Intercropping maize with forage grasses is an economical and environmentally sound practice that is increasingly being adopted to enhance resilience in tropical agriculture. Although intensifying integrated cropping systems can increase the sequestration of carbon (C) from plant residues, it also unleashes priming of old soil C enhancing C cycling, particularly under nitrogen (N) fertilization. However, the extent of these competing processes in intercropped maize–forage systems is poorly understood. This four-year study assessed whether new C inputs from maize (Zea mays) intercropped with ruzigrass (Urochloa ruziziensis), palisade grass (Urochloa brizantha), or Guinea grass (Megathyrsus maximum) in the presence or absence of N fertilization affect soil aggregation and C cycling in the soil and within macroaggregates (>0.250 mm) and microaggregates (<0.250 mm) down the soil profile. C cycling was assessed by measuring variations in the abundance of the natural isotope 13C. N fertilization of the intercropped maize–forage systems reduced the proportion of aggregates > 2 mm and the mean weight diameter of aggregates by reducing soil pH. Under N fertilization, the geometric mean diameter of aggregates were 42 % larger under palisade than under Guinea grass. New C inputs from intercropping maize with forage grasses promoted C cycling in bulk soil, particulate organic matter (POM), mineral-associated organic matter (MAOM), and macro- and microaggregates, although these effects were restricted to topsoil. No N fertilization increased ruzigrass C input into MAOM with no clear link with 13C enrichment, suggesting that N fertilization does not impair C stabilization in this pool. Aggregates >2 mm and >0.5 mm were key sinks of C and N up to a soil depth of 40 cm in this intercropped system. Our findings provide insights into the extension of C cycling across SOM pools and aggregates, and the role of N management in intercropping maize forage systems.

中文翻译：

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受氮影响的间作玉米-饲料系统土壤碳循环的见解


玉米与牧草间作是一种经济且无害环境的做法，越来越多地被用于增强热带农业的复原力。虽然强化综合种植系统可以增加植物残留物中碳 （C） 的封存，但它也会释放旧土壤 C 的启动，从而增强 C 循环，尤其是在氮 （N） 施肥的情况下。然而，人们对间作玉米-饲料系统中这些竞争过程的程度知之甚少。这项为期四年的研究评估了在存在或不存在氮肥的情况下，玉米 （Zea mays） 与茸茸草 （Urochloa ruziziensis）、栅栏草 （Urochloa brizantha） 或几内亚草 （Megathyrsus maximum） 间作的新碳输入是否会影响土壤中以及土壤中的大团聚体（>0.250 mm）和微团聚体（<0.250 mm）内的土壤聚集和碳循环。通过测量天然同位素 13C 丰度的变化来评估 C 循环。间作玉米-饲料系统的氮肥通过降低土壤 pH 值来降低聚集体 > 2 mm 的比例和聚集体的平均重量直径。在氮肥下，栅栏下团聚体的几何平均直径比几内亚草下大 42%。玉米与牧草间作的新碳输入促进了块状土壤、颗粒有机物 （POM）、矿物相关有机物 （MAOM） 以及大团聚体和微团聚体中的碳循环，尽管这些影响仅限于表层土壤。无氮肥增加了 MAOM 中 ruzigrass C 的输入，与 13C 富集没有明确的联系，表明氮肥不会损害该池中的 C 稳定性。聚合 >2 mm 和 >0。在这个间作系统中，5 mm 是 C 和 N 的关键汇，土壤深度可达 40 cm。我们的研究结果为碳循环在 SOM 池和聚集体中的扩展以及氮管理在间作玉米饲料系统中的作用提供了见解。