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Banded Phosphorus Effects on Alfalfa Seedling Growth and Productivity After Temporary Waterlogging

^a Dep. of Horticulture and Crop Science, 2021 Coffey Rd., The Ohio State Univ., Columbus, OH 43210-1086 USA

sulc.2{at}osu.edu

	ABSTRACT

TOP NOTES ABSTRACT INTRODUCTION Materials and methods Results and discussion Conclusions REFERENCES

 
Phosphorus applied in a band below alfalfa (Medicago sativa L.) seed can increase seedling growth. A field study was conducted to evaluate the effect of banded-P and temporary flooding stress on alfalfa seedling growth in the autumn and subsequent productivity. Experiments were seeded in late August 1994 and 1995 at two locations in Ohio on soils having P levels typical for the region. Fertilizer treatments included no fertilizer P and 27 kg P ha^-1 (62 kg P₂O₅ ha^-1) banded under the seed. Flooded and unflooded treatments were imposed 21 to 26 d after seeding. Flooding was maintained for 11 to 18 d, then plots were allowed to drain naturally. Before flooding was imposed, banded-P increased seedling dry weight by an average of 60%. Flooding reduced seedling dry weight regardless of P treatment. At end of the flooding period, seedlings with banded-P were larger than the flooded, no-P controls at three of the four locations. In November, flooded seedlings with banded-P had greater root dry weight at two locations and greater shoot dry weight at one location compared with the flooded, no-P controls. Flooding in the autumn reduced dry matter yield the next year at two locations. In 1995, banded-P increased yield the year after seeding 15% in the unflooded treatment at one location and 15% in the flooded treatment at the other location. Although banded-P increased seedling growth in the autumn regardless of flooding treatment, its effect on stand density and yield the year after establishment was minimal.

Abbreviations: NSC, nonstructural carbohydrates

	INTRODUCTION

TOP NOTES ABSTRACT INTRODUCTION Materials and methods Results and discussion Conclusions REFERENCES

 
ALFALFA is best adapted to well-drained, fertile soils. This requirement limits its production potential on a relatively large number of soils that do not meet those criteria (Lowe et al., 1972). While low fertility can often be corrected by the use of lime and fertilizer, excess soil moisture is much more difficult to rectify (Alva et al., 1985). In addition, a large proportion of annual rainfall in the midwestern U.S. occurs in the spring and autumn, precisely when new alfalfa stands are being established. This often results in temporarily waterlogged soils, especially in low-lying fields or low areas within a field. Excess soil moisture can profoundly affect the establishment and persistence of alfalfa stands.

Waterlogging reduces the growth of alfalfa seedlings (Fick et al., 1988), a direct result of hypoxic conditions in the rhizosphere (Noble and Rogers, 1994). Barta (1980) found that 7 d of flooding reduced both root and shoot dry weight of alfalfa by 60% in comparison with an unflooded control. Similarly, Thompson and Fick (1981) reported that 20 d of flooding reduced alfalfa root dry weight by 80% and shoot dry weight by 35%. A reduction in the seedling growth rate during establishment can lead to less vigorous stands with a higher incidence of seedling mortality (Sheard et al., 1971).

Phosphorus is an important nutrient for alfalfa seedling development. Several investigators have demonstrated that a band of P fertilizer placed directly below the seed is an efficient method of providing plant-available P to developing alfalfa seedlings, resulting in increased growth rates during the early establishment phase and in some cases increased seedling survival (Brown, 1959; Haynes and Thatcher, 1951; Henderlong, 1961; Robinson et al., 1959; Sheard et al., 1971; Tesar et al., 1954). Despite this benefit to early seedling growth, banded-P has not been shown to affect consistently alfalfa yield the year following establishment. Carmer and Jackobs (1963) reported that yield increases from banded-P were dependent upon environmental conditions following seeding. For example, under hot and dry conditions, a yield advantage from banded-P was observed; however, no increase in yield was observed under conditions favoring rapid seedling growth. The variable effect of banded-P on yield and seedling survival seen in past research may also have been the result of differing soil fertility levels. Because soil fertility was not adequately documented in many past studies, definitive conclusions cannot be drawn.

