Water use and soil nitrate nitrogen changes under supplemental irrigation with nitrogen application rate in wheat field

- Nitrogen applied under supplemental irrigation adjusted the irrigation amount.
- Nitrogen applied as 210 kg N ha−1 (N2) enhances soil water consumption.
- N2 treatment improved wheat's absorption for NO3N in 60-120 cm soil layers.
- N2 treatment increased grain yield and water use efficiency in winter wheat.

Excessive or improper nitrogen (N) application rates and water shortages negatively affect crop production and thereby food security, particularly for winter wheat production in the Huang-Huai-Hai Plain of China. Therefore, it is highly important to study effects of N application rates under supplemental irrigation on water use and changes in soil nitrate-N (NO3N) content in winter wheat in this region. In a field experiment, we tested four N application rates: 0 (N0), 180 (N1), 210 (N2) and 240 (N3) kg N ha−1. Under different N treatments, supplemental irrigation raised soil water content in the 0-140 cm profile to 70% field capacity (FC) at both jointing and anthesis in the period from 2012 to 2013 and 70% FC at jointing and 65% FC at anthesis in the period from 2013 to 2014. The total amount of supplemental irrigation for N2 was lower than that for N3. The highest crop evapotranspiration, water consumption after anthesis and soil water consumption were observed in N2. Soil water consumption in N2 in 60-140 cm soil layers was significantly greater than in other treatments. The net photosynthesis rate, transpiration rate and stomatal conductance of flag leaves from N2 were greater than those from other treatments from 7 to 21 days after anthesis. But NO3N content of N2 was significantly lower than that of N3 in 0-120 cm soil layers at anthesis and in 60-160 cm soil layers at maturity. The highest grain yields of 8923.2 and 9064.9 kg ha−1 were attained in N2 with a high water use efficiency of 20.9 and 18.8 kg ha−1 mm−1 in periods from 2012 to 2013 and 2013 to 2014, respectively. These results indicate that the optimal N application rate was 210 kg N ha−1 under supplemental irrigation.