4 ), was utilized with a portable field spectrometer (550 nm) and field chart to analyze labile C (Fig. 4 A-C). Near infrared range spectroscopy (NIR) was conducted using a portable field NIR spectrometer (Fig. 4 D-E). Near infrared range spectroscopy (NIR) was conducted using a portable field NIR spectrometer (Fig. 4 D-E). Diffuse Reflectance Fourier Transform Infrared Analysis (DRIFT) was conducted using mid- infrared spectroscopy (Fig. 4 F).Diffuse Reflectance Fourier Transform Infrared Analysis (DRIFT) was conducted using mid- infrared spectroscopy (Fig. 4 F). Fig. 4 A-F. (A) KMnO4, (B) Portable field spectrometer (550 nm), (C) Field chart, (D-E) Portable field spectrometer (NIR), (F) MIR spectrometer II. Bolivia Fig. 5 A-E. Mean values for bulk density (g. cm 3 ), KMnO 4 (mg. kg -1 ), water soluble C (mg. L -1 ), particulate OC (%), and total C (%). The same lower-case letter (0-10 cm.) and the same upper-case letter (10-20 cm.) do not differ significantly by LSD (p ≤ 0.05). Fig. 6 A-D Determination of soil organic carbon fractions [ A) water soluble C (mg. L -1 ), B) KMnO 4 (mg. kg -1 ), C) POM-C (%) and D) total C (%)] in two 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 that: for the soils from Bolivia (Fig. 6 A-D) show that: Soil organic C increased with increasing fallow length or was higher in the uncropped land (Fig 6D). Soil organic C increased with increasing fallow length or was higher in the uncropped land (Fig 6D). Labile C, water soluble C, and total C in San Juan Circa were higher than in San José. These results suggest that other factors such as fallow vegetation, or soil properties affect SOC during the fallow period. Labile C, water soluble C, and total C in San Juan Circa were higher than in San José. These results suggest that other factors such as fallow vegetation, or soil properties affect SOC during the fallow period. Effects of fallow vegetation may be important for restoration of soil fertility during the fallow period. Effects of fallow vegetation may be important for restoration of soil fertility during the fallow period. I. Sanborn Field A. B. D.C. E. A. C. B. D. C. B.A. A. F. E. D. C. Based on farmer surveys in the Bolivian communities, the major soils-related constraints to plant growth are: Low soil quality and soil fertility (low soil nutrient content, high clay content and stoniness) Low soil quality and soil fertility (low soil nutrient content, high clay content and stoniness) Excessive water and wind-induced soil erosion Excessive water and wind-induced soil erosion Insufficient soil moisture due to lower rainfall Insufficient soil moisture due to lower rainfall Inadequate soil management practices (In appropriate tractor tillage practices, lack of a suitable crop, rotation strategy, insufficient soil fertility inputs, and overgrazing by sheep). Inadequate soil management practices (In appropriate tractor tillage practices, lack of a suitable crop, rotation strategy, insufficient soil fertility inputs, and overgrazing by sheep). B. Altiplano San Juan Cerca San José de Llanga Fig. 3 A-B. Location of the study communities and villages in the Altiplano of Bolivia. Fig. 2 A-B. Fallow vegetation has an important role in (A) grazing for sheep, and (B) a source of fuel for cooking A. B. A B Fig. 7 A-B. Farmers of the Bolvian Altiplano collecting soil samples from a fallow field. A. B.