Sheard et al. (1971) concluded that slow development of forage species during establishment makes seedlings more vulnerable to death when environmental stresses are present. It is reasonable to predict that larger, more developed alfalfa seedlings resulting from increased P nutrition may be better able to withstand excess soil-moisture stress during establishment. Rapid seedling growth is especially critical for late summer seedings. Because the interaction of P nutrition on alfalfa seedling response to waterlogging stress has not been investigated, this study was designed to evaluate the effect of banded-P on alfalfa seedling growth in the autumn and subsequent productivity after temporary flooding stress on soils having P levels typical to the greater Ohio region.

	Materials and methods

TOP NOTES ABSTRACT INTRODUCTION Materials and methods Results and discussion Conclusions REFERENCES

 
Field experiments were established in late August 1994 at The Ohio State University in Columbus (40°00' N, 83°00' W), and at the Ohio Agricultural Research and Development Center (OARDC) in Wooster (40°25' N, 81°75' W). In 1995, experiments were again seeded in late August at Wooster and at OARDC's Western Branch Research Center near South Charleston (39°45' N, 83°45' W).

The experimental sites were selected to provide variation in soil type and represent the soil P levels commonly found in Ohio. The soil at Columbus and S. Charleston was Crosby silt loam (fine, mixed, mesic Aeric Ochraqualfs). The soil at Wooster for both years was a Wooster-Riddles silt loam (fine-loamy, mixed, mesic Typic Fragiudalfs and fine-loamy, mixed, mesic Typic Hapludalfs). Initial soil samples were taken before planting at each site with a 2-cm diam. probe by randomly collecting 20 samples (depth = 15 cm) across the experimental area. The soil cores at each site were composited and a subsample was dried, ground, and analyzed to determine soil fertility status. Soil pH was determined on a 1:1 soil-to-water extract, P was determined using Bray P-1 extraction, and K was determined using ammonium acetate extraction. At the Wooster 1994 location, 240 kg K ha^-1 (290 kg K₂O ha^-1) was applied before seeding. At S. Charleston, 93 kg K ha^-1 (112 kg K₂O ha^-1) was broadcast uniformly in early April 1996.

The previous crop at the Wooster location for both the 1994 and 1995 trials was oat (Avena sativa L.). Seedbed preparation at the Wooster location in both years included plowing, disking, and cultimulching. Cabbage (Brassica oleracea L.) was the previous crop at the Columbus location and tillage included plowing, disking, and cultimulching. The 1995 seeding at S. Charleston was preceded by soybean (Glycine max L. Merr) and seedbed preparation included chisel plowing in the fall and disking and cultimulching prior to seeding. Seedbeds at all locations were firm, but fine with minimal surface residue.

All plots were band-seeded using an 8-row drill with press wheels. `WL 323' alfalfa, which is highly resistant to phytophthora root rot (Phytopthora megasperma Drechs. f. sp. medicaginis T. Kuan and D.C. Erwin) and resistant to aphanomyces (Aphanomyces euteiches Drechs.), was seeded at 16.8 kg ha^-1 in rows spaced 15 cm apart. The seed was inoculated with Rhizobium meliloti Dangeard and treated with metalaxyl [N-(2,6-dimethylphenyl)-N-(methoxyacetyl)-alanine methyl ester] before planting. Seeding depth was 0.5 to 1.0 cm. Plot size was 3.1 by 6.1 m. The plots were divided lengthwise; one-half of the plot was used for plant sampling and the other half was harvested for forage yield the year after seeding. A randomized complete-block design in a split-plot treatment arrangement with four replications was used. Whole plot treatments were flooded and unflooded (natural precipitation). Split-plot treatments were no-P fertilizer added and 27 kg P ha^-1 (62 kg P₂O₅ ha^-1) banded 4 to 5 cm below the seed. Triple superphosphate fertilizer was used. Plots were irrigated as needed to ensure uniform and timely germination and emergence.

