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Switchgrass establishment as affected by seeding depth and soil type
Industrial Crops and Products 41 (2013) 289–293
Contents lists available at SciVerse ScienceDirect
Industrial Crops and Products journal homepage: www.elsevier.com/locate/indcrop
Switchgrass establishment as affected by seeding depth and soil type Marisol T. Berti ∗ , Burton L. Johnson Department of Plant Sciences, North Dakota State University, NDSU Dept. 7670, Fargo, ND 58108-6050, USA
a r t i c l e
i n f o
Article history: Received 20 February 2012 Received in revised form 11 April 2012 Accepted 14 April 2012 Keywords: Pure live seed emergence Emergence index Soil texture Depth Dormancy
a b s t r a c t Switchgrass (Panicum virgatum L.) has been identified as a potential bioenergy crop for the North Central Region of the USA. One of the limitations to successful production of switchgrass is poor seedling establishment affected by the interaction between seeding depth and soil physical characteristics. The objective of this study was to determine the effect of seeding depth and soil types on switchgrass seedling establishment in a greenhouse and field experiment. The greenhouse experiment included seven seeding depths (0, 13-, 19-, 25-, 38-, 51-, and 64-mm deep), three soil types, and one cultivar, Dacotah. Soil types for the greenhouse experiment were brought in from three North Dakota State University research sites located at Fargo (silty-clay, 6.1% organic matter (OM)), Prosper (fine-silty, 3.3% OM), and Carrington (coarse loamy, 2.5% OM). The field experiment was conducted at Fargo and Prosper, ND, in 2010, and included four seeding depths (13-, 19-, 30-, and 38-mm deep) and two cultivars Dacotah and Forestburg. Results from the greenhouse experiment indicated pure live seed emergence (PLSE) differed among seeding depths and soil textures. Only the surface seeding (0-mm depth) had a significantly lower PLSE. Seeding depths from 13- to 64-mm depth were not significantly different and fluctuated between 64 and 74% PLSE. The silty-clay soil at Fargo had significantly higher PLSE (74%) across all seeding depths than the fine-silty soil at Prosper, and the coarse-loamy soil at Carrington (60% PLSE). In the field experiment, the Forestburg cultivar had very poor emergence at all seeding depths and environments. The PLSE for ‘Forestburg’ was 10%, from the 13-mm depth averaged across both locations. The PLSE for Dacotah across both locations was 80, 42, 18, and 5% for the 13-, 19-, 30-, and 38-mm depths, respectively. Under controlled conditions (greenhouse experiment), seeding depth was not a major factor affecting seedling establishment except for the surface seeding where the lack of seed and soil contact and surface dryness reduced emergence. Pure live seed emergence and emergence index were greater in the silty-clay soil at Fargo across all seeding depths, presumably due to a better seed–soil contact. Under field conditions, the 13-mm depth had significantly higher PLSE indicating other factors are interacting with the seeding depth. As a general recommendation to growers switchgrass should be seeded no deeper than 13-mm depth. Testing the germination of the seed lot, without stratification, before planting is recommended to better estimate field establishment success. © 2012 Elsevier B.V. All rights reserved.
1. Introduction Switchgrass has been identified as one of the potential lignocellulosic biofuel feedstocks for the north central and southern regions of the USA. As a new crop to these regions development of management guidelines is recommended for successful production of switchgrass. Poor seedling establishment of switchgrass in North Dakota has been a limiting factor for large scale production. Establishment in grasses has two distinct phases: seedling emergence and seedling establishment (development of an adventitious root system) (Newman and Moser, 1988). Suboptimal temperatures when
∗ Corresponding author. Tel.: +1 701 231 6110; fax: +1 701 231 8474. E-mail addresses: [email protected], [email protected] (M.T. Berti). 0926-6690/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.indcrop.2012.04.023
seeded, excessive seeding depth, inadequate soil surface moisture, seed dormancy, small seed size, and low seedling vigor are factors that impact successful seedling establishment of grasses (Newman and Moser, 1988; Aiken and Springer, 1995; Smart and Moser, 1999). Extended or unpredictable seed dormancy in seed grasses is also detrimental for seedling establishment and agronomic success. Switchgrass seed dormancy has been studied extensively (Duclos et al., 2009; Sarath et al., 2006, 2007; Shen et al., 2001); however, reduced stand establishment due to seed dormancy still exists. The mechanisms of seed dormancy in switchgrass are not well understood. Duclos et al. (2009) examined the effect of seed covering layers: lemma, palea, and pericarp, and found that the pericarp was the major layer responsible for dormancy. These seed covering layers may act as a barrier for gas diffusion and/or for the diffusion of inhibitory compounds leaking into the environment.
