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© 2004 Plant Management Network.
Accepted for publication 13 July 2004. Published 5 August 2004.

Zinc Enhances Sugar Beet Emergence and Yield on a Calcareous Soil with Marginal Zinc Availability

W. Bart Stevens, Department of Renewable Resources, and Abdel O. Mesbah, Department of Plant Sciences, University of Wyoming, Powell Research and Extension Center, 747 Road 9, Powell 82435

Corresponding author: W. Bart Stevens. wstevens@uwyo.edu

Stevens, W. B., and Mesbah, A. O. 2004. Zinc enhances sugar beet emergence and yield on a calcareous soil with marginal zinc availability. Online. Crop Management doi:10.1094/CM-2004-0805-01-RS.

Abstract

Zinc fertilization by broadcast, foliar, and seed-row application methods were evaluated as a means to enhance sugar beet (Beta vulgaris L.) production on a calcareous soil with marginal (0.5 to 1.0 ppm) Zn availability. Seed-row-applied ZnSO₄ (ZnSO₄ at 6 lb/acre, Zn at 2 lb/acre) resulted in the most consistent benefit to root yield over the three year study, resulting in an 11% (2.8 ton/acre) root yield increase compared to no Zn application. Broadcast and foliar applications of Zn plus B, Fe, and Mn produced lesser and more sporadic yield increases than did seed-row-applied ZnSO₄. Placing the salt-based ZnSO₄ in direct contact with seed did not appear to have inhibited seedling emergence; rather it enhanced the rate of emergence in two of the three years. There was evidence that seed-row application of ZnSO₄ resulted in stronger and more vigorous seedlings than those obtained with other Zn application methods. Because this study was conducted at only a single location, additional research at other locations is necessary to validate results and justify changes to current guidelines.

Introduction

Sugar beet (Beta vulgaris L.) is an important cash crop in the U.S. where 2001 production on 1.37 million acres generated $1.02 billion in gross farm income (10). Information regarding the requirements of sugar beet for primary nutrients is abundant, but research on micronutrients is less common even though sugar beet is moderately sensitive to deficiencies of most micronutrients (8). Zinc availability is limited in soils with high pH ( > 7.0), high free calcium carbonate, sandy texture, low organic matter, and where subsoil has been exposed by land leveling (18). Zinc availability may be further reduced by heavy P applications. These conditions are common in many of the U.S. sugar beet growing areas and Zn fertilization is routinely recommended for other crops in these areas (4,9,12,16,17). For instance, a response by dry bean (Phaseolus vulgaris L.) to added Zn has been reported even when soil test Zn was sufficient (2). Despite this, Zn application to sugar beet has not produced yield increases in most reported studies (7,15), especially when Zn is applied to another crop in the rotation. While past research has failed to show a benefit to Zn fertilization of sugar beet, much of this work was conducted using varieties and production practices common 30 to 40 years ago. We felt there was a need to re-evaluate Zn application with modern, high-yielding varieties using current production practices.

Options for applying Zn fertilizer are numerous. While broadcast applications of Fe and Mn are usually not effective in calcareous soils because of rapid fixation reactions, insoluble Zn compounds form less quickly in these soils, resulting in a substantial period of residual availability (5). Consequently, broadcast applications of Zn have proven effective for correcting deficiencies (2,8). In addition, foliar and banded applications are also sometimes recommended to improve the efficiency of Zn assimilation (4,9,12,16,17). The objective of our research was to evaluate different methods for applying Zn to sugar beets grown on calcareous soils with marginal Zn availability.

Field Experiment Implementation

The experiment was conducted over three years at the University of Wyoming Powell Research and Extension Center (PREC). Plots were moved to a new location each year to avoid effects of Zn carryover. The seed bed was prepared using tillage operations typical for the area including moldboard plowing, roller harrowing and leveling. Soil at PREC is classified as a Garland clay loam (fine-loamy over sandy or sandy-skeletal, mixed, superactive, mesic Typic Haplargids) and the chemical characteristics of each plot area are shown in Table 1. Study areas were located in fields with a 2-yr history of sugar beet-barley rotation and no recent Zn fertilization.

Table 1. Initial soil properties within plot areas located at the Powell Research and Extension Center, Powell WY.

 ^x Saturated paste pH and EC; AB-DTPA K, Cu, Fe, Zn and Mn; Olsen P; hot water B. Sampling depth was 6 inches.

