Nitrous Oxide Emission from Grazing Is Low across a Gradient of Plant Functional Diversity and Soil Conditions

Abstract

Nitrous oxide (N2O) emissions from pastures can vary significantly depending on soil and environmental conditions, nitrogen (N) input, as well as the plant’s ability to take up the N. We tested the hypothesis that legume-based N sources are characterized by significantly lower emission factors than mineral N based dairy systems. Therefore, this study monitored N2O emissions for a minimum of 100 days and up to two growing seasons across a gradient of plant species diversity. Emissions were measured from both, grazed pastures and a controlled application of urine and dung using the static chamber method. About 90% of the accumulated N2O emissions occurred during the first 60–75 days. The average accumulated N2O emissions were 0.11, 0.87, 0.99, and 0.21 kg ha−1 for control, dung, urine patches, and grazed pastures, respectively. The N uptake efficiency at the excreta patch scale was about 70% for both dung and urine. The highest N2O-N emission factor was less than half compared with the IPCC default (0.3 vs. 0.77), suggesting an overestimation of N2O-N emissions from organically managed pastures in temperate climates. Plant diversity showed no significant effect on the N2O emissions. However, functional groups were significant (p < 0.05). We concluded that legume-containing pasture systems without a fertilizer addition generally appear capable of utilizing nitrogen inputs from excreta patches efficiently, resulting in low N2O emissions.

Toward Specialized or Integrated Systems in Northwest Europe: On-Farm Eco-Efficiency of Dairy Farming in Germany

“…In the grazed systems, the annual emissions were significantly lower than the former IPPC default factor advised (IPCC, 2006); however, they are in accordance with the refined factors currently released for wet areas (IPCC, 2019). Such lower emission factors have also been reported from other grazing experiments in South Africa (Smit et al, 2020) and New Zealand (van der Weerden et al, 2020) as well as on the same experimental site over a long gradient of plant diversity and environments (Nyameasem et al, 2021). In addition to N-excreted by grazing animals, BNF was a major N-input in the IF and IFG systems.…”

“…This can be achieved through a high frequency of short grazing intervals (i.e., rotational grazing), as this ensures that forage is offered with high energy and protein contents. Further improvements can be gained by including forage legumes in grass-clover swards, as this reduces costs further, and also can reduce GHG emissions (Li et al, 2011;Nyameasem et al, 2021). In comparison with confinement systems, these low-cost full-grazing strategies need adjustments in the choice of the animal breeds and calving interval.…”

“…The main advantages of an IFG is the possibility of the inclusion of leys in a cash-crop arable system to accelerate C and N accumulation in the soil as a result of BNF from grass-clover leys and animal-N excreta; and in terms of forage provision the benefits of continuous progress in forage plant breeding, as expressed as high energy and protein values similar to concentrate feed, can be gained by frequent renovation of the seeded leys. Moreover, leys offer the opportunity to include alternative species such as forage herbs that may benefit the digestibility and forage intake of grazing animals (Loza et al, 2021) at low N 2 O emissions from pasture land (Nyameasem et al, 2021). Lorenz et al (2019), moreover, noticed that the efficiency of the proposed dairy systems depends on the farm management and that the evaluation of such systems needs accurate estimates of the forage efficiency.…”

Very Low Nitrogen Leaching in Grazed Ley-Arable-Systems in Northwest Europe

“…It was also suggested by Crème et al [67] that the soil organic matter can counteract GHG emissions and enhance C sequestration. A study conducted by Nyameasem et al [34], on the same experimental site, reported low levels of N 2 O emissions which further indicates the effective use of N in the low-input system [20]. With regard to the N on a farm-level, a low-input ley-systems based on grazing allows for high productivity in combination with high biodiversity effects [68], low GHG emissions [16,34] and milk production with a low carbon footprint, thereby resulting in eco-efficient dairy systems [69].…”

“…However, the intensification and mismanagement of pastures can increase the rate of nutrient losses and may lead to the imbalance of nutrients in such systems [33]. Moreover, with an increase in the sward age, intensive grazing management may increase the risk of N surpluses, due to the accumulation of organic N from faeces only becoming erratically available for plant growth with increasing soil N during the weeks after excretion [34].…”