The effect of planting date of maize hybrids in the different maturity groups on quantitative and qualitative yield of forage in Hamadan region

Introduction
Maize (Zea mays L.) has high yield potential and suitable ensiling properties and is a valuable source of energy and nutrients for cattle (Johnson et al., 1999). Timely planting is critical for maximizing yield for both grain and biomass in maize and therefore, growers are concerned about the yield response of maize to planting date. However, optimum planting date may vary from area to area due to differences in climate and the length of the growing season where the crop is produced (Maresma et al., 2019). The cultivation of maize hybrids in Hamedan is done regardless of their growth period. So, the present study was conducted to determine the appropriate date for planting the hybrids of silage maize in the different maturity groups in Hamedan region.
Materials and Methods
A two-year experiment (2017 and 2018) was conducted at Ekbatan station of Agriculture and Natural Resources Research and Education Center in Hamedan province, Iran. The statistical design of experiment was a split plot, where planting dates (22 May, 10 June, 1 July and 21 July) were used as the main plot, and the hybrids with different maturity time (KSC201, KSC260, KSC400, KSC647, BC678, KSC703 and KSC70) as the subplots. Ten plants were randomly selected from each plot and plant height, stem diameter and fresh weight ratios of ear, stem and leaf to plant aerial parts were measured. To determine the fresh forage yield, a sample of 4 square meters was taken from each plot and weighed. Then, the samples were placed in an oven at 70 °C for 48 hours and after drying, they were weighed again to estimate the dry forage yield. The percentage of crude protein in dry forage was measured by Kajeldal method. Considering the occurrence of severe autumn cold in early of November that prevented the timely harvesting of hybrids with long growth period of KSC703 and KSC704 cultivated on the forth planting date, only the data obtained from the first to third planting dates was subjected to statistical analysis.
Analysis of variance and comparisons of the mean effect of planting date and hybrid and their interactions were performed based on the least significant difference test (LSD) at a 5% probability level.
Results and Discussion
The results of compound analysis indicated that different planting dates differed in terms of all traits, except protein yield, and the highest amounts of fresh and dry forage yields (60008 and 18595 kg.ha-1, respectively) were for the first planting date and the lowest amounts of the mentioned traits (50643 and 14672 kg.ha-1, respectively) were for the third planting date. It seems that the high forage yields on the first planting date were due to the suitable temperature conditions that allowed the plant completed its growth period and increased the accumulation of photosynthetic materials. The effect of hybrid on all the traits was significant and KSC703 and KSC704 hybrids gave the highest values of fresh (71322 and 68443 kg.ha-1, respectively) and dry matter (21527 and 20197 kg.ha-1, respectively). The superiority of late (and medium) maturing hybrids over early maturing hybrids in terms of fresh and dry yields, may be due to the longer growth period. Despite KSC201, KSC260 and KSC400 hybrids gave the lowest amounts of growth period (78.06, 89.61 and 97.22 days), fresh yield (37469, 40499 and 45732 kg.ha-1, respectively) and dry yield (11620, 12395 and 14720 kg.ha-1, respectively), these hybrids showed the highest values of crude protein (14.63, 14.09 and 14.04%, respectively) and ear to plant weight ratio (38.44, 35.97 and 34.95%, respectively). Therefore, cultivation of the early maturing hybrids is recommended if high quality forage is targeted. Also, it is not recommended to delay the planting FAO maturity groups 700 and 600 maize to early summer season, due to excessive delay in land preparation for the cultivation of autumn crops.
Conclusion
Due to the possibility of timely harvest, acceptable yield and suitable forage quality of early maturing hybrids on the last planting date, in case of delay in planting date to late July in Hamedan region and areas with similar climate, planting early maturing hybrids (especially KSC400) is recommended.