Effect of different combinations of dripping and spreading fertilization of N, P and K fertilizers on uptake, distribution and utilization of 15N in Fuji apple

Abstract:【Objective】Fertigation is a new technology for integrated agricultural water and fertilizer management, which can effectively achieve simultaneous supply and efficient use of water and fertiliz-er. Fertigation technology is widely used in China in the production of maize, tomatoes, bananas and other fruits and vegetables, but the application in apple industry is far behind other countries. We aimed to study the effects of tree uptake, distribution and utilization of 15N under different combinations of drip-ping and spreading fertilization of N, P and K fertilizers to obtain the proper way of fertilization.【Meth-ods】The trial was conducted with 2- year- old nursery trees of Yanfu 3/T337/ Malus baccada (Linn.)Borkh. as test materials, and the pot test and drip irrigation bags were used to simulate dripping fertiliza-tion. Five treatments were set up for dripping and spreading application of nitrogen (N), phosphorus and potassium (PK) fertilizers. T1: N spreading, PK dripping; T2: N spreading, PK spreading (water soluble PK fertilizer); T3: N drip irrigation, PK drip irrigation; T4: N drip irrigation, PK sprinkle (water soluble  PK fertilizer); T5: N driping, PK spreading (common PK fertilizer). All fertilizers were applied in May, June and July 2019. The amount of fertilizer applied each month was one third of the total fertilizer. The fertilizers used for spreading fertilization in the trial were spread on the pots and then mixed with the soils on the 5th day of each month, 1/3 amount of the fertilizers were used for each month. The fertilizers used for dripping fertilization treatment were used three times for each month at an interval of 7-10 days. All treatments were repeated three times. The total amount of the fertilizers used for each pot (the weight of dry soil in a pot was about 20 kg) was 10 g of N, 5 g of phosphorus pentoxide and 5 g of potas-sium oxide. The specific fertilizer dosage was calculated based on the actual nutrient content of the fertil-izer. The whole plant was covered with a screen net. The leaves were collected in October 2019.【Results】The total whole plant nitrogen was not significant different among the different treatments, but it was slightly lower under the T1 and T2 treatments (N used by spreading) than those under the T3, T4 and T5 treatment (N used by driping). The nitrogen content of annual branches was highest under the T3 treatment and significantly different from the T5 treatment. The nitrogen content of main roots was high-est under the T1 treatment and significantly different from that under the T4 treatment. The total nitrogen of leaves and annual branches was highest under the T3 treatment. The total nitrogen of perennial branches and intermediate rootstock was highest under the T5 treatment. The total nitrogen of the main stems was highest under the T5 treatment and significantly different from those under the other treat-ments. The total nitrogen of main root was highest under the T1 treatment and lowest under the T3 treat-ment, and the total nitrogen under the T1 and T5 treatments were significantly higher than that under the T3 treatment. The total N of lateral roots and capillary roots was highest under the T4 treatment. The overall Ndff values of the plants varied with the treatments, and the Ndff values under the N dripping irri-gation treatments (T3, T4, T5) were higher than those under N spreading treatments (T1, T2), and were highest under the T3 treatment and significantly different from those under the T1 and T2 treatments. The overall 15N uptake of the plants varied with the treatments, and the 15N uptake under N dripping irri-gation treatments (T3, T4, T5) were all higher than those under the nitrogen fertilizer spreading treat-ments (T1, T2), and were highest under the T3 treatment, and was significantly different from those un-der the T1 and T2 treatments. The Ndff values of the leaves were highest under the T3 treatment and were significantly higher than those under the other treatments. The Ndff values of perennial branches were highest under the T3 treatment which was significantly different from those under the T1 and T2 treatments. The Ndff values of the inter-stock and hair roots were highest under the T3 treatment, and were significantly different from those under the T1, T2 and T5 treatments. Meanwhile, the15N uptake of the leaves and annual branches was highest under the T3 treatment. The 15N uptake of perennial branches was highest under the T3 treatment and was significantly different from that under the T1 treatment.The 15N uptake of the inter-stock was highest under the T3 treatment. The 15N uptake of the main stems and main roots was highest under the T5 treatment and was significantly different from those under the other treatments. The 15N uptake of the lateral roots was highest under the T4 treatment and was signifi-cantly different from those under the T1 and T2 treatments. The 15N uptake of hair roots was highest un-der the T4 treatment. The overall N fertilizer utilization rate of the plants significantly varied with the treatments, and the highest N fertilizer utilization rate was 28.83% under the T3 treatment, which was 10.13% and 10.56% higher than those under the T1 and T2 treatments, and there was no significant dif- ference between T4 and T5 treatments and T3. The leaf nitrogen fertilizer allocation rate was highest un-der the T2 treatment and was lowest under the T5 treatment. The N fertilizer distribution rate of the annu-al branches was highest under the T3 treatment. The N fertilizer distribution rate of the perennial branch-es was highest under the T2 treatment. The N fertilizer distribution rate of the main stems was highest under the T5 treatment and was significantly higher than those under the other treatments. The N fertiliz-er distribution rate of the inter- stock was highest under the T5 treatment. The N fertilizer distribution rate of the main roots was highest under the T1 treatment. The N fertilizer distribution rate of the lateral roots and hair roots was highest under the T4 treatment. The leaf blades and annual branches had the highest N fertilizer utilization rate of 5.80% and 6.72% under the T3 treatment, respectively. The peren-nial branches had the highest nitrogen fertilizer utilization rate of 5.83% under the T3 treatment, which was significantly different from that under the T1 treatment. The inter-stock had the highest N fertilizer utilization rate of 2.21% under the T3 treatment. The highest N fertilizer utilization rate of the main stems was 2.79% under the T5 treatment, which was significantly different from those under the other treatments. The highest N fertilizer utilization rate of the main roots was 2.84% under the T5 treatment. The lateral roots had the highest N fertilizer utilization rate of 2.92% under the T4 treatment, which was significantly different from those under the T1 and T2 treatments. The hair roots had the highest N fertil-izer utilization rate of 4.68% under the T4 treatment.【Conclusion】In summary, different combinations of dripping fertilization had different effects on 15N uptake , distribution and utilization in apple trees.The N fertilizer uptake and utilization were highest when all fertilizers were used by dripping. Howev-er, the N fertilizer uptake and utilization under N, P, K dripping treatments was not different from that under N dripping fertigation and P, K spreading fertigation treatments. Considering that the costs of the water soluble phosphorus and potassium fertilizers are much higher than those of common phosphorus and potassium fertilizers, it would be recommended that nitrogen fertilizer could be used by dripping and common phosphorus and potassium fertilizers could be used by spreading in practice.