PLFA

Soil is a complex ecosystem that provides habitat for an endless array of micro and macro organisms. These include bacteria, fungi, protozoa, nematodes, earthworms, etc. These organisms are responsible for much of the nutrient cycling that takes place in the soil. They provide the breakdown of crop residues, store plant nutrients, create stable organic matter in the form of humic acid, and help build soil structure, thus leading to reduced compaction and erosion, while increasing water holding capacity and allowing for deeper root structures. The relationship between different microorganisms and plants is dynamic. The predatory action of protozoa on bacteria helps release nitrogen into the soil and symbiotic bacteria and fungi aide the plant in acquiring more nutrients. Through better understanding of soil microbial communities we can begin to allow these organisms to work for us in our goal of high yielding, sustainable agriculture.

Soil microbial community testing at Ward Laboratories is conducted by analyzing phospholipid fatty acids or PLFA. These fatty acids are found in the cell membranes of living organisms, from bacteria to plants and animals. However, they degrade relatively quickly in the soil when an organism dies and the membrane begins to break down. These characteristics make extracting and quantifying PLFA from the soil a powerful tool for estimating living microbial biomass. In addition, PLFA biomarkers, or signature fatty acids, allow us to identify the presence or absence of various functional groups of interest such as different bacterial groups, actinomycetes, arbuscular mycorrhizal fungi, rhizobia, protozoa, etc. PLFA is a snapshot of community structure and abundance at the time of sampling. As environmental conditions such as pH, temperature, and moisture change so does the microbial community. These communities are also influenced by soil type, organic matter, intensity and type of tillage, crop rotations, cover crops, and herbicide or pesticide applications. The ability of microbial communities to change rapidly provides producers with a tool to compare agricultural management techniques with respect to overall better soil health and fertility.

Soil fertility and biological tests can be run on any soil samples you wish. However, there is no baseline for biological testing as there is for chemical analysis. Therefore, this test is most useful in making comparisons between management conditions. The list of management conditions can be anything you are interested in, perhaps till vs. no-till, different fertilizer applications, crop rotations, various mono cover crops or mixes, grazing vs. no grazing, etc. The main focus is to compare various agricultural techniques and their effects on soil microbiology as well as fertility. Trying to tie the two related, but different, forms of testing together for sustainable farming is the main goal.

Additional information will be added to the website as new information becomes available. Any questions regarding biological testing may be directed to biotesting@wardlab.com.

Sampling for biological testing is slightly different than regular soil testing. It is very important to treat all the samples equally. Listed here are general guidelines to sample for biological testing:

1. Collect all of your samples for comparison on the same day if possible. Samples may be collected on different days but try to keep sampling events to one week or less if comparisons are to be made between the samples. This reduces changes that may take place if moisture or temperature fluctuates between sampling times.
2. Use a standard soil core sampler. DO NOT use any form of lubricants on the soil core sampler.
3. Take 10-15 cores roughly 0-8 inches deep next to the plants or near the rooting structures. You may also choose the same depth that is normally used for a topsoil sample as long as it is consistent.
4. Combine all the cores, preferably in a zip lock freezer bag or plastic-lined paper soil bag. DO NOT use cloth bags for submitting samples.
5. Add all sample identification information you need to the sample bag and place in a cooler (A Styrofoam cooler with a lid works fine) or a regular box if shipment times are relatively quick.
6. Mark each sample and the shipping container BIOTESTING or PLFA to ensure proper handling on our end.
7. Ice packs can be used if sampling during hot weather. Remember to treat all samples equally for individual sampling periods. In warm seasons, samples may be refrigerated and shipped on ice. 
8. Samples can be mailed to or dropped off at Ward Laboratories Inc, 4007 Cherry Avenue, Kearney, NE 68848. When mailing samples it is best to send them overnight in a cooler

Additional information will be added to the website as new information becomes available. Any questions regarding biological testing may be directed to biotesting@wardlab.com.

Download the PDF here

Download the SHA example report here

SHA Guidelines & Interpretations

List of Peer-reviewed References used for PLFA/FAME Analysis at Ward Laboratories, Inc.

*Not peer-reviewed reference material.

