Effect of Plant Density on Allometric Relationships between Plant Height and Vegetative Traits of Wheat

Crop models are the most important parts of ecological models. These models could provide the possibility of crop systems prediction in addition to increase the understanding of their performance. Allometric relationships of plants show the changes of growth of one part in comparison to the other parts of the plant. Determining the appropriate plant density in crops, especially wheat has the high importance which affects some characteristics such as yield and yield components. This effect varies between different stages of plant growth.
This research has been done in research station of Gorgan University of Agricultural Sciences and Natural Resources (37 45N, 54 30E and 120m asl) in the growing season of 2012-13. The experiment was conducted in a factorial experiment with randomized complete block design with four replications as base. Treatments consisted of two wheat cultivars (Koohdasht and Morvarid) and 7 plant densities (50, 100, 200, 350, 500, 650, 800 seed.m2). Each replication consisted of 14 plots and each plot had 10 rows with length of 5 m, width of 2 m and a row spacing of 20 cm. Plot distances from each other was 40 cm and block distances was 1 m to each other. Measurements were done from tillering to the end of the growing every 7 to 10 days (depending on weather conditions). Cumulative thermal units were calculated using GDD_Calc program. Power model and non-liner segmented regression model were used to describe allometric relationships.
In fitting allometric equations related to plant height, results showed that plant height in wheat starts from emergence and reaches the maximum in the anthesis stage and then remains constant. Hence, fitting equations were done to find allometric relations of wheat plant height and coefficient of 0.94 and root mean square error between 6.80 and 5.16 showed that the equation could well describe the height of plant during the growing season. Checking coefficients showed that there was no significant differences between a coefficient but significant differences was investigated in b coefficient and X0 coefficient. The analysis of the relationship between plant height and the number of leaves in main stem showed a significant effect according to b coefficient with coefficient of determination of 0.92, in different densities. Coefficient of determination values greater than 0.97 indicated a strong relationship between plant height and shoot dry weight, but the analysis showed no significant effect in terms of a (plant height when shoot dry weight is 1 gr) and b coefficients. In addition, regarding the relationship between the height and total dry weight of vegetative parts in different plant density, coefficient of determination values greater than 0.97 and ranges of root mean square error between 4.86 and 9.119, belong to the plant densities of 50 and 800, respectively, which showed a very good correlation between the height and the total dry weight of vegetative parts. The a coefficient (plant height when total dry weight is 1 gr) had significant difference and decrees about 0.0036 unit according to each plant more dense but for b coefficient, there was no significant difference.
In general, the results revealed that plant height has significant correlation with the number of leaves in main stem, shoot dry weight and total dry weight of vegetative parts by coefficient of determination 0.93, 0.97 and 0.96, respectively. In addition, the correlation coefficient for producing leaves in main stem was 0.93.