Agronomy Journal 93:152-157 (2001)
© 2001 American Society of Agronomy
SOIL FERTILITY
Evaluation of Zinc Seed Treatments for Rice
Nathan A. Slatona,
Charles E. Wilson, Jr.b,
Sixte Ntamatungiroa,
Richard J. Normanc and
Danny L. Boothea
a P.O. Box 351, Univ. of Arkansas Rice Res. and Ext. Cent., Stuttgart, AR 72160
b Jr., P.O. Box 3508, Univ. of Arkansas Southeast Res. and Ext. Cent., Monticello, AR 71656
c Dep. of Crop, Soil, and Environ. Sci., Univ. of Arkansas, Plant Sci. 115, Fayetteville, AR 72701
Corresponding author (Nslaton{at}uaex.edu)
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ABSTRACT
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Zinc seed treatments for rice (Oryza sativa L.) were previously evaluated as an alternative to soil-applied Zn. Recommendations concerning the effectiveness of Zn seed treatments were never clearly stated. Our objectives were to evaluate the utility of Zn seed treatments for supplying Zn to rice grown on soils prone to Zn deficiency. In 1998, a study with three cultivars compared Zn-treated seeds [2.8 g Zn (kg seed)-1] with a control and 11 kg Zn ha-1 as ZnSO4 applied to the soil. Because tissue Zn concentration did not differ among cultivars, a single cultivar, Drew, was used in studies at two locations in 1999. The control and the soil-applied Zn were compared with seeds that were treated with three rates of ZnSO4 and ZnEDTA (ethylenediaminetetraacetic acid). Analysis showed net seed concentrations of 1.0, 2.2, and 4.7 g Zn (kg seed)-1 as ZnSO4 and 1.4, 2.8, and 5.7 g Zn (kg seed)-1 as ZnEDTA. In 1998, neither visual Zn deficiency symptoms nor significant yield differences were observed among treatments. Soil-applied Zn and Zn seed treatments increased tissue Zn concentration by 11.9 and 4.7 mg Zn kg-1, respectively, above that of the control (19.7 mg Zn kg -1). In 1999, Zn deficiency occurred at both locations. Measurements of dry matter, tissue Zn concentration, and grain yield showed that Zn-treated seed performed equal to or better than soil-applied Zn. These data suggest that seed Zn concentrations between 2.2 to 5.7 g Zn (kg seed)-1 are an economical alternative to soil-applied Zn.
Abbreviations: ICAP, inductively coupled Ar plasma spectrophotometry • PPI, preplant incorporated • PTBS, Pine Tree Branch Station • RREC, Rice Research and Extension Center • TDM, total dry matter
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INTRODUCTION
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ZINC SEED TREATMENTS WERE EVALUATED in rice as an alternative to soil- or foliar-applied Zn by several researchers in the early 1970s with limited success (Haghighat and Thompson, 1982; Giordano and Mortvedt, 1973; Mengel et al., 1976; Rush, 1972). Due to the limited amount of research, Zn seed treatments for rice and recommendations concerning their effectiveness were never clearly stated. Despite the lack of formal recommendations, Zn-treated seed rice is available throughout the southern USA rice-growing area. Literature concerning the efficacy of micronutrient fertilizer applications to crop seeds is limited. Rasmussen and Boawn (1969) determined that Zn seed treatment alone was not effective in preventing Zn deficiency of kidney beans (Phaseolus vulgaris L.). Yilmaz et al. (1997) also concluded that soil-applied Zn was a superior fertilization method compared with Zn-treated wheat (Triticum aestivum L.) seed or foliar Zn applications. Other studies have found that the application of Zn to seeds has either failed to prevent Zn deficiency or reduced emergence (Martens and Westermann, 1991). These studies have not investigated a complete range of Zn seed treatment rates and sources to compare with standard soil or foliar Zn fertilization methods.
