Maize Straw and Nitrogen Fertilizer Alter Soil Carbon and Nitrogen Mineralization during the Fallow Period in the Oasis Farmland area

Combining straw with nitrogen fertilizer is an important strategy that influences soil fertility and crop yield. N availability may further affect carbon mineralization (C-min) and nitrogen mineralization (N-min) in the soil by influencing the microbial decomposition of straw. The effects of straw return on carbon mineralization (C-min) and nitrogen mineralization (N-min), as well as the apparent soil organic carbon balance (C-ab) in agricultural fields at different nitrogen (N) levels, have not been widely studied in semi-arid oasis areas. Therefore, we conducted an incubation experiment in the Minqin oasis area to assess the soil C-min, N-min, and C-ab characteristics during the fallow period. A 141-day in-situ incubation experiment was established with the following six treatments: (i) soils were treated with low nitrogen (S0N1) or high nitrogen (S0N2) respectively; (ii) soils were treated without nitrogen (S1N0), low nitrogen (S1N1) and high nitrogen (S1N2) incorporated into maize straw respectively; (iii) soil only (S0N0, refer as CK). Nitrogen (N) sources came from urea (CO(NH2)(2)). The results showed that (1) Maize straw incorporation significantly increased soil cumulative C-min (6.83 g kg(-1)) as compared to the non-straw application (1.01 g kg(-1)) during 141 days of incubation. (2) Compared to S0N0, straw incorporated into N fertilizer (S1N0, S1N1, S1N2) significantly increased the potential mineralized carbon (C-0) content and mineralization rate (dC(min)/dt) (P < 0.05), but the effect on potential N mineralization (N-0) appeared to be reversed, with N-min being more affected by N addition. (3) C-ab found a maximum in the S1N1 treatment (3.57 g kg(-1)), which was five times higher than the treatment without added straw, 40% higher than in S1N0, and 46% higher than in S1N2, not proportional to the added N treatment. (4) Soil temperature and soil moisture contributed more to soil C-min and N-min during the fallow period, reaching 26.9% for C-min and 40.29% for N-min. It can be concluded that straw return incorporated into nitrogen will greatly affect soil carbon and nitrogen mineralization in the Minqin oasis area, which in turn affects soil nitrogen use efficiency and organic carbon balance.