Seasonal effects reveal potential mitigation strategies to reduce N2O emission and N leaching from grassland swards of differing composition (grass monoculture, grass/clover and multispecies)

The Effect of Inorganic Nitrogen Fertilizers on the Quality of Forage Composed of Various Species of Legumes in the Northern Part of a Temperate Climate Zone

“…Also, our study confirms that monoculture grass sward productivity requires the application of N fertilizers [38]. Meanwhile, several researchers have obtained similar results, as long as the proportion of mixed grass-legume swards is sufficient to take up mineral N from the soil [39], it can be expected that this will prevent N losses via leaching [40]. Dindova et al (2019) studied the relationships between long-term fertilization management and forage nutritive value in grasslands and also found that the effect of fertilization on the proportion of functional groups was visible across cuts and years [27].…”

Inundation impacts on diversified pasture biomass allocation and soil particulate organic matter stocks

“…Nonetheless, the use of diverse forage species mixtures can promote benefits to the ecosystems, other than those evaluated in this study (forage production and soil C sequestration). As such, soil microbial communities and nutrient cycling can be improved (Yan et al, 2022), specially N, which can be fixed by legumes, and gradually used by grasses growing in the mix, reducing the demand for synthetic N-fertiliser (Lüscher et al, 2014) and reducing environmental burdens related to nitrous oxide emissions (Bracken et al, 2022) or nitrate leaching (Eriksen et al, 2015). In addition, species diverse systems can create favourable habitat for wildlife and pollinators and promote weed and pest suppression, optimizing ecosystem services and sustainability in agricultural production (Isbell et al, 2017).…”

Multispecies forages in the Australian dairy feedbase: is there a biological business case?

“…Previous studies have measured N derived from symbiotic sources in legume-containing mixtures in excess of 200 kg N/ha.annum, a rate that completely negates the need for additional inorganic N application (Nyfeler et al 2011). However, there is a risk that practitioners will continue to apply inappropriately high inorganic N fertiliser rates to multispecies swards with high concentrations of fixed N in the soil, which would lead to N loss to the environment as leached nitrate and as gaseous compounds, namely, nitrous oxide, ammonia, dinitrogen, and nitric oxide (Bracken et al 2020;Bracken et al 2022). Nitrous oxide is a potent greenhouse gas (GHG) and therefore any environmental benefits of multispecies swards could be negated should they lead to increased GHG emissions.…”

“…In an Irish study, Bracken et al (2020) first demonstrated that a mixture comprising 75% grass and 25% legume resulted in a cumulative release of ~50 g N 2 O-N/ha in the 2 months post-fertilisation with 40 kg N/ha, whereas a mixture comprising 25% grass and 75% legume resulted in ~150 g N 2 O-N/ha released when both swards were fertilised at the same rate. However, in a follow-up study by Bracken et al (2022), where the study was repeated but with reducing fertiliser rates matched to sward legume content, PRG monocultures fertilised at 250 kg N/ha.annum produced a 71% increase in N 2 O emissions relative to a legume-heavy mixture receiving no N fertiliser. Since Bracken et al (2022) reported no significant difference in the herbage yield achieved from these two treatments, the mixture resulted in the least GHG emission for the same biomass yield.…”