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M.T. Berti, B.L. Johnson / Industrial Crops and Products 41 (2013) 289–293
Several treatments have been proposed to overcome seed dormancy in switchgrass. A 2-week chilling (stratification) is the most commonly applied treatment to break dormancy in seed testing, followed by determining germination at an alternating 15/30 ◦ C for an additional 14 days (Association of Official Seed Analysts (AOSA), 2010). Unfortunately, laboratory germination test results do not always correlate with field performance since there are many factors that affect seed germination and emergence. Other studies indicate that nitric oxide from the donor sodium nitroprusside, promoted germination of switchgrass CV. Kanlow in alternating light and dark intervals at 25 ◦ C, across a broad range of concentrations (Sarath et al., 2006). Shen et al. (2001) indicated that short-term stratification treatments could successfully overcome dormancy if seeds were not dried and allowed to germinate. Mitchell and Vogel (2012) evaluated the ability of seed quality tests to predict field establishment. Of all test evaluated the best predictor of field establishment was emergence from 4 cm of sand, which had an establishment index that was 3.5 times greater than only using the pure live seed method. Proper seeding depth is also an important factor involved in successful establishment of switchgrass. Newman and Moser (1988) indicated seedling emergence decreased when depth exceeded 30mm. Aiken and Springer (1995) evaluated seeding depths of 5-, 10-, and 20-mm in a sandy and two silty-loam soils. They found no differences in seedling emergence at different depths in the silty-loam soils but a decline in emergence as planting depths increased in the sandy soil. The objective of this study was to determine the effect of seeding depth in different soil types on seedling establishment.
2. Materials and methods 2.1. Greenhouse experiment The greenhouse experiment included six seeding depths (0, 13-, 25-, 38-, 51-, and 64-mm deep), one cultivar, and three soil types brought into the greenhouse from three experiment stations of North Dakota State University, from Fargo, Prosper, and Carrington. Soil texture and chemical composition of three soils were reported in Table 1. The cultivar Dacotah, released in North Dakota in 1989, was used for this experiment. Dacotah is an upland type, winter-hardy, leafy type with high plant vigor and seed yield and reaches anthesis earlier than most upland cultivars. It is shorter in height and has less coarse growth than most lowland types (Sedivec et al., 2011). The experimental design was a RCBD with a factorial arrangement with four replicates and two runs (repetition of the complete experiment). For each run, one hundred seeds of switchgrass were planted in 12-cm diameter pots at each of the desired seeding depths, with each of the three soil types, for each replicate. All pots were watered with the same amount every other day to replenish evaporated water. The pots had perforated bottoms to enable drainage and avoid saturated soil conditions. Seedling emergence was recorded every 3 days for 35 days after starting the experiment, in both runs. Run 1 and 2 were started on February 1 and February 23, respectively, in 2010. Seed germination for ‘Dacotah’ was 58%. This germination was obtained in our laboratory by germinating 100 seeds, replicated 3 times, in Petri dishes with a filter paper, at 20 ◦ C for 14 days without previous stratification. This germination was used to calculate pure live seed. Pure live seed emergence and was determined by the following formulas, seed purity used was 100% (AOSA, 2010): PLS (%) =
purity (%) × germ (%) 100
(1)
PLSE (%) =
nse × 100 (nsp × PLS (%))/100
(2)
