Nitrogen uptake from soil residual fertilizer by subsequent crops: regulatory effects of previous nitrogen...

Soil residual fertilizer nitrogen (SRFN) represents an important nitrogen resource that can be reused by subsequent crops.

In this study, two independent ¹⁵N tracing experiments were conducted under two crop rotation systems ("pakchoi-pakchoi" and "pakchoi-tomato") to investigate the effects of previous nitrogen application rates (80, 120, 160 kg N/ha) and subsequent irrigation regimes (for pakchoi: 60%, 70%, 80% of field capacity; for tomato: 50%-60%-60%, 60%-70%-70%, 70%-80%-80%) on the uptake and utilization of SRFN by subsequent crops.

The results showed that 2.48%-8.95% of the applied fertilizer nitrogen was absorbed by the subsequent crops. Under different previous nitrogen application rates, the maximum ¹⁵N uptake by subsequent pakchoi and tomato reached 3.97 kg/ha and 10.46 kg/ha, respectively. Among the irrigation regimes, the lower limits of 70% (for pakchoi) and 60%-70%-70% (for tomato) most significantly promoted root dry matter accumulation (p < 0.05), increased SRFN uptake by 0.45-1.01 kg/ha and 1.94-2.56 kg/ha, respectively, and achieved the highest fertilizer nitrogen reuse rates (4.05% and 8.95%, respectively). Correlation analysis further revealed that the efficiency of SRFN uptake and utilization by crops was closely related to the distribution, form, and quantity of SRFN in the soil, as well as the root biomass of the subsequent crops.

In conclusion, the previous nitrogen application rate and subsequent irrigation regime regulate the uptake and utilization of SRFN by subsequent crops through influencing the soil status of SRFN and root growth. The "pakchoi-tomato" rotation combined with the 60%-70%-70% irrigation lower limit was the most effective in promoting crop uptake and utilization of SRFN.