Introduction
Hamedan is considered a suitable area for harvesting alfalfa seeds, because, in arid conditions, the seeds typically ripen uniformly, resulting in the harvesting of high-quality seeds at the optimal time. Using the best planting density with the desired row spacing is of great importance, because if attention is paid to both forage production and seed production when planting seeds, the appropriate planting density will be effective in attracting pollinating insects. Harvesting of alfalfa seeds is done in the fields of Hamedan province from the second harvest onwards, but special cultivation is not allocated specifically for seed production. In some years and harvests, the same crops cultivated for fodder production are dedicated to seed production. Since in fodder harvesting, the field must have reached 10% flowering and in seed harvesting, at least two-thirds to three-fourths of the pods of a plant should be dark brown, arrangements for harvesting fodder and seeds are made in the second and third harvest of this experiment, respectively. Accordingly, the purpose of this research is to evaluate the effect of planting density and the harvest time of fodder in the second harvest, aiming to achieve a balanced density and an appropriate harvest time to maximize seed yield.
Materials and Methods
The experiment was carried out using strip plots with four replications in a randomized complete block design during two cropping years 2018-2019 and 2019-2020 at Bu-Ali Sina University. The study area in Hamedan city was relatively mountainous, with a cold climate, an average annual rainfall of 300 mm, and a semi-arid climate. It was located at 48 degrees and 28 minutes east longitude, 34 degrees and 54 minutes north latitude, and an altitude of 1810 meters above sea level. In this research, the effect of planting density treatment at three different levels (40, 50, and 60 cm row spacing) in vertical plots and the fodder harvest time treatment in the second harvest in horizontal plots at four phenological stages: (1. the appearance of flower buds, 2. the appearance of flowers 30 days after the first harvest, 3. 10% flowering 45 days after the second harvest, and 4. 50% flowering 60 days after the second harvest) on the traits such as the number of pods per plant, plant height, seed yield, thousand seed weight, seed weight per plant, germination rate of production seeds and germination percentage of production seeds were studied. The experimental statistical data were normalized using the square root method and analyzed using SAS software (v.9.12). Comparison of means was performed using the LSD method at a probability level of 5%.
Results and Discussion
The results showed that the germination rate of produced seeds, the weight of 1000 seeds, the weight of seeds per plant, and the yield of seeds were affected by the investigated treatments. The highest germination rate of the produced seeds was observed with a row spacing of 50 cm and harvesting fodder at the stage of flower bud emergence. The highest weight of 1000 seeds were obtained with a row spacing of 60 cm and harvesting at the stage of flower bud emergence, so that it increased by 66% and 42.8%, respectively, compared to harvesting at the stages of 10% and 50% flowering in the same distance of the row. Increasing the row spacing to 50 and 60 cm and harvesting fodder at the stages of flower bud emergence and flower emergence led to a significant increase in seed weight per plant. The highest seed weight per plant was observed with a row spacing of 60 cm and harvesting fodder at the stage of flower emergence. The highest seed yield was obtained with a planting density of 50 cm row spacing and fodder harvesting at the stage of flower bud emergence.
Conclusion
Cultivation density and fodder harvesting time had a significant effect on seed yield through their impact on yield components in this experiment. It seems that the increase in seed yield is related to the lengthening period from forage harvest to seed ripening and enough time for maximum use of natural resources, physiological ripening of seeds, more transfer of nutrients to seeds, and the opportunity to store dietary materials in seeds. Thus, based on the obtained results, it is recommended to cultivate with lower density and fodder harvesting at the beginning of the flowering period in the second harvest to achieve the maximum yield of alfalfa seed yield in subsequent harvests.