Nitrogen use efficiency and fate of new urea types in a winter wheat-summer maize rotation system

Objectives In this paper, the effects of new urea types on two successive crops were assessed in a winter wheat-summer maize rotation system in North China plain.

Methods A field microplot experiment was conducted at Mazhuang Experimental Station of Hebei Agricultural University, Xinji City, Hebei Province in October 2016 through September 2017. The area of each plot was 1 m² and the total N input in each plot, except control, was N 225 kg/hm². Five types of urea were used as treatments, namely: common urea, urea + nitrification inhibitor Nr (UNr), controlled loss urea (CLU), shaped-energy network urea (ENU), and humic acid urea (HAU). The nitrogen (¹⁵N)-use efficiency, residual amount of nitrogen in 0–200 cm soil depth, and the nitrogen loss rate were examined and analyzed after wheat and maize harvest.

Results The highest grain yield of winter wheat was achieved in CLU treatment (8123 kg/hm²), followed by HAU (8083 kg/hm²) and ENU (8049 kg/hm²). The total ¹⁵N utilization rates of wheat in CLU, HAU, ENU, UNr, and common urea were 43.6%, 41.1%, 37.8%, 34.2%, and 32.2%, respectively. All the new urea types, especially CLU and HAU treatments enhanced the total ¹⁵N-use efficiency of the wheat crop compared with common urea. CLU, HAU, and ENU enhanced the ¹⁵N efficiency of wheat compared with common urea by 35.4%, 27.6%, and 17.4%, respectively. The residual effect of urea on ¹⁵N utilization rate of the following maize was similar among the five urea types (2.98%–3.62%). After wheat harvest, all the four types of urea significantly increased the residual nitrate N in 0–40 cm soil depth with less potential for loss through leaching, while the total fertilizer N loss was in the order: CLU, ENU < HAU, UNr < common urea.

Conclusions The new urea types significantly promotes the absorption and utilization of nitrogen by crops, realize high yields, and reduces losses of N. Compared with other three new types of urea and common urea, CLU promotes the highest biomass production and N efficiency with less residual nitrogen in the soil and low loss rate. On the other hand, ENU promotes higher nitrogen retention in the soil with low loss rate.