BOLD References – Significant Importance

1. Abiven, S., Menassari, S., Angers, D.A., Leterme, P., 2007. Dynamics of aggregate stability and biological binding agents during decomposition of organic materials. Eur. J. Soil Sci. 58, 239-247.
2. Acosta-Martinez, V., Acosta-Mercado, D., Sotomayor-Ramirez, D., Cruz-Rodriguez, L., 2008. Microbial communities and enzymatic activities under different management in semiarid soils. Appl. Soil Ecol. 38, 249-260.
3. Acosta-Martinez, V., Burow, G., Zobeck, T.M., Allen, V.G., 2010. Soil microbial communities and function in alternative systems to continuous cotton. Soil Sci. Soc. Am. J. 74, 1181-1192.
4. Acosta-Martinez, V., Mihka, M.M, Vigil, M.F., 2007. Microbial communities and enzyme activities in soils under alternative crop rotations compared to wheat-fallow in the Central Great Plains. Appl. Soil Ecol. 37, 41-52.
5. Allison, V.J., Yermakov, Z., Miller, R.M., Jastrow, J.D., Matamala, R., 2007. Assessing soil microbial community composition across landscapes: Do surface soils reveal patterns? Soil Sci. Soc. Am. J. 71, 730-734.
6. Ashman, M.R., Hallett, P.D., Brookes, P.C., Allen, J., 2009. Evaluating soil stabilisation by biological processes using step-wise aggregate fractionation. Soil Till. Res. 102, 209-215.
7. Bligh, E.G., Dyer, W.J., 1959. A rapid method of total lipid extraction and purification. Can. J. Biochem. Physiol. 37, 911-917.
8. Bossio, D.A., Girvan, M.S., Verchot, L., Bullimore, J., Borelli, T., Albrecht, A., Scow, K.M., Ball, A.S., Pretty, J.N., Osborn, A.M., 2005. Soil microbial community response to land use change in an agricultural landscape of Western Kenya. Microb. Ecol. 49, 50-62.
9. Bossio, D.A., Scow, K.M., 1998. Impacts of carbon and flooding on soil microbial communities: Phospholipid fatty acid profiles and substrate utilization patterns. Microb. Ecol. 35, 265-278.
10. Bossio, D.A., Scow, K.M., Gunapala, N., Graham, K.J., 1998. Determinates of soil microbial communities: Effects of agricultural management, season, and soil type on phospholipid fatty acid profiles. Microb. Ecol. 36, 1-12.
11. Bronic, C.J., Lal, R., 2005. Soil structure and management: A review. Geoderma 124, 3-22.
12. Brussard, L., De Ruiter, P.C., Brown, G.G., 2007. Soil biodiversity for agricultural sustainability. Agr. Ecosyst. Environ. 121, 233-244.
13. Buckley, D.H., Schmidt, T.M., 2003. Diversity and dynamics of microbial communities in soils from agro-ecosystems. Environ. Microbiol. 5, 441-452.
14. Buyer, J.S., 2002. Rapid sample processing and fast gas chromatography for identification of bacteria by fatty acid analysis. J. Microbiol. Meth. 51, 209-215.
15. Buyer, J.S., 2003. Improved fast gas chromatography for FAME analysis of bacteria. J. Microbiol. Meth. 54, 117-120.
16. Buyer, J.S., Roberts, D.P., Russek-Cohen, E., 2002. Soil and plant effects on microbial community structure. Can. J. Microbiol. 48, 955-964.
17. Buyer, J.S., Teasdale, J.R., Roberts, D.P., Zasada, I.A., Maul, J.E., 2010. Factors affecting soil microbial community structure in tomato cropping systems. Soil Biol. Biochem. 42, 831-841.
18. Cavigelli, M.A., Robertson, G.P., Klug, M.J., 1995. Fatty acid methyl ester (FAME) profiles as measures of soil microbial community structure. Plant Soil 170, 99-113.
19. Cosentino, D., Chenu, C., Bissonnais, Y.L., 2006. Aggregate stability and microbial community dynamics under drying-wetting cycles in a silt loam soil. Soil Biol. Biochem. 38, 2053-2062.
20. Cruz-Hernandez, C., Destaillats, F., 2010. Recent advances in fast gas-chromatography: Application to the separation of fatty acid methyl esters. J. Liq. Chromatogr. R. T. 32, 1672-1688.
