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To increase ruminant production efficiency, the environmental impact of growing forage must be reduced, through lowering system inputs and increasing crop resilience to extreme weather. Here we examined the role of red clover (cv. AberClaret) in minimising nitrogen (N) requirements, alongside two novel grass varieties, (1) a festulolium (cv. AberNiche), developed for drought tolerance, with potential for deep-rooting, and (2) a ryegrass hybrid (cv. AberEcho), developed for high-sugar content, which may enhance ruminant N-uptake in-vivo. Field trials were conducted at two UK sites, growing festulolium and ryegrass ± red clover (at 29% of the seed mix weight) at a range of N fertilisation rates (0 – 600 kg N ha−1) for 2 years (six harvests). We assessed sward performance (N offtake, herbage quality, and grass N use efficiency), rooting depth and N transfer from clover to grasses using 15N natural abundance. Across both sites and years, dry matter yield and herbage-N content were overall greater from the swards that included clover. Dry matter yields from festulolium were not greater than from ryegrass under the drought conditions experienced in 2018, despite its greater root mass. Agronomic efficiency of fertiliser N was similar between grasses (19 – 22%), however the festulolium more effectively used endogenous soil N than the ryegrass. Inclusion of clover in the sward affected forage quality, with increased crude protein and metabolisable energy content and reduced sugar and fibre (NDF) content. Among the grass types, metabolisable energy was greater and NDF content less for ryegrass than for festulolium. A strong reliance on biological N fixation (80 – 94%) for clover was observed, however, N transfer from clover to the neighbouring grass was not evident from the ẟ15N signatures. We conclude that red clover is a viable fertiliser-N replacement strategy in short-term leys, and that grass varieties with improved herbage quality may provide a better option for optimising sward performance than drought tolerant grass varieties. • Festulolium gave no yield advantage over a ryegrass hybrid under drought conditions. • Ryegrass hybrid provided higher quality feed without compromising yield. • Herbage yields were greater when red clover was included within the sward. • Inclusion of red clover with grass increased sward N and metabolisable energy content. • Including red clover in grass swards replaced the need for N fertilization. [ABSTRACT FROM AUTHOR]

The use of nitrogen (N) fertilizers is essential to produce enough food for the growing worldpopulation. Their uncontrolled use in agroecosystems has environmental implications, suchas the release of gaseous pollutants (as N2O and NH3) and eutrophication of waterbodies (due to NO3− and other dissolved N forms). The main objective of thisstudy was to assess different strategies to minimize N pollution associated withagroecosystems. Field experiments located in North Wales and Southwest England focused on (i) assessingN offtake, N loss pathways, and the environmental and societal externalities associated withthe use of different inorganic N fertilizers [urea (U), ammonium nitrate (AN) and U + ureaseinhibitors (UI) in grasslands]; (ii) the study of two different grass varieties (AberEcho-high insugar content and AberNiche-drought resistant) subjected to different N rates (0-600 kg Nha−1) and with/without red clover (at two N rates only: 0 and 50 kg N ha−1), tostudy which combination was more appropriate from the point of view of primaryproductivity and environmental protection; and (iii) the use of nitrification inhibitor (NI)and pH reduction to mitigate gaseous N losses (N2O and NH3) when an organic(food-based digestate from a biogas plant) N source was applied to a winter-wheatcrop. NH3 emissions were reduced by 48-65% in grassland under the U + UI treatment relativeto U alone, and by 95% under the acidified digestate relative to non-acidified digestate forwinter-wheat. N2O emissions were not significantly reduced through the use of NI in anyway. The use of UI, acidification of organic N fertilizer and clover in combination with thelowest N rates minimised N losses. [ABSTRACT FROM AUTHOR]