Common purslane (Portulaca oleracea L.) was controlled in the 1994 seeding at Columbus, before the flooding treatment was imposed, using 2,4-DB [4-(2,4-dichlorophenoxy) butanoic acid] at 0.84 kg a.i. ha^-1. At Wooster in 1995, volunteer oat was controlled before flooding with sethoxydim [2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one] at 0.24 kg a.i. ha^-1. After flooding, 2,4-DB was applied at 1.68 kg a.i. ha^-1 for control of common lambsquarter (Chenopodium album L.). At S. Charleston, common chickweed (Stellaria media L.) was controlled using imazethapyr [(±)-2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-5-ethyl-3-pyridinecarboxylic acid] at 0.07 kg a.i. ha^-1 in the spring following establishment.

The flooding treatment was imposed by placing trickle irrigation tubing between each row of alfalfa in the flooded plots. Water flow was regulated to keep the soil saturated and allow some ponding on the soil surface. A 3-m border between flooding treatments and a series of diversion ditches ensured that unflooded plots did not receive moisture from the flooded areas. Flooding was initiated in the 1994 seedings when the seedlings had reached the 7th to 8th trifoliolate leaf stage (26 d after seeding, 20 September 1994) at Columbus and the 4th to 5th trifoliolate stage (27 d after seeding, 15 September 1994) at Wooster. The duration of flooding was based on the visible plant damage symptoms in the flooding treatment. Symptoms included chlorosis, cupping of the leaves, and stunted growth. Plants were flooded for 15 d at Wooster and 18 d at Columbus in 1994. Flooding was initiated in the 1995 seedings when seedlings were in the 2nd to 3rd trifoliolate leaf stage at both Wooster (21 d after seeding, 13 September 1995) and S. Charleston (27 d after seeding, 25 September 1995). Flooding was maintained for 11 d at Wooster and 17 d at S. Charleston.

The following parameters were evaluated: (i) root and shoot dry weight, (ii) stand density, (iii) plant heaving, (iv) forage yield the year after establishment, and (v) root nonstructural carbohydrate (NSC) concentrations. In addition, a sample of plants representing all plots for a given location and year were sent to The Ohio State University Extension Plant and Pest Diagnostic Clinic in Columbus for phytophthora root rot testing using the ELISA test (Agri-Screen Phytophthora Detection Kit, Neogen Corp., Lansing, MI).

Plants were harvested for root and shoot dry weight immediately before flooding, 2 to 3 d after flooding, and in late autumn near the time of a killing frost (about 7 wk after the termination of flooding). Autumn sampling dates at Wooster in 1994 were 15 September, 5 October, and 18 November. Plots at Columbus in 1994 were sampled on 19 September, 13 October, and 28 November. Sampling dates for the Wooster 1995 seeding were 13 September, 27 September, and 17 November. For the 1995 seeding at S. Charleston, samples were taken 25 September, 16 October, and 14 November. Whole plants with their roots encased in soil were carefully dug from three to four randomly chosen areas within each plot, placed on screens, and carefully washed. After washing, whole plant samples were placed on ice for transport to the lab where they were separated at the junction of the crown and taproot. The shoots were dried in a forced-air oven at 60°C for 3 to 4 d and the roots were freeze-dried for 3 to 5 d. Root and shoot dry weight were expressed on a per plant basis.

Stand density was measured before flooding in the seeding year and the following year after the last harvest. Plants were counted in 1.22 m of row at two randomly chosen areas within each subplot. Linear plant counts were converted to an area basis for analysis and presentation. Winter heaving was assessed when it occurred by visually rating the percentage of plants heaved in each subplot. Plots were harvested four times for forage yield the year after seeding when alfalfa reached the late bud to early bloom stage of growth (35-d intervals after the first harvest). The harvest area was 1.1 by 6.1 m. At each harvest, forage was removed with a flail-type mower to a 7-cm stubble height and fresh weight was recorded for each subplot. Forage samples of 600 to 800g fresh wt. were weighed, then dried at 60° C to determine dry matter content.

