Fifty Years of Agricultural Soil Change in Iowa Jessica Veenstra Iowa State University
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Iowa State University Capstones, Theses and Graduate Theses and Dissertations Dissertations 2010 Fifty years of agricultural soil change in Iowa Jessica Veenstra Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/etd Part of the Agronomy and Crop Sciences Commons Recommended Citation Veenstra, Jessica, "Fifty years of agricultural soil change in Iowa" (2010). Graduate Theses and Dissertations. 11428. https://lib.dr.iastate.edu/etd/11428 This Dissertation is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Graduate Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. Fifty years of agricultural soil change in Iowa by Jessica Jeanne Veenstra A dissertation submitted to the graduate faculty in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Co-majors: Soil Science (Soil Morphology and Genesis); Environmental Science Program of Study Committee: C. Lee Burras, Major Professor Jonathan Sandor Richard Cruse Matthew Liebman Robert Horton Iowa State University Ames, Iowa 2010 Copyright © Jessica Jeanne Veenstra, 2010. All rights reserved. ii Table of Contents List of Figures iv List of Tables v Chapter 1. General Introduction 1 Chapter 2. Soil changes after 50 years of agricultural land use: a pedological analysis 4 Abstract 4 Introduction 4 Materials and Methods 5 Study Area 5 Historical Database of Soil Properties 5 Soil Sampling 6 Soil Core Characterization 6 Variation in soil description techniques 6 Bulk Density 7 Soil Texture 7 Laboratory measurements 8 Land use history reconnaissance 9 Statistical Analysis 9 Results and Discussion 9 Acidification 9 Soil Organic C and Total N 11 Cation Exchange Capacity and Extractable Bases 12 Structure and Bulk Density 14 Redoximorphic features 16 Conclusions 18 Chapter 3. A process-based model of agricultural anthropedogenesis 23 Abstract 23 Introduction 23 Materials and Methods 24 Pedological Context 24 Historical Database of Soil Properties 24 Soil Sampling 25 Soil Core Characterization 25 Land use history reconnaissance 25 Results and Discussion 26 Reference depth 26 Destruction of Granular Soil Structure 27 Soil erosion, cumulization and melanization 27 Dissolution, Translocation and Precipitation of Organic C, Total N and Carbonates 28 Oxidation and braunification 30 A synthesized model of anthropedogenesis 30 Conclusions 31 iii Chapter 4. Is soil really eroding at tolerable rates? 36 Introduction 36 Materials and Methods 37 Results and Discussion 38 Calculating Erosion Rates 38 Highly Erodible Land 41 Soil Loss and Yield Loss 41 Summary 42 Chapter 5. Effects of agriculture on the classification of Black Soils in the Midwestern United States 45 Abstract 45 Introduction 46 Materials and Methods 47 Historical Database of Soil Properties 47 Land Use 48 Classification 48 Canadian Soil Taxonomy 48 US Soil Taxonomy 49 FAO-WRB 49 Defining characteristics of Black Soils 49 Results 50 Diversity of pedons sampled 50 Classification change by hierarchical level 50 Significant properties in all taxonomic systems 51 Comparison of three taxonomic systems 52 Discussion 52 Chapter 6. General Conclusion 57 References 59 Appendix 66 Acknowledgements 68 iv List of Figures Figure 1.1. Word cloud showing most common words used in this dissertation. 2 Figure 1.2. Iowa counties with sites sampled across landform regions. 3 Figure 2.1 pH, cation exchange capacity (CEC), sum of extractable bases, extractable Ca2+, Mg2+, K+ (cmol(+)/kg of soil) and percent base saturation by depth. 19 Figure 2.2. Total organic C and total N (g/100 g of soil) by depth. 21 Figure 2.3. Bulk density (g/cm3) by depth. 22 Figure 3.1. Comparisons of changes in soil properties across landscape positions, using the soil surface as the reference depth. 32 Figure 3.2. Comparisons of changes in soil properties across landscape positions, using the depth to gravels/contrasting texture as the reference depth. 33 Figure 3.3. Comparison of soil morphology using the depth to gravels/contrasting texture as the reference depth. 34 Figure 3.4. A generalized model of agricultural anthropedogenic processes of material transport through soil profiles and across landscapes. 35 Figure 5.1. Word cloud showing most common words used in the taxonomic names of the 82 pedons sampled in the three taxonomic systems. 56 v List of Tables Table 2.1. Changes in soil chemical properties. 20 Table 2.2. Number of sites sampled that had a pH below 5.5 in each depth. 20 Table 2.3. P values for the t-tests of the changes in total organic C and total N from 1959 to 2007. 21 Table 2.4. Profile total organic C and total N in mass per area for different depths. 21 Table 2.5. Bulk density (g/cm3) by depth. 22 Table 2.6. Changes in minimum depth (cm) to soil properties. 22 Table 3.1. Changes in minimum depth (cm) to soil properties. Reference depth is the soil surface. 