Integrated Crop and Livestock Systems for Enhanced Soil Carbon Sequestration and Microbial Diversity in the Semiarid Texas High Plains

Integrated Crop and Livestock Systems for Enhanced Soil Carbon Sequestration and Microbial Diversity in the Semiarid Texas High Plains

Summary

Our project proposed two years of data collection to determine the effects of integrated crop-livestock systems on the soil microbial community composition, soil organic matter (SOM) pools, C sequestration and greenhouse gas (GHG) emissions for the Southern High Plains (SHP) semiarid region. One important goal was to increase producer and consultant awareness regarding the direct and indirect positive effects for managing agricultural lands to achieve enhanced soil functioning. This report will summarize our accomplishments for the second year. Unfortunately, in the second scheduled year of sampling (July 2012), the entire region experienced one of the worst droughts on record and resulted in substantial alteration of experimental design. For the first time in over 8 years, plots did not get planted (applies to cotton/millet plots only), irrigation was not applied (deficit levels originally scheduled would not sustain viable forage growth) and cattle were not brought in. The lack of treatments imposed and the extreme drought (< 68 mm from Oct 2010-July 2011) and high temperatures (48 days > 100F) experienced, we reevaluated the best use of our resources (financial, human-power, etc.). For example, without adequate soil moisture, trace gas measurements flat-lined to near zero levels. Additional data, if sampling had occurred, would not reflect typical conditions, thus skewing any potential interpretations for a second year of data. The intense sampling effort was thus canceled and resources reallocated to assess additional important chemical, microbial and biochemical assessments given the long-term nature of our field plots. To compensate for the lack of a second year of sampling, we were able to use the funds for 4 additional assessments on the samples taken in year 1, which expanded on the original objective to characterize soil microbial communities and their functionality. The three additional assessments were: 1) fungal community structure via pyrosequencing analysis, 2) detailed chemical composition of whole and soil aggregates via FTIR spectroscopy, 3) fungal functionality using Fungilog C utilization plates, and 4) general microbial functionality via multiple enzyme activity assessments involved in C, N, P, and S nutrient cycling.

Our results can be summarized into 2 major sections. The first investigated the role of soil bacterial communities and C sequestration at the aggregate scale and has recently been published (Davinic et al. 2011). Different soil aggregate fractions supported distinct bacterial assemblages and organic and mineral chemical composition. This information provides important implications on how C sequestration occurs within aggregates and the microbial assemblages involved on this process. The abstract from this manuscript is provided in the impacts section below. The second research component specifically investigated the various vegetation types and effects of grazing in three integrated crop and livestock systems (ICL) as well as two continuous cotton systems on soil C content, aggregate distribution and stability, trace gas emissions, and microbial properties. Preliminary evaluation of the data suggest that within 6-8 years, regardless of the cropping system, the perennial grass components (e.g., bermudagrass, old-world bluestem, native grasses mixture) of an ICL stores more C and has more protected soil aggregates (i.e., increased resilience to erosion) compared to the annual cropping components (e.g., cotton-foxtail millet rotation and continuous cotton). Furthermore, the microbial communities were distinct between the perennial grasses and annual crops with the perennial grasses containing higher microbial biomass, enzymatic activities, relative abundance of arbuscular mycorrhizal fungi, and enhanced fungal C utilization efficacy. The irrigated perennial grasses also had higher CO2 and N2O fluxes compared to annual crops but not compared to non-irrigated grasses. However, the cotton-millet rotation was not differentiated from the continuous cotton system. This lack of differentiation is likely due to irrigation differences (rotation is not irrigated whereas our continuous cotton systems are subsurface drip irrigated), the winter fallow periods used in the rotation, and the fact that cotton is such a low residue returning crop, any effects from millet may be masked.

Objectives/Performance Targets

1. 1. Measure the amount of C stored in active, intermediate and passive SOM pools using a detailed physical fractionation method, which provides eight different soil aggregate fractions.
   2. Evaluate greenhouse gas fluxes (CO2, CH4, and N2O) to calculate global warming potential within each system.
   3. Characterize soil microbial community structure using fatty acid methyl ester (FAME) profiling and microbial biomass C (MBC) including bacterial diversity in whole soil and different soil aggregate fractions using a novel molecular biological tool (i.e., pyrosequencing).
   4. Translate results from Objectives 1 through 3 into practices incorporated in agriculture in the THP and similar ecosystems. Specifically, we will increase producer and consultant awareness regarding the direct and indirect positive effects for managing agricultural lands to achieve enhanced soil functioning.

Accomplishments/Milestones

We have successfully met the goals of objectives 1-3 above for sampling year 1.