PLS is the pure live seed; purity (%) the seed lot purity, 100% was used; germ (%) the percent germination of seeds planted; nse the number of seeds emerged; nsp the number of seeds planted and PLS planted is the number of pure live seed planted. The emergence index (EI) was determined for the germination period according to the formula: EI = a1
1 xi
+ · · · + ˛n
1 xn
(3)
where a is the number of seeds with exposed coleoptile each day, xi is the number of days after initial emergence of coleoptile, and xn is the last day of emergence (Anfinrud and Schneiter, 1984). 2.2. Field experiment The field experiment was conducted at Fargo and Prosper, ND, in 2010, and included four seeding depths (13-, 19-, 30-, and 38-mm deep) and two cultivars Dacotah and Forestburg. The Forestburg cultivar is an upland type released in 1987 in South Dakota. Forestburg has superior winter hardiness and persistence and is earlier maturing than most cultivars except for Dacotah. Biomass production is superior to Dacotah (Sedivec et al., 2011). Forestburg may have high levels of seed dormancy. Switchgrass seed marketed for commercial sale is tested in seed laboratories where the standard germination test is conducted after 2 weeks of cold stratification at 5 ◦ C (AOSA, 2010). Therefore the germination on the seed label may not predict stand establishment performance in the field. The Forestburg seed used in our study had 58% germination when stratified for 2 weeks at 5 ◦ C prior to the germination test, but only 2% germination without stratification. The tetrazolium viability test (TZ) as well as the germination test was performed according to the AOSA methods at the North Dakota State Seed Department. The TZ test value for the Forestburg seed indicated 64% viable seed which is close to the germination value after stratification. Seeding date was May 25 and May 28, 2010, at Fargo and Prosper, ND. The experimental design was a RCBD, with four replicates, in a split-plot arrangement where cultivar was the main plot and seeding depth the sub-plot. Each experimental unit had 6 rows 30-cm apart and 9-m in length. The same plot planter was used to adjust seeding depth to 13- and 25-mm deep. The planter was an Almaco1 plot seeder with six belt cones each delivering seed to a set of double disk openers with twin-V arranged press wheels. Seedlings emergence was determined from a 2-m section from each plot center row and expressed on a pure live seed basis. Pure live seed was calculated for both cultivars with 58% germination. Plant density was calculated from the plants emerged from a 2-m section from the two center rows in each plot. The 4-center rows of each plot were harvested with a Carter forage harvester on 19 and 25 August at Prosper and Fargo, respectively. A moisture sample was taken during harvest, dried and biomass yield for each experimental unit was calculated and expressed on a 10% moisture basis. 2.3. Statistical analysis The greenhouse and field experiments were analyzed separately. The two runs in the greenhouse experiment were considered fixed effects and analyzed as samples in a randomized complete block with a factorial arrangement using the GLM procedure of SAS (SAS Institute, 2009).
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Table 1 Soil classification, texture, and chemical characteristics of soils from Carrington, Prosper, and Fargo, ND. Location
Chemical characteristicsa
Soil classification Soil texture
Mineral class
Sub group
pH
OM (%)
Greenhouse experiment Heimdahl loam Carrington Fargo-Ryan Fargo Prosper Perella-Bearden
Soil type
Coarse-loamy Silty-clay Fine-silty
Mixed Montmorillonitic Mixed
Calcic Hapludoll Vertic Haplaquoll Typic Endoaquolls-Aeric Calciaquolls
7.7 7.1 6.4
2.5 6.1 3.3
– – –
– – –
– – –
Field experiment Fargo-Ryan Fargo Perella-Bearden Prosper
Silty-clay Fine-silty
Montmorillonitic Mixed
Vertic Haplaquoll Typic Endoaquolls-Aeric Calciaquolls
7.6 7.2
5.9 2.9
166 83
15 20
400 355
a
N-NO3 (mg/kg)
P (mg/kg)
K (mg/kg)
pH, organic matter (OM), P, K for 0–15 cm depth, N-NO3 from 0 to 60 cm depth.
