Grain and forage yield response of two maize (Zea mays L.) cultivars to planting date and nitrogen management under different environmental conditions

Introduction: Maize (Zea mays L.) is one of the most important field crops worldwide and plays a critical role in food security due to its high genetic diversity, broad adaptability, substantial dry matter production, and favorable nutritional value. Because maize yield and productivity are strongly influenced by environmental conditions, genetic characteristics, and agronomic management, the adoption of region-specific management strategies is essential for achieving sustainable production. Accordingly, the present study aimed to optimize the production of two maize cultivars under contrasting environmental conditions in Guilan Province through the management of planting date and nitrogen fertilizer application.

Materials and Methods: The experiment was conducted as a factorial split-plot design within a randomized complete block design (RCBD) with four replications at two locations, Rasht and Bandar Anzali, Guilan Province. Nitrogen fertilizer levels (0, 180, and 360 kg ha⁻¹, applied as urea) were assigned to main plots, while the factorial combination of two maize cultivars (KSC704 and Kousha) and three planting dates (May 26, June 16, and July 6) was allocated to subplots. Grain yield, biomass yield, and yield components were measured. Data were subjected to analysis of variance (ANOVA) and stepwise regression analysis using SAS software.

Results and Discussion: Combined analysis of variance revealed that the four-way interaction of planting date × nitrogen fertilizer × cultivar × location had significant effects on leaf area, ear dry weight, and biomass yield. In addition, the interaction of planting date × nitrogen fertilizer × cultivar significantly influenced the number of kernels per row and grain yield. The number of kernels per ear was significantly affected by the interactions of planting date × nitrogen fertilizer × cultivar and location × nitrogen fertilizer × cultivar. For 100-kernel weight, significant interactions were observed for location × planting date × cultivar and nitrogen fertilizer × planting date × cultivar, whereas the main effect of cultivar was significant for the number of rows per ear. Mean comparisons indicated that cultivar KSC704 consistently outperformed Kousha in terms of both grain and biomass production across all experimental conditions. The highest grain yield of KSC704 (10,579.55 kg ha⁻¹) was obtained at the May 26 planting date with the application of 360 kg ha⁻¹ nitrogen fertilizer, which was approximately 31% higher than the maximum grain yield achieved by cultivar Kousha. The highest biomass yield of KSC704 was jointly recorded at the May 26 and June 16 planting dates under 360 kg ha⁻¹ nitrogen application in Bandar Anzali. Stepwise regression analysis showed that the number of kernels per ear, 100-kernel weight, and biomass yield together explained 97% of the variation in grain yield.

Conclusion: Given the significant superiority of cultivar KSC704 over Kousha, planting this cultivar on May 26 combined with the application of 360 kg ha⁻¹ nitrogen fertilizer is recommended to achieve maximum grain yield. However, when forage production is the primary objective, planting cultivar KSC704 in Bandar Anzali between May 26 and June 16 with 360 kg ha⁻¹ nitrogen fertilizer represents the optimal management strategy.