Efficiency of radiation and water use of four contrasting soybean (Glycine max (L.) Merril) cultivars grown in the rainfed area of northern Argentina

Soybean production in water-limited environments is affected by both water supply and resource use efficiency. However, their impact on different soybean maturity groups (MGs) remains unclear. A three-year study was undertaken to assess the performance of four soybean cultivars (CVs) differing in MG (V-VIII) in the semi-arid environment of northern Argentina (Chaco Seco ecoregion, EChS). MG VII and VIII (longer cycles) are the most widely sown in EChS, while MG V and VI (shorter cycles) may perform better in water-limited regions. In-season precipitation varied with each experimental year, being 182 mm, 663 mm, and 337 mm. Data on phenology, intercepted photosynthetically active radiation (IPAR), actual evapotranspiration (ETa), aboveground biomass, and seed yield were collected periodically. There were hardly any seasonal ETa differences among CVs, but the ETa fraction for the reproductive growth (RG) period was higher in shorter-cycle CVs, while long-cycle CVs experienced more severe water deficits during this period. Shorter MGs had a lower seasonal IPAR but a higher IPAR fraction and crop growth rate in the RG period, and a higher harvest index than longer MGs. The shorter-cycle CVs achieved higher seed yields than the longer-cycle CVs. On average, seed yield of the earliest-maturing CV (MG V) exceeded that of the latest-maturing CV (MG VIII) by almost 1000 kg ha⁻¹. The highest seed yields obtained in the shortest-cycle CV were associated with the highest radiation use efficiency and water use efficiency for yield, while the opposite was true for the longest-cycle CV. Evidence from this work points out at an association between high yields and high resource use efficiency in soybean production, suggesting avenues for future crop improvement and management. Additionally, switching to short-cycle CVs would allow the sowing of a second autumn-winter crop or to include a cover crop in the rotation, thus contributing to the sustainable intensification of cropping systems in EChS.