Fate and efficiency of fertilizer nitrogen in spring wheat production under drip irrigation based on the ¹⁵N tracing method

Objectives The contribution of fertilizer to wheat N absorption and the behavior of residual fertilizer N in the soil were studied using the ¹⁵N tracing method. We aim to provide a scientific basis for optimal N fertilizer management in Xinjiang wheat production under drip irrigation.

Methods Field experiment was conducted at the Experimental Station of College of Agriculture Shihezi University from April to July 2019, using spring wheat cultivars ‘Xinchun 38’ (XC38, high-gluten) and ‘Xinchun 49’ (XC49, medium-gluten) as test materials. The seven N-level treatments used were N 300, 285, 270, 255, 240, 225, and 0 kg/hm², namely, N300, N285, N270, N255, N240, N225, and N0 treatments. A PVC tube (11 cm in diameter, 65 cm high) was installed in each plot, and the ¹⁵N labeled fertilizer was applied at the same N rate as the treatment plot. At maturity, the plant and 0–40 cm deep soil samples were collected from the PVC tube to determine ¹⁵N abundance and the N content; the dry biomass and wheat yield of he plot were also investigated simultaneously.

Results Fertilizer applications accounted for 30.49%–36.06% of the N absorbed by the two wheat cultivars, with soil N contributing more than 60%. Higher N application rates result in a high contribution to wheat N. The ¹⁵N residual rate in soil was 24.05%–31.60%, and mainly concentrated in 0–40 cm soil layer. The ¹⁵N utilization rate increased at first and then decreased with a decline in the N application rate. In contrast, the ¹⁵N residue in the soil increased with increasing N application rates, while the ¹⁵N total recovery rate increased progressively. The amount of fertilizer N absorbed by wheat cultivar XC38 was 43.1–61.3 kg/hm², accounting for 30.81%–34.39% of total N uptake. These values were higher than 42.3–54.5 kg/hm² and 30.81%–32.50% recorded for XC49. The highest grain yield (7384.0 kg/hm²) of XC38 was obtained from N270 treatment, and XC49 had the highest yield (7236.1 kg/hm²) in N255 treatment.

Conclusions Under the drip fertigation system, 19.79% of N fertilizer was average absorbed by wheat, and 27.86% average remained in 0–60 cm soil, with a average total recovery rate of 47.64%. Increasing the N fertilizer application rate enhances the nitrogen absorption by wheat and the proportion from fertilizer, and the residual amount in the soil, which becomes the supplement of the soil N pool. The strong gluten cultivar XC38 absorbs more N fertilizer than medium gluten cultivar XC49, which does not affect fertilizer N basic behavior. The proper N application rate for high yield, N use efficiency, and soil residue is 270 kg/hm² and 255 kg/hm² for XC38 and XC49, respectively.