Statistical analysis was conducted by using standard procedures for a randomized complete-block design (Steel and Torrie, 1980). Each location-year combination was defined as an “environment” and was considered a random effect in the statistical analysis. Seeding depth and cultivar treatments were considered fixed effects. Environments were analyzed individually by ANOVA. Trait mean square errors were tested for homogeneity before analysis was performed across environments. To separate treatment means, F-protected LSD comparisons with P ≤ 0.05 was applied. The estimated variance of pairwise mean differences and the corresponding degrees of freedom was calculated to estimate the correct LSD values for comparison of significant interactions (Carmer et al., 1989). The SAS System was used to analyze the data (SAS Institute, 2009). Regression analysis was considered for trait responses when there was a significant main effect or interaction for any of the fixed effects. Linear and polynomial regression models were tested.
maximum PLSE and emergence index occurred at 41- and 29-mm depth, respectively, this was calculated by deriving the models to obtain the maximum (Fig. 2). Similar results were found by Aiken and Springer (1995) who evaluated seeding depths of 5, 10, and 20 mm in one sandy and two silty-loam soils also in a greenhouse experiment. They did not find differences in seedling emergence at different depths in silty-loam soils, but a decline in emergence as planting depths increased in the sandy soil.
3. Results and discussion 3.1. Greenhouse experiment Seeding depth by soil type interaction was not significant for any of the variables evaluated (Table 2). Pure live seed emergence and emergence index differed among soil types (Fig. 1). The PLSE and emergence index were higher for the silty-clay soil across all seeding depths. Coarser soil textures had a lower average PLSE mainly because the PLSE at the surface seeding depth was lower in those textures and it was observed that the soil surface dried between waterings. Evers and Parsons (2003) also determine that seedling emergence and survival was greater on clay soils at all watering intervals in a greenhouse experiment conducted with several soil types from southern Texas. Only the surface seeding (0-mm depth) had a significantly lower PLSE and emergence index across soil types (Fig. 2). Seeding depths from 13- to 64-mm depth were not significantly different and fluctuated between 64 and 74% PLSE. Based on the regression models, PLSE = 42.7 + 1.6x − 0.0196x2 , r2 = 0.91, and EI = 11.7 + 0.8x − 0.014x2 , r2 = 0.89 (x = seeding depth in mm), the
Fig. 1. Effect of soil texture on mean pure live seed emergence (PLSE) and emergence index (EI) of Dacotah switchgrass averaged across seven seeding depths and two experiment runs for the greenhouse experiment.
Table 2 Mean squares for pure live seed emergence (PLSE) and emergence index (EI) for seven seeding depths and three soil types in the greenhouse experiment. SOV
df
PLSE
EI
Rep Soil Depth Soil × depth Error CV, %
2 2 6 12 73
27 2559*** 1561*** 204 188 21
151 1051*** 531*** 78 59 21
***
Significant at 0.001.
Fig. 2. Effect of seeding depth on mean pure live seed emergence (PLSE) and emergence index (EI) of Dacotah switchgrass averaged across three soil types and two experiment runs for the greenhouse experiment.
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Table 3 Mean squares of pure live seed emergence (PLSE), plant density, and dry matter biomass yield for the combined analysis from the field experiment at Fargo and Prosper, ND. SOV
df
PLSE
Plant density
Biomass yield
Environmenta Rep (Env) Cultivar C × Env Rep × C × Env Seeding depth SD × Env SD × C SD × C × Env Error CV, %
1 6 1 1 6 3 3 3 3 36
63 459 17,997* 38 430 5373* 309 3289* 350 127 58
552 4002 159,201* 324 3887 45,214* 2686 29,552* 3028 1092 58
44.4 9.3 247.8 24.1 8.4 53.5** 1.2 8.0* 0.8 1.8 41.0
* ** a
Significant at 0.05. Significant at 0.01. Environment (Env), seeding depth (SD), cultivar (C).
