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Fluid Journal : Winter 2015
16 The Fluid Journal Winter 2015 N or S, while at Lewiston the unfertilized plots received the full 80 lbs of N/acre sidedress application rate. Other nutrients were applied based on the soil test recommendations. In-season development Plant population was measured by counting the number of emerged seedlings in two ten-foot sections of row. Plant population counts were taken at 7, 10, 14, and 21 days after planting. Plant heights were measured weekly beginning with the appearance of the second true leaf and measured from the ground to the apical meristem on five randomly selected cotton plants per plot. At the appearance of the first square, the total number of nodes were counted weekly on five randomly selected plants per plot. Plant height and total node measurements ceased with the appearance of the first white flower at each location. Tissue sampling Beginning the first week of bloom, twenty-four cotton petioles were sampled from the first and fourth rows of each plot. The fourth leaf and petiole down the main stem of the cotton plant were sampled and separated immediately. Petioles were sampled weekly for the first nine weeks of bloom. Petioles sampled during the seventh through ninth weeks of bloom were taken from the third leaf down the main stem as there were not enough leaves in the fourth position for a complete sample. The maturity level of the leaves was thought to be similar as vegetative growth had ceased prior to this stage of development. The plant tissue samples were sent to Water's Agricultural Laboratories (Camilla, GA) for analysis. The petioles were analyzed for nitrate-N, P, and S. Nutrient concentrations in petioles were plotted against time. Leaf samples were collected during the first and fifth weeks of bloom only, and a complete nutrient analysis was conducted on the leaf tissue. Defoliation Defoliation timing of cotton varies, depending on the growing season and development of the crop. The trial was defoliated when 50 to 60 percent of the bolls were opened. Harvesting Seed cotton was harvested using two- row commercial cotton pickers modified for small plot harvesting. The center two rows of each plot were harvested and plot weights recorded. Cotton lint A one pound subsample of seed cotton was ginned on a 10-saw micro- gin to determine lint percentage. Seed cotton weights were multiplied by the lint percentage to calculate lint yields. Cotton lint was sent to the USDA cotton quality lab in Florence, SC for lint quality analysis. The lint was analyzed using a High Volume Instrument (HVI) to determine fiber length (staple), strength, micronaire, color, and leaf (trash) grade. Statistical analysis The data set separated into two separate data sets and analysis of variance (ANOVA), using PROC MIXED in SAS 9.3, was used to determine differences among treatments. The first data set consisted of the different nutrient management systems tested at the 100 percent P and K rate based on soil test recommendations. The nutrient management systems were analyzed as single treatment factors in a randomized complete block design. The second data set was used to determine the effect of P and K rate and placement on each of the measured dependent variables. The data set was analyzed as a 3 x 2 factorial treatment design in a randomized complete block design, using ANOVA. Differences among treatments in each analysis were determined using the Tukey-Kramer HSD at = 0.1 level of significance. Results General comments. The 2013 growing season was very unique in the upper Southeast coastal plain of the United States. A cool wet May delayed cotton planting for up to two weeks and cooler than normal temperatures prevailed for much of the growing season. The shortened cotton season seemed to have little impact on yield in Virginia as the two study locations produced exceptional yields. The Lewiston location was planted later than was expected and suffered sand burn damage very early in the growing season (Figure 2). The decision was made not to abandon the location since treatments had been applied. Luckily, the first sampling for plant population had been conducted before the damage and another plant population count was conducted after the damage. With the two plant population sampling intervals it was found that, on average, the injury reduced plant populations by two plants per ten feet of row. This is not an insignificant loss of stand and represents a decrease in the plant population of 2,904 plants per acre. The cotton was slow to recover from the damage and in-season plant measurements were affected by the variation introduced by the sand burn damage at Lewiston. The delay in development of the cotton at Lewiston allowed the first initial petiole results to come in for TAREC. The petiole results indicate elevated P concentration in petiole for the unfertilized checks, as well as N deficiency. The decision was made to apply sidedress N at Lewiston and test the hypothesis that N deficiency produces elevated P concentration in cotton petioles. If this hypothesis is proven to be true, then decisions about P management in cotton cannot be made off petiole concentrations if there is a known N deficiency. For growers looking to improve nutrient use efficiencies with petiole testing, this knowledge will increase the efficacy of their in-season nutrient management decisions. Nutrient management Plant growth. In-season plant growth measurements were initiated seven days after planting with plant population counts. Among the nutrient management systems there were no differences in plant population at any sampling intervals (data not shown). Emergence Figure 2: Sand-burn injury 6/17 (A) and 7/2 (B)