Long-term no tillage straw mulching increased soil water and nitrogen storage in dryland wheat on the Loess Plateau, but may increase dissolved organic nitrogen leaching

Abstract

Context

Compared to conventional tillage (CT), conservation tillage has been widely proven to better improve the soil structure, increase soil water content, and enhance crop yield, especially in arid rain-fed agricultural regions.

Objective

The aims of this study are to investigate the effects of long-term no tillage (NT) on wheat yield, vertical distribution of soil water and nitrogen (N), and their use efficiency, and uncover the mechanisms by which NT straw covering enhances yields in dryland wheat systems.

Methods

Here a two-year experiment (2021–2023) was conducted on a 30-year-old experimental site to compared the long-term effects of two different tillage (CT with straw incorporated into the soil and NT with straw mulching) on soil water and N storage, wheat yield, and water and N use efficiency.

Results

Compared to CT, NT led to higher wheat yield and biomass, and the yield difference between the two treatments increased over time. NT increased soil water storage by 9.95 %-33.22 % at different growth stages, enhancing water retention. NT also significantly raised surface soil nitrate N levels and increased soil total N and nitrate N storage in the 0–200 cm soil depth before sowing. Tillage had no clear effect on soil ammonium N, but altered dissolved organic N (DON) dynamics. As soil depth increased, both DON content and its proportion in dissolved total N (DTN) rose for both treatments. NT reduced DON content and storage before sowing but increased DON storage from the booting to maturity stages. Additionally, NT improved water and N use efficiency by 8.3 %-13.1 % and 21.5 %-21.4 % over the two years, respectively.

Conclusion

NT with straw mulching in the Loess Plateau drylands effectively conserved water and N, boosted wheat yield, and improved resource use efficiency. However, the contribution of soil water and DON storage to yield increase was greater than that of soil inorganic N storage.

Implications

This study further revealed the main reasons for the increase in wheat yield under the dryland NT system, and also identified the issue of DON loss. Attention to DON leaching, especially in NT, is necessary, and measures like optimized N fertilization and straw management should be considered to mitigate this risk.