Response Of Root Growth Of Apple Trees To Different Nitadgct Levels Under Water Storage Pit Irrigation

Water storage pit irrigation is a new method for middle and deep depth irrigation in arid and semi-arid areas in north China.The water storage pit irrrigation method transports the required water,moisture and nutrients directly to the root soil of the fruit tree through the pit dug around the fruit tree.Water storage pit irrigation can improve soil permeability of fruit trees effectively,and it can make full use of rainfall runoff,reduce soil erosion and promote the growth and development of deep root system of fruit trees.In this experiment,24 seven-year-old red Fuji apple trees in good growing condition are selected.A total of eight treatments including CK(the control group of surface nitrogen application)and T1,T2,T3,T4,T5,T6 and T7(the experimental treatment group of water storage pit irrigation)were set,each treatment has three duplicates.Urea(nitrogen content 46.7%)was applied as the nitrogen fertilizer,and potassium dihydrogen phosphate was used as the phosphate potash fertilizer,with the same amount of 17kg/ha applied in each treatment.CK adopts the method of ground broadcast while fertilizer of T1,T2,T3,T4,T5,T6 and T7 are fully integrated into water and then poured into the storage pit.The total nitrogen application amounts of T1,T3 and T5 were 20kg/ha,the total nitrogen application amounts of T2,T4 and T6 were 40kg/ha,and T7 did not apply nitrogen fertilizer,T1 and T2 nitrogen fertilizer were applied in the period after flowering,and T3 and T4 nitrogen fertilizer were applied in the period of fruit enlargement,T5 and T6 nitrogen fertilizer were applied in half in each of the two topdressing stages,and the nitrogen application amount in CK treatment was completely consistent with that in T5 treatment.The growth and development of root system of apple trees in different nitrogen application stages and different nitrogen application stages were studied by outdoor orchard sampling and indoor analysis.At the same time,the relationship between the growth of apple tree shoots,the distribution of soil nitrate nitrogen and the growth of root system was studied.Finally,the following conclusions are drawn:1?Root length density response to nitrogen:The root system of ground irrigation is mainly distributed on the surface,and the root system of water storage pit is mainly distributed in the deep layer of soil.The vertical distribution of root length density increases first and then decreases with the increase of soil depth.The application of nitrogen fertilizer could promote the growth of root length effectively.The root length of treated roots with a nitrogen application rate of 20kg/mu was the best in a single topdressing stage.The treatment of nitrogen application rate of 40kg/mu inhibited the development of roots to some extent.When the total nitrogen application rate is the same,the effect of applying half of the fertilization method in the two top dressing periods is optimal.The total root length change trend of each treatment was increased first and then decreased.The total root length of the treatment was 20 kg/mu in both topdressing periods.The total root length of T6 was observed in the whole growth period.Maximum,CK total root length is less than puddle irrigation.Based on the above analysis,T6 treatment with 20 kg/mu of nitrogen fertilizer applied during the two topdressing periods is the best treatment for the growth of root length of apple trees.2?Root surface area density response to nitrogen:The high surface area density of surface irrigation is located at 0-40cm,and the high surface area density of water storage pit is located at 20-80cm.The vertical distribution of root surface area density increases first and then decreases with the increase of soil depth.The treatment of root surface area with the nitrogen application rate of 20kg/mu in a single topdressing period was the best.The treatment with the same total nitrogen application rate had better effect on the root surface area of apple trees during the fruit expansion period.The method of applying half nitrogen fertilizer in each two top dressing stages was the best nitrogen application method.3?New shoot growth law and correlation analysis between shoot growth and root growth:Topdressing nitrogen fertilizer can promote the growth of new shoots of apple trees effectively,and the cumulative growth of new shoots increases with the increase of nitrogen application rate.After the flowering period,the growth rate of the new shoots slowed down slightly,and the increase of the new shoots before the fruit enlargement period was significantly increased.The growth rate of the new shoots decreased after the fruiting period.Under the same nitrogen application rate,the cumulative growth of new shoots in the treatment of water storage pits is greater,and the water storage pit irrigation is more conducive to the growth of new shoots of apple trees.Root growth and shoot growth showed alternating growth,and the correlation coefficient between root growth and shoot growth did not reach significant.The content of nitrate nitrogen in soil increased with the increase of nitrogen application rate.The more nitrate nitrogen in the soil,the better the growth of roots.With excessive application of nitrogen fertilizer,soil nitrate nitrogen content increased but root development was inhibited.Under the same nitrogen application rate,the nitrate nitrogen in the ground irrigation soil was mainly concentrated in the soil surface layer,and the surface root system developed better.The soil nitrate nitrogen in the water storage pit was mainly concentrated in the deep layer of the soil,and the root system in the middle and deep layers developed better.