This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 862357 Legume-based intercropping: A pathway to reduced N2O emissions from agriculture? Methods Treatments Barley (Hordeum vulgare ‘Laureate’) and pea (Pisum sativum ‘Prophet’) were planted in isolation (Sole crop) and together (Intercrop) using three fertilizer rates (Table 1) Plots organized in a randomized block design, replicated four times (Fig 1). Luke Harrold, Kairsty Topp, Christine Watson & Robin Walker Introduction Intercropping of legumes with cereal crops can play a crucial role in the path towards sustainable agriculture and achieving net-zero. Literature and IPCC report suggests a reduction in N2O emissions in legume intercropped systems. However, reductions have been shown to be dependent on the variety of pea used. We tested if legume-based intercropping systems (pea/barley) can support sustainable farming by balancing environmental (N₂O emission, soil health) and economic (yield) goals. Figure 2 – Gas sampling from static chamber. Two static chambers per subplot. Photo by Robin Walker. Results Nitrous oxide emissions Intercrop with half-rate or without added N emitted the same amount of N2O over a 114 day period as sole barley with full-rate N addition (Fig 4). With no synthetic nitrogen addition the pea treatment maintained a cumulative N2O emission that does not significantly differ from the barley which received 120 kg N ha-1 (Fig 4). N₂O flux closely linked to soil water content, peaks corresponding to higher soil moisture (Fig 3). N addition to barley doubled mean N₂O emissions over 114 days compared to no-N barley (Figure 4). Periodically soil samples were taken to determine mineral N (NH4 + and NO3 -). Soil moisture and temperature probes measured continuously on an hourly basis. Conclusions Intercropping of these varieties of barley and pea failed to reduce N2O emission over 114 days even with no synthetic nitrogen addition. Pea added sufficient nitrogen to maintain the same yield-to-seed ratio for barley as the full rate fertilizer treatment and a half rate of N led to a greater barley yield-to-seed ratio when intercropped. Other pea varieties have been shown to reduce N2O in intercropping systems suggesting that the right mix of cereal/legume would need to be found for particular soil types/region. Figure 4 – Cumulative emission of N2O over 114 days Treatment Fertiliser Sole crop Barley (Laureate) Full N 120 kg/ha Sole crop Pea (Prophet) No N Intercrop Barley/Pea No N Intercrop Barley/Pea Half N 60 kg/ha Sole crop Barley No N Table 1 – Crop treatment including fertilizer addition Figure 3 – N2O flux and soil moisture over 74 days. Solid lines show the flux of N2O over time with the left-hand y-axis. Dashed lines show the soil moisture content (%) overtime with the right-hand y- axis. Standard error is shown. Gas sampled from chambers on days 1,2,4,8 and 10 then twice a week for four weeks followed by once per month until experiment end. N2O concentration measured via gas chromatograph. Also measured Bulk density Infiltration Soil carbon (POXC) Soil structure (VESS) Earthworm count Figure 1 – Plot layout, external plots used for GHG sampling (Fig 2) and destructive harvesting (described below) and internal plots used for yield. @SoilandGas Figure 5 – a) Yield of barley, the mass of pea has been removed b) barley yield normalised by sowing rate Much of the N2O derived from the pea-only treatment seems to be associated with a wetting event. A similar peak is evident in the barley with full nitrogen addition but to a lesser degree. Yield Despite having half the sowing rate, the two intercrop treatments have the same yield as the unfertilised barley (Bar_NoN) treatment at full sowing rate (Fig 5a). Similarly, despite receiving no fertilizer the unfertilised intercrop achieved half the yield of the fertilised full sowing rate barley (Bar_FullN) resulting in the same yield per