Postponed topdressing of nitrogen fertilizers to meet nitrogen requirement of maize under full plastic film mulching in Oasis Irrigation Region

Objectives In area of water and heat resource shortage, plastic film mulching has been widely used in the production of maize, however, it usually causes an advanced N requirement and leads to the insufficient supply of N at late growth stages of maize. In this study, the postponed ratio of topdressing nitrogen fertilizer was studied, to provide reference for the optimization of N-fertilizer management in maize production under the full plastic film mulching.

Methods A field experiment was carried out in Hexi Oasis Irrigation region. All the treatments received the same rate of total N of 450 kg/hm², of which 20% was basally applied, 40% top-dressed at pre-tasseling stage, and the allocation ratios of the left 40% at jointing and post-flowering stages were setup as treatments, N1 (10% and 30%), N2 (20% and 20%), N3 (traditional practice, 30% and 10%), the treatment without N application was setup as control. Accordingly, the dynamic of N accumulation and nitrogen use status of maize were investigated.

Results The postponed application of N-fertilizer had no significant influence on N accumulation at early growth stages, while significantly improved the cumulative uptake of N at the late growth stages of maize. Compared with N3, the N accumulation in maize plants and grains under N₁ treatment was increased by 10.0% and 44.6%, respectively, and the grain yield and harvest index of maize were increased by 15.8% and 12.2%; there was no significant difference between those indexes under N2 treatment and those under N3. Compared with N3, the nitrogen harvest index, NUE, NAE and NPE of maize under N1 were increased by 31.0%, 15.1%, 79.4% and 55.7%, respectively; whereas those under N2 were not significantly increased. Consequently, the grain yield and nitrogen use efficiency of maize under the treatment with N 90 kg/hm² postponed application were greatly improved.

Conclusions For the total N input of 450 kg/hm², topdressing N at jointing, pre-tasseling and post-flowering stages of N 45 kg/hm², 180 kg/hm² and 135 kg/hm² could effectively matching the supply and demand of maize to nitrogen during the whole growth cycle, which significantly increases the N accumulation and nitrogen harvest index of maize. Therefore, the allocation ratio should be considered as a favorable agronomic practice for enhancing grain yield and nitrogen use efficiency of maize in Oasis Irrigation Region.