Effects of fertilization with injection to the rhizosphere on nitrogen absorption and utilization, fruit yield and quality of apple in the Loess Plateau

【Objectives】 The drought in spring and low fertilizer utilization efficiency limit the high quality apple production in the Loess Plateau in northwest region of China. Fertigation is usually used in abroad to overcome the problem of low fertilizer utilization efficiency. But this technology is difficult to spread in China for its strict requirements of irrigation system and investment at the level of farmer household in the short run. In recent years, fertilization with injection to the rhizosphere is used broadly in many places of China. This technology needs low cost and is simple.15N urea was used in this experiment as tracer to study the effects of fertilization with injection to the rhizosphere on nitrogen absorption and utilization, fruit yield and quality of apple in the Loess Plateau.【Methods】 The 9-year-old Fuji treesMalus pumila Mill cv.Red Fuji/M26/Malus Sieversii (Ledeb) Roem and15N tracer element which was measured by MAT-251 mass spectrometer were used to calculate the fertilizer utilization efficiency of various tree organs and soil. SPAD-502 was used to determine the SPAD value of marked leaves. Sponge soaked in a solution of glycerol phosphate was used to measure the amount of field soil ammonia volatilization. Static chambers-gas chromatography was used to determine the soil N2O fluxes. These methods were used to explore the effect of fertilization either with injection or traditional ring ditch on nitrogen absorption, distribution and utilization, fruit yield and quality of apple in the Loess Plateau.【Results】 The results show that the advantages of apple orchard fertilization with injection to the rhizosphere in the Loess Plateau are as follows: 1)Within one month after fertilization, the gaseous nitrogen loss in apple orchard changed. The amount of soil ammonia volatilization of fertilization with injection to the rhizosphere was significantly less than the traditional ring ditch fertilization by 54.9%, and the N2O flux was 5.0%. 2)After fertilization with injection to the rhizosphere, the distribution range of water and fertilizer increased at the same time, the volume of fertilizer absorbed by apple tree roots was expanded eventually, the percentage nitrogen derived from fertilizer (Ndff%) of new shoot leaves and fruits was always at a high level throughout the whole growing season. After the fruits were harvested, the absorption rate of the whole tree was 53.04%, and 12.25 percentage points higher than the control. This result indicated nitrogen was absorbed more quickly following fertilization with injection to the rhizosphere, and nitrogen utilization efficiency was significantly improved. 3)In the end of growth season, the 0-60 cm soil nitrogen residual rates of treatment of fertilization with injection and the control were 36.55% and 43.13%, respectively. And the former was significantly lower than the latter. 4)The chlorophyll content (SPAD value) of new shoot leaves was maintained in higher level than the treatment of traditional ring ditch fertilization in the whole growing season. Compared with traditional ring ditch fertilization, fruit weight and yield of per tree in treatment of fertilization with injection were higher than the control by 3.8% and 19.7%, respectively.【Conclusions】 The technology of fertilization with injection in the Loess Plateau region can increase tree nitrogen absorption, utilization and decrease soil nitrogen residual significantly. So the water and fertilizer distributed evenly in soil and the purpose to save water and fertilizer can be achieved eventually. Fertilization with injection also avoided the root damage caused by traditional digging and reduced labor costs at the same time. On the whole, fertilization with injection is an effective way to improve the fertilizer and water use efficiency in dryland apple production in the Loess Plateau.