矮化中间砧苹果施氮位置对细根分布、氮素吸收和产量品质的影响

为明确矮化中间砧苹果树合理的施肥位置,减少氮肥的浪费。试验于2018年和2019年,以‘烟富3’苹果/SH6/八棱海棠为试材,借助15N同位素示踪技术,研究了萌芽前在树冠投影范围距树干由近及远的3个水平距离——内环、中环和外环施氮对新梢旺长期细根和土壤15N分布、树体15N吸收以及果实产量和品质的影响。结果表明:各处理的苹果细根(直径≤2 mm)根长密度均在水平方向和垂直方向呈衰减规律,主要分布在距离树干水平方向0~100 cm、垂直方向0~40 cm土层范围;与不施肥(对照)相比,施氮增加了细根根长密度,以施氮区内细根根长密度增加最为显著;从垂直方向0~20 cm土层施氮区细根根长密度增加量来看,内环施氮处理增幅最大,为对照的1.33倍~1.36倍,其次是中环施氮处理。各处理土壤15N含量峰值在水平方向均出现在施氮区域,在垂直方向均出现在0~20 cm土层。不同处理间树体细根根长密度与土壤15N分布空间吻合度(RLD-15N)差异显著,内环施氮处理显著高于中环和外环施氮处理。内环施氮显著提高了新梢旺长期树体新生器官氮素累积量,树体15N利用率表现为内环施氮>中环施氮>外环施氮;内环施氮和外环施氮土壤15N残留率无显著差异,但均高于外环施氮。与外环施氮处理相比,内环施氮处理显著提高了果实产量、可溶性糖含量和糖酸比,而硬度和可滴定酸含量无显著差异。可见,矮化中间砧苹果内环施氮有利于提高细根根长密度与土壤氮的空间分布吻合度,增加了生长前期新生器官含氮量,提高了树体15N利用效率,提高了果实产量和可溶性糖含量。因此实际生产中成年矮化中间砧苹果树推荐在靠近树干位置的1/3树冠投影面积处,即约为距树干水平距离0~75 cm范围内施氮肥。

Effects of Nitrogen Application Position on Fine Root Distribution,Nitrogen Absorption,Yield and Quality of Dwarfing Interstock Apple Trees

In order to clarify the reasonable fertilization position of dwarfing interstock apple trees,reduce the waste of nitrogen fertilizer.In 2018 and 2019,we studied the effects of nitrogen application in three horizontal distance of inner ring,middle ring and outer ring of the apple crown projected on soil 15N distribution,apple tree 15N absorption and utilization,and yield and quality on 8-year-old‘Yanfu 3’/SH6/Malus robusta using the 15N isotope tracer technique.The results showed that the root length density of apple fine roots(diameter≤2 mm)in all treatments presented attenuation rules in both horizontal and vertical directions,and it was mainly distributed in the range of 0-100 cm from the horizontal direction of the trunk and 0-40 cm from the vertical direction.Compared with the control group,the fine root length density of the treated area increased significantly.Judging from the increase in fine root length density in the nitrogen application zone of the 0-20 cm soil layer in the vertical direction,nitrogen application in inner ring had the largest increase,1.33 to 1.36 times of the control,followed by nitrogen application in middle ring.Under different treatments,the peak of soil 15N content in the horizontal direction appeared in the area where the fertilization area was located,and in the vertical direction in 0-20 cm soil layer.The spatial concordance index between the density of apple fine root length and soil 15N content(RLD-15N)showed significant differences among different treatments,and the nitrogen application in inner ring was significantly higher than that in middle and outer ring.The application of nitrogen in the inner ring significantly increased the that of the new organs of the tree during the new shoot growing stage.The 15N utilization rate of the tree was nitrogen application in inner ring>nitrogen application in middle ring>nitrogen application in outer ring.There was no significant difference in 15N residue rate between nitrogen application in inner ring and in outer ring,but both were higher than that in outer ring.Compared with nitrogen application in outer ring,nitrogen application in inner ring significantly improved fruit yield,soluble sugar content and sugar acid ratio,but there was no significant difference in hardness and titratable acid content.It can be seen that the application of nitrogen in the inner layer of dwarfing interstock apple was conducive to improving the spatial concordance index between the density of apple fine root length and soil 15N content,increasing the nitrogen content of new-born organs in the early growth period,improving the 15N utilization efficiency of the tree,and increasing the fruit yield and soluble sugar content.Therefore,in actual production,it is recommended to apply nitrogen fertilizer at the 1/3 crown projection area close to the trunk of adult dwarfing interstock apple trees,that is,approximately 0-75 cm from the horizontal distance of the trunk.