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Complex crop rotations improve organic nitrogen cycling
Soil Biology and Biochemistry ( IF 9.8 ) Pub Date : 2022-12-10 , DOI: 10.1016/j.soilbio.2022.108911
Lauren C. Breza , Maria Mooshammer , Timothy M. Bowles , Virginia L. Jin , Marty R. Schmer , Bennett Thompson , A. Stuart Grandy

Nitrogen (N) availability in agroecosystems is often poorly coupled to plant N uptake, leading to inefficient fertilizer use and environmental losses. Building soil organic N pools and enhancing internal recycling of N with crop rotations while reducing synthetic inputs may help improve N use efficiency. The organic N pool could be a valuable source of N that could help farmers reduce reliance on large inorganic N inputs if controls on its availability were better understood. While we know that the breakdown of high-molecular weight organic N compounds is the rate-limiting step to accessing bioavailable N from organic sources in natural ecosystems, there has been little work in agroecosystems to identify how management influences this inflection point in the N cycle. To provide insight into how growers can manage the organic N pool to reduce fertilizer input, we examined gross protein depolymerization rates within an agricultural context. Specifically, we investigated 1) how crop rotations affect organic N pools and alter the rate of organic N cycling, and 2) whether inorganic N fertilization enhances, has no effect, or suppresses soil N cycling responses to crop rotation. To test this, we measured gross rates of protein depolymerization, amino acid consumption, mineralization, and ammonium consumption using 15N isotope pool dilution assays on soils collected from a long-term crop complexity experiment near Mead, NE, USA. Treatments sampled included both 0 kg and 180 kg N ha−1 fertilization levels in continuous corn, corn-soybean, and corn-soybean-sorghum-oat/clover rotations. We found that higher cropping complexity coupled with zero fertilization increased gross depolymerization and amino acid consumption rates by 193% and 93%, respectively, relative to fertilized, monocrop plots. Gross mineralization was 2.7 and 3.9x higher in complex rotations than corn-soybean and continuous corn rotations, respectively, while ammonium consumption was 4x higher in fertilized plots than unfertilized plots across all cropping regimes. We show that within our study system internal N cycling is stimulated by cropping system complexity; however, N fertilization suppresses some of the benefits of temporal crop diversification. Balancing reduced mineral fertilizer application rates with increased cropping complexity has the potential to promote internal N cycling while minimizing N losses in agroecosystems.



中文翻译:

复杂的作物轮作改善有机氮循环

农业生态系统中的氮 (N) 可用性通常与植物的氮吸收不相关,导致肥料使用效率低下和环境损失。建立土壤有机氮库并通过作物轮作加强氮的内部循环,同时减少合成投入可能有助于提高氮的利用效率。如果更好地了解对其可用性的控制,有机氮库可能是一种有价值的氮源,可以帮助农民减少对大量无机氮投入的依赖。虽然我们知道高分子量有机 N 化合物的分解是从自然生态系统中的有机来源获取生物可利用 N 的限速步骤,但农业生态系统中几乎没有工作来确定管理如何影响 N 循环中的这个拐点. 为了深入了解种植者如何管理有机氮库以减少肥料投入,我们检查了农业背景下的总蛋白质解聚率。具体而言,我们研究了 1) 作物轮作如何影响有机氮库并改变有机氮循环的速率,以及 2) 无机氮施肥是否增强、无效或抑制土壤氮循环对作物轮作的响应。为了测试这一点,我们测量了蛋白质解聚、氨基酸消耗、矿化和铵消耗的总速率,使用 或抑制土壤氮循环对作物轮作的反应。为了测试这一点,我们测量了蛋白质解聚、氨基酸消耗、矿化和铵消耗的总速率,使用 或抑制土壤氮循环对作物轮作的反应。为了测试这一点,我们测量了蛋白质解聚、氨基酸消耗、矿化和铵消耗的总速率,使用对从美国内布拉斯加州米德附近的长期作物复杂性实验收集的土壤进行15 N 同位素库稀释测定。采样处理包括 0 kg 和 180 kg N ha -1连续玉米、玉米-大豆和玉米-大豆-高粱-燕麦/三叶草轮作中的施肥水平。我们发现,相对于施肥的单一作物地块,较高的种植复杂度加上零施肥使总解聚率和氨基酸消耗率分别增加了 193% 和 93%。复杂轮作的总矿化量分别比玉米-大豆轮作和连续玉米轮作高 2.7 倍和 3.9 倍,而在所有种植制度中,施肥地块的铵消耗量比未施肥地块高 4 倍。我们表明,在我们的研究系统中,内部 N 循环受到种植系统复杂性的刺激;然而,施氮肥会抑制暂时性作物多样化带来的一些好处。

更新日期:2022-12-10
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