Effects of Semiarid Wheat Agriculture on Soil Microbial Properties: A Review

H. Rodgers, J. Norton, L. Van Diepen
University of Wyoming
Semiarid grain agriculture: our most important crops in our most vulnerable landscapes
  • Wheat constitutes 1/5th of the global food supply [3]
  • Most wheat is grown in semiarid lands, which are deteriorating under the pressures of population growth and climate change [4]
Soil microorganisms are critical for sustainable and resilient food production
  • Microbe-rich soils both mitigate climate change (by sequestering carbon) and adapt to it (by resisting extreme events such as floods and drought)
  • Soil microbes show promise as soil health indicators because they respond to management change much more rapidly than soil chemistry or structure [1-2]
  • The relationships between soil microbial properties and management practices are poorly understood in semiarid environments
  1. Which management practices consistently support microbial soil health in semiarid wheat agriculture?
  2. How can microbial properties be used to indicate changes in soil health & carbon sequestration, and crop yield?
We reviewed 60 research papers published 2000-2020 that analyzed soil microbial properties in semiarid non-irrigated wheat fields under different management systems.
Figure 1. The reviewed studies took place in seven countries and were organized into sections on fertilization, tillage, and cropping system.
Reduced tillage, increased cropping intensity, and organic matter inputs consistently support soil microbial health
  • Prevents erosion of microbe-rich topsoil and improves soil moisture retention and temperature regulation
  • Increases microbial biomass and activity in the top 10 or 15 cm [5, 7]
  • Stratifies both bacteria and fungi by depth [8-9]
  • Fungi are more affected by tillage but take longer to recover (4+ years) after tillage than bacteria
  • Representative study: conversion to no-till increased wheat yield (by 20%), the activities of four enzymes, microbial biomass (by 50%), and SOC (by 25%) in 0-10cm after 15 years [5]
  • Improves SOC, microbial activity, and fungi
  • Fungi and fungi:bacteria ratio are particularly reliable indicators of increasing C storage due to changes in cropping [11]
  • In drier areas, reducing fallow from every other year to every third year may provide as many benefits as eliminating fallow entirely
  • Legumes increase microbial activity and especially microbial groups associated with N fixation and cycling, and these effects can last several years
  • Great Plains continuous wheat systems have higher SOC (by 17%), fungal biomass (by 300%), and aggregate stability (by 200%) than wheat-fallow, on average [11]
  • Fertilization (particularly chemical fertilizers) impact bacteria more than fungi, decreasing fungi:bacteria ratio [13-14]
  • Organic amendments (compost, manure, or biosolids) provide increasing SOC and fungi as well as bacteria, and these effects can last more than a decade in semiarid environments [15]
Microbes are sensitive soil health indicators
  • When sampled correctly, microbes reliably respond to management changes and can predict changes in soil health, C sequestration, and yield sometimes years before these changes are significant
  • Microbial and fungal biomass, enzyme activity, glomalin, and fungi:bacteria most reliably indicated soil health change in the reviewed studies [5-6, 10, 12]
  • Microbial community structure & diversity is sensitive to management but not easily interpretable [1, 2]
Figure 2. The most common microbial analyses performed by the reviewed studies were microbial biomass, gene sequencing, and enzyme activities.
Sampling and analyses must be tailored to the system being studied
Tillage Sample at multiple depths to detect changes in microbial stratification
Fertilization & Amendment
Analyze fungi and bacteria separately. Bacteria and enzyme activities are more sensitive to nutrient status than fungi, but a brief abundance in N-cycling bacteria and reduction in F:B does not indicate long-term soil health improvement
Cropping System

Analyze fungi for a more reliable indicator of increasing SOC. Fungi are more sensitive to plant dynamics and SOC than bacteria [14, 16-18].

Monitor soil moisture, as increases in cropping intensity may not have the desired effect if soil water is depleted

Table 1. Sampling recommendations for the different management systems reviewed.
  • Microbial properties can vary widely over time, so whenever possible, microbial indicators should be considered in relation to a nearby reference system considered “healthy” based on the research objectives
  • Longer-term experiments may choose to focus on fungal properties as more reliable, stable soil health indicators, whereas experiments less than five years or based mostly on soil nutrient differences may need to rely on bacterial indicators and labile C pools
Future research that links short-term microbial change to long-term yield and SOC change in agricultural fields can help understand which microbial analyses best indicate long-term change in specific systems.

1. Fierer, N.; Wood, S.A.; Mesquita, C.P.B. de How Microbes Can, and Cannot, Be Used to Assess Soil Health; EcoEvoRxiv, 2020;

2. Stott, D. Recommended Soil Health Indicators and Associated Laboratory Procedures. 2019, 76.

3. Shiferaw, B.; Smale, M.; Braun, H.-J.; Duveiller, E.; Reynolds, M.; Muricho, G. Crops That Feed the World 10. Past Successes and Future Challenges to the Role

  Played by Wheat  in Global Food Security. Food Secur. 2013, 5, 291–317, doi:10.1007/s12571-013-0263-y.

