STUTTGART, Ark. - Phosphorous and nitrogen are major costs in producing a rice crop. Rice producers can spend as much as $85 an acre to fertilize fields, which highlights the grower's need to use the best management practices possible.
Nitrogen and the cost of applying it can be more than $40 an acre, making it essential that growers make the most efficient use of the nutrient,” says Chuck Wilson, Extension rice specialist with the University of Arkansas’ Rice Research and Extension Center near Stuttgart.
"The primary focus of our nitrogen research is to optimize management efficiency by evaluating nitrogen rates, timing and fertilizer sources," Wilson says. "We conduct studies evaluating these factors in association with different varieties and soil types to obtain the best yield with the least amount of fertilizer."
Much of the research is funded by grower checkoff dollars administered by the Arkansas Rice Research and Promotion Board.
Nitrogen is the costliest item in a grower's fertilizer budget. It can cost more than $40 an acre with application costs, depending on the current price of urea.
“All counties use the nitrogen research we conduct," Wilson says, "because management of nitrogen is so critical for the best yields."
Phosphorus research has focused on refining soil test parameters for making phosphorus recommendations and evaluating optimum fertilizer timing. "Based on phosphorus research over the past five-plus years, we recommend phosphorus on soils with high pH and low soil test phosphorus," Wilson says.
Much of the phosphorus work has been done in Cross and Poinsett counties in northeast Arkansas.
“What we've seen is that the phosphorus levels are more critical to good rice production than potash," says Rick Wimberley, Cross County Extension staff chair. "What we've done in the last three years has been to look at the application timing of phosphate. Traditionally, producers apply it before planting. What we've seen is that phosphate applied in the pre-flood situation remains more available to the plant."
Other ongoing studies examine the effects nitrogen has on rice plants. Effectively managing nitrogen fertilizer presents the greatest challenge to rice producers, says Rick Norman, agronomy professor at the University of Arkansas Agricultural Experiment Station in Fayetteville.
"No other nutrient requires as much detailed management attention as nitrogen fertilizer," Norman says. "No other nutrient can deliver greater benefits in increased rice grain yields for effective management.
"We expend so much effort to determine the proper nitrogen fertilizer rate for each new rice variety prior to its release," Norman says.
Nathan Slaton, UA assistant professor in soil testing, says that in 2003 research to investigate the response of rice grown on clay soils to zinc fertilization was initiated in six grower fields in Jefferson, Poinsett and St. Francis counties and two experiment stations at Keiser (Mississippi County in northeast Arkansas) and Rohwer (Desha County in southeast Arkansas).
Results show that the availability of zinc on silt and sandy loam soils is known to decrease as soil pH increases, especially when soil pH is greater than 7.0.
Results from 2003 are only preliminary, and additional data is needed from many other fields to determine whether observations made in 2003 can be consistently repeated and final zinc fertilizer recommendations can be developed for rice grown on clay soils.
Lamar James is a writer for the University of Arkansas Cooperative Extension Service.