Significant findings related to objective #1 include the following:
Preliminary evaluation of the data suggest that within 6-8 years, regardless of the cropping system, the perennial grass components (e.g., bermudagrass, old-world bluestem, native grasses mixture) of an ICL stores more C and has more protected soil aggregates (i.e., increased resilience to erosion) compared to the annual cropping components (e.g., cotton-foxtail millet rotation and continuous cotton). However, the cotton-millet rotation was not differentiated from the continuous cotton system. This lack of differentiation is likely due to irrigation differences (rotation is not irrigated whereas our continuous cotton systems are subsurface drip irrigated), the winter fallow periods used in the rotation, and the fact that cotton is such a low residue returning crop, any effects from millet may be masked. Of the perennial grasses, the irrigated bermudagrass paddocks had the highest total soil C content and a greater proportion of this C stored in protected aggregate microsites. No differences in whole total soil C were measured between grazed and non-grazed sites. Aggregate analysis is pending. Our results highlight the importance of different perennial grasses and their potential system-specific impacts on C storage potential. **Manuscript link has been uploaded for further details with figures, tables, etc.

Greenhouse gases (CO2 and N2O) were monitored from June 2010 until July 2011, when treatments (planting, irrigation, cattle incorporation) were halted due to the extreme drought conditions of 2011. Regardless, during year 1, we found higher CO2 fluxes in the irrigated bermudagrass (highest) and Old-World bluestem plots (red symbols in Figure 1) compared to the non-irrigated perennial native grass mixture (second highest) and cotton-millet rotation (lowest) paddocks (blue symbols) during the “active” growth phase (Figure 1).

N2O fluxes appeared to be highly dependent upon the interaction of irrigation/precipitation events and fertilization as the bermudagrass plots (highest irrigation and fertilization rates of all treatments) were the only fields where we had measurable fluxes (Figure 2).

We are currently evaluating the net effect of the positive C impacts from bermudagrass (greater total C storage and enhanced aggregation) with the potentially negative impacts due to greater greenhouse gas fluxes. Additionally, we will evaluate how these results compare with published data in other regions involving other crops and more temperate regions.

Results from our work on bacterial communities within whole and soil aggregate fractions were recently published in Soil Biology and Biochemistry (Davinic et al., 2011). The first and second authors were Ph.D. students partially supported by this grant. Our study suggests that the relative abundance of soil bacteria within soil aggregate fractions are driven more by shifts in chemical composition of SOM than C quantity (content). Specific bacterial assemblages were associated with particular soil chemistries within the soil microenvironment and these associations differed from those found in the whole (non-fractionated) soil samples. The less dominant bacterial taxa were more important for differentiating between communities in soil microenvironments and revealed the importance of robust molecular tools in soil ecological studies. Our findings that the less dominant bacterial taxa showed stronger relationships with specific chemical functional groups than the more dominant bacterial taxa should be further explored to reveal potential linkages between specific bacterial assemblages with C sequestration.

We are currently in the process of drafting another manuscript specifically evaluating the soil bacterial communities as affected by vegetation type within each agroecosystem.

In the second scheduled year of sampling (July 2012), the entire region experienced one of the worst droughts on record and resulted in substantial alteration of experimental design. For the first time in over 8 years, plots did not get planted (applies to cotton/millet plots only), irrigation was not applied (deficit levels originally scheduled would not sustain viable forage growth) and cattle were not brought in. Due to the lack of treatments imposed and the extreme drought (< 68 mm from Oct 2010-July 2011) and high temperatures (48 days > 100F) experienced, we reevaluated the best use of our resources (financial, human-power, etc.). For example, without adequate soil moisture, trace gas measurements flat-lined to near zero levels. Additional data, if sampling had occurred, would not reflect typical conditions, thus skewing any potential interpretations for a second year of data. The intense sampling effort was thus canceled and resources reallocated to assess additional important chemical, microbial and biochemical assessments given the long-term nature of our field plots.

To compensate for the lack of a second year of sampling, we expanded on the original objective (#3 above) which was aimed only at the characterization of the bacterial soil community to cover the costs associated with the characterization of the fungal community using pyrosequencing analyses in both whole soil and soil aggregates. At the time of writing this proposal, previous studies using pyrosequencing to characterize the fungal communities were limited and met with marginal success. The Research and Testing Laboratory we contract our pyrosequencing analyses have had recent success and better developed primers and post-processing analyses. Our ability to add this important community level information will bring new insights regarding the contributions of fungi to C, aggregate stability, and nutrient cycling, especially important in non-irrigated, perennial systems.

A preliminary figure (Figure 3) is provided as an example ordination plot showing that there were distinct soil fungal communities associated with each vegetation type within the ICLs investigated (except that the two irrigated crops, Old-world bluestem and bermudagrass had similar community composition). This figure highlights the distinction between perennial and annual crops.

Additionally, we added a fungal functional assessment to characterize saprotrophic fungal metabolic function in the agroecosystems using FungiLog substrate utilization patterns. This involved a new collaboration with Dr. John Zak from Biology Department in Texas Tech. He is a soil fungal expert and is recognized as the pioneer of the BIolog and FungiLog techniques for the characterization of the C utilization patterns of soil microbial communities.