Root samples for NSC determination were collected after flooding, in late November, and the following spring at 2- to 4-wk intervals up to the day of the first harvest. Roots were dug, placed on ice, and brought back to the lab where they were washed and separated at the crown and 5.1 cm below it. The 5.1 cm upper root section was freeze-dried, ground through a Wiley Mill (Arthur H. Thomas Co., Philadelphia, PA) with a 20-mesh screen and then through a cyclone sample mill (Udy Analyzer Co., Boulder, CO) equipped with a 1-mm screen. Two subsamples (50 mg each) were analyzed for NSC. Free sugars were extracted using 80% (v/v) ethanol. Anthrone assay was used to quantify free sugars (Koehler, 1952). A modified enzymatic method from Smith (1981) was used to determine starch concentration. Total NSC was calculated by addition of total free sugars and total starch, on a dry weight basis.

Analysis of variance was used to test for statistical significance of environments (year-location combinations), treatment effects, and interactions. Flooding and P treatments were considered fixed variables, while years and locations were considered random variables. Separation of P treatment means within flooding treatments was accomplished using LSD. Pearson correlation coefficients were examined to determine the association between NSC concentration in late autumn and forage yield the year after seeding for each experimental site.

	Results and discussion

TOP NOTES ABSTRACT INTRODUCTION Materials and methods Results and discussion Conclusions REFERENCES

 
Data were analyzed and presented by environment (location-year combination) because treatment x environment interactions (P < 0.05) were observed. Differences in soil type, soil fertility (Table 1) , plant stage at onset of flooding, and weather conditions may have contributed to the significant interactions observed in this study. Rainfall was 50 mm below normal for the month following seeding (September) at all locations (Table 2) . For the 1994 seedings at Wooster and Columbus, rainfall in October also was more than 30 mm below normal (Table 2). Although irrigation was used to ensure uniform and timely germination, plots were not irrigated on a regular schedule after emergence. Post-emergence irrigation was used only to facilitate digging of root samples. No appreciable differences in temperature were observed among sites during flooding or within several weeks after the flooding treatments were imposed. Killing frosts (-3° C) occurred in mid-November at both locations in 1994, and in early November at both locations in 1995.

View larger version (50K): [in this window] [in a new window]   Fig. 1 Treatment effects on alfalfa root dry weight in the establishment year. Bars followed by the same letter within the same sampling date, location and year are not significantly different according to

View larger version (48K): [in this window] [in a new window]   Fig. 2 Treatment effects on alfalfa shoot dry weight in the establishment year. Bars followed by the same letter within the same sampling date, location and year are not significantly different according to

Approximately 5 to 7 d after the start of flooding, seedlings in the flooded treatment started to show visible signs of plant injury in the above-ground tissue (chlorosis of the shoots and cupping of the leaves). Root and shoot dry weight averaged over P treatments were reduced by flooding at all harvests in all environments, except for root dry weight after flooding at S. Charleston in 1995 and shoot dry weight in late autumn at Columbus in 1994 (Fig. 1 and 2). The observation of decreased dry weight for flooded plants is in general agreement with the results obtained by other researchers (Barta, 1980; Cameron, 1973; Heinrichs, 1972; Rai et al., 1971; Thompson and Fick, 1981; Yu et al., 1969).

Flooded seedlings established with banded-P had greater dry weight than the flooded, no-P controls at the termination of flooding at all locations, except Columbus (Fig. 1 and 2). The advantage of P-banding in the flooded treatment continued to be observed in late autumn at S. Charleston for both root and shoot dry weight, and at Wooster in 1995 for root dry weight. In several cases, flooded seedlings with banded-P had similar or greater dry weight than the unflooded control seedlings without banded-P. Such was the case right after flooding at Wooster and S. Charleston in 1995 (Fig. 1 and 2). This trend continued until late autumn at S. Charleston but not at Wooster.

A flooding x P treatment interaction for root dry weight after flooding and in late autumn was observed only for the Wooster 1995 location (Fig. 1). For shoot dry weight, flooding x P treatment interactions were observed after flooding and in late autumn at S. Charleston, and in late autumn at Wooster in 1995 (Fig. 2). Those interactions were primarily due to differences in the magnitude of the P-banding response within flooding treatments.

In summary, banding P directly below alfalfa seed resulted in larger seedlings at the onset of flooding. Shoot and root dry matter accumulation continued during flooding in both the flooded and unflooded treatments, and at the end of flooding, the seedlings established with banded-P still had greater dry weight than the no-P controls, except at Columbus where soil P levels were very high. Banded-P continued to show a benefit for root dry weight of flooded seedlings in late autumn at both locations in 1995, but not in 1994.