Martens et al. (1973) concluded that band application of Zn fertilizer in contact with the corn (Zea mays L.) seeds at rates ranging from 0.34 to 1.34 kg Zn ha-1 produced grain yields equal to those achieved when 26.9 kg Zn ha-1 as ZnSO4 was broadcast on the soil surface and incorporated before planting. Earlier research with rice (Haghighat and Thompson, 1982; Giordano and Mordvedt, 1973; Mengel et al., 1976; Rush, 1972) also suggested that the application of low rates of Zn to rice seeds or dipping the roots of transplanted rice in a Zn solution may be effective alternatives to broadcast applications of Zn fertilizer.
In Arkansas, Zn fertilizer recommendations for rice are currently based on the soil pH and texture. Zinc is recommended for rice, regardless of soil test Zn levels, grown on silt and sandy loam soils having a pH >6.5. Sedberry et al. (1980) and Wells (1980) both found the soil pH to best predict rice response to Zn fertilization during the early 1970s. However, much of this research was conducted before the widespread use of Zn fertilizers. Since the development of Zn fertilizer recommendations, the low native soil Zn concentrations have increased appreciably due to repeated broadcast applications of inorganic Zn sources to each rice crop. Subsequently, the frequency of both Zn deficiency symptoms and documented rice yield responses to Zn fertilization has declined (Slaton et al., 1995; Thompson and Kasireddy, 1975). Until a critical soil test Zn level for Zn fertilizer recommendations is established, alternative methods of supplying Zn to the rice crop on high-pH soils are being investigated.
Because the application of small amounts of Zn to rice seeds would be more economical and convenient than either soil or foliar applications, our objectives were to evaluate the effect of Zn seed treatments on the dry matter production, tissue Zn concentration, and grain yield of rice in comparison with the standard recommendation of broadcast soil applied Zn. A secondary objective of our studies was to determine the effect of Zn seed treatment on germination and the lengths of the radicle and coleoptile.
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Materials and methods
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A preliminary field study was conducted at the Rice Research and Extension Center (RREC) near Stuttgart, AR (34.30° N lat) during 1998 on a DeWitt silt loam (fine, smectitic, thermic, Typic Albaqualfs) that had received 4480 kg ha-1 lime (CaCO3) in 1996. Rice grown in this field in 1997 exhibited Zn deficiency symptoms after flood application. Soil samples collected before seeding were analyzed for extractable cations (including Zn2+) by Mehlich 3 extraction (Mehlich, 1984). Soil pH was determined in a 1:2 soil water suspension with a glass electrode. Selected soil chemical properties are listed in Table 1.
Seeds of the rice cultivars `Cypress', `Drew', and `Jefferson' that were treated with either Vitavax (Carboxin) (5,6-dihydro-2 methyl-N-phenyl-1,4-oxathiin-3-carboxamide) or Vitavax plus Zn (Zn Starter, Agtrol Chem., Houston, TX) (J. Garrett, personal communication, 1998) were obtained from Garrett Seed Farms (Danbury, TX). An elemental analysis of the Zn-treated seeds indicated a net concentration of 2.8 g Zn (kg seed)-1 (0.34 kg Zn ha-1). Zinc-treated seeds were compared with seeds that received no Zn seed treatment but were fertilized with either 0 or 11 kg Zn ha-1 (ZnSO4-31% Zn, Tetra Micronutrients1, The Woodlands, TX) applied to the soil and preplant incorporated (PPI). Rice was seeded on 23 June at a rate of 120 kg ha-1 in plots consisting of nine rows that were 4.88 m long and spaced 17.8 cm apart.
In 1999, studies were conducted at the RREC on a DeWitt silt loam and at the Pine Tree Branch Station (PTBS) near Colt, AR (35.08° N lat) on a Calloway silt loam (fine-silty, mixed, thermic, Glossaquic Fragiudalfs). Selected soil chemical properties are listed in Table 1. Because 1998 experiments failed to show Zn deficiency symptoms, 2240 kg ha-1 lime was applied at the RREC. Soil Ca and Mg levels were higher at the PTBS location, so lime was not applied. Split applications of 68 kg P ha-1 were made at both locations before seeding and again before establishment of the permanent flood to enhance the likelihood of Zn deficiency. Potassium fertilizer was broadcast across all treatments as needed according to soil analysis.
