Introduction: Cotton (Gossypium hirsutum L.) is one of the oldest agricultural crops, cultivated in over 100 countries with a total production of approximately 25 Mt. This plant's oil, protein, and seed cotton are used in human and animal nutrition, and as the best coating raw material for spinning mills, respectively. Cotton, following sugarcane (Saccharum officinarum) and sugar beet (Beta vulgaris), is Iran's third largest industrial crop and first oil crop. Appropriate agronomic practices, such as plant density and fertilizer management, have a substantial impact on crop development and final yield. Adjusting the distance between cotton rows has been a technique used to increase yield. Typically, cotton is planted in rows separated by 70 to 100 cm. Ultra narrow row (UNR) cotton production has been proposed as a cost-effective method for increasing yields and decreasing production expenses. The fertilizer needs of UNR cotton are not well-established, and the lint yield of UNR cotton relative to that of conventional-row (CR) cotton has been variable. This research aimed to determine the optimal nutrition systems for UNR and CR cotton production.
Materials and Methods: This research was conducted on a private farm in Rudab (Khorasan Razavi province), 60 km from Sabzevar at a latitude of 36° 13',  longitude of 57° 44', and an elevation of 990 m above sea level, during 2019 and 2020. The experimental design consisted of a split plot arrangement of treatments with three replicates in a completely randomized complete block design. The type of fertilizer, which included chemical, organic, chemical+organic, and control (without fertilizer), was regarded as the main plot, while the planting method, which included conventional and ultra-row spacing cultivation, was regarded as the sub plot. Each plot consisted of four 50 cm (UNR) or 25 cm (CR) rows with a length of 4 m and a 20 cm plant spacing. Utilizing a pneumatic seeder and Varamin cultivar, sowing was performed. Before planting, a physicochemical analysis of the experimental soil was conducted. In accordance with the recommendation of the soil test, a uniform dose of phosphorus (150 kg ha^-1) in the form of Triple Super Phosphate was applied at the time of sowing as part of the chemical treatment. The recommended amount of N (250 kg ha^-1) was applied as urea. One-third of the N was applied at the time of sowing, and the remaining two-thirds were applied in two equal splits at the first and second weedings (50 and 80 days after sowing, respectively). In organic treatment, the rate of poultry manure application was 3000 kg ha^-1. In the chemical+organic treatment, each organic and chemical fertilizer was applied at a rate of 50%. At the time of harvest, five plants were randomly selected from the middle rows of each plot and their final height, number of branches, and number of bolls per plant were measured. In order to determine the weight of bolls, 10 bolls were selected at random from the harvested plants and their average weight was determined. The seed cotton yield was harvested at one stage after approximately 90 percent of the bolls had opened. The lint and seeds were separated and weighed separately from the seed cotton. The lint percentage was calculated by dividing the lint weight by the seed cotton weight. The collected data on various parameters were statistically analyzed using SAS (Version 9.4), and the least significant difference (LSD) test at a 5% probability level was used to compare the treatment means.
Results and Discussion: Chemical and organic treatment increased the number of lateral branches (48.7 percent), number of bolls per plant (88.9 percent), and boll weight (131 percent) compared to the control, while organic fertilizer treatment increased lint percentage (42.3 percent). In all nutrition systems, conventional cultivation produced more bolls per plant than ultra-row spacing, and integrated treatment and conventional cultivation produced the greatest number of bolls per plant. In ultra-row spacing and integrated nutrition systems, seed cotton yield was increased by 18.5% over conventional and organic fertilizer and cultivation, and lint yield was increased by 9.28% over conventional cultivation.
Conclusion: Overall, the results of this experiment demonstrated that it is possible to produce a satisfactory seed cotton yield by substituting 50 percent of the chemical fertilizers in an integrated system with 50 percent less organic fertilizer and by utilizing ultra-row spacing.