Results and Discussions

Results

FINDING (1):

Total organic carbon and total nitrogen:

  • TOC and TN amounts are the highest in adaptive multi-paddock practices in all four depths except for depths 15-30 cm (Figures 8 and 9).

  • Conventional and transitional practices have less effect on increasing TOC and TN in all soil depths (Figures 8 and 9).

  • Overall amount of TOC and TN decreased by increasing soil depth (Figures 8 and 9).

Figure 8: Total organic carbon (TOC) change by management and soil depth. Management includes: Irrigated or Conventional crop (CROP), rotationally grazed practice (RGR), and adaptive multi-paddock (AMP).

Figure 9: Total nitrogen (TN) change by management and soil depth. Management includes: Irrigated or Conventional crop (CROP), rotationally grazed practice (RGR), and adaptive multi-paddock (AMP).

Soil properties:

  • Bulk density (BD) is higher in adaptive multi-paddock (AMP) practice and lower in rotationally grazed (RGR) and conventional cropland (CROP), respectively. This parameter increases with the increase in soil depth (Figure 10).

  • Soil texture, silt clay ratio, is higher in RGR compared to other practices. There are also outliers in soil texture data which may affect the analysis (Figure 11).

  • Soil pH tends to be low in CROP management, and it becomes more basic as the increase in depth in AMP and RGR practices, respectively (Figure 12).

Figure 10: Soil bulk density (BD) change by management and soil depth. Management includes: Irrigated or Conventional crop (CROP), rotationally grazed practice (RGR), and adaptive multi-paddock (AMP).

Figure 11: Soil texture (Silt: Clay ratio) changes by management and soil depth. Management includes: Irrigated or Conventional crop (CROP), rotationally grazed practice (RGR), and adaptive multi-paddock (AMP).

Figure 12: Soil pH changes by management and soil depth. Management includes: Irrigated or Conventional crop (CROP), rotationally grazed practice (RGR), and adaptive multi-paddock (AMP).

FINDING (2):

Total organic carbon and total nitrogen with soil properties:

  • TOC and TC are negatively correlated with BD under AMP practice compared to the other two practices (P-value:0.03692 and 0.002962 for TOC and TN, respectively). The correlation is more intense in the soil's first layer and lowers as depth increases (P-value 0.0257 and 0.026399 for TOC and TN, respectively) (Figure 13 and table 5).

  • No evidence for the strong correlation between TOC and TN with soil texture (Silt: Clay) and pH under three management practices in all soil layers (P-value: 0.6933616 and 0.641288 for Si: Cl and pH respectively) (Figure 13 and table 5).


Figure 13: Correlation between variables in different practices and layers. Variables include total organic carbon (TOC), total nitrogen (TN), bulk density (BD), pH, Silt Clay ratio (Si: Cl), and carbon-nitrogen ratio (C: N).

FINDING (3):

Checking the correlation and regression assumptions:

  • To check the models and assumptions, the parameter values are standardized according to figures 14 to ).



Figure 14: Total organic carbon (TOC) model check

Figure 15: Total nitrogen (TN) model check

Figure 16: Carbon nitrogen ratio (C:N) model check

Figure 17: Bulk density (BD) model check

Figure 18: Silt clay ratio (Si:Cl) model check

Figure 19: Soil pH model check

Table 5: Summary of analysis of variance for total organic carbon (TOC), total nitrogen (TN), soil texture (Silt: Clay ratio), under management, and soil layers.

CONCLUSION

The objective of this study was to investigate the different effects of conventional and regenerative agriculture on soil organic carbon and nitrogen that may be intended as indexes of soil health. The results showed a significant interaction between management type and soil organic carbon and nitrogen. However, conventional agriculture negatively impacted the TOC and TN, and regenerative agriculture (e.g., adaptive multi-paddock) positively influenced the TOC and TN. This is due to the results that intensive farming has on soil's physical and chemical properties and, consequently, on the soil ecosystem.

Soil properties such as soil bulk density (BD) influenced TOC and TN under the management practices. A decrease in BD increased TOC and TN in regenerative agriculture. This could be explained in organic farming compared to intensive farming; soil aggregates are more stable (due to low disturbance in soil structure); hence bulk density decreases. Also, an increase in SOC decreases BD.

Silt Clay ratio and pH had the lowest impact on TOC and TN among soil properties. Nevertheless, we can't significantly explain this because of the missing data and outliers the dataset had. So, more investigation with specific datasets and other statistical analyses must be done to achieve better conclusions.