How many samples? Soil variability affects confidence in the use of common agroecosystem soil indicators

Alef, 1995, Dehydrogenase activity Bispo, 2009, Indicators for monitoring soil biodiversity, Integrated Environ. Assess. Manage., 5, 717, 10.1897/IEAM-2009-064.1 Blackmore, L.C., Searle, P.L., Daly, B.K., 1987. Methods for chemical analysis of soils. NZ Soil Bureau Scientific Report 80. Blake, 1986, Bulk Density Champely, S., 2018. pwr: Basic Functions for Power Analysis. R package version 1.2-2. https://CRAN.R-project.org/package=pwr. Culman, 2012, Permanganate oxidizable carbon reflects a processed soil fraction that is sensitive to management, Soil Sci. Soc. Am. J., 76, 494, 10.2136/sssaj2011.0286 Dhillon, 2017, Soil organic carbon sequestration by shelterbelt agroforestry systems in Saskatchewan, Can. J. Soil Sci., 97, 394 Doran-Browne, 2017, Offsets required to reduce the carbon balance of sheep and beef farms through carbon sequestration in trees and soils, Animal Product. Sci., 58, 1648, 10.1071/AN16438 Godde, 2016, Understanding the impacts of soil, climate, and farming practices on soil organic carbon sequestration: a simulation study in Australia, Front. Plant Sci., 7, 661, 10.3389/fpls.2016.00661 Gollany, 2018, Measurements and models to identify agroecosystem practices that enhance soil organic carbon under changing climate, J. Environ. Qual., 47, 579, 10.2134/jeq2018.05.0213 Grunwald, 2016, What do we really know about the space–time continuum of soil-landscapes?, 16 Hendrickson, J., Sanderson, M., 2017. Perennial-Based Agricultural Systems and Livestock Impact on Soil and Ecological Services. In: Soil Health and Intensification of Agroecosytems, pp. 151–171. Keuskamp, 2013, Tea Bag Index: a novel approach to collect uniform decomposition data across ecosystems, Methods Ecol. Evol., 4, 1070, 10.1111/2041-210X.12097 Kort, 1998, Carbon reservoir and biomass in Canadian prairie shelterbelts, Agrofor. Syst., 44, 175, 10.1023/A:1006226006785 Kratz, 1998, The bait-lamina test: general aspects, application and perspectives, Environ. Sci. Pollut. Res., 5, 94, 10.1007/BF02986394 Kremen, 2015, Reframing the land-sparing/land-sharing debate for biodiversity conservation, Ann. N. Y. Acad. Sci., 1355, 52, 10.1111/nyas.12845 Manning, 2018, Redefining ecosystem multifunctionality, Nat. Ecol. Evol., 2, 427, 10.1038/s41559-017-0461-7 Mize, 2008, Ecological development and function of shelterbelts in temperate North America, Vol. 4, 27 Moir, J.L., Fertsak, U., Cameron, K.C., Di, H.J., 2006, July. The spatial distribution and area coverage of urine depositions in grazed dairy or sheep and beef pastures in New Zealand. In: Proceedings of the 18th World Congress of Soil Science, vol. 160. Nair, 2009, Soil carbon sequestration in tropical agroforestry systems: a feasibility appraisal, Environ. Sci. Policy, 12, 1099, 10.1016/j.envsci.2009.01.010 Newsome, 2000 Norton, 2013 O'Brien, 2016, Spatial scale drives patterns in soil bacterial diversity, Environ. Microbiol., 18, 2039, 10.1111/1462-2920.13231 O'Donnell, 2001, Plants and fertilisers as drivers of change in microbial community structure and function in soils, Plant Soil, 232, 135, 10.1023/A:1010394221729 R Development Core Team, 2017. R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. URL https://www.R-project.org. Söderström, 2014, What are the effects of agricultural management on soil organic carbon (SOC) stocks?, Environ. Evidence, 3, 2, 10.1186/2047-2382-3-2 Stark, 2008, Differences in soil enzyme activities, microbial community structure and short-term nitrogen mineralisation resulting from farm management history and organic matter amendments, Soil Biol. Biochem., 40, 1352, 10.1016/j.soilbio.2007.09.025 Stevenson, 1959, Dehydrogenase activity in soils, Can. J. Microbiol., 5, 229, 10.1139/m59-026 Thalmann, 1968, Zur methodik der bestimming der dehydrogenaseaktivitaet im boden mittels triphenyltetrazoliumchlord TTC), Landwirtschaftliche Forschung, 21, 249 Torne, 1990, Assessing feeding activities of soil-living animals I. Bait-Lamina tests, Pedobiologia, 34, 89 Weil, 2003, Estimating active carbon for soil quality assessment: a simplified method for laboratory and field use, Am. J. Altern. Agric., 18, 3, 10.1079/AJAA2003003 Welsch, 2014, Trees on farms: investigating and mapping woody re-vegetation potential in an intensely-farmed agricultural landscape, Agric. Ecosyst. Environ., 183, 93, 10.1016/j.agee.2013.10.031 Williams, 2018, Carbon storage and land-use strategies in aricultural landscapes across three continents, Curr. Biol., 28, 2500, 10.1016/j.cub.2018.05.087 Zar, 1999