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° 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, 1^st 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.

中文翻译：

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地中海灌溉系统晚熟组大豆产量最大化

语境

欧盟的目标是通过一系列适合不同气候条件的谷物豆类，以盈利和可持续的方式提高植物蛋白生产。大豆（Glycine max Merrill）可能是一个重要的焦点，因为这种作物适应不同的条件，并且每公斤谷物的蛋白质含量最高。在地中海灌溉条件下，大豆无论是作为一年生单一作物（SCS）还是作为冬季作物后的连续双季作物（DCS）的一部分都具有高产潜力。然而，西班牙等一些南部地区缺乏实验数据和知识，导致使用成熟度较早的群体（指更多北部和东部地区的经验），而这些群体在南部纬度（即<42°N）表现不佳。

客观的

目的是 (i) 探索比目前用于 SCS 和 DCS 的大豆成熟组更晚的大豆成熟组，以及 (ii) 量化其在地中海灌溉条件下表现的驱动因素。

方法

在西班牙东北部（2019 年、2020 年和 2021 年）以裂区设计进行了四次重复的田间试验。在主要地块中，测试了 SCS 和 DCS 播种日期。在子小区中，每年测试 8-13 个品种，覆盖从 00 月初到 III 月底的 MG。在大豆发育过程中进行了五个生物量采样，以拟合每个 MG 和播种日期的生长曲线。在生理成熟时测定籽粒产量、籽粒蛋白质含量、籽粒m ^-2、千粒重、第一^{荚高和生物固氮。}

结果

生长曲线渐近线与大豆籽粒产量（r = 0.95）和籽粒数 m−2（r = 0.88）的相关性最强。与早期的 MG 相比，在 SCS 和 DCS 中发现 MG II 和 III 的产量一致较高（分别为 4476 和 5314 kg ha−1）。后期MG中谷物蛋白质浓度有所降低，但在所有情况下均超过40 g 100 g ^-1。在DCS中，与SCS相比，观察到晶粒产量降低了25%，这主要是由于晶粒m ^-2较少造成的。由于土壤氮残留量较高，生物固氮能力较低（平均30 g 100 g ^{−1 ）。}

结论

在南海，使用较晚的 MG（II 和 III）可提高大豆产量。然而，探索 MG III 或更高版本的进一步研究将更好地确定大豆在这些系统中的潜力。虽然 DCS 中后期 MG（II 和 III）的农艺性能很有希望，但技术方面如收获日期较晚（水分、豆荚破碎等）或谷物蛋白质浓度略有下降（尽管仍高于 40 g 100 g）⁻¹ ) 应予以考虑。

影响或意义

我们的研究建议在地中海灌溉种植系统中转向使用后期大豆 MG，作为提高其竞争力并可能提高农民采用率的策略。这项研究强调了将大豆生产扩大到具有高产潜力的地中海灌溉地区的潜力。