Abstract: To explore the response of yield and nitrogen use efficiency of winter wheat to different former crops and nitrogen application levels, a split plot experiment with wheat ‘YN211’ was conducted. Factors in the main plots were three former crops, including sole maize (SM), maize intercropped with soybean (MS), and sole soybean (SS). In the subplots, there were four nitrogen levels, N0 (0 kg·hm^-2), N180 (180 kg·hm^-2), N240 (240 kg·hm^-2), and N300 (300 kg·hm^-2). The results showed that compared with SM, winter wheat yield significantly increased by 4.74%-10.01% and 5.12%-17.05% in MS and SS respectively under different nitrogen levels. Former crops had significant effects on spike number and kernel number per spike, but had no effect on 1000kernel weight. Compared with SM, winter wheat spike number increased by 10%-15% and 4%-19%, and kernel number per spike increased by 2%-21% and 4%-20% in SS and MS, respectively. Nitrogen application had a remarkable effect on spike number and 1000kernel weight, but had no effect on kernel number per spike. Former crops and nitrogen application interacted to affect grain number per spike and 1000kernel weight. Under same nitrogen application levels, the agronomic efficiency and partial factor productivity (PFP) of nitrogen fertilizer was the highest in SS, followed by MS and SM, which were significant at the nitrogen levels of N180 and N240. Based on the equation of N application level against yield, the yield of winter wheat was stable in SS and MS when the N application level was reduced, which has practical implications for guiding fertilization in wheat production under different former crops. The nitrogen application levels of optimum economic yield and maximum yield in winter wheat were 243 and 262 kg·hm^-2 under SM, respectively. In SS and MS, the nitrogen application levels of optimum economic yield were 196 and 210 kg·hm^-2, and those of maximum yield were 205 and 222 kg·hm^-2, respectively.

Key words: ecological experiment, research network, prior probability, filed experiment, citizen science