Ecological Studies on Environmental Adaptation in Weeds
2. The Effect of Nitrogen Level on Growth and Seed Productive Structure of Large Crabgrass and Common Purslane
1980 Volume 25 Issue 2 Pages 88-92
Details
1980 Volume 25 Issue 2 Pages 88-92
In this experiment, the effects of nitrogen application on the growth and seed productive structure of large crabgrass and common purslane were investigated from the same viewpoint as the previous report. Nitrogen was applied at rates of 0, 10, 50 and 100kg per 10a for each of two species of weeds.
1. The growth increments of each weed generally were promoted with the increase of nitrogen application. In common purslane, however, most characters examined, such as stem length, number of leaves, total dry weight and pyxis per plant, showed the maximum value at the 50kg level, and decreased at the 100kg level. In large crabgrass, on the other hand, total dry weight, culm length and number of heads per plant showed the maximum value at the 50kg level, and others such as number of seeds and seed weight per head and 1, 000 kernel weigth showed the maximum value at the 10kg level beyond which those decreased with the increase of nitrogen application.
2. The degrees of phenotypic plasticity obtained in several characters at vegetative and maturity stage were generally higher in large crabgrass than in common purslane, and those on number of leaves and heads per plant in large crabgrass were considerably high as compared with the other characters. On the contrary, the degree of phenotypic plasticity on 1, 000 kernel weight of both weeds was the lowest among the characters examined. From this results, it seemed that 1, 000 kernel weight was a relatively stable character to environmental stress condition.
3. Both weeds had the lowest crude reproductive efficiency (CRE) at the 0kg level, and CRE of both weeds showed a tendency to increase with the increase of nitrogen application. The maximum CRE in common purslane was 28.5% at the 100kg level, but that in large crabgrass was 25.3% at the 50kg level beyond which CRE decreased.
4. Variations between individuals within a plot, which were examined on some characters in relation with nitrogen application level, were observed clearly to increase both at the plots with excess application of nitrogen and without nitrogen.
5. Based on the results of reproductive efficiency, phenotypic plasticity and individual variations within each nitrogen level, the problems on environmental adaptation of weeds were discussed.