21. Dierksen, K.P., Whittaker, G.W., Banowetz, G.M., Azevedo, M.D., Kennedy, A.C., Steiner, J.J., Griffith, S.M., 2002. High resolution characterization of soil biological communities by nucleic acid and fatty acid analyses. Soil Biol. Biochem. 34, 1853-1860.
22. Doran, J.W., Elliott, E.T., Paustian, K., 1998. Soil microbial activity, nitrogen cycling, and long-term changes in organic carbon pools as related to fallow tillage management. Soil Till. Res. 49, 3-18.
23. Dowling, N.J.E., Nichols, P.D., White, D.C., 1988. Phospholipid fatty acid and infra-red spectroscopic analysis of a sulphate-reducing consortium. FEMS Microbiol. Ecol. 53, 325-334.
24. Drenovsky, R.E., Elliott, G.N., Graham, K.J., Scow, K.M., 2004. Comparison of phospholipid fatty acid (PLFA) to total soil fatty acid methyl esters (TSFAME) for characterizing soil microbial communities. Soil Biol. Biochem. 36, 1793-1800.
25. Drinkwater, L.E., Snapp, S.S., 2007. Nutrients in agroecosystems: Rethinking the management paradigm. Adv. Agron. 92, 163-186.
26. Dunfield, K.E., Xavier, L.J.C., Germida, J.J., 1999. Identification of Rhizobium leguminosarum and Rhizobium sp. (Cicer) strains using a custom fatty acid methyl ester (FAME) profile library. J. Appl. Microbiol. 86, 78-86.
27. Entry, J.A., Mills, D., Mathee, K., Jayachandran, K., Sojka, R.E., Narasimhan, G., 2008. Influence of irrigated agriculture on soil microbial diversity. Appl. Soil. Ecol. 40, 146-154.
28. Fierer, N., Schimel, J.P., Holden, P.A., 2003. Variations in microbial community composition through two soil depth profiles. Soil Biol. Biochem. 35, 167-176.
29. *Findlay, R.H., 2004. Determination of microbial community structure using phospholipid fatty acid profiles, in: Molecular Microbial Ecology Manual, 2nd Edition. Kluwer Academic Publishers, Netherlands, pp. 983-1004.
30. Frostegard, A., Baath, E., Tunlid, A., 1993. Shifts in the structure of soil microbial communities in limed forests as revealed by phospholipid fatty acid analysis. Soil Biol. Biochem. 25, 723-730.
31. Frostegard, A., Tunlid, A., Baath, E., 1991. Microbial biomass measured as total lipid phosphate in soils of different organic content. J. Microbiol. Meth. 14, 151-163.
32. Frostegard, A., Tunlid, A., Baath, E., 2011. Use and misuse of PLFA measurements in soils. Soil Biol. Biochem. 43, 1621-1625.
33. Garcia-Teijeiro, R., Lightfoot, D.A., Hernandez, J.D., 2009. Effect of a chemical modified urea fertilizer on soil quality: Soil microbial populations around corn roots. Commun. Soil Sci. Plan. 40, 2152-2168.
34. Gomez-Brandon, M., Lores, M., Dominguez, J., 2010. A new combination of extraction and derivatization methods that reduces the complexity and preparation time in determining phospholipid fatty acids in solid environmental samples. Bioresource Technol. 101, 1348-1354.
35. Haack, S.K., Garchow, H., Odelson, D.A., Forney, L.J., Klug, M.J., 1994. Accuracy, reproducibility, and interpretation of fatty acid methyl ester profiles of model bacterial communities. Appl. Environ. Microbiol. 60, 2483-2493.
36. Hamel, C., Hanson, K., Selles, F., Cruz, A.F., Lemke, R., McConkey, B., Zentner, R., 2006. Seasonal and long-term resource-related variations in soil microbial communities in wheat-based rotations of the Canadian prairie. Soil Biol. Biochem. 38, 2104-2116.
37. Hamer, U., Makeschin, F., 2009. Rhizosphere soil microbial community structure and microbial activity in set-aside and intensively managed arable land. Plant Soil 316, 57-69.
38. Hedrick, D.B., Peacock, A., Stephen, J.R., Macnaughton, S.J., Bruggemann, J., White, D.C., 2000. Measuring soil microbial community diversity using polar lipid fatty acid and denaturing gradient gel electrophoresis data. J. Microbiol. Meth. 41, 235-248.
