Growth and yield response of faba bean to soil moisture regimes and sowing dates: Field experiment and modelling study

In semiarid environments, faba bean (Vicia faba L.) production shows high year to year variability. In order to implement measures that minimize this variability, it is important to understand how abiotic and management factors affect its growth and yield. The aim of this study is to determine supplemental irrigation strategy and sowing date that maximize yield and water productivity of faba bean. A field experiment and simulation modelling were conducted on a mid-flowering faba bean cultivar under different sowing dates and watering regimes in south-eastern Australia. Drip irrigation, with two laterals plot, was used. At sowing, 20 kg P ha⁻¹ of single-phosphate was applied. Four watering regimes were applied: not irrigated (NI), fully irrigated (FI = 245.1 mm), vegetative-stage irrigated (VI = 60.1 mm), reproductive-stage irrigated (RI = 106.4 mm). Soil water tension was measured monitored using gypsum blocks at 15, 45 and 75 cm depths. The Agricultural Production Systems sIMulator (APSIM) was used to simulate grain yield. Sowing dates were 22 April (SD1) and 20 May (SD2). There was no significant difference between the yields of SD1-fully irrigated (5.24 t ha⁻¹), SD1-reproductive stage irrigated (5.85 t ha⁻¹), SD2-fully irrigated (5.52 t ha⁻¹), and SD2-reproductive stage irrigated (5.24 t ha⁻¹) treatments. The highest grain water use efficiencies, 1.65 kg m^-3 and 1.63 kg m^-3, were obtained from the reproductive stage irrigated SD1 and SD2, respectively. Harvest index and seed weight were significantly affected by sowing dates while the number of pods per plant and grain water efficiencies were significantly affected by irrigation. There was positive linear relationship between grain yield and post-flowering, rather than pre-/during flowering, green canopy cover. APSIM simulated faba bean yield with RMSE of 468 t ha⁻¹. Simulation modelling showed that supplemental irrigation applied from mid-September to the end of October increased grain yield by 23% relative to the rainfed treatment while supplemental irrigation from mid-August to the end of September resulted in 13% increase. Sowing in the first week of May or in the first week of June, instead of in the first week of April, decreased grain yield by 26% and 52%, respectively.