1. Shifts in nematode foodweb structure following sustainable soil management in a Pinot Noir vineyard in California
Holly Deniston-sheets1*, James Smith1, Amanda K Hodson2, Katherine Watts3, Forest C. Richmond3, Steve Mais4, Jean C. Dodson Peterson4, Cristina Lazcano1
1 Natural Resources Management and Environmental Sciences Department, California Polytechnic State University, San Luis Obispo, CA, USA.
2 Department of Entomology and Nematology, University of California Davis, CA, USA.
3 Department of Chemistry and Biochemistry, California Polytechnic State University, San Luis Obispo, CA, USA.
4 Department of Wine and Viticulture, California Polytechnic State University, San Luis Obispo, CA, USA. *
Introduction and Objectives
Methods
Conclusions
Soil health is the ability of a soil to function as a living ecosystem. It requires an intact soil foodweb, as soil organisms are responsible for ecosystem functions such as decomposition, nutrient cycling, regulation of pests, and soil structure modification. Such functions can be impaired by agricultural management, such as fertilization or weed control. Inorganic fertilizers may reduce soil foodweb functions and simplify the soil foodweb, including reducing nematode omnivores and predators. Tillage can alter soil carbon content and soil structure, but is used to reduce weed competition and suppress pest species. Soil structure, however, is crucial to the soil foodweb; nematodes in particular rely on pore necks for movement between pores.
The study took place in a Californian vineyard. Grapes are the 3rd largest commodity in California. The massive scope of this industry means that defining the effects of agricultural management could have large impacts on soil health.
The goal of this study was to analyze the effects of varying fertilizer or weed management strategies on soil health, using well-established nematode indices as bioindicators. Specifically, it looked at organic vs. synthetic fertilizer, and herbicide compared to tillage for weed control.
Study Site
Experiments were conducted in a commercial Pinot Noir vineyard on the central coast of California in San Luis Obispo County.
Experimental Design
Fertilizer trial plots received either organic fertilizer (Organic Farms applied at 1000 lbs/acre), synthetic fertilizer
(Agropell at 400 lbs/acre), or no fertilizer (control). Weed management plots either received an herbicide
application (Rely 280 Herbicide from Bayer Crop Science at 3.5 pts/acre with PHT Crop Oil Concentrate from Simplot at
1.2 qts/acre) or were tilled (Clemens Radium Cultivator, 4 times over the growing season). Treatments were applied for
two years.
Each trial had 6 replicates per treatment. Plots were arranged following a complete randomized design within each
trial. Soil samples were taken during the 2nd year in May, July, and September, corresponding to physiologically important
phases of crop growth (bloom, veraison, and harvest). Three samples were taken within each plot and combined for a
composite sample. Data presented here are averages from all sample dates and replicates.
Nematode Community Analysis
Nematode extraction was done via sieving and sucrose centrifugation. Abundance was determined by counting. Identification was done via morphology. Community Analysis was done using Nematode Indicator Joint Analysis. This uses abundance and the values assigned to nematode groups along a colonizer-persister scale (cp) from 1 - 5, which incorporates trophic groups and roughly corresponds to r & k strategists.
Maturity Index: a measure of disturbance or environmental stability
Structure Index: a measure of the stability of soil community
Data Analysis
General Linear Models, using JMP 13.0 (SAS, Cary, NC).
The use of organic inputs and reduction of tillage disturbance benefits soil health by increasing the stability of the soil food web.
Results indicate that, when compared to herbicide, tilled plots exhibit more disturbance, less structure, and have fewer omnivores and individuals of high cp classes.
Results indicate that plots which received synthetic fertilizer exhibited more community disturbance, fewer persister traits, and lower food web diversity and regulatory functions than plots which received organic herbicide.
Figure 1. Map of experiment area.
Figure 3. Pratylenchus, an herbivorous nematode.
Figure 4. Tripylidae, a predacious nematode.
