Data_Sheet_1_Effect of summer cover crops on cabbage yield, weed suppression, and N mineralization in a low input cropping system.docx

Summer cover crops (SCCs) provide valuable agroecosystem services to growers using spring and autumn vegetable crop rotations. Choosing the right SCCs to maximize agroecosystem services and fit growers' interests is challenging due to the wide array of SCC functions and one benefit may come at the cost of another (i.e., a tradeoff). In particular, fast-growing grasses may produce greater SCC biomass but may immobilize plant-available N needed by the autumn vegetable crop. We conducted a field study in Ames, Iowa US to compare agroecosystem services – weed suppression, autumn cabbage yield, soil nutrients, and net nitrogen (N) mineralization of eight SCC species over 2 years. Cover crop species were grown for an average of 55 days and included: brown top millet (Panicum ramosum L., BTM), buckwheat (Fagopyrum esculentum Moench, “Mancan”, BW), cowpea (Vigna unguiculata (L). Walp., “Iron and Clay”, CP), flax (Linum usitassimum L. “Golden”, GF), mung bean (Vigna radiata (L.) R. Wilczek, MB), sunnhemp (Crotalaria juncea L., SH), sorghum sudangrass (Sorghum bicolor L. Moench x Sorghum sudanense Piper Staph. “Sorgrow BMR Dwarf”, SS), and Teff grass (Eragrostis tef (Zuccagni) “Selam”, TEF), and a no-SCC control (NCC) treatment. The range of mean cover crop biomass was 0.8 (cowpea) to 7.5 (teff grass) Mg ha−1. There was a strong, negative correlation between SCC biomass and weed biomass (R2 = 0.83). Low biomass producing legumes resulted in greater weed biomass, but 34–58% greater cabbage yield in one of two experimental years. Ion exchange membranes (IEMs) were not able to capture differences in total net N mineralization among SCC treatments however, soil inorganic N was greater under legume SCCs at SCC termination. We show there are tradeoffs when choosing SCCs between weed suppression and net N mineralization and that the environmental conditions, i.e., climate, regulate whether these tradeoffs favor greater vegetable crop yields.

夏季覆盖作物（SCCs）为采用春季和秋季蔬菜作物轮作的种植者提供了宝贵的农业生态系统服务。由于覆盖作物功能多样，且一种利益可能以另一种代价为前提（即权衡），因此选择合适的SCCs以最大化农业生态系统服务并符合种植者的利益是一项挑战。特别是，快速生长的禾本科植物可能产生更大的SCC生物量，但可能会固定秋季蔬菜作物所需的植物可利用氮（N）。我们在美国爱荷华州的艾姆斯市开展了一项田间研究，比较了八种SCC物种在两年内对农业生态系统服务——杂草抑制、秋季卷心菜产量、土壤养分和净氮（N）矿化的影响。覆盖作物物种的平均生长时间为55天，包括：褐顶黍（ Panicum ramosum L.，BTM）、荞麦（Fagopyrum esculentum Moench，“Mancan”，BW）、绿豆（Vigna unguiculata (L). Walp.，“铁和粘土”，CP）、亚麻（Linum usitassimum L. “Golden”，GF）、绿豆（Vigna radiata (L.) R. Wilczek，MB）、太阳麻（Crotalaria juncea L.，SH）、高粱苏丹草（Sorghum bicolor L. Moench x Sorghum sudanense Piper Staph. “Sorgrow BMR Dwarf”，SS）和提费草（Eragrostis tef (Zuccagni) “Selam”，TEF），以及无SCC对照（NCC）处理。平均覆盖作物生物量范围为0.8（绿豆）至7.5（提费草）Mg ha−1。SCC生物量与杂草生物量之间存在强烈的负相关性（R2 = 0.83）。低生物量产生豆科植物导致杂草生物量增加，但在两个实验年份中的一个中，卷心菜产量增加了34-58%。离子交换膜（IEMs）无法捕捉到SCC处理之间的总净N矿化差异，然而，在SCC终止时，豆科SCC下的土壤无机氮含量更高。我们表明，在选择SCCs时，在杂草抑制和净N矿化之间存在权衡，而环境条件，即气候，调节这些权衡是否有利于提高蔬菜作物产量。