| The differences in the structure of high and low canopy structures in the intercropping system of grasses can maximize the absorption and utilization of water,photothermal and nutrient resources,and improve the yield and land utilization of intercropping groups.However,the difference in the structure of high and low crops between grasses led to the obstruction of light in kidney beans of low-level crops,which affected the growth and development.Nitrogen is an essential nutrient element for crop growth and development,and nitrogen application in intercropping systems can increase the dry matter accumulation and yield of inferior crops,improve photosynthetic performance,and promote plant nitrogen accumulation.Therefore,combined with the fertility characteristics of kidney beans,the influence of nitrogen fertilizer on the growth and development of low-level kidney beans under the intercropping mode of grain and bean was explored,and the reasonable intercropping mode and suitable nitrogen fertilizer application rate were clarified to improve the intercropping contribution rate and nitrogen fertilizer utilization rate,which is of great practical significance for the rational utilization of cultivated land resources and nitrogen resources in dry farming areas.The experiment was carried out in Yulin,Shaanxi Province from 2021 to 2022,using a split-plot design,and the main treatment in 2021 was 4:2（T1）,3:3（T2）,2:4（T3）,millet monocropping（T4）,kidney bean monocropping（T5）five planting modes,and the secondary treatment was 0 kg·hm-2（N0）,135 kg·hm-2（N1）,90 kg·hm-2（N2）,45kg·hm-2（N3）four nitrogen fertilizer levels.In 2022,the main treatment was 4 planting modes of grain bean intercropping 4:2（T1）,2:4（T3）,millet monocropping（T4）and kidney bean monocropping（T5）,and the secondary treatment was 4 nitrogen fertilizer levels of 0 kg·hm-2（N0）,135kg·hm-2（N1）,90 kg·hm-2（N2）,and 180 kg·hm-2（N3）.To explore the effects of nitrogen application rate on dry matter accumulation and yield composition factors of intercropping kidney beans,photosynthetic characteristics and nitrogen uptake and utilization characteristics of kidney bean leaves,the following main conclusions were drawn.（1）Field trials in 2021 and 2022 showed that intercropping increased kidney bean plant height and reduced pod number per plant compared with kidney beans monocropping.The accumulation and yield of dry matter in the aerial part of intercropping kidney beans decreased.Nitrogen fertilizer effectively promoted the growth and development of kidney beans,improved the intercropping conditions and caused adverse changes in kidney bean agronomic traits,and effectively increased the number of pods per plant of kidney beans.The application of nitrogen fertilizer significantly increased the dry matter accumulation,100-grain weight and yield of kidney beans in the aboveground.In 2021,the yield of kidney beans was the highest under N1(135 kg·hm–2)treatment,and in 2022,the yield of kidney beans was highest under N3(180 kg·hm–2)treatment,but the difference was not significant with N1(135 kg·hm–2)treatment.The land equivalent ratio of LER was greater than 1 under T1（grain bean 4:2）and T3（grain bean 2:4）modes in the 2-year experiment,which showed the advantage of intercropping,and the agronomic traits and yield of kidney beans were well performed under the intercropping T3 mode.（2）Under the grain bean intercropping system,the photosynthesis of kidney bean leaves was blocked,and the net photosynthetic rate and transpiration rate of kidney bean leaves were reduced compared with single cropping,but the chlorophyll fluorescence parameters of the leaves were increased compared with single cropping,and the increase of chlorophyll fluorescence parameters indicated that the photosynthetic performance of kidney beans was improved.Compared with no nitrogen application,the net photosynthetic rate of kidney bean leaves increased by 2.10%～10.97%and the transpiration rate by 1.65%～24.26%on average under the T1 mode nitrogen application treatment of intercropping kidney beans.Under the T3 mode nitrogen application treatment of intercropping kidney beans,the net photosynthetic rate of leaves increased by 3.91%～25.47%,and the transpiration rate increased by 3.99%～27.42%on average.Nitrogen application could improve the chlorophyll fluorescence parameters of leaves,enhance the PSII.reaction center activity of intercropping kidney bean leaves,and the actual photochemical efficiency of PSII.of intercropping T1mode kidney bean leaves after nitrogen application increased by 2.45%～38.68%compared with N0 on average.The actual photochemical efficiency of PSII.leaves in intercropping T3mode increased by 3.47%～47.91%compared with N0 on average.After nitrogen application,the non-photochemical quenching coefficient of intercropping T1 mode was reduced by6.37%～47.72%compared with N0.The non-photochemical quenching coefficient of intercropping T3 mode was reduced by 3.12%～48.76%compared with N0 on average.（3）Reasonable intercropping mode and appropriate amount of nitrogen fertilizer can effectively improve the nutrient utilization rate of intercropping system.Compared with monocropping,the aboveground nitrogen accumulation of intercropping kidney beans was lower than that of single cropping,but nitrogen fertilizer application effectively promoted the accumulation of aboveground nitrogen in kidney beans at each growth stage,and the average aboveground nitrogen accumulation in intercropping T1 kidney beans increased by28.13%,46.03%,47.11%and 43.26%at the nitrogen levels of 45 kg·hm–2,90 kg·hm–2,135kg·hm–2and 180 kg·hm–2,respectively.The average aboveground nitrogen accumulation in intercropped T3 kidney beans increased by 33.14%,42.14%,36.15%and 55.58%at the nitrogen levels of 45 kg·hm–2,90 kg·hm–2,135 kg·hm–2and 180 kg·hm–2,respectively.The average nitrogen utilization rate of kidney bean intercropping under T1 mode nitrogen application was reduced by 31.65%～34.80%,and the nitrogen harvesting index was reduced by 20.07%～30.42%.The average nitrogen utilization rate of kidney bean intercropping under T3 mode nitrogen application was reduced by 23.27%～31.91%,and the nitrogen harvesting index was reduced by 23.33%～33.31%.Comprehensive analysis showed that intercropping reduced the dry matter accumulation,yield formation,light energy use efficiency and nitrogen conversion and utilization of kidney bean plants,but nitrogen application improved the adverse performance of intercropping on the agronomic traits and yield formation of kidney beans to a certain extent,improved the photosynthetic performance of intercropping kidney beans,enhanced the PSII.reaction center activity of kidney bean leaves,and effectively promoted the accumulation of nitrogen in the aerial parts of kidney bean plants.Under intercropping T3（grain bean 2:4）mode,the nitrogen application rate of 135 kg·hm–2kidney beans performed relatively well. |
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