Figure 2. Rhabditidae, a bacterivore nematode and an r strategist.
Results and Discussion
Effects of weed management strategies on the nematode foodweb
Effects of fertilizer management strategies on the nematode foodweb
Plots which received herbicide application had a higher Sigma Maturity Index (entire nematode community) and Maturity Index (non-herbivorous nematodes only) than plots which were tilled. They also had a higher structure index.
Plots which received organic fertilizer had the highest Maturity and Structure Index values.
This indicates that tillage is more disruptive to the stability of the nematode community than the application of herbicide. In comparison, herbicide applied plots may have:
more “persister” traits present (e.g. k strategists)
greater food web diversity
increased length of the micro-food web, with more linkages in the food chain
more buffering of opportunistic guilds or regulatory functions
greater resilience
These results indicate that the addition of organic fertilizer increases the stability of the nematode foodweb compared to synthetic or no fertilizer. Organic plots likely have:
more “persister” traits (e.g. k strategists)
less environmental and community disturbance
greater food chain linkages
more buffering of opportunistic organisms
Increased herbivore regulation
P-value = 0.040
P-value = 0.008
P-value = (SMI) 0.006, (MI) 0.004
P-value = 0.005
Figure 9. Mean Maturity Index (± s.e) for all sample dates in the 0 – 20 cm depth for fertilizer trials (0 – 5 scale), showing greater values for plots treated with organic fertilizer.
Figure 10. Mean Structure Index values (± s.e) for all sample dates in the 0 – 20 cm depth for fertilizer trials (0 – 100 scale), showing greatest values in plots treated with organic fertilizer.
Figure 5. Mean sigma maturity index and maturity index (± s.e) for all sample dates in the 0 – 20 cm depth, by treatment (on a scale of 0 -5), showing greater values in herbicide-applied plots.
Figure 6. Mean structure index (± s.e) for all sample dates in the 0 – 20 cm depth, by treatment (on a 0 – 100 scale), showing greater values in herbicide-applied plots.
Despite differences however, all plots are still in the “disturbed” category. Although perennial fields typically have higher structure values, low values in this case could be driven by biennial ripping that is used to treat compaction.
However, both treatments fell into a “disturbed” category based on their enrichment and structure index values. This is fairly typical for an agricultural system, and plots which received herbicide instead of tillage are closer to a maturing system than tilled plots.
Higher index values in herbicide applied plots appear to be driven by the groups below, which were found in greater quantities in herbicide treated plots than in those which were tilled.
Higher values in organic plots appear to be driven by the following groups, which were found in greater quantities in the plots which received herbicide:
Nematode
Trophic Group
Mean no. individ
P-value
Herb App
Tilled
Aporcelaimidae (cp-5)
Omnivore
35.80
6.71
0.013
Prismatolaimus (cp-3)
Bacterivore
31.20
0.71
0.016
Xiphinema (pp-5)
Herbivore
5.66
0.00
0.003
Nematode
Trophic Group
Mean no. of individ.
P-value
Organic
Synthetic
None
Aporcelaimidae (cp-5)
Omnivore
45.87
9.24
7.89
0.022
Aprutides (cp-2)
Fungivore
406.56
171.54
62.90
0.048
Aphelenchoides (cp-2)
414.34
159.36
315.19
0.091
Figure 11. Classification of the soil samples according to their Enrichment and Structure Indexes. Values are averages for each sampling date.
Figure 8. Classification of the soil samples according to their Enrichment and Structure Indexes. Values are averages for each sampling date.
Figure 12. Aporcelaimidae, an omnivorous nematode
Figure 7. Prismatolaimus nematode
Acknowledgements
Many thanks to my collaborators:
Craig Stubler
Janina Milkereit
And everyone on the Lazcano Lab Team
And the Pacific Vineyard Company, including Erin Amaral
                                      
Research and Economic Development
Research, Scholarly and Creative Activities grants