Abstract
Fertilized agricultural soils serve as a primary source of anthropogenic N2O emissions. In South Africa, there is a paucity of data on N2O emissions from fertilized, irrigated dairy-pasture systems and emission factors (EF) associated with the amount of N applied. A first study aiming to quantify direct N2O emissions and associated EFs of intensive pasture-based dairy systems in sub-Sahara Africa was conducted in South Africa. Field trials were conducted to evaluate fertilizer rates (0, 220, 440, 660, and 880 kg N ha−1 year−1) on N2O emissions from irrigated kikuyu–perennial ryegrass (Pennisetum clandestinum–Lolium perenne) pastures. The static chamber method was used to collect weekly N2O samples for one year. The highest daily N2O fluxes occurred in spring (0.99 kg ha−1 day−1) and summer (1.52 kg ha−1 day−1). Accumulated N2O emissions ranged between 2.45 and 15.5 kg N2O-N ha−1 year−1 and EFs for mineral fertilizers applied had an average of 0.9%. Nitrogen in yielded herbage varied between 582 and 900 kg N ha−1. There was no positive effect on growth of pasture herbage from adding N at high rates. The relationship between N balance and annual N2O emissions was exponential, which indicated that excessive fertilization of N will add directly to N2O emissions from the pastures. Results from this study could update South Africa’s greenhouse gas inventory more accurately to facilitate Tier 3 estimates.
Highlights
The main greenhouse gas (GHG) contributors towards net global warming potential from the agricultural sector are carbon dioxide (CO2 ), methane (CH4 ), and nitrous oxide (N2 O) [1]
Our study indicated that the inclusion of the Intergovernmental Panel on Climate Change (IPCC) default value for animal excreta heavily overpredicted the measured N2 O emissions
Our results indicated that the relationship between N2 O-N losses and N input, when plant N demand is considered, can best be described by a nonlinear function rather than a linear function
Summary
The main greenhouse gas (GHG) contributors towards net global warming potential from the agricultural sector are carbon dioxide (CO2 ), methane (CH4 ), and nitrous oxide (N2 O) [1]. N2 O is released into the atmosphere during the processes of denitrification (reduction of nitrate (NO3 − ) to di-nitrogen gas (N2 ) by soil microbes) under anaerobic conditions and nitrification N2 O has a 121-year atmospheric life span and a global warming potential of 265 times that of CO2 compared over a 100-year period [3]. This makes mitigation strategies of N2 O critical to control GHG emissions from the agricultural sector. It is predicted that South African agricultural soils are responsible for 28% of N2 O emissions from the AFOLU sector as a result of fertilizer application, urea for animal feed, and animal excreta [7]
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