## 4 Discussion
### Soc, TN, TP, N-NO\({}_{3}\)\({}^{-}\), and N-NH\({}_{4}\)\({}^{+}\)  
Dry-land farming and an applied pattern of tillage in association with N fertilizer was fruitfully documented to hasten essential soil nutrient release, consequently enhancing the soil nutrient status and availability to crops; this mainly happened via the synergistic regulation of the soil hydrothermal situation. However, excessive N fertilization, intensive cropping, and continuous soil inversion led to serious soil fertility deterioration, which threatens sustainability of both crop and soil [44; 45; 46; 47; 48]. SOC is the main source of many of the nutrients needed by plants and is also the most critical attribute of soil that forms the core of soil quality [8; 49]. Our results showed that the total SOC content of the NT, NTN, NTM, and NTNM was higher than CT, CTN, CTM, and CTNM treatments, and SOC decreased with increasing soil depth. This is because no-till cultivation does not involve turning the soil, which reduces soil interference and reduces CO\({}_{2}\) emissions, thereby effectively reducing the mineralization of SOM and promoting the increase in surface SOC [48]. Additionally, because no-till causes less damage to the soil structure, it further increases the protection of SOC levels. At the same time, the combined application of N fertilizers alleviated the decline in soil pH, improved the soil physical and chemical properties, maintained higher soil porosity, and was conducive to the accumulation of SOM [50]. With increasing soil depth, the decrease in SOC may be due to the decomposition of aboveground litter. During the decomposition of litter, large numbers of nutrients enter in the soil and accumulate at the soil surface, resulting in an increase in SOM in the surface soil layer. However, plant roots absorb nutrients from the middle and lower layers of the soil, resulting in a decrease in the nutrient content of these soil layers [51]. Tillage practices and N fertilization are important techniques that affect soil N content [52]. Our results showed that the TN contents of the NT, NTN, NTM, and NTNM treatments were higher than CT, CTN, CTM, and CTNM treatments. The TN content in the soil profile decreased with increasing soil depth but tended to be stable in the 60-100 cm profile, which is similar to the results of two previously published studies [53; 54]. This isbecause no-till farming preserves the soil structure, protects the soil, reduces soil erosion, and improves soil fertility [55]. Additionally, the application of N fertilizers improves the distribution of soil nutrients, improves soil fertility, and increases the content of soil-available nutrients, thus increasing the soil TN content. The decrease in soil TN content with increasing soil depth may be affected by the decomposition of surface litter and fertilization. The decomposition of litter and fertilization will result in the accumulation of nutrients at the soil surface. At a soil depth of 60-100 cm, the TN content tends to be stable, which may be due to the short root system of wheat, which is unable to absorb and utilize nutrients in deep soil layers, making nutrients in the deeper soil layers more stable [20]. Our results depicted that the TP content of soil did not significantly change under different treatments. This is due the source of phosphorus in the soil is relatively fixed, and it is a sedimentary mineral, and the soil phosphorus mobility is often low, so the distribution of TP in the whole soil layer is relatively uniform, and it is difficult to be affected by external source within short-term implementation. This is maybe as a consequence of the short-term tillage and N fertilizer application, and possibly tillage, particularly in the NT, and N fertilization approaches, needs more time for total soil phosphorous improvement. This is consistent with findings reported by [21, 56].