Effect of fertilization depth on maize root and rhizosphere soil fertility vertical distribution in immature loess subsoil

This study was set up to determine the effect of fertilization depth on maize (Zea mays L.) productivity, root growth and rhizosphere soil fertility in immature loess subsoil. To that end, a sample of immature loess subsoil was analyzed for the effect of different fertilization depths (020 cm, 6080 cm, 100120 cm, 140160 cm and 180200 cm) of bio-organic fertilizer on maize productivity and the vertical distribution of root weight, rhizospheric soil enzyme activity and rhizosphere soil nutrients in a 2-year root-tube soil column culture. The control treatment (CK) was not treated with fertilizer. The results showed that: 1) indicators such as maize productivity, total root weight, etc., increased at the start and then decreased with increasing fertilization depth from 0 cm to 200 cm. The largest root weight (52.3 g) and productivity (361.0 g) of maize were obtained under the 100120 cm fertilization depth. 2) In all the treatments, the vertical distribution of maize root weight followed a T-shape and the largest maize root weight was noted in the 020 cm soil layer, which accounted for up about 50% of the total root weight. Root weight significantly declined with increasing soil depth (P < 0.05). Under 100120 cm fertilization depth treatment, both total root weight and root weight of 040 cm soil layer (27.19 g) reached the highest level, furthermore, N, P and K accumulation in the root were moderate with 6.60 gkg1, 2.38 gkg^-1 and 8.16 gkg^-1, respectively. 3) Fertilization significantly increased enzymes activities and nutrients contents in rhizospheric soil. Urease activity in 0 200 cm rhizospheric soil increased 0.1080.354 mg(NH_3-N)g^-1(soil)24h^-1 in the 6080 cm fertilization depth treatment. In the 140160 cm fertilization depth treatment, sucrase activity and available phosphorus content of 0200 cm rhizospheric soil increased to 12.919.6 mg(glucose)g^-1(soil)24h^-1 and 4.316.02 mgkg^-1, respectively. Maize rhizosphere soil organic matter content was higher (5.557.14 gkg^-1) in the 180200 cm fertilization depth treatment. When fertilization depth was less than 100 cm or deeper than 120 cm, maize rhizospheric soil alkline phosphatase activity and available nitrogen content kept higher level, which were more than 0.497 mg(phenol)g1(soil)24h^-1 and 25.4 mgkg^-1, respectively. 4) Significant correlations among root weight, root NPK nutrient, three rhizospheric soil enzyme activities and three rhizospheric soil nutrients under different fertilization depth treatments were observed in the immature loess subsoil. 5) The optimized fertilization depth was 60160 cm for improving maize shoot-root-soil systems in the immature loess subsoil based on FACTOR and CLUSTER analyses. This study provided a new idea for speeding up the raw soil maturation process through changing fertilizers application depth.