Document Type

Dissertation - Open Access

Award Date

2024

Degree Name

Doctor of Philosophy (PhD)

Department / School

Agronomy, Horticulture, and Plant Science

First Advisor

Sharon Clay

Abstract

Dryland contributions to greenhouse gas (GHG) emissions are increased by N fertilizer applications and high soil water contents. Fertilizer timing and spring growth of cover crops prior to cash crop planting were investigated in separate studies to examine impacts on overall GHG emissions using a near continuous measurement system. There was a significant interaction between N fertilizer rate (0 vs. 224 kg N ha-1 surface-applied as urea) and application date (p= 0.01) for CO2 emissions. This interaction occurred because N fertilizer increased CO2 emissions by 35% for the 21 d interval following early spring application. When application was delayed until mid-spring, the opposite response occurred, and N fertilizer application reduced CO2 emissions by 19% (p=0.06). CO2 and non-CO2 emissions (N2O plus CH4) were analyzed separately in this study because previous research demonstrated that C addition from crop residues can offset CO2 emissions at this location. The soil was a CH4 sink for all six application dates, but atmospheric CH4 consumption was 85% greater during spring and early summer [averaging -85.8 g CO2e (ha×h)-1] than during fall/early winter [averaging -46.3 g CO2e (ha×h)-1]. The soil consumed CH4 at a rate to offset N2O emissions by 9.6% during midspring and early summer when N fertilizer wasn’t applied and by 3.1% when N fertilizer was applied. Dormant-seeded cereal rye (Secale cereale L.) produced an average of 445 kg biomass ha-1 during the first three weeks of spring growth, which is normally prior to corn (Zea mays L.) emergence. The cover crop reduced N2O emissions by 53% and did not increase CO2 emissions. However, since N2O emissions only made up 4% of total GHG emissions, the cover crop only reduced total GHG emissions by 2%. These results indicate that early spring in eastern South Dakota climates may be a key time to target mitigation strategies for soil GHG emissions in a corn and soybean production system. Delaying N fertilizer application from early spring to mid-spring has more potential to reduce these emissions (26% reduction) than growing a cereal rye cover crop that is terminated just prior to corn planting (2% reduction).

Publisher

South Dakota State University

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Rights Statement

In Copyright