Nt at p 0.05. A: Total N2 O; B: urea-derived N2 O; C: soil-derived N2 O; D: total NH4 + -N; E: total NO3 – -N; F: urea-derived NH4 + -N; G: urea-derived NO3 – -N; H: soil-derived NH4 + -N; I: soil-derived NO3 – -N; J: AOA amoA; K: AOB amoA; L: nirS; M: nirK.4. Discussion The N2 O fluxes of all treatments L-Palmitoylcarnitine custom synthesis increased rapidly and were all larger than that of CK just after the application of urea, then decreased gradually, indicating that the application of urea could promote the production of N2 O, related to previous studies [279]. This was mainly due to the fast increase in soil mineral nitrogen immediately after urea application (Figure 2A,B) [29]. Using the improve in urea application, the appearance in the N2 O peak was delayed, its intensity elevated, and the N2 O flux lasted longer (Figure 1). The achievable cause was that as the quantity of urea increased, the content material of mineral nitrogen utilized for nitrification and denitrification inside the soil enhanced [16], but the initially higher NH4 + -N concentration had a toxic effect on soil nitrifying bacteria [30], thereby inhibiting the look time of your N2 O peak, but when the quantity of NH4 + -N subsided, this phenomenon was alleviated [31]. Regardless of how much corn stalk residue was added to soil, the higher the quantity of urea, the greater the accumulation of N2 O, plus the quicker the enhance of N2 O together with the enhance in nitrogen (Table 1), related to the exponential improve of N2 O with all the enhance in N observed by Hoben et al. [32]. Having said that, Chen et al. [33] believed that when the nitrogen application rate was greater than 900 mg N kg-1 , N2 O wouldn’t continue to raise due to the limitation of higher ammonium concentrations; perhaps the nitrogen application price in our experiment didn’t reach such a maximum threshold worth. The production of N2 O was substantially positively correlated using the content material of NH4 + -N and NO3 – -N in the soil (Table 2) [19], indicating that ammonia oxidation and denitrification occurred simultaneously in the soil through the incubation period [29]. The significant positive correlation among N2 O production and AOA amoA, nirS and nirK in this experiment also supports this point. AOA amoA would be the important gene of N2 O production inside the nitrification pathway, and nirS and nirK are the key genes of N2 O production inside the denitrification pathway [4]. Among them, ammonia oxidation could be the principle pathway of N2 O production. The production of N2 O was most strongly correlated using the content of NH4 + -N; in addition, the higher sand content within the experimental soil was conducive to the production of N2 O by nitrification [34]. In addition, the presence of corn stalks and collecting N2 O samples soon after sealing for 24 h may have increasedAgronomy 2021, 11,9 ofoxygen consumption [34,35], as a result underestimating the N2 O made by the ammonia oxidation process. This was diverse from the study of Hink et al. [36], who believed that the N2 O created by denitrification in 60 water-filled pore space may very well be ignored. N2 O production in the present study was primarily affected by urea-derived NH4 + -N and NO3 – -N (Table two; Figure two), but mainly came in the soil-derived NH4 + -N and NO3 – -N (78.64.6 ; Table 1), which was related for the results of prior research [27,37,38]. It may be that NH4 + -N and NO3 – -N derived from urea are much easier to be employed by microorganisms in comparison to native soil N, as a result advertising a rise inside the number of microorganisms, accelerating the mineralization.