39. Helgason, B.L., Walley, F.L., Germida, J.J., 2009. Fungal and bacterial abundance in long-term no-till and intensive-till soils of the Northern Great Plains. Soil Sci. Soc. Am. J. 73, 120-127.
40. Helgason, B.L., Walley, F.L., Germida, J.J., 2010a. No-till soil management increases microbial biomass and alters community profiles in soil aggregates. Appl. Soil. Ecol. 46, 390-397.
41. Helgason, B.L., Walley, F.L., Germida, J.J., 2010b. Long-term no-till management affects microbial biomass but not community composition in Canadian prairie agroecosystems. Soil Biol. Biochem. 42, 2192-2202.
42. Hill, G.T., Mitkowski, N.A., Aldrich-Wolfe, A., Emele, L.R., Jurkonie, D.D., Ficke, A., Maldonado-Ramirez, S., Lynch, S.T., Nelson, E.B., 2000. Methods for assessing the composition and diversity of soil microbial communities. Appl. Soil Ecol. 15, 25-36.
43. Ibekwe, A.M., Kennedy, A.C., 1999. Fatty acid methyl ester (FAME) profiles as a tool to investigate community structure of two agricultural soils. Plant Soil 206, 151-161.
44. Ibekwe, A.M., Kennedy, A.C., Frohne, P.S., Papiernik, S.K., Yang, C.-H., Crowley, D.E., 2002. Microbial diversity along a transect of agronomic zones. FEMS Microbiol. Ecol. 39, 183-191.
45. Insam, H., 2001. Developments in soil microbiology since the mid 1960s. Geoderma 100, 389-402.
46. Kang, S., Mills, A.L., 2006. The effect of sample size in studies of soil microbial community structure. J. Microbiol. Meth. 66, 242-250.
47. Kaur, A., Chaudhary, A., Kaur, A., Chaudhary, R., Kaushik, R., 2005. Phospholipid fatty acid – A bioindicator of environment monitoring and assessment in soil ecosystem. Curr. Sci. India 89, 1103-1112.
48. Keinanen, M.M., Korhonen, L.K., Martikainen, P.J., Vartiainen, T., Miettinen, I.T., Lehtola, M.J., Nenonen, K., Pajunen, H., Kontro, M.H., 2003. Gas chromatographic-mass spectrometric detection of 2- and 3-hydroxy fatty acids as methyl esters from soil, sediment and biofilm. J. Chromatogr. B. 783, 443-451.
49. Kent, A.D., Triplett, E.W., 2002. Microbial communities and their interactions in soil and rhizosphere ecosystems. Annu. Rev. Microbiol. 56, 211-236.
50. Kirk, J.L., Beaudette, L.A., Hart, M., Moutoglis, P., Klironomos, J.N., Lee, H., Trevors, J.T., 2004. Methods of studying soil microbial diversity. J. Microbiol. Meth. 58, 169-188.
51. Kremer, R.J., Means, N.E., 2009. Glyphosate and glyphosate-resistant crop interactions with rhizosphere microorganisms. Eur. J. Agron. 31, 153-161.
52. Liu, M., Hu, F., Chen, X., Huang, Q., Jiao, J., Zhang, B., Li, H., 2009. Organic amendments with reduced chemical fertilizer promote soil microbial development and nutrient availability in a subtropical paddy field: The influence of quantity, type and application time or organic amendments. Appl. Soil Ecol. 42, 166-175.
53. Maul, J., Drinkwater, L., 2010. Short-term plant species impact on microbial community structure in soils with long-term agricultural history. Plant Soil 330, 369-382.
54. Meriles, J.M., Gil, S.V., Conforto, C., Figoni, G., Lovera, E., March, G.J., Guzman, C.A., 2009. Soil microbial communities under different soybean cropping systems: Characterization of microbial population dynamics, soil microbial activity, microbial biomass, and fatty acid profiles. Soil Till. Res. 103, 271-281.
55. *MIDI, Inc. Staff. 2011-2012. Personal communications and onsite training. Newark, DE.
56. Miller, L.T. 1982. Single derivatization method for routine analysis of bacterial whole-cell fatty acid methyl esters, including hydroxy acids. J. Clin. Microbiol. 16, 584-586.
57. Muruganandam, S., Israel, D.W., Robarge, W.P., 2010. Nitrogen transformations and microbial communities in soil aggregates from three tillage systems. Soil Sci. Soc. Am. J. 74, 120–129.
