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Fluid Journal : Winter 2015
17 The Fluid Journal Winter 2015 was 50 to 60 percent of the final plant population seven days after planting at TAREC and was nearly 100 percent of the final plant population ten days after planting at TAREC (data not shown). Emergence was similar at Lewiston up to the sand-burn injury, which reduced plant populations by two plants per ten row feet (data not shown). Plant heights were very responsive to nutrient management systems at every sampling interval, except one (Table 3). The plant heights in TAREC were not significantly different on the first sampling interval, however by the second sampling interval all fertilizer treatments produced taller plants than the unfertilized check (Table 3). Plant heights were significantly taller using the 2 x 2 band (100%) program (12.1 in.) than the unfertilized check (9.4 in.) and broadcast program (10.5 in.) on June 20 (Table 3). Plant heights were significantly taller using the broadcast program than the unfertilized control on June 20. The 2 x 2 band (100%) program produced the tallest plants in each of the remaining sampling intervals. The 2 x 2 band (100%) program produced significantly taller plants than deep placement (100%), broadcast control, and unfertilized check on the June 26 and July 3 sampling intervals (Table 3). Both the deep placement (100%) and broadcast control resulted in taller plants than the unfertilized control on June 26 and July 3. The data indicate that the 2 x 2 placement of nutrients promotes early- season growth compared to the other placement strategies at the TAREC location. Sidedress N was applied at TAREC on June 27 and plant growth regulators were applied to the rest on June 28 and helps explain why observed differences in plant heights at TAREC on fertilized plots were reduced after the June 26 sampling date. No plant height differences were observed among nutrient management systems at the Lewiston location and were most likely due to the early sand-burn injury (data not shown). Petiole/tissue analysis. Petiole and tissue testing allow producers and consultants to gain insight into the nutrient status of cotton during the growing season. The bloom period is when cotton is actively fruiting and establishing bolls, which determines the amount of harvestable lint at season's end. Petiole and leaf tissue were monitored during the bloom period with petiole tested weekly for the first nine weeks of bloom and leaf tissue sampled during the first and fifth weeks of bloom. At TAREC, all nutrients monitored in cotton petioles decreased throughout the bloom period (Figure 3). The overall ANOVA p-value was significant for petiole P among nutrient management systems during every week except the second week of bloom at TAREC (Figure 3B). The unfertilized check had the highest petiole P concentrations of the nutrient management systems, which was surprising as no P was applied. Nitrate --N concentrations in cotton petioles differed in four out of the first five weeks of bloom, the unfertilized control had the lowest nitrate-N values during this time period (Figure 3C). Sulfur concentrations in cotton petioles increased from the first to the second week of bloom and then decreased for the remaining bloom period sampling intervals (Figure 3D). Sulfur petiole concentrations were lowest in the unfertilized control to begin the bloom period, however late in the bloom period the unfertilized control had the highest S concentrations (Figure 3D). At the Lewiston location, the unfertilized control received an N application at sidedress, whereas the unfertilized control at TAREC received no in-season N application. Petiole nutrient concentrations at Lewiston were affected by the early- season sand-burn damage. However, certain trends are apparent in the data. At Lewiston, the unfertilized control had lower numerical K, P, and S concentrations in cotton petioles than the fertilized treatments (Figure 4A-D). The variability introduced from the early-season injury most likely masked any effect of nutrient management on petiole K, P, and S. Fertilizing with N at Lewiston lowered the K, P, and S concentrations compared to the fertilized treatments. Also, the damage suffered early in the season seems to delay the peak nutrient content ofNandKforaweekandpeakPlevels were delayed 4 to 6 weeks (Figure 4A-C). Nitrate-N, among nutrient management systems, did not differ during any of the first nine weeks of bloom. The nitrate-N concentrations had less variability among nutrient management systems than the other petiole nutrients tested at Lewiston. The petiole results from both locations during the 2013 growing season indicate that the N status of the cotton plant will influence petiole K, P, and S concentrations. If the hypothesis is true then in-season decisions based on petiole nutrient concentrations must start with the N status of the crop. If N is deficient, then accurate inferences about K, P, and S status for the cotton crop cannot be made due to elevated nutrient levels resulting from N deficiency. This seems to be especially true for petiole P concentrations. Also, the early season injury at Lewiston seemed to delay the time of peak nutrient concentrations, which is also helpful if using the strategy to manage in-season nutrient applications. If a producer knows the crop was severely stressed early, then testing petioles during the first week of bloom may produce a false negative nutrient concentration as the plant is still recovering physiologically from the injury. That producer may want to wait and test during the second and third week of bloom before making a management decision as the petiole nutrient concentration may increase. Results from the leaf tissue analyses reinforced the petiole tissue sampling program. Nitrogen concentrations in leaf tissue were highest in the 2 x 2 band (100%) and significantly higher than the deep placement (100%) and unfertilized control (data not shown). Table 3: Early season plant height of cotton grown under different nutrient management systems at TAREC Treatment Plant Height (in.) 4-Jun 13-Jun 20-Jun 26-Jun 3-Jul 10-Jul Unfertilized Check 4.8 7.4c¶ 9.4c 13.2d 18.0c 22.0b Broadcast Control 4.8 8.5ab 10.5bc 15.4c 22.4b 29.6a Starter Control 5.0 9.6a 11.1ab 17.8ab 24.1ab 31.4a 2 x 2 Band (100%) 5.2 9.4ab 12.1a 18.6a 25.9a 32.0a Deep Placement (100%) 4.9 8.7ab 11.3ab 16.9bc 23.9b 30.9a ANOVA (Pr > F) NS* 0.0033 0.011 < 0.0001 < 0.0001 < 0.0001 * The overall ANOVA was not significant at =0.1 ¶ Values with the same letter are not significantly different at =0.1