Thwarting climate change using simple practices in complex and adaptive agricultural systems
Open Access
- Author:
- Burton, Amanda
- Graduate Program:
- Agronomy
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- February 25, 2021
- Committee Members:
- Armen R. Kemanian, Dissertation Advisor/Co-Advisor
Armen R. Kemanian, Committee Chair/Co-Chair
Heather D Karsten, Committee Member
Carolyn Lowry, Committee Member
John Tooker, Outside Member
Gregory Wayne Roth, Special Member
Erin L Connolly, Program Head/Chair - Keywords:
- climate change
silage
corn
maize
soy
sorghum
dairy
Pennsylvania
United States
agriculture
grain
climate
sunflower
abiotic
stress
production - Abstract:
- Climate change threatens the production of staple crops, like maize, both in the USA and worldwide, due to variations in precipitation and temperature patterns. This shift in climate can have negative abiotic effects on crops like biomass reduction, increase yearly crop yield variability, and exacerbate nutrient pollution like soil mineral nitrogen loss to water bodies. Our ability to create agricultural production systems that mitigate these negative abiotic effects of climate change is imperative. This dissertation aims to investigate the use of polycultures, a diversity of species grown in the same space at the same time, and hybrids with diverse physiological traits to help mitigate these abiotic effects. The use of polycultures in modern large-scale agricultural systems is not new; maize + soy silage polycultures have been investigated since the early 20th century. Chapter 2 collates a century of published maize + soy polyculture data and teases apart the important variables for determining biomass yield. Results show that biomass in polycultures is driven by maize, but a lower density than that of maize monocultures can provide similar biomass. Further, silage may be diversified with soy without sacrificing yield. Finally, the factors in determining polyculture yield are region-specific due to climate. This chapter provides historical context for the use of maize polycultures for silage in modern large-scale agricultural systems. Chapter 3 consists of a field study comparing maize monoculture to sorghum monoculture, soy monoculture, and several polycultures including maize + soy, maize + sorghum, and maize + soy + sorghum + sunflower. The concept is that diverse physiological traits and niche partitioning in each species may improve the year-to-year yield stability and provide other environmental benefits like reduced residual soil mineral nitrogen. Results showed that maize + sorghum polycultures can yield similarly to maize monocultures in terms of biomass while improving the potassium content of the silage and potentially decreasing the residual soil mineral nitrogen compared to a maize monoculture. Maize + soy polyculture can increase the nitrogen and phosphorus concentration of the silage, but also reduces biomass yield compared to maize monoculture. These results are promising and indicate that maize silage may be diversified without a loss of biomass and diversification may provide additional benefits to the production system. Chapter 4 uses the agroecosystem model Cycles to expand the research area of maize + sorghum polycultures for silage, which showed promising results in the field study, beyond the confines of Pennsylvania. Maize, forage sorghum, and maize + sorghum silage systems were simulated by county within the USA (approximately 3,100 simulations for each system). Results indicate that on average, maize + sorghum polycultures for silage may yield similarly to maize monocultures in parts of the Midwest, particularly what is known as the sorghum belt which spans from Texas to South Dakota. Additionally, the yield stability from year to year was similar to that of maize monocultures. Data from this chapter may be used to inform and target field studies in the USA. Chapter 5 further investigates the use of diverse physiological traits and niche partitioning in silage polycultures. Water status and biomass yield was measured in maize monocultures, sorghum monocultures, and a maize + soy + sorghum + sunflower polyculture. The idea was that a polyculture may be able to better withstand drought stress compared to a monocultural stand by mixing species that have different patterns of water capture and use (i.e., isohydric like maize and anisohydric like sorghum and sunflower, or differing traits in soil exploration by roots). Because Pennsylvania received adequate precipitation during the experiments in Chapter 3, water was excluded from the experimental plots using roofing panels laid in the inter-row space. Though the panels did exclude water and measurably dried the plots, they did not induce the level of stress desired. Biomass and harvest index were not impacted by water exclusion and the polyculture yielded similarly to maize monoculture, a further indication that maize monocultures may be diversified without large biomass losses. Community composition of the experimental plots (i.e., monoculture maize, monoculture sorghum, or polyculture) did not affect the water potential of any species, a possible indication that conditions were not stressed enough. Chapter 6 uses a maize for grain system and investigates the use of diverse hybrids (drought tolerant hybrid, non-drought tolerant hybrid, or mix), row density (low or high), and planting arrangement (low-low, high-high, or low-high) to create a system that both retains high production in both water stressed and unstressed years, and provides economic benefits to producers. Producers must balance costs with yield. In the case of withstanding drought stress, producers may opt to plant drought tolerant hybrids. However, these hybrids usually comes with an increased price compared to non-drought tolerant hybrids. A producer may have decreased profits in two cases 1) if a producer plants a non-drought tolerant hybrid and the year is dry (profit loss due to low yield) or 2) if a producer plants drought tolerant hybrid but there is no drought (profit loss due to high-cost seed). Additionally, lower density plantings may allow for the transmission of more photosynthetically active radiation through the canopy, thus opening the possibility for the adoption of green practices like cover crops. Though neither year of this experiment was droughty, results showed that low-density plantings (approximately 4.6 plants m-2) had the highest economic returns while mixing low-cost with drought-tolerant hybrids may provide yield and economic stability. Further, the incorporation of low-density rows provided measurable gaps in the canopy, thus potentially allowing for the interseeding of cover crops. In sum, these results show that traditional maize systems may be diversified to provide additional benefits to the system and producer without sacrificing yield. In silage systems, maize monocultures may be diversified with other species based on producer goals: retaining high biomass or increasing nutritional quality. Additionally, diversification may provide environmental benefits like reduced residual soil mineral nitrogen. In maize for grain systems, including a diversity of traits within a stand of the same species (like drought tolerant and non-drought tolerant) may provide both yield and economic stability. Future work may aim to test these systems under drier conditions, where the added benefits of diverse species and physiological characteristics may express more strongly.