Performance the Year After Seeding
Late winter heaving of alfalfa plants was observed at all locations except Columbus. Severe heaving in late February 1996 at Wooster resulted in total stand death. This was a widespread phenomenon observed in alfalfa fields across Ohio that year. Even established alfalfa stands, regardless of age, suffered severe frost heaving on soil types similar to those found at the Wooster site. Flooding increased heaving at Wooster in 1995 (73% heaved plants in flooded vs. 22% heaved plants in unflooded) and at S. Charleston in 1996 (24% heaved plants in flooded vs. 1% heaved plants in unflooded). Banded-P reduced heaving slightly in the flooded treatment at Wooster in 1995 (65% heaved plants with P vs. 80% heaved plants without P). Banded-P had no effect on heaving at the other locations. Thus, the ability of banded-P to decrease heaving was at best variable in this study, and appears to have little effect under severe heaving conditions like those observed at Wooster in 1996. The effect of banded P on winter heaving may be influenced by environmental conditions following seeding, soil drainage, severity of heaving, type of seeding (no-tillage vs. conventional tillage), root development of the seedling, and snow cover.

Total yield the year after establishment was reduced by flooding the previous autumn at Wooster in 1995 and at S. Charleston in 1996 (Table 3) . Banded-P increased total yield for the unflooded treatment at S. Charleston in 1996 and for the flooded treatment at Wooster in 1995 (Table 3). There was no yield response to banded-P at Columbus. The variable yield response to banded-P in the present study is consistent with the observation of Carmer and Jackobs (1963), who reported that the yield advantage from banded-P was dependent on environmental conditions following seeding.

	Conclusions

TOP NOTES ABSTRACT INTRODUCTION Materials and methods Results and discussion Conclusions REFERENCES

 
Flooding reduced root and shoot dry weight of alfalfa seeded in late summer regardless of P treatment. Banding P under the seed at establishment did not eliminate the harmful effects of flooding injury in seedling alfalfa, but it did improve seedling growth in both flooded and unflooded treatments at three out of four sites. At two sites, seedlings established with banded-P had greater dry weight after flooding than unflooded seedlings established without banded-P. Although banded-P generally increased root and shoot dry weight of seedlings in the autumn, its effect on heaving, stand density, and yield the year after establishment was minimal and variable, regardless of flooding treatment. Despite the variable response in subsequent productivity to banded-P in this study, banded-P can be advantageous to seedling growth in the autumn. Banded-P did not consistently improve alfalfa establishment under temporary waterlogging and therefore should not be employed solely as a means of protecting against flooding injury, but rather as a way to accelerate plant development in late summer seedings. On soils where P fertilizer is recommended prior to seeding alfalfa, applying at least part of it as a band of P below the seed is a relatively inexpensive and efficient method for ensuring that alfalfa seedlings have the best opportunity for rapid and successful establishment.

	ACKNOWLEDGMENTS

 
We thank Dave Bauerbach, John McCormick, Lee Duncan, and Greg Smith for their technical assistance. We also thank Dr. J.J. Volenec and Dr. V.N. Owens for their helpful advice with the root NSC analyses.

	NOTES

TOP NOTES ABSTRACT INTRODUCTION Materials and methods Results and discussion Conclusions REFERENCES

 
Salaries and research support provided in part by State and Federal funds appropriated to the Ohio Agricultural Research and Development Center, The Ohio State University. Manuscript Number 98-21.

Received for publication December 2, 1998.

	REFERENCES

TOP NOTES ABSTRACT INTRODUCTION Materials and methods Results and discussion Conclusions REFERENCES

 

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This Article Abstract Figures Only Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (3) Citing Articles via Google Scholar Google Scholar Articles by Teutsch, C. D. Articles by Barta, A. L. Search for Related Content PubMed Articles by Teutsch, C. D. Articles by Barta, A. L. Agricola Articles by Teutsch, C. D. Articles by Barta, A. L. Related Collections Forage Management Alfalfa Nutrient Management Seed Production