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Fluid Journal : Early Spring 2013
6 The Fluid Journal Early Spring 2013 differences in corn plants treated with four different N rates before the V8 growth stage of corn. Methodology Location. This experiment was conducted in a greenhouse at Colorado State University. Soils. Among five locations where soil was collected, the soil with the lowest residual N content was chosen as the soil used for the greenhouse study. Soil texture was classified as a sandy clay loam and residual NO3-N content was 1.7 mg/kg. Containers. Corn plants were grown in eighty 11-liter plastic pots. Each pot contained 8 kg of soil. There were three corn plants per pot. Weeds were hand- removed every other day. Water was supplied by drip irrigation every day. Treatments. Four nitrogen rates were used: • Control • Low (75kg/ha) • Intermediate (150kg/ha) • High (150 kg/ha). Prior to planting, N was added as NH4NO3 at rates of: • 0 mg/pot for control • 583 mg/pot for low N pots • 1,167 mg/pot for intermediate N pots • 1,750 mg/pot for high N pots. Parameter Description Formula* NBI_R Nitrogen balance index (red) ∑= 500 1 500 1 i R UV i i RF FRF NBI_G Nitrogen balance index (green) ∑= 500 1 500 1 i G UV i i RF FRF *Fluorescence waveband is indicated as FRF for far-red fluorescence and RF for red fluorescence and induction waveband is in subscript. UV=Ultra- violet; G=Green; R=Red. Table 1: Parameters used for this study along with their description and formula. Potassium phosphate and zinc were added at rates of: • 2,899 mg of KH2PO4 • 53mgofZnSO4 Sensor used for the study was a Multiplex®3 hand-held multi-parameter optical sensor. It automatically computes two N balance indices: the green (NBI_G) and red (NABI_R) shown in Table 1. Results promising Fluorescence. Two parameters were investigated to detect corn N deficiency. The first parameter was the N balance index measured with red excitation (NBI_R) and it presented good potential for N-deficiency detection from V5 growth stage of corn (Figure 1). From V7, all four N-rate treatments were significantly different. The second parameter was the N balance index measured with green excitation (NBI_G) and it presented good potential for N-deficiency detection from V6 growth stage of corn (Figure 1). From V7, all four N treatments were significantly different. N effect. The different N treatments had a significant effect on dry weight (Figure 2). Dry weights resulting from 150 kg/ha N and 225 kg/ha N were not significantly different from each other. All Figure 1: Different letters indicate significant difference within same growth stage and fluorescence parameter.
Late Spring 2013