58. Nannipieri, P., Ascher, J., Ceccherini, M.T., Landi, L., Pietramellara, G., Renella, G., 2003. Microbial diversity and soil functions. Eur. J. Soil Sci. 54, 655-670.
59. Ngosong, C., Jarosch, M., Raupp, J., Neumann, E., Ruess, L., 2010. The impact of farming practice on soil microorganisms and arbuscular mycorrhizal fungi: Crop type versus long-term mineral and organic fertilization. Appl. Soil Ecol. 46, 134-142.
60. O’Donnell, A.G., Seasman, M., Macrae, A., Waite, I., Davies, J.T., 2001. Plants and fertilisers as drivers of change in microbial community structure and function in soils. Plant Soil 232, 135-145.
61. Peacock, A.D., Mullen, M.D., Ringelberg, D.B., Tyler, D.D., Hedrick, D.B., Gale, P.M., White, D.C., 2001. Soil microbial community responses to dairy manure or ammonium nitrate applications. Soil Biol. Biochem. 33, 1011-1019.
62. Petersen, S.O., Frohne, P.S., Kennedy, A.C., 2002. Dynamics of a soil microbial community under spring wheat. Soil Sci. Soc. Am. J. 66, 826-833.
63. Petersen, S.O., Klug, M.J., 1994. Effects of sieving, storage, and incubation temperature on the phospholipid fatty acid profile of a soil microbial community. Appl. Environ. Microbiol. 60, 2421-2430.
64. Piotrowska-Seget, Z., Mrozik, A., 2003. Signature lipid biomarker (SLB) analysis in determining changes in community structure of soil microorganisms. Pol. J. Environ. Stud. 12, 669-675.
65. Puglisi, E., Nicelli, M., Capri, E., Trevisan, M., Del Re, A.A.M., 2005. A soil alteration index based on phospholipid fatty acids. Chemosphere 61, 1548-1557.
66. Ramsey, P.W., Rillig, M.C., Feris, K.P., Holben, W.E., Gannon, J.E., 2006. Choice of methods for soil microbial community analysis: PLFA maximizes power compared to CLPP and PCR-based approaches. Pedobiologia 50, 275-280.
67. Rillig, M.C., 2004. Arbuscular mycorrhizae, glomalin, and soil aggregation. Can. J. Soil Sci. 84, 355-363.
68. Ringelberg, D.B., Sutton, S., White, D.C., 1997. Biomass, bioactivity and biodiversity: Microbial ecology of the deep subsurface: Analysis of ester-linked phospholipid fatty acids. FEMS Microbiol. Rev. 20, 371-377.
69. Sanchez-Moreno, S., Ferris, H., Young-Mathews, A., Culman, S.W., Jackson, L.E., 2011. Abundance, diversity and connectance of soil food web channels along environmental gradients in an agricultural landscape. Soil Biol. Biochem. 43, 2374-2383.
70. Schutter, M.E., Dick, R.P., 2002. Microbial community profiles and activities among aggregates of winter fallow and cover-cropped soil. Soil Sci. Soc. Am. J. 66, 142-153.
71. Sekora, N.S., Lawrence, K.S., Agudelo, P., van Santen, E., McInroy, J.A., 2009. Using FAME analysis to compare, differentiate, and identify multiple nematode species. J. Nematol. 41, 163-173.
72. Singh, J.S., Pandey, V.C., Singh, D.P., 2011. Efficient soil microorganisms: A new dimension for sustainable agriculture and environmental development. Agr. Ecosyst. Environ. 140, 339-353.
73. Soderberg, K.H., Olsson, P.A., Baath, E., 2002. Structure and activity of the bacterial community in the rhizosphere of different plant species and the effect of arbuscular mycorrhizal colonisation. FEMS Microbiol. Ecol. 40, 223-231.
74. Strickland, M.S., Lauber, C., Fierer, N., Bradford, M.A., 2009. Testing the functional significance of microbial community composition. Ecol. 90, 441-451.
75. Sundh, I., Nilsson, M., Borga, P., 1997. Variation in microbial community structure in two boreal peatlands as determined by analysis of phospholipid fatty acid profiles. Appl. Environ. Microbiol. 63, 1476-1482.
76. Tang, J., Mo, Y., Zhang, J., Zhang, R., 2011. Influence of biological aggregating agents associated with microbial population on soil aggregate stability. Appl. Soil Ecol. 47, 153-159.
