Background The combination of mulch with N fertilizer application is a common agronomic technique used in the production of rainfed maize (Zea mays L.) to achieve higher yields under conditions of optimum planting density and adequate N supply. However, the combined effects of mulch, planting density, and N fertilizer application rate on plant N uptake and N translocation efficiency are not known. The objective of this study was to quantify the interaction effect of mulch, planting density, and N fertilizer application rate on maize grain yield, N uptake, N translocation, and N translocation efficiency. The experiment was arranged in a randomized complete block design with three factors (2 mulch levels × 2 planting densities × 4 N fertilizer application rates) replicated four times. Results There was a significant interaction among mulch, plant density, and N fertilizer on maize grain yield, kernel number per cob, N uptake, N translocation, and N translocation efficiency. Averaged over the 3 years of the study, total plant N uptake at silking ranged from 79 to 149 kg N ha− 1 with no mulch and from 76 to 178 kg N ha− 1 with mulch. The N uptake at silking in different plant organs ranked as leaf > grain > stem > cob. Averaged across all factors, the highest N translocation was observed in leaves, which was 59.4 and 88.7% higher than observed in stems and ears, respectively. The mean vegetative organ N translocation efficiency averaged over mulch, planting density, and N fertilizer application rate treatments decreased in the order of leaf > stem > cob. Conclusions Mulch, planting density, and N fertilizer application rate not only have significant effects on improving maize grain yield and NUE, but also on N uptake, N translocation, and N translocation efficiency. Our results showed clearly that under high planting density, the combination of mulch and moderate N fertilizer application rate was the optimal strategy for increasing maize grain yield and N use efficiency.

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Millions of small farmers rely on maize (Zea mays L.) produced in the Loess Plateau of China. The purpose of this study was to find a fine maize variety in the Check Dam and to reveal the reasons for the effects of white plastic film mulch and maize varieties on crop yield and photosynthetic characteristics. Three maize cultivars (Dafeng 26 [DF], Xianyu 335 [XY], and Tianci 19 [TC]) were grown with and without plastic mulch in 2016 and 2017 in Ansai County, Shaanxi Province, China. Results showed that mulch increased grain yield by 10.5% in 2016 and 11.3% in 2017 across all cultivars. Among all cultivars, XY had the highest grain yield under both mulch and no mulch. Grain yield was significantly correlated with soil water content in the 0-20 cm layer. Soil temperature under mulch decreased with increasing soil depth. On average, mulch increased soil temperature from 0.2 to 1.9 • C over the entire growing season. Photosynthetic characteristics were directly determined for all tested maize cultivars. Grain yield was more closely related to photosynthetic rate in July (r = .828, P = .001; n = 12) than in August (r = .617, P = .032; n = 12). Moreover, grain yield was correlated with stomatal conductance and transpiration rate in July and August (r = .913-.928, P < .001; n = 12). Our findings suggest that photosynthetic characteristics were an important index affecting maize grain yield for small farmers using check dams in the Loess Plateau.

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