Plots were organized into a randomized complete block design with five replications. Individual plots were six rows wide and 35 feet long. Prior to planting, zinc was broadcast and incorporated either alone or in combination with manganese, copper, boron, and iron. Pre-plant N and P2O5 were applied uniformly to all plots at 100 lb/acre each using a blend of ammonium nitrate (34-0-0) and mono-ammonium phosphate (11-52-0). Hilleshog-Monohy 9155 (2000 and 2001) and Geyser (2002) sugar beet varieties (Syngenta, Seeds, Inc., Longmont, CO) were planted between April 25 and May 1 using pelleted seed placed in 22-inch rows at a depth of 1 inch using John Deere 71 planter units set to place seeds 7 inches apart. Aldicarb insecticide was applied to the seed bed at a rate of 1.8 lb ai/acre in a 7-inch band and was incorporated to a depth of 1.5 inches. Seed-row-applied zinc sulfate and ZnEDTA treatments were applied using planter-mounted Gandy boxes equipped with vinyl tubing which directed the materials into the seed row immediately behind the seed drop tube. Foliar treatments containing zinc sulfate, zinc chelate (ZnEDTA), or a combination of Zn plus B, Fe, and Mn were applied in late June and early July in 20 gal of water per acre. Weed control was accomplished with three broadcast applications using a mixture of desmedipham-phenmedipham (0.95 lb ai/acre) + triflusulfuram (0.016 lb ai/acre) + clopyralid (0.094 lb ai/acre) and two manual weedings.

Plant population was evaluated three times (Figs. 1 to 3) during the growing season to determine effects of fertilizer treatments on germination and emergence. Supplemental N (125 lb/acre) was applied in mid-June by injecting liquid urea-ammonium nitrate solution (32% N) 8 inches from the plant row and 3 inches deep. Following removal of tops (leaves, petioles, and crowns), sugar beet roots were harvested from 30 feet of one center row in early October using an International Harvester M-10 one-row sugar beet harvester equipped with an electronic load cell and weighing basket. As sugar beet roots were harvested, a sub-sample comprised of six roots was collected from each plot to be analyzed for tare (mud adhering to root), sucrose content, and impurities by Western Sugar Co. in Billings, MT. Data were analyzed using the general linear model (GLM) in SAS statistical software (11), employing the Duncan Multiple Range test for mean separation where significant differences were identified by an analysis of variance.

Fig. 1. Influence of Zn application method on sugar beet seedling emergence in 2000 as indicated by plant population at 14, 18, and 56 days after planting (DAP). Within a sampling date, bars with the same letter above them are not significantly different (P < 0.05).		Fig. 2. Influence of Zn application method on sugar beet seedling emergence in 2001 as indicated by plant population at 21, 32, and 51 days after planting (DAP). Within a sampling date, bars with the same letter above them are not significantly different (P < 0.05).

Fig. 3. Influence of Zn application method on sugar beet seedling emergence in 2002 as indicated by plant population at 16, 23, and 48 days after planting (DAP). Within a sampling date, bars with the same letter above them are not significantly different (P < 0.05).

Yield Response

Zinc treatments affected root and sugar yield at a 95% confidence level in the first of three years and affected root yield at a 90% confidence level in the third year (Table 2). In 2000, broadcast application of Zn plus B, Fe, and Mn yielded 3.5 ton/acre (14%) more sugar beet roots than when no Zn was applied. However, ZnSO₄ applied in the seed row at 6 lb/acre (Zn at 2 lb/acre) was the highest yielding treatment producing a root yield that exceeded the check by 4.2 tons/acre (17% increase). Broadcast application of Zn alone did not produce a significant yield increase. Additional treatments were added in 2001 and 2002 to evaluate seed-row-applied ZnEDTA and foliar applications of ZnSO₄, ZnEDTA, and Zn plus B, Fe, and Mn. Zinc application did not affect yield at the 2001 site, which had the highest soil test Zn levels of the three study sites (Table 1). Differences in root yield were significant only at a 90% confidence level in 2002, but when data from 2001 and 2002 were pooled, seed-row-applied ZnSO₄ again produced the highest yield, which was 8.6% higher than the check (P < 0.05). No other treatment provided a significant benefit (Table 2). Sugar content of the roots was unaffected by any of the Zn treatments in any of the three years (data not shown), but did vary from year to year with averages of 15.8, 17.7, and 17.8% sugar for 2000, 2001, and 2002, respectively. Sugar yield, which was calculated as the product of root yield and sugar content, exhibited trends similar to those observed for root yield (Table 2).

Table 2. Influence of broadcast (Bcst), foliar (Fol), and seed-row (SR) applications of Zn on root yield, sugar content, and total sugar yield.

 ^x Average of 2001 and 2002 means.

 ^y Means within a column followed by the same letter are not significantly different (P < 0.05), except where noted by footnote z.

 ^z Differences among means are not significant at a probability level of 95% (P < 0.05), but are significant at a 90% probability level (P < 0.1). Means separation performed using = 0.1.

The observed response to seed-row-applied Zn may be due to limited Zn availability in the cool spring soils combined with the seedlings’ limited root systems, which may be incapable of exploiting the volume of soil necessary to absorb adequate amounts of the immobile Zn ions. This is analogous to responses observed when starter fertilizers containing P produce an early-season response even when soil test P levels are sufficient (6). For immobile nutrients such as Zn and P, band applications can be expected to promote early season growth more effectively than do broadcast applications because placing fertilizer where seedling roots will quickly intercept the nutrients greatly increases uptake efficiency (1). Recent Minnesota research with sugar beets showed that seed-row-applied P fertilizer was five times more effective than broadcast P (13).

