Effects of nitrogen application and plastic film mulching on nitrogen uptake and allocation in dry-land spring maize

Objectives This experiment is to investigate the effect of nitrogen (N) application and plastic film mulching on dry matter accumulation, yield and N uptake and utilization of spring maize.

Methods A field experiment was conducted from 2016 to 2017 in the Changwu County, Xianyang City, Shaanxi Province, which belonged to typical gully region of the Loess Plateau with the dark loessial soil. A split design was applied for the experiment, the main factors included plastic film mulching (FM) and no mulching (NM), and the sub-factors included four different N application rates of 0, 100, 250 and 400 kg/hm². Plant samples for measuring total biomass were collected at different growth stages, 6 expanded leaves (V6), 10 expanded leaves (V10), silking stage, milking ripening and entire ripening stage. The samples were divided into different parts as required, and the total N contents were determined.

Results 1) Both N application and plastic film mulching significantly increased grain yield of spring maize. N application improved the yield of spring maize more effectively under plastic film mulching. High grain yields of spring maize from 12.8 to 16.4 t/hm² were obtained at N rates of 250 kg/hm² and 400 kg/hm², but there was no significant difference between two treatments. Under no mulching, the grain yield at N rate of 400 kg/hm² was significantly lower than that of N rate of 250 kg/hm². 2) N application, plastic film mulching significantly increased pre-silking and post-silking N and dry matter accumulation of spring maize, the effect of their interactions on the N and dry matter accumulation in post-silking was more effective than that of pre-silking. Under plastic film mulching, the proportion of N and dry matter accumulation in post-silking was 51.5% to 54.9% and 51.1% to 59.9%, respectively. High nitrogen and dry matter accumulation of pre-silking and post-silking were obtained with N rates of 250 kg/hm² and 400 kg/hm² under plastic film mulching, but N and dry matter accumulation at N rate of 400 kg/hm² did not significantly increase compared with N rate of 250 kg/hm². 3) As the interaction between N application and plastic film mulching significantly increased pre-silking N accumulation and promoted post-silking growth, the interaction significantly promoted the translocation amount of N in vegetative organs of spring maize. Under plastic film mulching, N rates of 250 kg/hm² and 400 kg/hm² effectively promoted translocation of more N stored in the vegetative organs into grains. Under the same mulching condition, there was no significant difference between the N rates of 400 kg/hm² and 250 kg/hm² in N translocation from the vegetative organs. 4) Plastic film mulching significantly increased nitrogen agronomic efficiency and N partial factor productivity under the same N application rate. N application, plastic film mulching and their interactions significantly increased N harvest index, which was 65.1% to 75.4% at N application rates of 250 kg/hm² and 400 kg/hm², there was no significant difference between two treatments.

Conclusions  The interaction between N application and plastic film mulching significantly promoted the N and dry matter accumulation of pre- and post-silking periods of spring maize, while this effect was more effective in the post-silking than in pre-silking, thus promoting N translocation from the vegetative organs into grain. The two factors synergistically increased the yield and the N harvest index of spring maize.