Six enzyme activities involved in C, N, P, and S cycling were also added. As illustrated in Figure 4. The geometric mean of all six activities were higher in the perennial grasses (PNG = perennial native grass, CTN = cotton, OWB = Old World Bluestem, BER= bermudagrass) compared to annual crops (continuous cotton shown in green and the cotton-millet rotation shown in blue). Furthermore, the 0-5cm values for the annual crops were comprable to the 5-20cm depth values for the perennial crops indicating an impact at depth with the introduction of perennial grasses into the agroecosystem.

We also established collaboration with another USDA soil scientist, Dr. Francisco Calderon, who we contracted with to analyze the soil chemical composition using Fourier Transformed Infrared Spectroscopy (FTIR). This allowed us to begin to link the microbial (bacterial in yr1) and fungal (in yr2) communities with the chemical composition of the soil and specifically the qualities of this composition.

In 2011, one peer-reviewed publication has been submitted and accepted and eight presentations (all presented by the PhD students affiliated with this project) at international scientific meetings including, ASA-CSSA-SSSA, Ecological Society of America Annual Meeting, and American Geophysical Union Annual Meeting.

• Figure 1. CO2 fluxes measured from June 2010 thru July 2011
• Figure 2. N2O fluxes measured June 2010 thru July 2011
• Soil Biology and Biochemistry Publication
• Figure 3. Ordination plot of fungal pyrosequencing data for each of the studied vegetation types.
• Figure 4. Geometric mean of the six enzyme activities.

Impacts and Contributions/Outcomes

1. Publications (accepted):
   Marko Davinic*, Lisa J Fultz, Veronica Acosta-Martinez, Francisco J Calderon, Stephen R Cox, Scot E Dowd, Vivien Allen, John Zak, Jennifer Moore-Kucera. 2011. Pyrosequencing and mid-infrared spectroscopy reveal distinct aggregate stratification of soil bacterial communities and organic matter composition. Soil Biology and Biochemistry 46:63-72.

   In prep:
   M. Davinic, J. Moore-Kucera*, V. Acosta-Martinez, J. Zak, and V. Allen. Soil fungal composition and functionality as affected by integrated cropping-livestock systems using EL-FAME and FungiLog methods. To be submitted to Applied Soil Ecology.

Lisa M. Fultz*, Vivien Allen, Jennifer Moore-Kucera. Increases in protected soil organic carbon found in perennial grassland vegetation as part of integrated crop-livestock systems. Abstracts, Ecological Society of America Annual Meeting. 5-10 August 2012, Portland, OR.

Lisa M. Fultz*, Vivien Allen, Jennifer Moore-Kucera. The story of soil organic carbon in the Southern High Plains. Abstracts, American Geophysical Union Annual Meeting, 5-9 December 2011, San Francisco, CA.

Marko Davinic, Lisa M. Fultz, Veronica Acosta-Martinez, Vivien Allen, Scot E. Dowd and Jennifer Moore-Kucera. 2011. Soil Microbial Dynamics in Alternative Cropping Systems to Monoculture Cotton in the Southern High Plains. Abstracts, Annual Meeting of the American Society of Agronomy, 16-19 October 2011, San Antonio, TX.

Marko Davinic, Lisa M. Fultz, Veronica Acosta-Martinez, John Zak, Vivien Allen and Jennifer Moore-Kucera. 2011. Soil Fungal Community and Functional Diversity Assessments of Agroecosystems in the Southern High Plains. Abstracts, Annual Meeting of the American Society of Agronomy, 16-19 October 2011, San Antonio, TX.

Marko Davinic, Lisa M. Fultz, Veronica Acosta-Martinez, Francisco Calderon, Vivien Allen, Scot E. Dowd and Jennifer Moore-Kucera. 2011. Aggregate Stratification Assessment of Soil Bacterial Communities and Organic Matter Composition: Coupling Pyrosequencing and Mid-Infrared Spectroscopy Techniques. Abstracts, Annual Meeting of the American Society of Agronomy, 16-19 October 2011, San Antonio, TX.

Lisa M. Fultz, Marko Davinic, Franchely Cornejo, Vivien Allen and Jennifer Moore-Kucera. CO2 and N2O Fluxes In Integrated Crop Livestock Systems. Abstracts, Annual Meeting of the American Society of Agronomy, 16-19 October 2011, San Antonio, TX.

Lisa M. Fultz, Marko Davinic, Vivien Allen and Jennifer Moore-Kucera. 2011. Dynamics of Soil Aggregation and Carbon in Long-Term Integrated Crop-Livestock Agroecoystems in the Southern High Plains. Abstracts, Annual Meeting of the American Society of Agronomy, 16-19 October 2011, San Antonio, TX.

Lisa M. Fultz, Marko Davinic, Vivien Allen and Jennifer Moore-Kucera. 2011. Long-Term Integrated Crop-Livestock Agroecosystems and the Effect on Soil Carbon. Abstracts, Annual Meeting of the American Society of Agronomy, 16-19 October 2011, San Antonio, TX.

Collaborators: