Effects of the application of different improved materials on reclaimed soil structure and maize yield of Hollow Village in Loess Area

Effects of the application of different improved materials on properties of reclaimed soil

Soil organic matter (SOM) and total nitrogen (TN)

After the application of different improved materials, the SOM and TN contents in both 0–0.15 m and 0.15–0.30 m layers of the hollow village reclaimed soil showed an overall increasing trend (Fig. 1). In the 0–0.15 m layer, the organic matter content increased by 9.6%, 79.0%, 90.0%, 61.4%, 120.1%, and 131.7% respectively under TM, TF, TO, TMF, TMO and TFO treatments compared with CK treatment, indicating that different improved materials all played important roles in improving the organic matter content of reclaimed soil (Fig. 1a). The improvement of organic matter content in the 0–0.15 m layer of reclaimed soil by the treatments of different improved materials showed as follows: TFO > TMO > TO > TF > TMF > TM > CK, and TO, TMO and TFO treatments with organic fertilizer addition could significantly improve the organic matter content of the reclaimed soil (P < 0.05), among which TFO treatment was the most effective on improvement of the organic matter content. In the 0.15–0.30 m layer, the results of significance analysis showed that TO, TMF, TMO and TFO treatments all significantly increased the organic matter content (P < 0.05), while TM and TF treatments had no significant difference in improving the soil organic matter content, with TFO treatment having the most significant effect.

Compared with CK, the concentration of TN in the two soil layers had similar increasing trends to SOM after the application of different improved materials (Fig. 1b). In the 0–0.15 m layer, TM, TF, TO, TMF, TMO and TFO increased by 14.29%, 16.33%, 26.53%, 20.41%, 28.57%, and 51.02%, respectively. In the 0.15–0.30 m layer, the concentration of TN also showed an increasing trend in varying degrees.

Size distribution of water-stable aggregates

Water-stable aggregates are important indicators for evaluating the structural stability and erosion resistance of soil, and their quantity and distribution can well reflect the changes in soil structure and quality²⁶. Compared with CK, significant changes in the distribution of water-stable aggregates were shown in the reclaimed soils in the 0–0.15 m and 0.15–0.30 m layers after the application of different improved materials (Figs. 2 and 3) (P < 0.05). In the 0–0.15 m layer, after the application of different improved materials in hollow village reclaimed soil, the proportion of water-stable macroaggregates (particle size > 0.25 mm) showed an overall increasing trend, and the water-stable microaggregates content (particle size < 0.25 mm) showed a decreasing trend. In particular, it showed that except for the treatment of maturing agent (TM), the proportion of water-stable aggregates (particle size > 2 mm, 1–2 mm, and 0.5–1 mm) were significantly increased under the TF, TO, TMF, TMO and TFO compared with CK, especially that of particle size > 2 mm (Fig. 2). The proportion of > 2 mm water-stable aggregates was increased by 88.1%, 194.5%, 203.7%, 376.2%, and 781.7% respectively under TF, TO, TMF, TMO and TFO compared with CK. The proportion of water-stable macroaggregates under different treatments showed as follows: TFO (35.8%) > TMO (20.7%) > TO (16.9%) > TMF (16.3%) > TF (12.3%) > TM (10.1%) > CK (9.0%), and the water-stable macroaggregates were increased by 328.2%, 130.0%, 87.8%, 81.1%, 36.7%, and 12.2% respectively compared with CK, with the maximum increase of 328.2%. In general, all six different amendment material treatments increased the proportion of water-stable macroaggregates in reclaimed soil and promoted the aggregation and cementation of water-stable microaggregates (< 0.25 mm) to water-stable macroaggregates (> 0.25 mm). And the TFO showed the best effect on the increase of water-stable macroaggregates, followed by TMO, TO, and TMF, while TF and TM treatments showed little effect.

In the 0.15–0.30 m layer, the change of water-stable aggregates showed a similar trend to that in the 0–0.15 m layer compared with CK treatment. TF, TO, TMF, TMO and TFO treatments all significantly increased the proportion of > 2 mm and 1–2 mm water-stable aggregates, and decreased the proportion of water-stable microaggregates (P < 0.05) (Fig. 3). In particular, TF, TO, TMF, TMO and TFO treatments increased the proportion of > 2 mm water-stable aggregates by 130.3%, 94.5%, 133.9%, 151.4%, and 309.2% respectively compared with CK, of which TFO treatment showed the most significant effect on the increase of the proportion of water-stable macroaggregates. Compared with the 0–0.15 m layer, the proportion of water-stable macroaggregates in the 0.15–0.30 m layer showed a gradual decrease with the increase of soil depth.

Water-stable aggregates structure stability

The mean weight diameter (MWD), geometric mean diameter (GMD), unstable aggregate index (E_LT), and fractal dimension (D) are important indicators reflecting the structural geometry and stability of soil aggregates, and it has been indicated in this research that the higher the MWD and GMD and the smaller the E_LT and D, the better the structural stability of the aggregates and the soil structure^27,28. Compared with CK treatment, the MWD and GMD showed a trend of significant increase while the D and E_LT showed a trend of significant decrease (P < 0.05) under TF, TO, TMF, TMO and TFO treatments after the application of different improved materials, and TM treatment had no significant effect on the indicators of aggregate stability (Table 1). In the 0–0.15 m layer, the MWD is increased by 6.19%, 27.66%, 22.16%, 49.71% and 125.96% and the GMD is increased by 4.09%, 12.46%, 9.34%, 19.82% and 49.15% respectively under TF, TO, TMF, TMO and TFO treatments compared with CK treatment, while the E_LT is decreased by 1.35% to 29.5%, and the D is decreased by 0.76% to 4.35% respectively compared with CK treatment. TF, TO, TMF, TMO and TFO treatments all improved the aggregation capacity of aggregates to different degrees and enhanced the structural stability and erosion resistance of the reclaimed soil, with TFO treatment having the best effect on improving the structural stability of aggregates. In the 0.15–0.30 m layer, the MWD, GMD, D, and E_LT also show significant increase under TF, TO, TMF, TMO and TFO treatments compared with CK treatment (P < 0.05). It can be seen from the data of aggregate stability indicators that the structural stability of water-stable aggregates in the 0.15–0.30 m layer shows a decreasing trend compared with the 0–0.15 m layer, which may be related to the higher organic content in the 0–0.15 m layer.

