Legume cover crops are often considered a valuable alternative for supplying nitrogen (N) to cropping systems. However, certain pathways of N released from their residues to successor crops remain unclear. Aiming to assess N contribution and residual N from hairy vetch ( Roth.) cover crop in succeeding crops, we examined i) soil N availability and mineralizable-N, ii) crop yields, and iii) plant N sourcing within the soybean [ (L.) Merrill]-wheat ( L.) cropping sequence in the southeastern Argentine Pampas. Three field experiments were conducted over three seasons: E1 (2018/19), E2 (2019/20), and E3 (2020/2021) in the southeast of Buenos Aires province. The crop sequence studied was hairy vetch/soybean-wheat. Factors investigated were hairy vetch inclusion and bare fallow, and wheat N fertilizer (150 and 0 kg N ha). Hairy vetch aboveground dry matter and its N concentration were measured at hairy vetch termination and six times thereafter (residues) during the succeeding soybean, using the litter bag method. Soybean biomass, N concentration, and the relative abundance of ureides (RAU) as an indicator of N fraction derived from biological nitrogen fixation (BNF), were examined. Soil NO-N and anaerobically incubated N (Nan) were sampled during the soybean season and at wheat sowing. At physiological maturity, soybean and wheat grain yields, along with grain N concentrations, were determined. Hairy vetch N released during soybean season ranged from 79 to 175 kg N ha. Soil NO-N content at soybean sowing increased 5.5 kg ha per Mg of hairy vetch dry matter, while Nan increased 3.6 mg kg per Mg of hairy vetch dry matter. Soybean seed yields, seed N content, and N uptake showed no significant change with increased hairy vetch dry matter. Likewise, RAU at R5 decreased from 2.4 to 5.5 units (%) per Mg of hairy vetch dry matter. Concerning wheat, hairy vetch produced a slight increase in soil residual N at sowing. Only in one experiment (E1), hairy vetch dry matter led to improvements in wheat grain yield and N content. Our study outlined new insights into hairy vetch N contribution, primarily linked to increased soil N availability in the immediate soybean, the relatively higher soybean N uptake from soil compared to BNF, and the dilution of soil N contribution to wheat as second crop in the sequence. These findings support the recommendation of using hairy vetch as a predecessor for an immediate cereal or non-N fixing crops.

中文翻译：

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评估大豆-小麦序列中毛野豌豆的氮供应


豆类覆盖作物通常被认为是向耕作系统提供氮 (N) 的宝贵替代品。然而，氮从其残留物释放到后继作物的某些途径仍不清楚。为了评估后续作物中毛野豌豆 (Roth.) 覆盖作物的氮贡献和残留氮，我们检查了 i) 土壤氮可用性和可矿化氮，ii) 作物产量，以及 iii) 大豆内植物氮来源 [ (L .) Merrill]-阿根廷潘帕斯东南部的小麦 (L.) 种植序列。在布宜诺斯艾利斯省东南部的三个季节进行了三个现场实验：E1（2018/19）、E2（2019/20）和E3（2020/2021）。研究的作物序列是毛豌豆/大豆-小麦。调查的因素包括毛野豌豆夹杂物和裸地休耕，以及小麦氮肥（150 公斤氮肥和 0 公斤氮肥）。使用垫料袋法，在毛野豌豆终止时以及随后的大豆期间测量六次（残留物），测量毛野豌豆地上干物质及其氮浓度。对大豆生物量、氮浓度和脲化物相对丰度 (RAU) 进行了检查，作为生物固氮 (BNF) 产生的氮分数的指标。在大豆季节和小麦播种时对土壤 NO-N 和厌氧培养的 N (Nan) 进行采样。在生理成熟时，测定了大豆和小麦籽粒产量以及籽粒氮浓度。大豆季节释放的紫云英氮量为每公顷 79 至 175 公斤。大豆播种时，土壤氮素含量每毫克毛苕干物质增加 5.5 千克/公顷，而大豆播种时每毫克毛苕干物质增加 3.6 毫克/千克。大豆种子产量、种子氮含量和氮吸收量随着毛野豌豆干物质的增加没有显着变化。同样，R5 的 RAU 从 2 下降。每毫克毛茸茸干物质含 4 至 5.5 单位 (%)。对于小麦而言，毛野豌豆在播种时使土壤残留氮略有增加。仅在一项实验（E1）中，毛茸茸干物质导致小麦籽粒产量和氮含量提高。我们的研究概述了对毛野豌豆氮贡献的新见解，主要与直接大豆中土壤氮利用率的增加、与 BNF 相比，大豆从土壤中吸收氮的相对较高以及土壤氮对作为第二作物的小麦的贡献的稀释有关。 。这些发现支持使用毛野豌豆作为直接谷物或非固氮作物的前身的建议。