4. O’Leary, G.J.; Aggarwal, P.K.; Calderini, D.F.; Connor, D.J.; Craufurd, P.; Eigenbrode, S.D.; Han, X.; Hatfield, J.L. Challenges and Responses to Ongoing and Projected Climate Change for Dryland Cereal Production Systems throughout the World. Agronomy 2018, 8, 34, doi:10.3390/agronomy8040034.

5.     Liu, E.K.; Zhao, B.Q.; Mei, X.R.; So, H.B.; Li, J.; Li, X.Y. Effects of No-Tillage Management on Soil Biochemical Characteristics in Northern China. J. Agric. Sci.2010.

6.     Araya, T.; Nyssen, J.; Govaerts, B.; Deckers, J.; Sommer, R.; Bauer, H.; Gebrehiwot, K.; Cornelis, W.M. Seven Years Resource-Conserving Agriculture Effect on Soil Quality and Crop Productivity in the Ethiopian Drylands. Soil Tillage Res. 2016, 163, 99–109, doi:10.1016/j.still.2016.05.011.

7.     Liu, Y.; Yang, L.; Gu, D.; Wu, W.; Wen, X.; Liao, Y. Influence of Tillage Practice on Soil CO2 Emission Rate and Soil Characteristics in a Dryland Wheat Field. Int. J. Agric. Biol. Pak. 2013.

8.     Madejón, E.; Moreno, F.; Murillo, J.M.; Pelegrín, F. Soil Biochemical Response to Long-Term Conservation Tillage under Semi-Arid Mediterranean Conditions. Soil Tillage Res. 2007, 94, 346–352, doi:10.1016/j.still.2006.08.010.

9.     Melero, S.; López-Bellido, R.J.; López-Bellido, L.; Muñoz-Romero, V.; Moreno, F.; Murillo, J.M.; Franzluebbers, A.J. Stratification Ratios in a Rainfed Mediterranean Vertisol in Wheat under Different Tillage, Rotation and N Fertilisation Rates. Soil Tillage Res. 2012, 119, 7–12, doi:10.1016/j.still.2011.11.012.

10.     Sainju, U.M.; Lenssen, A.; Caesar-Thonthat, T.; Waddell, J. Dryland Plant Biomass and Soil Carbon and Nitrogen Fractions on Transient Land as Influenced by Tillage and Crop Rotation. Soil Tillage Res. 2007, 93, 452–461, doi:10.1016/j.still.2006.06.003.

11.     Rosenzweig, S.T.; Fonte, S.J.; Schipanski, M.E. Intensifying Rotations Increases Soil Carbon, Fungi, and Aggregation in Semi-Arid Agroecosystems. Agric. Ecosyst. Environ. 2018, 258, 14–22, doi:10.1016/j.agee.2018.01.016.

12.     Biederbeck, V.O.; Zentner, R.P.; Campbell, C.A. Soil Microbial Populations and Activities as Influenced by Legume Green Fallow in a Semiarid Climate. Soil Biol. Biochem. 2005, 37, 1775–1784, doi:10.1016/j.soilbio.2005.02.011.

13.     Strickland, M.S.; Rousk, J. Considering Fungal:Bacterial Dominance in Soils – Methods, Controls, and Ecosystem Implications. Soil Biol. Biochem. 2010, 42, 1385–1395, doi:10.1016/j.soilbio.2010.05.007.

14.     Liao, H.; Zhang, Y.; Zuo, Q.; Du, B.; Chen, W.; Wei, D.; Huang, Q. Contrasting Responses of Bacterial and Fungal Communities to Aggregate-Size Fractions and Long-Term Fertilizations in Soils of Northeastern China. Sci. Total Environ. 2018, 635, 784–792, doi:10.1016/j.scitotenv.2018.04.168.

15.     Reeve, J.R.; Endelman, J.B.; Miller, B.E.; Hole, D.J. Residual Effects of Compost on Soil Quality and Dryland Wheat Yield Sixteen Years after Compost Application. Soil Sci. Soc. Am. J. 2012, 76, 278–285, doi:10.2136/sssaj2011.0123.

16.     Ai, C.; Zhang, S.; Zhang, X.; Guo, D.; Zhou, W.; Huang, S. Distinct Responses of Soil Bacterial and Fungal Communities to Changes in Fertilization Regime and Crop Rotation. Geoderma 2018, 319, 156–166, doi:10.1016/j.geoderma.2018.01.010.

17.     Cassman, N.A.; Leite, M.F.A.; Pan, Y.; de Hollander, M.; van Veen, J.A.; Kuramae, E.E. Plant and Soil Fungal but Not Soil Bacterial Communities Are Linked in Long-Term Fertilized Grassland. Sci. Rep. 2016, 6, 23680, doi:10.1038/srep23680.

18.     Hannula, S.E.; Kielak, A.M.; Steinauer, K.; Huberty, M.; Jongen, R.; Long, J.R.D.; Heinen, R.; Bezemer, T.M. Time after Time: Temporal Variation in the Effects of Grass and Forb Species on Soil Bacterial and Fungal Communities. mBio 2019, 10, doi:10.1128/mBio.02635-19.

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