Abstract The frequency and intensity of extreme weather events (e.g. flood, drought) are predicted to increase for the foreseeable future and it is expected that these will negatively impact upon agroecosystem functioning. Our understanding of how grassland ecosystems respond to extreme weather events occurring at different times of the year, however, is lacking. To better understand the seasonal response of grassland to flooding, we subjected an agricultural grassland to an 8-week extreme flood event at three different temperatures (5 °C-winter, 15 °C-spring/autumn and 25°C-summer) and then followed its subsequent recovery for 9 weeks after floodwater removal. We focused on key indicators of ecosystem functioning including primary production, nutrient cycling, greenhouse gas (GHG) emissions, ammonia (NH 3) volatilization, and soil microbial communities. The experiment used intact soil mesocosms (1 kg) with indigenous vegetation collected from a grassland with no previous history of flooding. Flooding reduced biomass production by 18% at 5 °C, 50% at 15 °C and 95% at 25 °C. Flooding also significantly disrupted elemental cycling (nitrogen, phosphorus and carbon) as evidenced by an increased release of P, Fe and NH 4 + into the soil and overlying floodwater and large amounts of CH 4 and NH 3 released to the atmosphere (mainly during the flooding). These effects were more pronounced at higher temperatures (e.g. 45–700 kg CH 4 C ha−1 and 1–5 kg NH 3 N ha−1 at 15 and 25 °C, respectively). In addition, after floodwater removal this NH 4 + was rapidly nitrified leading to large losses of N 2 O (1.0–14.2 kg N 2 O N ha−1 at 5–25 °C, respectively). Especially at higher temperatures, flooding resulted in a reduction in soil microbial biomass (more than 58% of the equivalent unflooded treatment at 25 °C) and changes in microbial community structure (assessed by PLFAs). Further, some of these changes persisted after flood removal including a loss of actinomycetes, arbuscular mycorrhizal fungi and fungi. Overall, we conclude that ecosystem responses to extreme weather events are critically dependent on temperature with those occurring at higher temperatures having a greater negative impact than those at the lowest temperature (5 °C). The large potential release of CH 4 and N 2 O also suggests that flood events should be considered as a potential source of GHGs when comparing top-down and bottom-up calculations of national inventories, and that further work is needed to better refine GHG emission estimates for these events. Highlights • Flooding induced a rapid release of nutrients, especially at higher temperatures. • 700 kg CH 4 C ha−1 and 5 kg NH 3 N ha−1 were released in the flood phase at 25 °C. • During soil recovery, nitrification led to 1.0–14.2 kg N 2 O N ha−1 losses at 5–25 °C. • Flooding reduced soil microbial biomass, actinomycetes and arbuscular mycorrhiza. • Flooding reduced biomass production by 18% at 5 °C, 50% at 15 °C and 95% at 25 °C. [ABSTRACT FROM AUTHOR]

Fertiliser nitrogen (N) is essential for maintaining agronomic outputs for our growing population. However, the societal, economic and environmental impacts of excess reactive N from fertiliser is rarely assessed. Here the agronomic, economic and environmental efficacy of three N-fertiliser sources, ammonium-nitrate (AN), urea (U), and inhibited-urea (IU; with NPBT) were evaluated at two grassland sites. Dry matter yield and herbage quality were measured at each silage-cut. Additionally, NH3-N and N2O-N losses were measured and used to calculate the effective N source cost and externality costs, which account for associated environmental and societal impacts. We found no effect of different N sources on yield or herbage quality. However, NH3-N emissions were significantly reduced under the IU treatment, by 48-65%. No significant differences in cumulative N2O emissions were observed. Incorporating externality costs increased fertiliser prices by 1.23-2.36, 6.51-16.4, and 3.17-4.17 times the original cost, for AN, U and IU, respectively, transforming U from the cheapest, to the most expensive of the N sources examined. However, with no apparent yield differences between N-fertiliser sources there is no economic incentive for the land-manager to use the more environmentally and socially acceptable option, unless externality costs are incorporated into fertiliser prices at the point of sale. [ABSTRACT FROM AUTHOR]