Soil bulk density and soil moisture content

Soil bulk density (BD) is one of the important indicators reflecting soil quality, and the BD at the 0–0.15 m and 0.15–0.30 m layers of the reclaimed soil decreased significantly after the application of different improved materials (P < 0.05) (Fig. 4a). In the 0–0.15 m layer, the BD, under TM, TF, TO, TMF, TMO and TFO treatments, was decreased by 5.71%, 7.74%, 8.57%, 8.69%, 8.79% and 9.13% respectively compared with CK, which indicated that the application of different improved materials all have a negative effect on the BD to a certain degree. However, the loosening effect on the reclaimed soil was different due to the different characteristics of the improved materials, and the BD of reclaimed soil under different treatments showed as follows: TFO > TMO > TO > TF > TMF > TM > CK. The combination of organic–inorganic improved materials can effectively reduce the BD of reclaimed soil, and the BD under TFO treatment was the smallest, 1.19 g cm⁻³. In the 0.15–0.30 m layer, through variance analysis, the effect of different improved materials on the BD showed a similar decreasing trend to that in the 0–0.15 m layer.

The soil moisture content (SMC) of the reclaimed soil in the 0–0.15 m and 0.15–0.30 m layers increased significantly after the application of different improved materials (P < 0.05), and the variation of SMC in the two soil layers under different treatments was basically similar, showing as follows: TFO > TMO > TMF > TO > TF≈TM > CK (Fig. 4b). In the 0–0.15 m soil layer, the SMC under TM, TF, TO, TMF, TMO and TFO treatments was increased by13.5%, 13.8%, 21.4%, 21.9%, 32.4% and 38.3% respectively compared with CK. The TMO and TFO showed the most significant positive effect on the SMC of reclaimed soil, and the mass water content was 17.4% and 18.2% respectively. In conclusion, compared with CK, these improved materials increased the SOM content and porosity, promoted the formation and stability of aggregates, and increased the retention and transmission of water, which was helpful to maintain more water. Among them, the coupling treatment of organic and inorganic improved materials can hold more soil moisture, and the most significant increase was observed under TFO and TMO.

Correlation analysis between soil organic matter and water-stable aggregates parameters

To further explore the correlation between the parameters of the reclaimed soil after the application of six different improved materials, a regression analysis was conducted in this paper on the correlation between the parameters of organic matter and water-stable aggregates with different particle sizes. From Table 2, it could be seen that the organic matter content had a highly significant positive correlation with MWD, GMD and > 2 mm water-stable aggregates content and a highly significant negative correlation with E_LT, D and water-stable microaggregates content (< 0.25 mm), indicating that soil organic matter was an important factor affecting the formation of water-stable aggregates and their structural stability., and higher organic matter content would promote the formation of macro water-stable aggregates and improve the structural stability of soil. The water-stable aggregates (particle size > 2 mm, 1–2 mm, and 0.5–1 mm) content had a significant positive correlation with MWD and GMD values and a highly significant negative correlation with E_LT and D values; water-stable microaggregates (< 0.25 mm) had a highly significant negative correlation with MWD and GMD values and a significant positive correlation with D, indicating that the increase of water-stable aggregates with larger particle size helped to promote the structural stability of soil aggregates. In summary, it showed that TM, TF, TO, TMF, TMO and TFO treatments of improved materials can effectively promote the formation of macro water-stable aggregates and improve their structural stability while promoting the increase of organic matter content in the hollow village reclaimed soil. In particular, TFO treatment was more beneficial to improve the structural properties of hollow village reclaimed soil, enrich the soil fertility, and enhance the erosion resistance.

Effects of application of different improved materials on maize yield

Different improved materials showed a different effect on maize yield (Table 3). In particular, the effect of different treatments on maize yield showed as follows: TFO > TMO > TO > TMF > TF > TM > CK, and different improved materials all significantly increased maize yield compared with CK (P < 0.05). The average kernels per ear and 100-kernel weight under different treatments showed a similar increasing trend to the maize yield, highest under TFO, following by TMO and TO. Compared with CK, the 100-grain weight increased by 2.0%, 3.9%, 8.1%, 4.8%, 4.9% and 12.5% respectively under TM, TF, TO, TMF, TMO and TFO treatments, and the maize yield increased by 10.1%, 18.2%, 34.1%, 24.9%, 38.8% and 53.4%, respectively. The maize yield under TFO was the highest, up to 11,558.79 kg ha⁻¹. In summary, it showed that organic improved materials had better effect on improving the maize yield than inorganic improved materials. The organic–inorganic coupling treatment of TFO and TMO had the best effect on improving the 100-grain weight and maize yield of the reclaimed soil. The possible reason was that the combination of organic and inorganic constituents can effectively increase the soil organic matter and total nitrogen contents, promote the formation and cementation of aggregates, increase the retention and transmission of water and improve the structural stability of hollow village reclaimed soil, which were confirmed by the results of the previous effects on SOM, total nitrogen, soil moisture content, aggregate proportion and aggregates structural stability index.

Source: Ecology - nature.com