Seedling Emergence

Despite the advantages of seed-row-applied fertilizers, there is also potential for seedling injury because fertilizer salts are placed in direct contact with seed. Snyder (14) reported that 50 lb/acre of a 10-10-10 fertilizer material placed in direct contact with sugar beet seedlings delayed emergence approximately 5 days compared to plots that received no fertilizer, while a broadcast application of 1000 lb/acre had no effect on seedling emergence. The salt-effect caused by seed-row fertilizer applications is exacerbated when soil moisture (14) and soil temperature (3) are below optimum levels.

Results from our study show no evidence that 6 lb/acre ZnSO₄ applied in the seed row delayed emergence or caused any seedling injury (Figs. 1 to 3). In fact, seed-row-applied ZnSO₄ applied in 2000 resulted in a 14% increase in plant population 14 days after planting (DAP) as compared to no Zn application (Fig. 1). Four days later (18 DAP), plant population in the check plots had increased to the same level as that in plots receiving seed-row-applied Zn, indicating that the increased Zn availability in the seed row caused sugar beet seedlings to emerge more quickly than when no Zn was added. Plant population was reduced substantially (27%) 20 DAP by heavy rain that buried small seedlings with soil. Though differences among treatments were not significant, the next time plant population was evaluated (56 DAP), the trend suggests that more seedlings survived the rain event with seed-row-applied Zn than with other treatments (Fig. 1). Enhanced Zn availability during germination and emergence likely resulted in larger, more vigorous seedlings that were better able to re-emerge from the crusted soil than where Zn availability was less.

Zinc application did not enhance plant population in 2001 (Fig. 2). Both seed-row application of ZnEDTA and broadcast application of Zn plus B, Fe, and Mn appear to have caused a 14% decrease in plant population compared to plots receiving no Zn, but there is no obvious explanation for this observation. Soil test Zn levels (Table 1) were higher at the 2001 site (1.7 ppm) than at the 2000 and 2002 sites (1.0 and 0.8 ppm, respectively) and likely explain the lack of response to seed-row-applied ZnSO₄ in 2001. However, evaluation of stand density was delayed in 2001 compared to the other two study years and may have been too late to reveal any differences in emergence. In 2000, the treatment effect was observed at 14 DAP, but was no longer apparent at 18 DAP (Fig. 1). By the time plant population was first evaluated in 2001 (21 DAP) the response may have already disappeared.

The beneficial effect of added Zn was again apparent in 2002, when seed-row and broadcast applications resulted in higher plant populations compared to plots receiving no Zn (Fig. 3). This effect was somewhat delayed in 2002 compared to the previous two years as indicated by the low and uniform plant population values observed at 16 DAP. Germination was delayed substantially by a brief cold period immediately following planting when daytime temperatures were 20°F below normal and nighttime temperatures were 20°F below freezing. Once soil temperatures warmed again, emergence proceeded and was near completion by 23 DAP, when the beneficial effect of Zn was observed.

Summary and Conclusions

Application of Zn materials to sugar beet grown on a calcareous soil with marginal Zn availability resulted in increased root and sugar yield in one of three years and when averaged across years. Seed-row application of Zn at 2 lb/acre as ZnSO₄ produced root and sugar yields that were consistently among the highest observed, while both broadcast and foliar application of Zn plus B, Fe, and Mn produced more sporadic results. When averaged over the 3-yr period, seed-row-applied Zn produced a root yield increase of 2.8 tons/acre (11%) and a sugar yield increase of 983 lb/acre (12%) compared to plots (check) that did not receive any Zn application. Seed-row-applied ZnSO₄ also enhanced emergence of sugar beet seedlings in two of three years, while broadcast Zn, whether alone or with other micronutrients, did not consistently affect plant population. The following conclusions were drawn from the results of this study:

1. Zinc sulfate may be safely applied to sugar beets in the seed row at up to 6 lb/acre (Zn at 2 lb/acre) on fine-textured soils with adequate soil moisture during germination.

2. Zinc availability in calcareous soils with marginal soil test Zn levels may limit growth during germination and early growth stages of sugar beets. Application of Zn in the seed row may be beneficial under these circumstances.

3. Broadcast and foliar applications of Zn plus B, Fe, and Mn produced positive, but inconsistent results and are not recommended unless deficiencies clearly exist or until further research establishes their efficacy.

While results from this single location are inadequate to justify altering current fertilizer management guidelines for sugar beet, they do provide reason for further investigation of the use of Zn in particular, and micronutrients in general, for enhancing early growth of sugar beet seedlings under both normal and stressed conditions.

Acknowledgments

Funding for this research was provided by the Western Sugar-Grower Joint Research Committee. The authors also wish to recognize staff at the University of Wyoming Powell Research and Extension Center for invaluable assistance in implementation and management of the experiment.

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