Influence of Row Configuration (Single Row, Twin Row, and Wide Bed), Seeding Rate, and Nitrogen Rate on Grain Sorghum Yield H.J. “Rick” Mascagni, Jr. and Bubba Bell Introduction Although sorghum is relatively tolerant to drought stress, maximum yield is possible only when plant growth and development is not restricted by environmental conditions. Yields fluctuate from year to year primarily because of varying environmental factors such as rainfall and temperature. Irrigation has been used in recent years for many of the row crops, including cotton, corn, and soybean, to lessen plant stress during times of low rainfall. Irrigation is a management tool that can better ensure yield stability over time. Traditionally, sorghum has not been irrigated because of its perceived tolerance to moisture stress and more importantly, to the step-child production philosophy of using minimal inputs for producing the crop. For maximum yield production, information is needed on the benefits of irrigation and the interaction of irrigation with other production practices. When using irrigation, other cultural practices such as row spacing and seeding rate may need to be modified for maximum yield. Research has indicated a consistent increase in grain sorghum yield when rows are narrowed from the traditional 36 to 40-inch row spacing. Narrowing the rows provides a more equidistant spacing among plants which increases the efficiency of light and moisture utilization. In recent years, planters have been introduced that have the capability of planting twin rows on raised beds. For example, commercial planters are available that plant two rows, 9.5-inches apart, on top of raised beds. Also, raised wide beds (76- to 80-inches wide) are becoming more common. On these beds, four 15-16-inch rows can be planted. This planting strategy improves drainage and permits use of furrow irrigation. Optimum seeding rate and nitrogen rate may need to be modified for this production system, particularly under irrigated conditions. Field experiments will be conducted to evaluate the interaction of irrigation, row configuration, seeding rate, and nitrogen rate on grain sorghum plant development and yield. Procedures A field experiment was conducted in 2009 on Sharkey clay at Northeast Research Station (NERS) to evaluate the influence of irrigation, row configuration, seeding rate, and nitrogen rate on yield of grain sorghum. Two irrigation treatments, a non-irrigated control and a furrow- irrigated treatment scheduled whenever the soil moisture deficit reaches 2-inches using the Arkansas Irrigation Scheduler, was evaluated. Row configurations were single and twin rows centered, 9.5-inches apart, on raised beds. Four 16-inch rows were also planted on 80-inch wide raised beds. Seeding rates were 4, 6, 8, and 10 seed/ft on single row and equivalent seeding rates on twin rows and wide beds. Nitrogen rates were 120 and 150 lb/acre broadcast as urea (with Agratain®). Single rows were planted with a JD 1700 and twin rows with a Monosem twin-row planter. Wide beds were planted with a JD 2100 cone planter configured with four planting units spaced 16-inches apart. Similar studies comparing single and twin rows were conducted on Gigger silt laom at the Macon Ridge Research Station in Winnsboro. Measurements will include yield and yield components (number of heads/acre, seed weight, and seed/head). Results and Discussion The trial at St. Joseph had extremely low yields, which was due in part to a relatively late planting date (May 8), a wet July (7.1 inches), and severe midge damage. An application of a pyrethroid was applied in early July for the control of midge but additional applications were not made. The data below is from the irrigated trial. There was a difference in row configurations with both the twin row and 16-inch rows on wide bed having higher yields than the single row. However, these results were confounded by the midge damage, with the single row treatment having more severe midge damage than the other two row configuration treatments. A complimentary study was conducted on a Gigger silt loam in Winnsboro. Nitrogen rate and the wide bed were not evaluated in this study. This trial was also planted late (May 19) but timely rains in July produced good yield on this dryland soil. Seeding rate did not affect yield; however, there was a difference in yield between the single row and twin row planting systems. Average yields were 5322 lb/acre for the single row and 542 lb/acre for the twin row. These findings are not very conclusive because of weather and insect damage, particularly at St. Joseph. Additional studies will better define optimum management practices that will maximize grain sorghum yield and profitability. Table 1. Influence of seeding and N rate on grain sorghum yield on single row, twin row, and wide bed on Sharkey clay in St. Joseph, 2009. Seeding rate1 N rate Single row Twin row Wide bed lb/acre ------------------------------lb/acre----------------------------- 1 120 1399 1781 1848 150 1421 1670 2337 2 120 1572 1865 1997 150 1403 1932 2333 3 120 1434 2010 2201 150 1295 1798 2141 4 120 1637 2110 1948 150 1315 1690 1565 Average 1435 1858 2042 1 The seeding rates of 1, 2, 3, and 4 were equivalent to 4, 6, 8, and 10 seed/ft for single row and 2, 3, 4, and 5 seed/ft for twin row and 16-inch rows on wide bed. Table 2. Influence of seeding rate on grain sorghum yield on single and twin row on Gigger silt loam in Winnsboro, 2009. Seeding rate1 Single row Twin row ----------------------------------lb/acre--------------------------------- 1 4991 5572 2 5553 5615 3 5276 5551 4 5470 5432 Average 5322 5542 LSD (0.10) 175 1 The seeding rates of 1, 2, 3, and 4 were equivalent to 4, 6, 8, and 10 seed/ft for single row and 2, 3, 4, and 5 seed/ft for twin row.
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