The cultivar Drew was seeded at the RREC and PTBS on 20 May and 22 April, respectively. Rice was seeded at a rate of 120 kg ha-1 in plots consisting of nine rows that were 4.88 m long and spaced 17.8 cm apart. The treatments included an untreated control, 11 kg Zn ha-1 PPI (as previously described), and six treatments with different amounts of Zn applied to seeds. Zinc was applied to seeds at three rates using either a ZnSO4 solution or liquid 9% ZnEDTA chelate (wt./wt.). The ZnSO4 solutions were prepared by dissolving 100, 200, or 400 g of reagent grade ZnSO4 · 7H2O in 1 L of H2O. The seeds were then treated by mixing 113.5 g of seeds with 7.5 mL of the ZnSO4 solution. For the EDTA treatment, 113.5 g of seeds was mixed with a total volume of 100 mL of EDTA solution of which 25, 50, or 100 mL was 9% ZnEDTA (wt./wt.).
To determine the amount of Zn coated on the seeds, treated and untreated seeds were digested with HNO3 and 30% H2O2 (wt./wt.) (Jones and Case, 1990) and analyzed by inductively coupled Ar plasma spectrophotometry (ICAP) (Soltanpour et al., 1996). Seed analysis showed a net Zn coating content of 1.0 (0.12 kg Zn ha-1), 2.2 (0.26 kg Zn ha-1), and 4.7 g Zn (kg seed)-1 (0.56 kg Zn ha-1) as ZnSO4 and 1.4 (0.17 kg Zn ha-1), 2.8 (0.34 kg Zn ha-1), and 5.7 g Zn (kg seed)-1 (0.68 kg Zn ha-1) as ZnEDTA. Therefore, approximately one-half of the added Zn was retained on the seeds.
For all studies, 150 kg N ha-1 was applied as urea [(NH2)2CO] to the dry soil surface immediately before flooding at the 4-leaf growth stage. Plant samples were collected 14 d after flooding by removal of the aboveground plant tissue in a 0.9-m row section of the second inside row. The tissue samples were immediately washed in deionized water, 0.1 M HCl, and rinsed in deionized water before drying to remove possible sources of contamination (Wells, 1980). The samples were dried at 60°C to a constant weight, weighed, and ground in a Wiley mill to pass a 2-mm sieve. The ground tissue (0.5-g subsample) was digested with concentrated HNO3 and 30% H2O2 (wt./wt.) for determination of the whole plant elemental composition (Jones and Case, 1990). An elemental analysis of the plant digests was performed by ICAP (Soltanpour et al., 1996). At maturity, 2.6 m2 from the center four rows of each plot was harvested for grain yield with a small plot combine. The reported grain yields were adjusted to 120 g kg-1 of moisture.
The treatments were arranged as a randomized complete block, 3 (cultivar) x 3 (Zn fertilizer treatments) factorial design with four replications in 1998. During 1999, each location was arranged in a randomized complete block with four replications. A split-plot analysis was used where location was the whole-plot factor and Zn fertilizer treatment was the subplot factor. All data were analyzed using the PROC GLM procedure of SAS. Differences among treatments were identified using Fisher's protected LSD test at the 0.05 or 0.10 significance level.
Seed Viability
To evaluate the effect of Zn seed treatment on seed viability, treated and untreated seeds from 1999 field studies were placed in a germinating chamber at 20°C, approximately 8 mo after treatment. Seeds were stored in paper envelopes at room temperature during this period. Fifty seeds from each treatment were placed in a petri dish, and 3 mL of deionized water was added to each dish. Each treatment was replicated three times. The germination of seeds was checked at 6, 8, and 10 d. A seed with a visible radicle or coleoptile was counted as germinated. Germination data are reported as the percent of seeds germinated. At the 10-d measurement, the emerged radicle and coleoptile of 10 randomly selected germinated seeds were measured from each treatment replicate.
The treatments were arranged as a randomized complete block design with three replications. All data were analyzed using the PROC GLM procedure of SAS. Differences among treatments were identified using Fisher's protected LSD test at the 0.05 significance level.
