Nitrogen (N) fertilizer deep placement has been widely adopted to improve nutrient use efficiency and maize yield in the semiarid regions of northwest China. However, previous studies on optimal fertilization depth have yielded inconsistent results across climate conditions, limiting its practical application. This study aims to determine the site-specific optimal N fertilization depth for spring maize by evaluating photosynthetic growth dynamics, yield formation, and N utilization in two contrasting semiarid regions. A two-year (2021–2022) field experiment was conducted in Dingxi (semiarid drought-prone region) and Jingning (typical semiarid region), with five fertilization depths: 0 cm (D0), 5 cm (D5), 15 cm (D15), 25 cm (D25), and 35 cm (D35). A 15N-labeled urea micro-plot experiment was additionally conducted to trace N fate. The results demonstrated that, compared with the conventional N placement treatment (D15), D25 increased soil total N storage, net photosynthetic rate, root bleeding rate, and the concentrations of NO3−-N and NH4+-N in the bleeding sap. PLS-PM analysis revealed that fertilization depths that are excessively deep (D35) or shallow (D0, D5, D15) adversely affect the photosynthetic parameters and root activity of maize, thereby inhibiting dry matter accumulation and grain N uptake, which ultimately reduces both yield and nitrogen use efficiency (NUE). Compared with D15, D25 increased grain yield, and NUE by 8.79% and 33.19% at Dingxi, and by 7.11% and 11.25% at Jingning. 15N isotope tracing revealed that D25 improved maize N uptake while reducing residual soil N and N losses. Regression analysis indicates regional differences in the optimal N application depth. To achieve the lowest N residual loss and the highest yield and NUE, Dingxi (23.49 cm) requires a deeper fertilization depth compared to Jingning (21.64 cm). In conclusion, N fertilizer deep placement is a viable strategy for enhancing agricultural productivity and efficiency in semiarid regions, but the appropriate depth should be selected based on local conditions.
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The aim of this study was to investigate the effects of long-term plastic film mulching farmland combined with different biochar input rates on soil aggregate stability and organic carbon in northwest China, in order to provide a scientific basis for improving the soil fertility and maintaining the sustainability of crop production for film-mulching field in semiarid regions.
Based on continuous years of double ridge furrow film mulching (D), the full film double ridge furrow mulching planting and traditional flat without film mulching planting were set as the main treatment, and four biochar input rates (no returning (N), 3 t·hm-2 (L), 6 t·hm-2 (M), and 9 t·hm-2 (H) ) were set as the secondary treatment respectively to investigate the effects of different biochar input rates on soil aggregate distribution, aggregate stability, aggregate organic carbon and maize yield.
The film mulching could significantly (P<0.05) increase the soil mechanical stable (6.1%-8.7%) and water-stable macro-aggregate contents (15.9%-83.6%) and maize yield (35.0%-41.8%). Under the film mulching planting, biochar inputs treatments could significantly (P<0.05) increase mechanical macro-aggregate and water macro-aggregate by 6.8% and 29.6% on average, respectively, and the effects gradually increased with the increase of biochar inputs rate. In addition, biochar inputs could also increase the soil organic carbon and aggregate organic carbon content in film mulching farmland, and the effects under DH (9 t·hm-2) were better than other treatments, with an average increased by 13.9% and 25.9%, respectively. Maize yield was significantly correlated with biochar addition rates ( λ=0.42, P<0.001 ), and DH had the highest yield with 12.8 t·hm-2.
Biochar input could significantly improve soil aggregrate characteristics and organic carbon content in plastic film mulching farmland, thus increase the maize yield and promote soil carbon sequestration, especially with 9 t·hm-2.
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