Rice: Early N increases growth, yield

From Robert H. Wells, Delta Research and Extension Center

STONEVILLE, MISS. - Research is proving what rice growers have suspected for years - that a low rate of nitrogen applied to rice in the 1- to 3-leaf growth stage has a positive effect on production.

“Collaborative research in 2005 and 2006 with the University of Arkansas, Mississippi State University and the University of Missouri showed that rice plant height was increased by about 2 inches when 20 pounds of nitrogen per acre was applied to two-leaf rice,” said Tim Walker, assistant agronomist at MSU’s Delta Research and Extension Center in Stoneville. “Yield, when averaged across 3 preflood nitrogen rates, was greater when ammonium sulfate or when diammonium phosphate was applied as the early-season nitrogen source compared to when none was applied."

In addition to Walker, researchers from the Mississippi River Delta rice-growing region - including Rick Norman of Arkansas and Brian Ottis of Missouri - began the early-season N research as a way to quantify the true value received from the application, especially as the price of nitrogen has continued to increase.

“Growers, professional consultants, Extension personnel and scientists have often noticed that applying a relatively low rate of nitrogen to rice in the1- to 3-leaf growth stage changes the appearance of rice,” Walker said. “Rice is often greener and more lush, and growers often say that they feel they flood this rice sooner than rice where no nitrogen has been applied.”

• Researchers used ammonium sulfate, diammonium phosphate and urea as nitrogen sources in the study.“The application should not be counted toward the total nitrogen budget because only about 10% of the 20 pounds of nitrogen applied at the 1- to 2-leaf stage is taken up by the plant,” Walker said. “Researchers will now try to identify methods to apply lower nitrogen rates and still achieve the same early-season growth benefits so that this application is more efficient.”
  
• The variety in each state was Cocodrie, grown on Sharkey clay.
  
• When the rice reached an average of 2 leaves per plant, researchers applied 20 pounds of nitrogen per acre in the form of 3 different sources: ammonium sulfate, diammonium phosphate or urea. If a substantial rain did not come within 3days after application, they flush-irrigated the plots to incorporate the nitrogen fertilizer.
  
• When rice reached the 5-leaf stage, researchers recorded plant height and total above-ground biomass and then applied three preflood nitrogen rates at 90, 120 and 150 pounds of nitrogen per acre. Biomass was recorded again at boot-split, and grain yields were obtained at maturity. Researchers used biomass samples at 5-leaf and at boot-split to analyze rice for N content and to determine total nitrogen uptake.
  

Growers’ check-off dollars sponsored the early-season nitrogen research through the Mississippi Rice Promotion Board.

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