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Results and discussion
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1998 Experiment
The total dry matter (TDM) production, harvest grain moisture, and grain yield of rice were not significantly affected by Zn fertilizer treatment or the cultivar x Zn fertilizer treatment interaction but were significantly different among cultivars (Table 2). The lack of differences among the Zn fertilizer treatments suggested that rice was not Zn deficient and would not show a significant yield and growth response to Zn fertilization. Although not statistically significant at the 0.05 level of probability (P = 0.16), the grain yield for both 11 kg Zn ha-1 PPI and 2.8 g Zn (kg seed)-1 was 214 and 360 kg ha-1 greater than the control, respectively, when averaged across the cultivars (Table 3).
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Table 2 Effect of rice cultivar on grain yield, total dry matter (TDM), and harvest moisture averaged across Zn treatments during 1998 at the Rice Research and Extension Center (RREC), near Stuttgart
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Table 3 Effect of Zn fertilizer treatment, averaged across cultivars, on grain yield and tissue Zn concentration of seedling rice 14 d after flooding during 1998 at the Rice Research and Extension Center (RREC), near Stuttgart
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The tissue Zn concentration of whole-plant seedlings 14 d after flooding did show significant differences between Zn fertilizer treatments (Table 3). The tissue Zn concentration followed the highest-to-lowest order of 11 kg Zn ha-1 PPI > 2.8 g Zn (kg seed)-1 > control. Rasmussen and Boawn (1969) suggested that Zn seed treatment of kidney bean was not an adequate alternative to broadcast Zn fertilizer applications to the soil because Zn deficiency symptoms occurred, and Zn seed treatment failed to produce yields equal to soil Zn application. Based on the 1998 tissue concentration data, 11 kg Zn ha-1 PPI was superior to 2.8 g Zn (kg seed)-1 for supplying Zn to seedling rice plants. However, both treatments increased tissue Zn in rice seedlings above the level considered deficient (20 mg kg-1) while the control was near the critical threshold (Sedberry et al., 1987). Although Zn tissue concentration data were a useful means of evaluation, the effectiveness of Zn seed treatments can best be made under Zn deficient conditions.
1999 Experiments
Zinc deficiency symptoms similar to those described by Sedberry et al. (1978) were observed at both locations in 1999. The symptoms were most severe in the control plots while few or no symptoms were observed in the 4.7 g Zn (kg seed)-1 as ZnSO4 and 5.7 g Zn (kg seed)-1 as ZnEDTA plots. The deficiency symptoms were most severe at the RREC. Thus, the response of the rice TDM among Zn treatments differed between locations for some treatments (Table 4). The rice TDM response at each location was indicative of the degree of Zn deficiency symptoms expressed among Zn treatments at each location.
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Table 4 Effect of Zn seed treatment source and rate on rice total dry matter (TDM) by 14 d after flooding compared with an untreated and standard check at two locations in 1999
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At the PTBS, seeds that were treated with Zn produced significantly greater TDM by 14 d after flooding than both the control and 11 kg Zn ha-1 PPI, regardless of the Zn source or rate. It is unclear why Zn deficiency symptoms occurred in the 11 kg Zn ha-1 PPI treatment. The random occurrence of deficiency symptoms within each 11 kg Zn ha-1 PPI plot suggests that uniform fertilizer distribution at the applied rate could not supply the plants that were physically located between fertilizer granules with adequate Zn nutrition. Both the control and 11 kg Zn ha-1 PPI treatments recovered from the early Zn deficiency symptoms within 14 d after plant samples were taken. Within the Zn seed treatments, the TDM tended to increase as the Zn application rate increased.
