عنوان مقاله [English]
Background and Goal: Planting density is one of the methods to increase yield per unit area. Recently, high density cotton planting under Ultra Narrow Row (UNR) was expanded in cotton producing countries. The results showed that increasing plant density by sowing in narrow rows increased cotton seed yield. Growing cotton in narrow rows or UNR (row spacing is 20-30 cm) reduces evaporation between two rows, which reduces water consumption and weed growth and increases radiation efficiency. In these systems (UNR), zero varieties are more effective and their efficiency is higher than that of common varieties, which is due to the lower growth of monopodial and sympodial branches. Therefore, it is necessary to study the response to growth, yield and morphological variations in these varieties on Ultra Narrow Row. Therefore, this project was carried out to determine the optimum planting density by planting at different row spacings in null varieties and conventional cotton varieties.
Material and Methods: After soil preparation, two cotton varieties (zero varieties), namely Kashmar and Khorshid, were planted with Khordad and Varamin cotton varieties (as control) at their row spacing (20, 40, 60 centimeters) and 20 centimeters in row. This experiment was conducted in 2014 and 2015 at the Kashmar Agriculture and Natural Resources Research Station in a factorial trial based on a randomized block design with three replications. Irrigation was done using a tape (negative pressure irrigation system) with 20 centimeter spacing and 4 liters per hour of runoff. Three plants were randomly selected in the first year. The samples were divided into three long sections, and in each section the number of nodes, boll, dry weight of seed tree wool, vegetative organs and the whole plant were weighed. The parameters measured were: Dry weight of seed cotton, vegetative components and whole plant in different plant layers, no boll per plant, seed cotton per plant and yield.
Results: The results showed that there were significant differences in morphological characteristics among cotton cultivars. Most dry weight of vegetative and economic components was observed in the middle and lower layers of the plant. The proportion of middle and lower plant layers in cotton seed production increased and decreased, respectively, and the result showed that the proportion of cotton seed in total dry weight was 57, 53, 55.8, and 54.4 percent in Varamin, Khordad, Kashma, and Khorshid, respectively. With increasing plant density, yield increased by 83.2 and 79.7 percent in the first and second year, respectively, compared to wider rows. The highest and lowest yields were obtained in Khorshid and Khordad varieties with 20 cm row spacing. In both years, planting in narrow rows (20-centimeter treatment) resulted in significant increase in cottonseed yield. The highest yield increase when planted at the highest density with 167%, 136%, 86% and 59% was obtained in Varamin, Khorshid, Kashmar and Khordad varieties, respectively.
Conclusion: In intensive agricultural systems, we must use low-cost cotton varieties that are especially suitable for mechanical harvesting. These varieties must have the least lateral growth of vegetative and reproductive branches. Kashmar and Khorshid were designated as zero type cotton varieties suitable for machine harvesting in this study. The results showed that these varieties responded better to high planting density than the common varieties (Varamin and Khordad). When grown in ultra- narrow rows, the results showed that the yields of the zero varieties were higher than those of the common varieties. Moreover, most dry weight of vegetative and economic components was observed in the middle and lower layers of the plant.