Maximising soybean productivity with late maturity groups in Mediterranean irrigated systems

Context: The EU aims to improve plant protein production profitably and sustainably with a range of grain legumes suitable to different climatic conditions. Soybean (Glycine max Merrill) could be one important focus as the crop is adapted to diverse conditions and has the highest protein content per kg of grain. Under Mediterranean irrigated conditions, soybean presents a high -yielding potential, either as an annual single crop (SCS) or as part of a sequential double cropping system (DCS) following a winter crop. However, the lack of experimental data and knowledge in some southern areas like Spain, led to the use of rather early maturity groups (referring to experiences from more northern and eastern areas) that are underperforming in southern latitudes (i.e. < 42(degrees )N). Objective: The aims were to (i) explore later soybean maturity groups than currently used for SCS and DCS and (ii) quantify the drivers of their performance under Mediterranean irrigated conditions. Methods: A field experiment was carried out in NE Spain (2019, 2020 and 2021) in a split -plot design with four replications. In the main plots, SCS and DCS sowing dates were tested. In the sub -plots, 8-13 cultivars were tested per year covering MG from early 00 to late III. Five biomass sampling dates during soybean development were performed to fit a growth curve for every MG and sowing date. Grain yield, grain protein content, grains m- 2, thousand -grain weight, 1st pod height and biological N fixation were measured at physiological maturity. Results: The growth curve asymptote showed the strongest correlation with the soybean grain yield (r = 0.95) and the number of grains m-2 (r = 0.88). Consistent higher yields for MG II and III (4476 and 5314 kg ha( -1), respectively) were found in the SCS and DCS compared to earlier MG. Grain protein concentration was reduced in the later MG but in all cases exceeded 40 g 100 g(-1). In the DCS, a grain yield reduction of 25 % compared to SCS was observed, mainly caused by fewer grains m- 2. Biological N fixation was low (30 g 100 g(-1), on average), resulting from high residual soil N. Conclusions: In the SCS, the use of later MG (II and III) increases soybean yields. However, further research exploring MG III or later would better define soybean potential in these systems. While the agronomic performance of late MG (II and III) in the DCS was promising, technical aspects such as later harvesting date (moisture, pod shattering, etc.) or a slight reduction in grain protein concentration (although still above 40 g 100 g(-1)) should be considered. Implications or significance: Our study proposes a shift towards the use of later soybean MG for Mediterranean irrigated cropping systems as a strategy to improve its competitiveness and, likely, farmer's adoption. This study highlights the potential to expand soybean production towards Mediterranean irrigated areas with a high yield potential.