Spatial and temporal variability of interactions in pea-oats mixed cropping on field-scale: Yield stability and nutrient use Julian Zachmann1, Iman Raj Chongtham2, Simone Graeff-Hönninger1, Erik Steen Jensen2, Sebastian Munz1 1Institute of Crop Science, University of Hohenheim, Stuttgart, Germany 2Department of Biosystems and Technology, Swedish University of Agricultural Sciences, Alnarp, Sweden Contact: julian.zachmann@uni-hohenheim.de Introduction - Cereal-grain legume mixtures have the potential to increase yield and cereal grain protein concentration and stabilize yields, particularly on fields where N is a limiting resource (Bedoussac et al., 2015). - Farmers’ fields may have a high heterogeneity in soil characteristics which influences spatial yield potential. According to the principle of “Ecological Precision Farming”, individual plants in mixed cropping can naturally adapt on a very small scale to a given heterogeneity resulting in higher yield stability, given the complementary use of resources (Jensen et al., 2015). This adaptation of cereal-legume mixtures to soil heterogeneity is investigated on a pea-oats mixture grown in Germany and Sweden. Main hypothesis are: - Mixtures are able to adapt to heterogeneity more efficiently than their respective sole crops by suppressing weeds and producing higher and more stable yields. - Mixtures use nitrogen more efficiently and oats achieve a higher grain protein content. - In mixtures, species can be differentiated by remote- sensing and their relative canopy cover can be determined. Methods In Germany, a two-year experiment (2018, 2019) on fields with a gradient in slope was established. Preliminary experiments showed a significant correlation between electromagnetic conductivity (EC) and soil clay-content as indicator for possible heterogeneity, e.g. in water availability. Sole and mixed crops were sown in replicated, parallel strips along the slope of the field. Sowing ratio in mixture was 50 % of oats sole crop (160 seeds m-² in mix) and 75 % of pea sole crop (60 seeds m-² in mix). No use of chemical plant protection. At maturity, 120 above ground samples (1 m²) were taken. Parameters of crops (e.g. thousand kernel weight and protein concentration) and soil (e.g. mineral nitrogen, phosphorus, clay content) will be measured in stored samples after yield analysis. Results - In intercropping (IC), mean oat grain yield was 3999 kg ha-1 compared to 5328 kg ha-1 in oats sole crop (SC) stripes, although oats crop density was only 50 % in IC (Figure 1). - Pea grains yielded 3400 kg ha-1 in SC and only 891 kg ha-1 in IC. - In IC, oats developed 36 % more shoots with panicles and peas had 43 % less pods per plant meanwhile thousand kernel weight did not change significantly. - Yield variation was high for pea in IC, medium for pea in SC and most stable for oats and total IC yield. - Differences in EC did not explain the variability in yield, tested for each cropping system. - Although there was no weed control, only little amount of weed biomass was found in oats SC and IC, meanwhile SC pea had a considerable higher weed biomass (Figure 2). Discussion and Outlook Oats are very plastic in tillering and have a high competitive potential (Sarunaite et al., 2013). Thus, oats were also suppressing the pea, resulting in lower pod production and yield. The higher yield stability in intercrops can be affiliated to the compensation potential of mixture partners. For further analysis of the variability, stored soil samples will be analyzed (e.g. nutrients, clay content and pH) and specific information like elevation and soil compaction will be considered. Fig 1. Grain yield of different cropping systems, hand harvested at UHOH in 2018. Bars headed with same capital letters are not significantly different (p<0.05). Error bars indicate standard error (n=120). CV is Coefficient of Variation. Fig 2. Dry matter of weeds biomass at crop maturity at UHOH in 2018. Bars with same capital letters ar