A single field study was established in 2001 at the Safford Agricultural Center to evaluate a twin-line cotton production system. This location was part of a larger, statewide program conducted in 2001. This location consisted of two separate planting dates (PD) in which two separate planting systems were used. Results from this location indicated trends in yield increases with the twin-line production system when compared to the single or conventional production system. Lint yield increases of approximately 200 lbs. lint/acre were observed on the second PD. Lower yields were observed in the twin-line planting with the first PD which was in part due to poor seed placement with the equipment used to plant the twin-line on the first PD. Results indicate the potential for increased yield with the twin-line production system with the caveat that the proper equipment be used to plant the twin-line system to ensure precise and consistent seed placement and spacing.

Three experiments were conducted in Maricopa, Marana, and Glendale, Arizona in 2001 to measure cotton growth, yield, micronaire, and production costs in single and double seed line per bed systems on 32 and 40 inch beds. Canopy development was faster and canopy closure was greater in the double seed line than in the single seed line systems and was greater in the 32 inch than in the 40 inch row systems. At Maricopa, the single line 32 inch system yield of 1571 lbs./A was significantly greater than the yields of the other seed line/row spacing systems. The yields of the single line 40 and the double line 32 inch systems were not significantly different at 1476 and 1411 lbs. of lint/A, respectively, and the yields of the double line 32 and the double line 40 inch systems also were not significantly different at 1411 and 1396 lbs. of lint/A, respectively. There were no significant lint yield differences at the Marana or Glendale location. At Marana, the lint yields were 1063 and 1066 lbs./A for the single and double seed line 40 inch row spacing systems, respectively. At Glendale, the single and double seed line 38 inch row spacing systems yielded 1474 and 1551 lbs. of lint/A, respectively. In all 2001 experiments, there was a trend for reduced micronaire in the double seed line per bed systems compared to the single seed line per bed systems. At Maricopa, the average micronaire was 5.0 and 4.7 for the single and double seed line per bed 32 inch row system, respectively, and 5.2 and 4.9 for the single and double seed line per bed 40 inch row systems, respectively. At Marana, the micronaire was 4.7 and 4.5 for the single and double seed line per bed 40 inch row systems, respectively. At Glendale, the micronaire was 5.1 and 4.6 for the single and double seed line per bed 38 inch row systems, respectively. Production costs were similar for the single and double seed line per bed systems. Additional research will be conducted in 2002 to determine the optimum plant populations and in-row plant spacings for double seed line per bed production systems.

Three experiments at the University of Arizona Maricopa and Marana Agricultural Centers in 2002 and 2003 measured effect of plant populations on the yield of cotton planted in the twin seed-line per bed configuration. In 2002 at the Maricopa Ag. Center, the plant populations were 52800, 69200, 82800 and 96200 plants per acre (PPA) for Stoneville 4892BR and 54800, 70800, 90500 and 104500 PPA for AG3601, respectively. The two lowest plant populations which were in the range of common commercial plant densities resulted in the greatest lint yields for both varieties (an average of 1708 and 1287 lb lint/A for ST4892BR and AG3601, respectively) but there was a significant linear decrease in yield with increasing plant population. In 2003, the cotton variety Delta Pine 449BR was planted and the population densities were 22000, 29000, 36000, 46000, 51000, 61000, and 64,000 PPA at the Marana Ag. Center and 24000, 34000, 41000, 56000, 63000, 71000, and 86,000 PPA at the Maricopa Ag. Center. Cotton yield did not vary significantly as a function of population density at Maricopa and averaged 1526 lb lint/A. At Marana there was a slight trend of increasing yield with increasing plant densities with the three highest plant populations averaging 1385 lb lint/A. In the experiments with ST4892BR and AG3601 at Maricopa in 2002 and with DP449BR in 2003 there was a linear decrease in fiber micronaire with increasing density but this effect of density on micronaire was not observed possibly because plant populations Marana were lower than in the other experiments.

Twin line (two seed lines 7.25 in apart per bed) and conventional single seed line per bed cotton production systems were compared at 18 sites across Arizona and the Palo Verde Valley near Blythe, Ca. in 2002 and 9 sites in 2003. Three experiments at the Chaffin site in 2002 compared twin line plant populations of 57,000 (57K), 75,000 (75K), and 90,000 (90K) plants per acre (ppa). In 2002, the twin line system produced more lint than the conventional single line system at 4 of 18 locations; the yields of the twin line and single line systems were 1273 and 1186 lb/acre, 1572 and 1461 lb/acre, 1478 and 1290 lb/acre, and 1309 and 1210 lb/acre, respectively, at the Grasty, Ramona, Rovey, and Wells sites, respectively. In 2003, none of the experiments resulted in higher twin line system lint yields. In 2002, there were no significant differences in yield or fiber micronaire in 7 of the 18 experiments. In 2003, there were no significant differences in yield in 3 of the 9 experiments. In 2002, the twin line system produced less lint than the conventional system at 5 of 18 locations; yields of the twin line and single line systems were 2019 and 2189 lb/acre, 1400 and 1489 lb/acre, 1537 and 1845 lb/acre, 1065 and 1200 lb/acre, and 1271 and 1431 lb/acre, respectively, at the Chaffin (75K), Cooley, Hull, Papago, and Wakimoto sites, respectively. In 2003, the twin line system resulted in less yield in 6 of the 9 experiments; yields of the twin line and single line systems were 1154 and 1285 lb./acre, 1906 and 2109 lb./acre, 1797 and 1938 lb./acre, 878 and 1114 lb./acre, 726 and 821 lb./acre, and 1230 and 1404 lb./acre, respectively, at the Hull, Marlatt 1, 2,, 3, Murphy Late Plant, and the University of Arizona (UA) Marana Agricultural Center sites respectively. In 2002, fiber micronaire was reduced in five experiments; the micronaire values were 4.25 and 4.73, 4.46 and 4.78, 4.60 and 4.85, 4.76 and 4.98, and 4.93 and 5.15, in the twin line and single line systems, respectively, at the Rogers, Papago, Grasty, Hull, and Perry sites, respectively. In 2003, there were no significant differences in fiber micronaire at all 9 test locations. In 2003, visual observations suggested that the spindle pickers were unable to effectively harvest bolls the lowest bolls primarily below the cross-over point of the two2 mainstems cross in the twin line system. Hand harvest comparisons of the twin and single line system resulted in yields of 1776 and 1661 lb./acre respectively, a 6% difference at the Maricopa Agricultural Center. It was concluded that tThe inability to effectively harvest the twin line cotton is the most significant system problem with this production system.