Study on the effects of long-term application of chemical fertilizer combined with manure on soil physical properties of apple orchard based on CT scanning technology

Objectives The study analyzed the water capacity related soil properties affected by long-term combining application of chemical fertilizer and manure, to deeply understand the mechanism of the measurement in soil fertility improvement.

Methods The study was based on a 12-years long term experiment in an apple orchard in dryland of northern Shaanxi Province. The soil samples of 0–10, 10–20 and 20–40 cm in depth were collected in the treatments of no fertilizer control (CK), chemical fertilizers (NPK) and chemical fertilizers with manure (MNPK). CT scanning method was used to quantitatively analyze the number and porosity of macropores (> 1000 μm), and the distribution of macropores in the soil layers. Field water capacity and soil saturated hydraulic conductivity (SHC), and soil bulk density were measured using conventional methods at the same time.

Results Compared to NPK, the soil macroporosity was slightly increased in the 0–20 cm soil layer, but significantly increased by 91.7% in the 20–40 cm soil layer under MNPK treatment. In the three soil layers, the highest number of macropores was all appeared in MNPK, and the number was significantly higher than those in NPK in the 0–10 and 20–40 cm layers, with an increment of 38.4% and 54.8%, respectively (P < 0.05). Compared to CK, NPK treatment only increased the SHC and field water capacity in the 10−20 cm soil, while MNPK treatment increased those indexes in all the three soil layers (P < 0.05), and soil bulk density was not affected by both MNPK and NPK treatments. Correlation analysis showed that the number of macropores, macropore porosities, field water capacity and SHC were positively correlated with each other (P < 0.01), and all of them were negatively correlated with soil bulk density (P < 0.01).

Conclusions Compared with pure chemical fertilizer application, the combination application of chemical and organic fertilizers could significantly increase the number of macropores and macroporosity in the 0−40 cm soil layer, which leads to the increase of soil water permeability, especially in the 20−40 cm soil layer.