Sunday, November 12, 2006 - 4:45 PM
10-6
Use of Flooding to Analyze N Infiltration and Movement in Clay Versus Silt-Loam Soil Used for Arkansas Rice Production.
Farmers report an additional 40 lb N/acre needs to be added to the 494,000 acres of rice grown on clay soils in Arkansas than the 776,000 acres planted on silt loam soils. These additional applications can increase total costs up to 2.2 million dollars. Objectives of this experiment were to compare 1) the degree in which ponding incorporated N applied as urea or ammonium sulfate into intact cores (7.2-cm dia., 10-cm depth) and 2) the distribution of N during 12 hours of ponding in cores containing DeWitt silt-loam soil or Sharkey clay soil. Soil nitrate and ammonium concentrations were analyzed at 2-cm depth intervals in cores following removal of the flood. After 12 hr of ponding, ammonium sulfate applied-N did not move below the surface 2-4 cm of soil regardless of soil type, with mean concentrations of 375 and 230 µg N /g soil for silt loam and clay, respectively. Noticeable differences between soils showed decreases occurring below 4 cm in the silt loam while N decreased below the top 2 cm in the clay, and N movement in different soil cores was more variable in the clay. Conversely, urea applied-N behaved differently in the silt loam compared to clay. For DeWitt silt loam, urea applied-N concentrations increased between 0-2 cm and 2-4 cm depth of soil during 12 hours of ponding. Although mean concentrations decreased below 4 cm, N was measured 8-10 cm deep. In Sharkey clay, movement of urea applied-N was observed only into the top 4 cm with little accumulation observed below 4 cm. Data suggest that N movement from urea applications was deeper than ammonium sulfate and deeper in cores containing DeWitt silt loam. The minimal movement of N into the clay reflects the effort of farmers to increase N fertilizer concentrations in the soil.
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