34 Table 4.1. Changes in depth of benchmark soil properties and corresponding erosion rates. 43 Table 4.3. Changes in depth of benchmark soil properties and corresponding erosion rates excluding the “gaining” hillslope positions (foot/toeslope). 43 Table 4.2. Changes in depth of benchmark soil properties and corresponding erosion rates for four hillslope positions (summit, shoulder, backslope and foot/toeslope). 43 Table 4.4. Soil series classified as Highly Erodible Land (HEL) and potentially HEL. 44 Table 4.5. Changes in depth of benchmark soil properties and corresponding erosion rates in soil series classified as HEL and potentially HEL (foot/toeslope excluded). 44 Table 4.6. Changes in depth of benchmark soil properties and corresponding erosion rates in all soil series not classified as HEL and potentially HEL (foot/toeslope excluded). 44 Table 5.1. Specific characteristics of Black Soils as defined by three different systems of soil taxonomy. 54 Table 5.2. Percent of sampled pedons that show a change in different levels of soil classification after approximately 50 years of agricultural land use. 54 Table 5.3. Change in the percent of sampled pedons that are classified as Black Soils in three different systems of soil taxonomy. 54 Table 5.4. Diversity of pedons sampled in terms of the original fundamental classification level. 55 Table 5.5. Example changes in soil classification in Canadian, US and FAO-WRB Soil Taxonomy after 50 years of agricultural land use. 55 Table 5.6. Other changes in classification specific to Canadian Soil Taxonomy. 56 Table 7.1 Reference depths for each pedon. 66 1 Chapter 1. General Introduction “The soil is the one indestructible, immutable asset that the nation possesses. It is the one resource that cannot be exhausted, cannot be used up. It may be impaired by abuse but never destroyed.” This was the view of Milton Whitney and the Federal Bureau of Soils in 1909 (as reported in Anderson, 1913). Fascinatingly, in some ways, our view of the nature of soil has not changed over the last 101 years. We still largely think of it as an immutable asset. We concede it can be damaged but, at least, pedologists in the USA do not really study soil as if it is exhaustable. Yes, the Natural Resource Conservation Service (NRCS), the current incarnation of the Federal Bureau of Soils, realizes, now, that soils are more tenuous than they once claimed. However, much of pedological theory and the premises of soil classification continue to be undergirded by this century-old idea that soil is relatively indestructible and that soils will not fundamentally change over human time scales. These ideas are perhaps most strongly held in the land-grant universities as evidenced by soil curricula that rarely offer courses on soil change, urban soils, or even soil-watershed relationships. Courses such as those have been left to other institutions to develop. With my dissertation research, I strive to examine the potential for soils to change with agricultural land use over human time scales. My basic goal has been testing the following hypothesis: Ho: After 50 years of agricultural land use, soil has changed insignificantly. H1: After 50 years of agricultural land use, soil has changed significantly. I test this hypothesis by sampling and describing 82 “representative pedons” from 21 counties in Iowa that were originally sampled and described between 1943 and 1963 by the National Cooperative Soil Survey (Figure 1.2). Nearly all of the sites sampled were in row crop production for the majority of the time period between sampling dates. The changes in soil properties over that time are presented in Chapter 2. From the data presented in Chapter 2, I have developed a model of anthropedogenesis (Chapter 3), which synthesizes the soil forming processes that humans influence with agricultural land 2 use. In Chapter 4, I estimate erosion rates. And Chapter 5 evaluates how the integration of the changes in discrete soil properties has resulted in a change in soil classification in three taxonomic systems. Figure 1.1. Word cloud showing most common words used in this dissertation. The larger the word the more commonly it was used. (Courtesy www.wordle.net.) 3 Figure 1.2. Iowa counties with sites sampled across landform regions (original map from Landforms of Iowa Prior, 1991). 4 Chapter 2. Soil changes after 50 years of agricultural land use: a pedological analysis Jessica J. Veenstra and C. Lee Burras A paper for submission to Journal TBD Abstract Many scientists have studied agricultural soil change. Most of these studies focus on changes in the surface 0 to 30 cm soil. In this study, we assess agricultural soil change to a depth of 150 cm by comparing current descriptions and laboratory data to historically described sites under predominantly row-crop agriculture in Iowa, United States.