Variable rate nitrogen
Nov 25, 2009 8:08 AM, By Roy Roberson, Farm Press Editorial Staff
Tests at Clemson University indicate variable rate application of side-dress nitrogen on cotton can save growers 30-50 percent on nitrogen use without loss of yield.
The spike in nitrogen fertilizer prices in 2008 and the continued volatility of both supply and cost, combined with continued low prices for cotton, has placed many growers in dire need of improving the efficiency of the fertilizer they use.
For the past three years Clemson researchers at the Edisto Research and Education Center in Blackville, S.C., have been testing three different options for variable rate application of side-dress nitrogen on cotton. In 2007 and 2008 they reduced total nitrogen use by 30 percent with no yield loss. In 2009, they upped the ante to saving 50 percent on nitrogen use.
The proof of the 50 percent reduction will come after cotton is harvested and yield and quality numbers are in, but so far tests on the research station and with cooperating farmers look good.
“If you look at cotton prices, they are about the same as in 2003. However, if you look at the price of nitrogen, despite a drop in price this year, it is still near record highs. The recession has kept prices low, but we don’t know where nitrogen prices will go next year,” says Clemson Researcher Wes Porter.
Porter is a graduate student working with Ahmad Khalilian, a Clemson University Professor of Agricultural & Biological Engineering and guru of precision agriculture for a number of years.
For the past three years Khalilian, Clemson Extension Precision Ag Specialist Will Henderson and a group of dedicated graduate students have tested variable rate technology for use in applying nitrogen and other fertilizers on cotton.
Porter says there are three routes a farmer can go to apply variable rates of nitrogen to cotton. The first is the simplest and least costly: A nitrogen ramp calibration strip (N-RCS) can serve as a simple guide to nitrogen use.
The N-RCS strips, usually 100-150-feet long, begin at a low rate of nitrogen in as close to an average soil type as possible and increase nitrogen rates to a rate higher than a cotton plant can use. The response of cotton to nitrogen rate will increase to a certain level of nitrogen, after which there will not be any significant increase in crop performance with increasing nitrogen rate. On a 150-foot test strip, the Clemson researchers upped nitrogen rates by 10 pounds per acre every 16 feet of the test row.
