The Effect of Row Spacing on Plant Architecture, Yield and Seed Quality of Cotton (Gossypium hirsutum L.)

Adjusting the distance between planting rows is one of the most important aspects of management in the process of crop production. The row spacing is effective on land cover, the amount of radiation, crop competitive ability against weeds, and pests and pathogens population and these methods affect the efficiency of crop production system. In general, row distance in cotton planting is more than other crops, ranged normally between 76 to 102 cm. But today, cotton cultivation in low row spacing (25-50 cm) and very low (row spacing 18-25 cm) is preferred. The advantages include increased potential for higher yield, declined production costs through reducing soil erosion in prone areas, reducing water losses, increased photosynthesis efficiency, reducing the cost of weed control and the possibility of mechanized harvesting which saves time.
This study was conducted in the factorial experiment in the Randomized Complete Block Design with four replications at research farm (No.1) of Gorgan University of Agricultural Sciences and Natural Resources (36°49' N, 54°19'E and 12m above sea level), 2012. Experimental treatments included row spacing at three levels (20, 40, and 80 cm), and three cultivars of Sahel, Sepid and Golestan. During the plant growth period changes in plant height, leaf area index and shoot dry weight were measured. Also, in the maturity, some other parameters such as the first boll height from the ground surface, the number of monopodial branches, the number of sympodial branches, the length of the highest monopodial branches, the number and weight of boll and yield were measured. In addition, after the separation of fibers from seeds, accelerated aging tests, germination at low and high temperature (warm and cold tests) and electrical conductivity test were applied to evaluate the seed quality. For better evaluation of seed samples, after warm and cold germination tests, the normal seedling percentages from the two tests were added together (vigor index). Thus, all seeds produced were classified in terms of seed vigor into four categories: excellent, good, medium and weak.
In this study, structure and geometrical characteristics of the plant were significantly affected by row spacing. Thus, the reduction of row spacing from 80 to 20 cm, reduced plant height and, the number and length of monopodial and sympodial branches. However, the leaf area index, dry matter and boll height increased significantly. Despite significant reduction of boll number and size per plant with the reduction of row distance, lint yield remained unaffected due to an increase in the number of plants and the number of bolls per unit of area. The highest seed quality observed in Golestan cultivar at a row spacing of 20 cm while for the other two cultivars it occurred at row spacing of 40 cm. The lowest seed quality in all three cultivars obtained in row spacing of 80 cm. Based on the seed vigor index (total normal seedlings in warm and cold germination tests) none of the seed samples could be categorized in an excellent group. The Golestan cultivar with row spacing of 20 cm could be placed in a good group and the other seed samples were found to be medium to weak. However, the least seed vigor index was found in Golestan and sepid cultivars in 80 cm row spacing and in Sahel cultivar in 20 cm row spacing. For Sahel cultivar, the maximum seed vigor index obtained in 40 cm row spacing.
There are advantages in narrow and ultra-narrow row spacing in comparison of traditional row spacing for cotton planting. These include generally, the reduction of plant height, increased height of boll formation which facilitates mechanized harvesting, and the increase of LAI and dry matter per area. Other advantages are the stability of lint yield and fiber quality, and ultimately increased seed quality in cultivations with lower row spacing.