At the RREC, the TDM for 11 kg Zn ha-1 PPI was significantly greater than the control, 1.0 g Zn (kg seed)-1 as ZnSO4, and 1.4 g Zn (kg seed)-1 as ZnEDTA treatments and equal to all other treatments. Stand loss occurred in two of four replications of the control plots at the RREC and resulted in a significantly lower TDM than the control at the PTBS. The only other treatments that showed significant differences between locations were the 11 kg Zn ha-1 PPI and 1.4 g Zn (kg seed)-1 as ZnEDTA treatments. It is unclear why the 11 kg Zn ha-1 PPI treatment responded differently between the two locations. The 1.4 g Zn (kg seed)-1 as ZnEDTA and 1.0 g Zn (kg seed)-1 as ZnSO4 treatments apparently contained insufficient Zn to maximize plant growth at the RREC. Based on the TDM data from both locations, Zn seed treatments should be applied at rates between 2.2 and 5.8 g Zn (kg seed)-1 for optimum growth under Zn deficient conditions, with the higher rate being preferred.
The tissue Zn concentration also showed a significant Zn fertilizer treatment x location interaction (Table 5). The general response of the tissue Zn concentration among Zn fertilizer treatments was similar to that found for the TDM. Comparison of data in Tables 4 and 5 reveals that the treatments at each location with the lowest tissue Zn concentrations also tended to produce the lowest TDM. The fact that Zn seed treatments increased the TDM and tended to increase the tissue Zn concentrations, and thus the total Zn uptake, suggests that Zn-treated seeds are capable of supplying sufficient Zn to maximize plant growth under conditions of Zn deficient soil. The total Zn uptake by rice at maturity is approximately 0.5 kg ha-1, and crop removal accounts for about one-half of the total Zn uptake (unpublished data, 1997). The application of Zn rates that are equal to the total crop uptake should be adequate to supply the crop nutritional requirements if the uptake of fertilizer Zn is highly efficient. Broadcast fertilizer applications made to the soil are about 20 times the total Zn requirement of rice.
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Table 5 Effect of Zn seed treatment source and rate on rice tissue Zn concentration by 14 d after flooding compared with an untreated and standard check at two locations in 1999
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The grain yield was significantly affected only by Zn fertilizer treatment, and thus was averaged between locations (Table 6). All of the treatments with Zn-treated seeds or 11 kg Zn ha-1 PPI produced significantly higher yields than the control. All of the Zn seed treatments produced yields that were similar to the standard recommendation of 11 kg Zn ha-1 PPI. The control also had the highest grain moisture at harvest, indicating that the application of Zn enhanced maturation, and thus normal crop growth and development (Table 6). Grain harvest moisture is not a parameter that is commonly reported to evaluate fertility treatments, except when the degree of maturation is important. When the Zn deficiency of flood-irrigated rice is uncorrected, as in the control of these studies, stand loss may occur, plant maturity may be delayed, or both. This can result in additional production costs and reduced milling (quality) and grain yields. Thus, harvest moisture provides valuable information concerning the effectiveness of treatments to supply the Zn that is required for normal plant growth, development, and grain production.
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Table 6 Effect of Zn seed treatment source and rate on rice grain yield and harvest grain moisture compared with an untreated and standard check in 1999 (data averaged across two locations)
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Rush (1972) found significant increases in rice grain yield from Zn seed treatments but also observed that some Zn products and application rates were toxic and reduced stand density. Rasmussen and Boawn (1969) also noted a delay in the germination and emergence of kidney bean as well as reduced seedling vigor for from some Zn seed treatments. Plant population measurements were not made in our field studies, but no visual differences were noticed among the treatments. However, germination data from seeds used in these tests did suggest that Zn seed treatments could influence stand establishment (Table 7). Although the seed germination among treatments by 6 d was not significant, the general order of germination established by 8 d was evident. By 8 d, the germination of untreated seeds was significantly lower than all of the Zn-coated seed treatments. By 10 d, the germination of untreated seeds and the 5.7 g Zn (kg seed)-1 as ZnEDTA treatment was lower than all other treatments, which were not different. The decrease in the germination of seeds treated with ZnEDTA was likely due to fungal growth. Fungal growth completely covered some ZnEDTA-treated seeds by 10 d, and thus hid the radicle or coleoptile from view. The trend for the percent germination to decline as the ZnEDTA rate increased was representative of the increased fungal growth. Despite the good initial germination of seeds treated with ZnEDTA, the potential may exist for this product to reduce seedling vigor, so it should be further evaluated before being used as a Zn seed treatment.