77. Tunlid, A., Hoitink, H.A.J., Low, C., White, D.C., 1989. Characterization of bacteria that suppress Rhizoctonia damping-off in bark compost media by analysis of fatty acid biomarkers. Appl. Environ. Microbiol. 55, 1368-1374.
78. *Tunlid, A., White, D.C., 1992. Biochemical analysis of biomass, community structure, nutritional status, and metabolic activity of microbial communities in soil, in: Stotzky, G., Bollag, J.-M. (Eds.), Soil Biochemistry Vol. 7. Marcel Dekker, Inc., New York, pp. 229-262.
79. Vestal, J.R., White, D.C., 1989. Lipid analysis in microbial ecology: Quantitative approaches to the study of microbial communities. BioScience 39, 535-541.
80. Wander, M.M., Hedrick, D.S., Kaufman, D., Traina, S.J., Stinner, B.R., Kehrmeyer, S.R., White, D.C., 1995. The functional significance of the microbial biomass in organic and conventionally managed soils. Plant Soil 170, 87-97.
81. Welbaum, G.E., Sturz, A.V., Dong, Z., Nowak, J., 2004. Managing soil microorganisms to improve productivity of agro-ecosystems. Crit. Rev. Plant Sci. 23, 175-193.
82. White, D.C., 1988. Validation of quantitative analysis for microbial biomass, community structure, and metabolic activity. Arch. Hydrobiol. Beih. Ergebn. Limnol. 31, 1-18.
83. White, D.C., Davis, W.M., Nickels, J.S., King, J.D., Bobbie, R.J., 1979. Determination of the sedimentary microbial biomass by extractible lipid phosphate. Oecologia 40, 51-62.
84. *White, D.C., Macnaughton, S.J., 1997. Chemical and molecular approaches for rapid assessment of the biological status of soils, in: Pankhurst, C., Doube, B., Gupta, V. (Eds.), Biological indicators or soil health and sustainable productivity. CAB International, Wallingford UK, pp. 371-396.
85. Widmer, F., Fleiβbach, A., Laczko, E., Schulze-Aurich, J., Zeyer, J., 2001. Assessing soil biological characteristics: A comparison of bulk soil community DNA-, PLFA-, and BiologTM – analyses. Soil Biol. Biochem. 33, 1029-1036.
86. Wright, A.L., Hons, F.M., 2005. Soil carbon and nitrogen storage in aggregates from different tillage and crop regimes. Soil Sci. Soc. Am. J. 69, 141-147.
87. Wright, S.F., Green, V.S., Cavigelli, M.A., 2007. Glomalin in aggregate size classes from three different farming systems. Soil Till. Res. 94, 546-549.
88. Wu, Y., Ding, N., Wang, G., Xu, J., Wu, J., Brookes, P.C., 2009. Effects of different soil weights, storage times and extraction methods on soil phospholipid fatty acid analyses. Geoderma 150, 171-178.
89. Young, I.M., Ritz, K., 2000. Tillage, habitat space and function of soil microbes. Soil Till. Res. 53, 201-213.
90. Zelles, L., 1999. Fatty acid patterns of phospholipids and lipopolysaccharides in the characterisation of microbial communities in soil: A review. Biol. Fertil. Soils 29, 111-129.
91. Zelles, L., 1997. Phospholipid fatty acid profiles in selected members of soil microbial communities. Chemosphere 35, 275-294.
92. Zelles, L., Bai, Q.Y., 1993. Fractionation of fatty acids derived from soil lipids by solid phase extraction and their quantitative analysis by GC-MS. Soil Biol. Biochem. 25, 495-507.
93. Zelles, L. Bai, Q.Y., Beck, T., Beese, F. 1992. Signature fatty acids in the phospholipids and lipopolysaccharides as indicators of microbial biomass and community structure in agricultural soils. Soil Biol. Biochem. 24, 317-323.
94. Zibilske, L.M., Bradford, J.M., 2007. Soil aggregation, aggregate carbon and nitrogen, and moisture retention induced by conservation tillage. Soil Sci. Soc. Am. J. 71, 793-802.

• Sustainable Crop Rotations with Cover Crops
• The Biology of Soil Compaction
• The Role of Soil Bacteria
• The Role of Soil Fungus
• The Role of Soil Protozoa and Nematodes
• Understanding Soil Microbes and Nutrient Cycling