Purpose

Nitrate (NO₃⁻) leaching has been recognized as a worldwide problem, and NO₃⁻ is a major pollutant in ground and surface waters. The gradual leaching of residual NO₃⁻ into soil layers below the root zone is the main way of nitrogen (N) loss in cropping systems. The interception of NO₃⁻ by subsurface roots is crucial for crops or vegetables to utilize N. However, few studies were focused on the mechanisms of NO₃⁻ leaching under intercropping of deep-rooted and shallow-rooted plants.

Materials and methods

In a greenhouse production system, we selected deep-rooted and shallow-rooted plants for single-season intercropping planting experiments (MP, monoculture of pepper; IPA, intercropping of pepper and alfalfa; IPM, intercropping of pepper and maize). Plants were grown in core drainage lysimeters for 4 months, and leachate was collected by soil solution samplers. The results revealed N transformations between monoculture and intercropping systems by comparing NO₃⁻ leaching, N use efficiency, and microbes involved in nitrification.

Results and discussion

NO₃⁻ accumulation mainly occurred in 25–40-cm soil layer, which was affected by root morphology. Compared with monoculture, intercropping reduced NO₃⁻ leaching, in particular, pepper/maize intercropping significantly reduced NO₃⁻ leaching losses. In deep soil layers, roots of alfalfa and maize were more developed than those of the other crops, which made this corresponding intercropping system more effective in absorbing N in the subsoil. N uptakes of pepper/alfalfa intercropping and pepper/maize intercropping were 19% and 28% higher than that from the monoculture, respectively. Ammonia oxidizing bacteria (AOB) were significantly stimulated with planting especial in the topsoil, while ammonia oxidizing archaea (AOA) decreased with planting along the soil profile. These results indicated that lush plant roots immobilized N from the deep soil and thus improved N use efficiency and reduced NO₃⁻ leaching in the deep-rooted and shallow-rooted intercropping system.

Conclusions

Intercropping of shallow-rooted pepper with deep-rooted alfalfa can enhance root nutrient absorption in deep soil layers, increasing N use efficiency and thus reducing NO₃⁻ leaching. The nitrification process in the intercropped soil was mainly regulated by AOB.

中文翻译：

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套种深根和浅根植物可减轻硝酸盐淋失

目的

硝酸盐（NO ₃ ^- ）浸出已被公认为世界性难题，和NO ₃ ^-是地下水和地表水的主要污染物。残余NO逐渐浸出₃ ^-到根区域下面土层是氮（N）的损失在耕作系统的主要途径。NO的拦截₃ ^-通过地下根系是至关重要的作物或蔬菜利用N.然而，一些研究主要集中在NO的机制，₃ ^-下根深蒂固的浅根性植物间作浸出。

材料和方法

在温室生产系统中，我们选择了深根和浅根植物进行单季间作种植试验（MP，辣椒单作； IPA，辣椒和苜蓿间作； IPM，辣椒和玉米间作）。使植物在核心排水测渗仪中生长4个月，并通过土壤溶液采样器收集渗滤液。结果由NO比较揭示单一栽培和间作系统之间的N个变换₃ ^-浸出，N利用效率，和涉及硝化微生物。

结果和讨论

NO ₃ ^-积累主要发生在25-40厘米的土壤层，其受根形态。与单作相比，间作降低NO ₃ ^-浸出，特别是胡椒/玉米间作显著NO减少₃ ^-浸出损失。在深层土壤中，苜蓿和玉米的根比其他作物的根更发达，这使相应的间作系统更有效地吸收了土壤中的氮。辣椒/苜蓿套作和辣椒/玉米套作的氮吸收量分别比单作高19％和28％。特别是在表层土壤中种植时，氨氧化细菌（AOB）受到显着刺激，而沿土壤剖面种植时，氨氧化古细菌（AOA）则下降。这些结果表明，茂盛植物的根从深土壤固定化N-从而提高氮效率和降低的NO ₃ ^-中的深层次和浅根间作系统浸出。

结论

浅根胡椒间作根深蒂固苜蓿可以增强土壤深层根营养吸收，增加氮效率，从而减少NO ₃ ^-浸出。间作土壤的硝化过程主要受AOB调控。