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Table 7 Effect of Zn seed treatment on rice seed germination, radicle length, and coleoptile length approximately 8 mo after zinc application
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Radicle and coleoptile measurements were made only on germinated seed at 10 d (Table 7). The radicle length of untreated seeds was greater than that of all of the treatments, except the 1.0 g Zn (kg seed)-1 as ZnSO4. The radicle length tended to decrease as the Zn rate increased, suggesting that Zn may inhibit radicle elongation. The coleoptile length was different only for seeds that were treated with ZnEDTA. Seeds that were treated with ZnSO4, regardless of the rate, and untreated seeds had significantly longer coleoptiles than seeds that were treated with all rates of ZnEDTA. The coleoptile length of seeds treated with ZnEDTA also tended to decline as the rate increased.
More germination and seedling vigor tests are needed to evaluate the effect of the Zn application rate, Zn source, temperature, and storage time on seed vigor and viability. These preliminary data from the germination chamber illustrate the importance of thorough testing of new recommendations, especially when stand failure is a potential risk. Although stand establishment problems were not observed in the 1999 field studies with any Zn seed treatment, environmental conditions in future years could favor the development of seedling diseases and stand loss. Growers and seed dealers are encouraged to use Zn seed treatments, but they should use only products that have been tested and deemed safe and effective.
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Summary
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Rice response to Zn fertilization by soil or seed treatment was limited in the 1998 study due to a lack of Zn deficiency. Despite the lack of yield response, the 1998 results showed that Zn seed treatments increased the Zn concentration of rice seedlings and may hold promise as an economical alternative to more expensive broadcast Zn fertilizer applications. Grain yield, tissue Zn concentration, and TDM data generated at two locations in 1999 support the use of Zn-treated seeds as a safe, effective means of fertilizing rice grown on Zn deficient soils. The grain yield was significantly improved by the use of Zn seed treatment compared with the control and was equal to the yield from the standard recommendation of 11 kg Zn ha-1 PPI.
Seeds that were treated with ZnSO4 had a higher germination rate than untreated seeds after an 8-mo storage period. Seeds that were treated with ZnEDTA also tended to germinate better than the untreated seeds, but ZnEDTA encouraged fungal growth and reduced the coleoptile length, thereby reducing vigor as the study progressed. Despite excellent results from field studies for TDM and grain yield, the ZnETDA sources should be avoided due to the potential risks of stand failure. The application of relatively low rates of Zn to rice seeds has potential for substantial cost savings to producers when compared with conventional broadcast soil or foliar Zn fertilization methods. Additional research studies are needed to develop recommendations for the best application rate and Zn source, possible interactions with other seed treatment chemicals, and the detrimental effects that have been observed with Zn seed treatments for the vast number of Zn products that are available. The potential use of Zn seed treatments for other Zn sensitive crops should also be investigated.
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NOTES
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Published with the approval of the director of the Arkansas Agric. Exp. Stn., Manuscript #00004. Research was partially funded by rice grower check-off contributions administered by the Arkansas Rice Research and Promotion Board.
1 Mention of trade names and commercial products in this article is solely for the purpose of providing specific information, does not constitute a guarantee or warranty, and does not signify that these products are approved to the exclusion of comparable products. 
Received for publication February 17, 2000.
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REFERENCES
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- Martens, D.C., and D.T. Westermann. 1991. Fertilizer applications for correcting micronutrient deficiencies. p. 549–592. In J.J. Mordvedt (ed.) Micronutrients in agriculture, 2nd ed.SSSA Book Ser. 4. SSSA, Madison, WI.
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N. A. Slaton, R. J. Norman, and C. E. Wilson Jr.
Effect of Zinc Source and Application Time on Zinc Uptake and Grain Yield of Flood-Irrigated Rice
Agron. J.,
January 1, 2005;
97(1):
272 - 278.
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TOP
ABSTRACT
INTRODUCTION
