Biochar and 3,4-dimethylpyrazole phosphate enhance seasonal wheat soil fertilizer N retention and subsequent maize N recovery under a delayed N application strategy: A data synthesis and field 15N tracer investigation

Biochar and 3,4-dimethylpyrazole phosphate (DMPP) influence soil nitrogen (N) transformation and crop N recovery. However, the specific impacts of these amendments on crop 15 N recovery and fertilizer 15 N fate under delayed N application remain unclear. To elucidate the impacts of biochar and DMPP amendments on N fate within a wheat–maize–soil system, a microplot experiment was conducted employing delayed application of 15 N-urea during the wheat season, with particular focus on tracing the fate of urea N. The experiment included eight treatments: control (CT); conventional N (CN; 270 kg N ha −1 ); reduced N (RN; 180 kg N ha −1 ); RN with biochar at 7.5 t ha −1 (RNB1) and 15 t ha −1 (RNB2); RN with DMPP (RND); and combinations of DMPP with RNB1 (RNDB1) and RNB2 (RNDB2). At wheat harvest, compared with the RN treatment, the CN treatment significantly decreased the urea 15 N recovery efficiency ( 15 NRE). Application of biochar alone resulted in a significant increase in 15NRE by 17.19 % and 18.10 %, respectively, whereas treatments incorporating DMPP had no significant effect on 15 NRE. The soil 15 N retention efficiency ( 15 NRE soil ) decreased with soil depth, with the 0–20 cm layer accounting for 56.11 %–70.12 % of the total 15 NRE soil in the 0–100 cm soil profile. Combination of biochar and DMPP significantly increased 15 NRE soil by 27.84 %–39.19 %, whereas biochar or DMPP alone had no significant effect on 15 NRE soil . At maize harvest, 15.9 %–20.8 % of the urea N applied during the wheat season was retained in the soil, and 5.44 %–7.19 % of the urea N was absorbed by maize, with biochar and DMPP significantly enhancing maize 15 NRE. The findings indicate that delayed N application increases 15 NRE, and combined application of biochar and DMPP significantly increases 15 NRE soil during the wheat season and markedly enhances subsequent maize 15 NRE.