The Bean YEN: Understanding bean yield variation on UK farms

Field beans (Vicia faba L.) are the most extensively grown grain legume in the UK but their contribution to farming and food systems could be improved if their yields were enhanced. Average on-farm bean yields have varied between 3 and 4 t ha⁻¹ for four decades but with much variation between individual crops. A “Bean Yield Enhancement Network” (Bean YEN) was initiated in 2019, supported by industry sponsors, to promote crop monitoring, sampling, and sharing of data between farms, thus learning about key yield-affecting factors. Bean YEN continues, gathering new data annually; data from crops harvested in 2019 to 2021 are reported here. For each crop entered, data were collated on agronomy, soil, and weather, samples were analysed for height, nutrient content, yield components, and seed quality, and accurate yields were recorded. A localised biophysical yield potential (Y_bp) was also estimated based on the best (repeatedly observed) resource capture and conversion coefficients and harvest index for beans, after accounting for costs of nitrogen (N) fixation. Over the three seasons, yields were collated from 26 winter bean and 63 spring bean crops, all well dispersed across the British Isles, with sufficient supporting information to make 87 estimates of Y_bp. Average winter bean yields were 5.1 t ha⁻¹ (range 1–8 t ha⁻¹) and spring bean yields were 4.9 t ha⁻¹ (range 1–7 t ha⁻¹), respectively 38 and 43% of Y_bp (13.7 & 11.2 t ha⁻¹); yield shortfalls from Y_bp averaged 7.2 t ha⁻¹ (range 2.4–12.6 t ha⁻¹). Yields correlated positively with plant height, thousand seed weight, total biomass shoot⁻¹, seeds pod⁻¹, harvest index and total straw biomass (t ha⁻¹) in both winter and spring crops. In spring crops, the number of pods shoot⁻¹ was also positively correlated with yield. Correlations suggested that growers could enhance yields by favouring an ideotype with deep roots, tall, multi-noded stems, and prolonged canopy survival. This ideotype will be subject to modification and improvement after data are collected through future seasons of Bean YEN. The accumulating Bean YEN dataset is enabling benchmarks to be derived for crop attributes that should guide growers in their quest for sustained yield enhancements.