The Effects of Tillage Intensities on Biological Control Potential in Organic Cropping Systems
Open Access
- Author:
- Tillotson, Shea
- Graduate Program:
- Entomology
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- May 30, 2024
- Committee Members:
- Mary Ellen Barbercheck, Thesis Advisor/Co-Advisor
Sara Hermann, Committee Member
Gary Felton, Program Head/Chair
John M Wallace, Committee Member - Keywords:
- Reduced-tillage
agroecology
tillage
entomopathogenic fungi
insect pest
biological control
predation - Abstract:
- Biodiversity is vital to sustainable agriculture. Soil health is the ability of soil to sustain life while also supporting a complex ecosystem, including plants, animals, and humans (Krauss et al., 2020; Lehmann et al., 2020) Without the use of synthetic pesticides, organic practices can encourage the establishment of diverse organisms. Soil organisms can contribute to soil health through processes such as decomposition, nutrient cycling, and biological control. Organic growers who are interested in improving their soil, may consider reducing soil disturbance through reducing tillage. Long-term and short-term reductions in tillage have been associated with greater soil nutrient retention and organic matter content, reduced risk of erosion, and support of beneficial biological communities, such as arthropod natural enemies and pathogens of insect pests. While organic growers tend to use inversion tillage implements, such as the moldboard plow, to incorporate soil fertility amendments, prepare seedbeds, and to control weeds, the high-speed disk (HSD) is an emerging tool of interest to growers because it can be operated at high speeds and disturbs soil to a shallow depth. This non-inversion tillage tool may allow growers to reduce deep soil disturbance while meeting the need for some soil disturbance in organic systems. However, little is understood about the effects of the high-speed disk with other conservations practices, including the use of a crop rotation, cover crops, and organic soil fertility amendments. In this thesis, I strived to compare and understand the effect of varying levels of soil disturbance imposed across a gradient in three approaches to soil management in organic systems over a three-year annual feed grain and forage rotation. These levels of disturbances included systems which imposed soil inversion with a moldboard plow, shallow disturbance with a high-speed disk, and no-till planting following the use of a roller crimper to terminate cover crops. This research focused on in-season and carry over, or legacy, effects of soil management using these tools on biological control potential in the soil, on the soil surface, and in crop foliage in organic production systems. These three chapters are focused on the effect of tillage system and management on predatory arthropod communities within the foliage of corn, epigeal natural enemy predation potential, and prevalence of the insect-parasitic fungus Metarhizium robertsii within the soil. This research reports results from assays conducted from 2021 through 2023 as a part of a multidisciplinary project that examines the effect of soil disturbance while intensifying organic grain production on multiple system characteristics. Experimental systems were developed to differ in terms of cover crop species, crop and cover crop establishment and termination method; tillage tools, and timing and frequency of their use; and in-season crop management. This thesis reports research aimed to determine the effects of tillage intensity and depth on potential biocontrol across a three-year annual feed grain and forage rotation. In Chapter 1, I reviewed and synthesized scientific literature related to the effects of tillage on beneficial soil organisms including predatory arthropods and entomopathogenic fungi. I also reviewed current knowledge about the western bean cutworm (Striacosta albicosta), a relatively new noctuid pest of corn and soybeans in the Northeastern United States. Damage by the western bean cutworm, potential biological control of the western bean cutworm, and western bean cutworm range expansion theories as they relate to reduced-tillage were considered in this chapter. In Chapter 2, I investigated the effects of the four experimental systems on the prevalence of the entomopathogenic fungus, M. robertsii in the soil and on biological control potential by predatory arthropods on the soil surface. The four systems include: 1. an inversion tillage system using standard practices in commercial organic agriculture; 2. a shallow-tillage system utilizing the emerging high-speed disk tillage tool as an attempt to reduce soil disturbance while using tillage management; 3. a reduced-tillage system using infrequent inversion tillage and no-till planting that attempts to reduced soil disturbance to the extent possible; and 4. a perennial alfalfa-orchardgrass sequence with multiyear establishment as a comparison between the annual systems in relation to soil health and agronomic performance. I hypothesized that tillage intensity and depth would negatively affect prevalence of M. robertsii in the soil and predation on the soil surface. Soil depth was determined using the Soil Disturbance Rating from the USDA