Background and aims

Nitrogen (N) deposition usually has adverse effects on various ecosystems. Farmland intercropping is a well-known planting model and agroecosystem with multiple benefits. However, research on N deposition in farmland, especially for intercropping systems remains limited.

Methods

Field experiments were conducted in three seasons to examine the effects of rice monocropping and rice-water mimosa (Neptunia oleracea Lour.) intercropping systems on rice growth and soil properties under N deposition. The simulated N deposition rate was set at two levels, which included low N (LN) deposition at a rate of 40 kg·ha⁻¹·yr⁻¹ N and high N (HN) deposition at a rate of 120 kg·ha⁻¹·yr⁻¹ N, which were applied in addition to 180 kg·ha⁻¹·yr⁻¹ N fertilization during the overall growth period of rice.

Results

With increasing N deposition, rice plant height, average root diameter and water mimosa yield, above-ground dry weight decreased in the monocropping treatment. Meanwhile, water mimosa yield, above-ground dry weight, and all of the indices of root morphology in 2022 early season decreased with the increasing N deposition in the rice-water mimosa intercropping system. Contents of soil total manganese (Mn), total zinc (Zn), total calcium (Ca), and cellobiosidase activity also declined with increasing N deposition. However, the land equivalent ratio (LER) of the intercropping system was greater than 1 even under N deposition. In addition, compared with monocropping, intercropping increased dry weight of stem and leaves, average root diameter of rice, contents of soil total nitrogen, total phosphorous, total Mn, total Zn, total Ca and the activity of acid phosphatase, and also enhanced soil microbial biomass carbon (MBC), nitrogen (MBN) and phosphorus (MBP), gram-positive bacteria, gram-negative bacteria, fungi, bacteria, methane-oxidizing bacteria contents and fungi/bacteria ratio.

Conclusion

The experiment results suggest that N deposition caused negative impacts on rice farming system. However, rice and water mimosa intercropping systems can reduce the negative effects of N deposition (especially LN) on rice and soil. The findings demonstrate that this intercropping system is advantageous under N deposition (especially LN) than rice monocropping.

中文翻译：

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水稻与含羞草 （Neptunia oleracea Lour.） 间作可以减轻模拟氮沉降对水稻和土壤的负面影响

 背景和目标

氮 （N） 沉积通常对各种生态系统产生不利影响。农田间作是一种众所周知的种植模式和农业生态系统，具有多种优势。然而，对农田中氮沉积的研究，特别是间作系统的研究仍然有限。

 方法

在三个季节进行了田间试验，以检验水稻单作和稻水含羞草 （Neptunia oleracea Lour.） 间作系统对氮沉降下水稻生长和土壤特性的影响。模拟的氮沉积速率设置为两个水平，包括以 40 kg·ha⁻¹·yr⁻¹ N 的速率进行低氮 （LN） 沉积和以 120 kg·ha⁻¹·yr⁻¹ N 的速率进行的高氮 （HN） 沉积，在水稻的整个生育期内，除了施用 180 kg·ha⁻¹·yr⁻¹ 氮肥外，还施用了这些氮肥。

 结果

随着氮沉降、水稻植株高度、平均根径和水含羞草产量的增加，单作处理地上部干重降低。同时，随着稻-水含羞草间作系统中氮沉降的增加，2022 年初期含羞草产量、地上干重和根系形态各项指标均呈下降趋势。土壤全锰 （Mn） 、总锌 （Zn） 、总钙 （Ca） 和纤维二糖苷酶活性也随 N 沉降量的增加而下降。然而，即使在氮沉积下，间作系统的土地当量比 （LER） 也大于 1。此外，与单作相比，间作提高了茎叶干重、水稻平均根径、土壤全氮、全磷、全Mn、全Zn、全Ca和酸性磷酸酶活性，还提高了土壤微生物量碳（MBC）、氮（MBN）和磷（MBP）、革兰氏阳性菌、革兰氏阴性菌、真菌、细菌、 甲烷氧化细菌含量和真菌/细菌比率。

 结论

试验结果表明，氮沉降对水稻种植系统造成了负面影响。然而，水稻和水含羞草间作系统可以减少氮沉积（尤其是 LN）对水稻和土壤的负面影响。研究结果表明，这种间作系统在 N 沉积（尤其是 LN）下比水稻单作更有利。