Leaf Area Expansion, Dry matter Accumulation and Grain Filling Trend as Affected by Planting Date and Seed size in Faba Bean (Vicia faba L.)

Green leaf area index and dry matter accumulation are closely associated with grain yield components (i.e., number of grains per unit area and grain size) and grain yield per unit area. This study was carried out to evaluate the effect of seed size used for planting and sowing date on leaf area expansion, dry matter accumulation and grain filling trend in faba bean, C.V. Barakat.
The experiment was conducted at the research field of Gorgan University of Agricultural Sciences, Gorgan, Iran, during 2013-2014 growing season. The experimental design was a split plot in a randomized complete block design with four replications. Planting dates (26 Nov., 19 Dec., 2013 and 11 Feb. and 10 Mar., 2014) and seed size (small, medium, large) were arranged in main- and sub-plots, respectively.
Based on the results of the analysis of variance, there was a significant interaction between seed size and planting date for maximum leaf area index (LAImax), dry matter yield (BY) and grain yield (GY). LAImax, BY and GY were variable between 0.75 and 5.3, 2.56 and 12.05 ton ha-1 and 0.43 and 5.20 ton ha-1, respectively. The lowest value for each of the above mentioned characteristics was obtained from combination of last planting date and small seed. The highest LAImax was observed in the first sowing date and large seed combination treatment, and the highest BY and GY was observed in the first planting date and medium seeds combination treatment. However, when large or medium seeds were used in this planting date, there was no significant statistical difference between the BY and BY.The time required to achieve LAImax and 50% of maximum dry matter (Wmax) and also grain filling period (SFP) significantly reduced in result of delaying in planting. LAImax was observed between 59.7 (for Mar. planting date) and 158.9 (for Nov. planting date) and Wmax was happened between 60.2 (for Mar. planting date) and 159.6 (for Nov. planting date) days after planting. Moreover, SFP declined by planting delay so that from 80 days (in 26 Nov. planting date) decreased to 33 days (in 10 March planting date). There was no reliable difference between three sizes of seeds on the three parameters mentioned above. According to the results of regression analysis, there was a linear relationship with high coefficient of determination between LAI as well as dry matter and grain yield, and between the duration of grain filling with grain weight, grain number per unit area and grain yield. So that the increase of values of the mentioned traits led to increase in grain weight, grain number and finally grain yield per unit area.
The results indicated a reduced LAImax, the maximum dry matter and days to LAImax with any delay in seeding. Furthermore, the phenological development stages passed rapidly and seed filling duration was shortened in delayed planting dates. As a result, the number of seeds per plant and per unit area decreased, the grain size became smaller, and finally grain yield was reduced. According to the regression results, an each unit increase in leaf area index, total dry matter (gr m-2) and grain filling duration (day) resulted in increasing grain yield as amount as 153.6, 0.53, 9.81 g m-2, respectively. Therefore, in consisting with findings of previous our studies, planting up to mid- autumn is necessary to achieve maximum LAI, total accumulative dry matter and grain yield of faba bean under Gorgan environmental conditions. In addition, due to positive correlation between seed size and three above mentioned parameters, the application of more large seeds for planting leads to a better result.