Natural Resources Conservation Services (NRCS, 2008). I hypothesized that 1) the inversion tillage system (System 1), which imposed the most intense and deepest soil disturbance with the moldboard plow, would result in the lowest soil surface predation rates and the lowest prevalence of M. robertsii; 2) the reduced-tillage system (System 3), which imposed the lowest intensity of disturbance on the annual crops, would result in the greatest soil surface predation rates and the greatest prevalence of M. robertsii within the annual crop systems (Systems 1- 3); 3) the high-speed disk system (System 2), with an intermediate intensity of disturbance between Systems 1 and 3, would result in an intermediate prevalence of M. robertsii in the soil and intermediate soil surface predation rates; and 4) the perennial alfalfa-orchardgrass sequence (System 4), with relatively low disturbance and multi-year establishment to allow comparison to the annual crop systems, would result in the overall greatest prevalence of M. robertsii and the greatest level of soil surface predation. To determine potential for soil surface predation, I conducted sentinel insect assays with last instar waxworms (Galleria mellonela). To determine prevalence of M. robertsii, I conducted sentinel infection assays with field-collected soil baited with mealworms (Tenebrio molitor) or waxworms (Galleria mellonella). Unexpectedly, the inversion tillage system (System 1) did not result in the lowest prevalence of M. robertsii. The lowest prevalence of M. robertsii was observed with the high-speed disk management (System 2). This could be due to the inversion and mixing of the soil throughout a deeper depth with the moldboard plow in System 1 than when utilizing the HSD in System 2. This soil inversion and mixing can distribute the fungal spores throughout the soil profile. All other comparisons between systems were not significant, including the comparison between the perennial alfalfa-orchardgrass forage and the annual tilled cropping systems. As hypothesized, soil surface predation was greater in System 3 (reduced-tillage), as compared to System 1 (inversion) or System 2 (HSD) in soybean, the rotation phase in which the different approaches to soil management were imposed. There were no differences among the three systems in corn, where tillage management was similar regardless of system. I detected no differences between corn, soybean, and alfalfa crops in System 1 (inversion) and 3 (reduced-tillage), however, this could be a function of intensity of soil disturbance, not inherent crop differences. The lack of a legacy effect of tillage management on the measured biological properties suggests that the occasional use of inversion tillage may not have lasting detrimental effects to beneficial soil-dwelling organisms. In Chapter 3, I investigated the legacy effects of and relationship between systems that varied in soil disturbance from tillage and the biological control potential in corn foliage in 2023. I hypothesized that 1) greater tillage intensity and depth would result in a lower predation rate of naturally occurring western bean cutworm (WBC) eggs and sentinel European corn borer (ECB) eggs, leading to 2) greater damage to corn ears in systems with greater intensity and depth of disturbance, and resulting in 3) lowest corn yield in systems with the greatest level of soil disturbance. I predicted that legacy effects stemming from different approaches to soil management in soybeans in 2021 would be expressed in the corn crops in 2023, which were managed relatively similarly across systems. Specifically, I hypothesized that System 1 would have the lowest biological control potential from natural enemies, leading to greater damage to corn ears and lower yields; System 3 would have the greatest biological control potential, resulting in the lowest amount of damage to corn ears and greatest yield; and System 2 would have an intermediate potential for biological control between System 1 and 2, resulting in an intermediate amount of damage to corn ears and yield. To determine the predation rate on naturally occurring western bean cutworm eggs and sentinel European corn borer eggs, I conducted egg predation assays in which I observed eggs on the corn foliage for signs of predation. To determine the types of predators that were present within the corn foliage, I conducted timed predator counts. I assessed ear damage and collected western bean cutworm larvae from corn ears to determine severity of ear damage and relative caterpillar abundance. I unexpectedly found that egg abundance, predation rate, and predator communities in corn were similar across the three experimental systems. The greatest caterpillar abundance and associated amount of ear damage was detected in System 2 (high-speed disk). There was no difference in yield across systems and I did not detect a significant legacy effect, indicating that tillage practices in the previous year may not affect predation of insect eggs in the following year. Management using the high-speed disk resulted in the greatest numbers of WBC caterpillars and the greatest level of damage to corn ears. Therefore, growers may want to avoid relying on the high-speed disk as their primary tillage tool.