عنوان مقاله [English]
Distribution of leaf area and dry matter are the effective factors that influence on absorption the radiation, evaporation and transpiration of canopy and eventually dry matter accumulation and grain yield in plants. Plant canopy is the spatial arrangement of shoots in a plant population. In plant canopy, leaves are responsible for radiation absorption and gas exchange with the outside. Stem and branches arrange photosynthetic organs somehow, which gas exchange and light distribution best done. The effect of canopy structure on gas exchange and absorption of radiation in plant communities caused detailed study of the canopy structure to be more important.
Materials and methods
In order to investigate the vertical distribution of leaf area and dry matter of borage and sweet basil in competition with weeds by cover crops treatments, a field experiment was carried out in a randomized complete block design with 8 treatments and 3 replications in Agricultural Sciences and Natural Resources University of Sari in 2013. Treatments were cover crops mung bean (Vigna radiata L.) and Persian clover (Trifolium resupinatum L.) in the rows between the sweet basil (Ocimum basilicum L.) and borage (Borago officinalis L.). Moreover, in order to evaluate the effectiveness of cover crops to control weeds, pure stand of sweet basil and borage in terms of weeding and no weed controls per replicates were used. Each plot was included 5 rows of medicinal plants. Cover crop inter-seeded simultaneously in the main crop. Estimation of leaf area and dry matter of each plant in different canopy layers (0-20, 20-40, 40-60, 80.100, 100-120 and 120-140 cm) were done after 75 planting days, with 1 m × 1 m quadrate per plot. For this purpose a vertical card board frame marked in 20-cm increments was used in the field as a guide to cut standing plants (crops, cover crops and weeds) into 20-cm strata increments (Mosier & Oliver, 1995). All samples were transferred to the laboratory, leaves and stem were separated and for every sample the area of green leaves was measured with a leaf area meter LICOR- 3000 A (LI-COR, Lincoln, NE, USA). Afterwards all samples were oven-dried at 70 ºC for 48 hours and weighted. Analysis of variance (ANOVA) was performed by application SAS (Ver. 9.2). In order to compare the average, least significant differences test (LSD) were used. Excel was used for charting.
Results and discussion
Results presented that vertical distribution of sweet basil leaf area was limited in top layer of canopy (40-60 cm) in all treatments except presence of weeds. But dry matter of sweet basil canopy was distributed in all layers in weed free treatment. In borage, omitting the competition with weeds, causes to distribute leaf area and dry matter in all three layers. Results showed that mung bean and Persian clover have same distribution of leaf area and dry matter in all layers in neighboring with sweet basil. Generally, the vertical distribution of dry matter of weeds in the fields of borage and sweet basil had more uniformity in the absence of cover crops. Planting cover crops between rows of main plants causes rapid occupation of empty spaces and lack of weed seed germination and also prevent seedling growth and development of weeds.
Shading can cause leaf abscission of sweet basil and borage in lower layers when competing with weeds. While, presence of cover crop made dry matter allocation to these lower layers in sweet basil. Moreover, borage allocated its dry matter in presence of Persian clover and also in weed free. No applying cover crops caused weed height increment, so with planting suitable cover crop, weed growing can be decreased.