Optimum times of nitrogen topdressing in high-yield maize under high plant density and fertigation

Objectives This study investigates the suitable nitrogen topdressing times in maize under high plant density and drip irrigation to achieve the highest yield and nitrogen efficiency.

Methods A field experiment was carried out in Shihezi City, Xinjiang. The maize variety Denghai 618 was planted in a high density of 12×10⁴ plants/hm². The rate of nitrogen fertilizer applied as base fertilizer was 36 kg/hm². The N rate of 324 kg/hm² was topdressed twice (NT2), 4 times (NT4), 6 times (NT6), 8 times (NT8) and 10 times (NT10), respectively. We studied the leaf area index (LAI), dry matter accumulation (DMA), yield, plant morphology, stem mechanical strength, and economic benefits.

Results Compared with the NT2, NT4, NT6, NT8, and NT10 increased the average LAI by 5.5%, 11.3%, 15.2%, and 15.1%, photosynthetic potential by 3.1%, 8.6%, 10.0%, and 5.7% from silking to maturity stage, and prolonged the duration of dry matter rapid accumulation by 2 days, 6 days, 8 days, and 5 days. Similarly, the maximum dry matter accumulation rates increased by 4.4%, 9.2%, 14.8%, and 7.2%, and the total shoot dry matter accumulation increased by 7.5%, 18.9%, 23.9%, and 10.8%, respectively. NT4, NT6, NT8 and NT10 increased yield by 6.2%, 8.7%, 12.3% and 7.1%, nitrogen partial productivity by 5.5%, 7.5%, 11.8% and 7.1%, and nitrogen agronomic efficiency by 40.8%, 51.5%, 82.5% and 48.1%, respectively. As a result, the economic benefits increased by 10.3%, 14.0%, 20.1% and 10.6%, respectively. An increase in the frequency of N fertilizer topdressing decreased maize dry matter transfer from the vegetative organs to dry grain weight before silking and subsequently increased. In contrast, the proportion of maize dry matter accumulation to dry grain weight after silking increased and subsequently decreased. The volume of dry matter translocation and dry matter accumulation after silking were higher in NT8 than in other treatments. The plant height, spike position, stem breaking strength, basal internode puncture strength, crushing strength and bending strength were higher in NT6 and NT8, and lower in NT2 and NT10.

Conclusion The appropriate N topdressing times delayed leaf senility at the later stage of spinning and maintained high photosynthetic potential, promoting the accumulation and translocation of dry matter after the silking stage. Thus, a high yield, N utilization efficiency, and economic benefit were achieved. Simultaneously, the appropriate N topdressing frequency also benefited the formation of stem mechanical strength and improved stem lodging resistance. Therefore, topdressing N 324 kg/hm² in 8 times showed the best result for yield, N utilization efficiency, and economic benefit under the high plant density and drip irrigation conditions.