Effects of soil-layer compounding schemes on the soil fertility of newly-constructed cultivated land

Abstract: The improvement of the quality of the newly-constructed cultivated land is of great significance to the effective utilization of the newly-constructed cultivated land after the implementation of the "Gully Land Consolidation Project" (GLCP) in Yan' an. To explore an effective method that can be used to quickly improve the newly-constructed cultivated land with poor quality of GLCP, a 4-year soil-layer compounding experiment was carried out in Yangjuangou watershed (109°31'-109°71' E, 36°42'- 36°82' N). Based on the complementary structure of the Red Clay (RC) and Malan Loess (ML), the different ratios of RC and ML were used for reconstruction of the 0-30 cm soil layer of the newly-constructed cultivated land (T0, undisturbed soil; T1, 100% RC; T2, 83.3% RC and 16.7% ML; T3, 66.7% RC and 33.3% ML; T4, 50% RC and 50% ML; T5, 33.3% RC and 66.7% ML; T6, 16.7% RC and 83.3% ML; T7, 100% ML) . The chemical and physical properties of the soil and the condition of crop were measured, and the soil fertility of each scheme was comprehensively evaluated by principal component analysis. The results of experiment showed: The >0.25 mm water-stable aggregates in T2 and T3 increased by 13.7 and 15.2 times, respectively, compared with T0. Compared with T0 treatment, the geometric mean diameter (GMD) and mean weight diameter (MWD) of water-stable aggregates >0.25 mm in T3 treatment were 20.9% and 29.1% higher while bulk density decreased by 11.1% and porosity increased by 15.3%. The contents of organic matter and nitrate nitrogen in T3 increased by 24.5% and 100%, respectively, compared with the control group. Compared with T0 treatment, the available potassium values in T2 and T3 treatment were increased by 29.3% and 17.6%, respectively. The results of principal component analysis showed that soil structure was the structural basis of soil fertility, and soil nutrient was an important part of soil fertility, which jointly determined soil fertility. And the order of the comprehensive fertility score from high to low was T3, T2, T1, T5, T6, T4, T7, T0. The maize in T3 treatment had the maximum aboveground biomass and 1000-grain weight, and the maize yield was also relatively high. It could be concluded that the scheme was the optimal one when the volume ratio of RC and ML was 66.7% and 33.3%, respectively for the soil having the highest comprehensive fertility and the crops growing relatively well. In conclusion, the experimental results show that soil-layer compounding is a feasible method to construct soil with high quality quickly, and the study provides practical reference for the improvement of the quality of newly-constructed land in the GLCP and the implementation of similar projects in the future.