Effects Of Subsurface Irrigation On Physiological Characteristics And Utilization Of ¹⁵N-urea For ‘Gala'/Malus Hupehensis

The current large amount of fertilizer in apple orchards and low fertilizer utilization limit the green sustainable development of the apple industry,which is relatedto the backwardness of our country's fertilizer application technology.Subsurface irrigation is buried in the underground irrigation pipe system,and the water and nutrients are transported to the soil layer where the plant roots are.The effect of saving fertilizer and water is significant,but the effect and specific application parameters on apples have not been reported.The experiments were carried out to study the effects of different fertilizer placements and methodson the characteristics of nitrogen absorption,distribution and utilization of fifteen year old apple trees¹⁵N urea tracer technique.The main results were as follows:1.The absorbed ¹⁵N by roots transfers to new vegetative organs prior at the new shoot growing stage and fruit rapid-swelling stage under the different horizontal fertilization placements.The Ndff values of fruits are the highest among the organs at the fruit maturity stage under the three fertilization treatments.The Ndff values of the same organ are different under different fertilization treatments,and the Ndff values of the organs under the subsurface irrigation are significant higher than those under the drip irrigation and surface applicator treatments,especially for fruits.The Ndff values of fruits under the three treatments all present an increasing tendency as the phonological phase changing and reach the maxima at the fruit maturity stage,and the Ndff values of fruits in subsurface irrigation and drip irrigation are respectively 1.45 and 1.30 times of that surface applicator.The result of the Ndff values of fruit at the new shoot growing stage and fruit rapid-swelling stage is subsurface irrigation>drip irrigation>surface applicator.The NUE of trees under the Subsurface irrigation treatment is 29.13%,which is significantly higher than those under the other two treatments?23.36%and 19.56%?.Fertilization methods significantly affects plant organs ability of absorbing fertilizer,especially roots.The experiment,suggests that subsurface irrigation could improve the utilization rate of nitrogen fertilizer.2.The isotope¹⁵N urea trials were carried out in field conditions with three different fertilizer application depth treatments.The difference of Ndff was significant in different organs among different buried depth treatments,and the 10 cm and 30 cm treatments were obviously lower than 20 cm treatment.At the full-bloom stage the Ndff of new organs was higher than that of the storage organs.The Ndff of fruit was the highest at fruit maturity stage.The distribution of ¹⁵N was different in various organs at different phonological stages,but there was no significant difference among three treatments.With the process of growth,the ratio of ¹⁵N utilization of apple trees in different treatments increased gradually and reached the highest,and the treatment of fertilizer in 20 cm was generally higher than that in 10 cm and in 30 cm treatments.Fertilizer application in 20 cm can enhance the absorption and ability to transfer N to apple tree,and also can increase the nitrogen use efficiency.