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Fluid Journal : Fluid Journal 2005-2007
Winter 2006 Fluid Journal 2 that the 4-leaf flood created conditions of maximum yield and/or increased soil N uptake. The fertilized rice plants also yielded signifi cantly more when flooded at the 4-leaf rather than the 6- leaf stage, possibly because 6-leaf flood prolonged the soil condition that encouraged denitrification. N treatment effect on rice yield was most evident under the 6-leaf flood, which caused rice yield to range from 5,200 to 6,200 lbs/A, the all-FF treatment applied during planting being the highest. N source effect on rice yield under the 4- leaf flood was less pronounced, ranging from 6,200 to 6,939 lbs/A. All-FF treatment applied during planting yielded 6,939 lbs/A, on a par with all dry fertilizer at planting. 2004. Since floodwater management did not significantly influence yield of N fertilized rice plants, yields in Figure 2 are the average of the 4- and 6-leaf flood yields on each soil type. On clay soil, all-FF applied at planting yielded 6,430 lbs/A, which was similar to rice for the 2-way split and about 500 lbs/A more than dry fertilizer at planting. On silt loam, soil yields were higher but N treatment effects were similar to those on clay soil. The higher yields on silt loam soil were probably because of better climatic conditions and because silt loam produced significantly more yield without N fertilizer (Figure 2). All- FF applied during planting yielded 8,440 lbs/A, which was on a par with 2-way N split. Economic effects Assumptions. Fertilizer and application costs in Figures 3 and 4 were derived from the following assumptions: 1) FF applied at $4/A in subsurface band at planting 2) $7.65/A aerial cost when applying less than 55 lbs/A, $8.15 when applying 56 to 110 lbs/A, and $7.65/cwt when applying more than 111 to 165 lbs/A Table 1. N uptake (lbs/A) at mid-season on clay soil flooded at the 4- or 6-leaf stage. In 2004, N uptake at booting averaged for 4- and 6-leaf floodwater management. 2003 (clay soil) 2004 Treatments --- 150 lbs/A of N: 4-leaf 6-leaf Clay Silt loam 1) Fluid at planting 103 93 152 142 2) Dry prior to planting 82 66 104 126 3) 2-way split (70% at planting 30% at mid-season) --- --- 105 113 4) 3-way split (dry 17% at planting + 50% at flood + 33% at mid-season) --- --- 105 143 5) Check 10 --- 24 45 Figure 1. Fertilizer treatment effects on yields at 4- and 6-leaf flood stages, 2003. Figure 2. Fertilizer treatment effects on yield on clay and silt loam soil, 2004.
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