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Economically efficient Finding best cotton seeding rate

We have been asked on multiple occasions recently if cotton farmers can save money by reducing their seeding rates. The cost of cotton seed per bag is higher than it was a few years ago, which warrants re-examining the optimal seeding rate.

In 2006 Larry Earnest, resident director in charge of the Southeast Research and Extension Center — Rohwer Division, organized a replicated study on a Herbert silt loam soil to compare cotton seeding rates using a BGII/Roundup Ready Flex cotton variety.

“Hill drop cotton is one of the most prevalent planting methods in the southeast Delta region. Producers believe it gives them a greater chance of achieving and maintaining adequate stands, especially when they plant early.

“Early plantings can often incur cooler and higher moisture conditions, which can prolong germination, reduce seedling vigor, compact soil and increase seedling disease pressure, which often leads to reduced stands,” said Earnest.

According to Earnest, Beltwide Cotton Genetics' variety 3255 B2RF was planted April 19, 2006, in four-row plots 40 feet long on 38-inch rows using a John Deer Max-Emerge 7300 vacuum planter with hill drop plates set to plant every 12 inches.

Emergence occurred April 28 with an average soil temperature of 61 degrees F at a 4-inch depth.

“Two rains that fell, back to back, less than 48 hours after planting compacted the soil around the seed. This had a negative impact on stands,” said Earnest.

The treatments were replicated four times and included (1) one seed per hill, (2) two seeds per hill, (3) three seeds per hill and (4) four seeds per hill.

The study was furrow-irrigated at a 2-inch soil moisture deficit using the UA Irrigation Scheduler Program. “Irrigation requirements began a few weeks earlier from the norm this year and average frequency occurred on an eight-day cycle through maturity,” Earnest said.

“Supplemental phosphorus, potassium and boron were added, prior to planting at the rate of 0-30-90-1 respectively, as recommended by a soil analysis conducted by the UA Soil Testing Lab at Marianna, Ark. A total of 110 pounds of nitrogen in the form of urea was applied in a split application at the two- and six-leaf stage,” said Earnest.

“A total post-emergence weed control system with Roundup Original Max at 22 ounces per acre and Dual Magnum at 16 ounces per acre was applied at the two-leaf stage followed by applications of Roundup Original Max at 22 ounces per acre at the eight-leaf and 12-leaf stages,” Earnest said.

“Plant bug pressure was less significant this year and only a single application of Bidrin, at the 8-ounce rate, was needed to control treatment levels,” said Earnest.

According to Earnest, Dropp, Def and Finish were used to condition the study crop for harvest, and on Sept. 29 the two middle rows of each plot were harvested with a Case IH 1822 picker that was modified with an on-board computerized weigh system.

The raw data are shown in the accompanying graph. The observations clumped together nicely and there is a trend of higher yield with increased seeding rate.

The data are compiled and subjected to an analysis of variance. At the 90 percent level of confidence, the mean yields for treatment 3 and treatment 4 are not statistically different. Treatments 1 and 2 are statistically different from each other and from 3 and 4.

In order to determine the economically efficient seeding rate, we converted the observed plot yields to cotton lint yield per acre and averaged across replications. The results are displayed in the accompanying table.

We valued this lint at 52 cents per pound, giving us the Total Value Product (TVP) for each seeding rate.

According to our 2006 cotton budgets, the cost of seed, technology fee and seed treatment for a Bollgard 2/Roundup Ready Flex variety is $95.94 per acre when planting four seed per row foot. Dividing this by four seeds gives us $23.99 per acre per seed.

Thus, the cost of planting one seed per hill is $23.99 per acre. The cost of seed, technology fee and seed treatment for all four seeding rates is listed in the table as Total Input Cost (TIC).

The economically efficient seeding rate is the one with the largest difference between TVP and TIC. Thus, four seeds per hill was the profit-maximizing choice for this comparison.

This study was only conducted for one year at one location and statistical difference between three and four seeds per hill was not obtained. However, the findings do not support the idea of reducing seeding rate to save money and thereby increase profits.

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