3.2. Field experiments The combined analysis of variance for the field experiments indicated a significant interaction for cultivar by seeding depth for PLSE, plant density, and biomass yield (Table 3). There was no significant interaction between environment and seeding depth or cultivar for PLSE, plant density, or biomass yield. The Forestburg cultivar had very poor emergence at all seeding depths, 10, 2, 0.5, and 0.2% PLSE at 13-, 19-, 30-, and 38-mm seeding depths, respectively, with highest PLSE (10%) from the 13-mm depth when averaged across environments (Fig. 3). The low percent emergence is largely explained by the high seed dormancy in this seed lot with a germination of 2% without stratification. In a seed with high levels of dormancy shallow seeding is even more important than in a seed with low dormancy because the few non dormant seeds will emerge easier from shallower seeding depths. Seed priming may help ensure growers a successful establishment especially with those seed lots that have high levels of dormancy (Hacisalihoglu, 2010). Also testing the seed lot for seedling emergence from 4 cm of sand resulted in a better predictor of field establishment (Mitchell and Vogel, 2012). The PLSE for Dacotah averaged across environments was 80, 42, 18, and 5% for the 13-, 19-, 30-, and 38-mm seeding depths, respectively (Fig. 3). Decline in PLSE as seeding depth increased does not appear to be caused by soil moisture limitations since moisture levels among the sampled depths were generally not different (data not shown). The 13-mm seeding depth actually had higher PLSE than other seeding depths when averaged across environments (Fig. 3). Newman and Moser (1988) indicated switchgrass seedling
Fig. 3. Effect of seeding depth and cultivar on mean pure live seed emergence (PLSE) averaged across two North Dakota environments, Fargo and Prosper, for the field experiment conducted in 2010. Regression models are for PLSE.
Fig. 4. Effect of seeding depth and cultivar on mean biomass yield and plant density averaged across two North Dakota environments, Fargo and Prosper, for the field experiment conducted in 2010.
emergence decreased when depth exceeded 30-mm depth in a field study conducted on a Kennebec silt–loam in Lincoln, NE. models for both cultivars: Dacotah, Regression PLSE = 196 − 11.1x + 0.164x2 , r2 = 0.99 and Forestburg, PLSE = 26.4 − 1.7x + 0.028x2 , r2 = 0.91, indicate that whether the cultivar has high or low dormancy the best recommendation is to seed shallow at 13-mm depth (Fig. 3). Growers should test seed germination without stratification before planting to have a better estimate of field establishment success. Also as indicated by Mitchell and Vogel (2012), testing the seed lot for seedling emergence from sand 4 cm of sand proved to be the best predictor of field establishment. The seeding depth by cultivar interaction is predominately magnitude related and shows biomass yield decreasing as seeding depth increased for both cultivars, but the yield levels where the response occurs are much higher for the cultivar Dacotah than Forestburg (Fig. 4). As seeding depth increased from 13-, 19-, 30-, to 38-mm, stand density decreased from 236-, 124-, 37-, to 32-plants m−2 , respectively for the cultivar Dacotah (Fig. 4). The cultivar Dacotah biomass yield was greatest, 7.5 Mg ha−1 , at the highest plant density of 236 plants m−2 and decreased linearly to 2.7 Mg ha−1 at the lowest plant density 32 plants m−2 . The cultivar Forestburg exhibited much lower PLSE values than Dacotah resulting in stand densities of 23, 4, 2, and 1 plant m−2 from seeding depths of 13-, 19-, 30-, and 38-mm, respectively. Consequently, biomass yield was limited because of low stand densities and decreased from 3.5 Mg ha−1 at the highest plant density (23 plants m−2 ) to 0.2 Mg ha−1 at the lowest plant density (1 plant m−2 ). Interestingly, biomass yield performance for Forestburg (3.5 Mg ha−1 ) and Dacotah (2.7 Mg ha−1 ) were generally similar when their plant densities were comparable. This occurred for Dacotah at the deepest seeding depth (32 plants m−2 ) and Forestburg at the shallowest seeding depth (23 plants m−2 ). Maximum biomass yield, in the seeding year, for the cultivar Dacotah was obtained with 175 plants m−2 by deriving the regression model, biomass yield = 1.13 + 0.07x − 0.0002x2 , r2 = 0.98 to obtain the plant density that maximizes biomass yield (Fig. 5). Vassey et al. (1985) obtained biomass yield of 4.6–8.9 Mg ha−1 , in the seeding year, with a plant density of 245 and 55 plants m−2 , respectively, with ‘Cave-in-Rock’ switchgrass in Ames, IA; however; in this study biomass yield depended more on seasonal rainfall than plant density. Switchgrass can compensate for biomass yield in the seeding year by producing more tillers or vertical rhizomes from the stem base. In the following years, switchgrass tillers develop from vertically and horizontally oriented rhizomes that colonize areas not established in the seeding year compensating for any possible
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Acknowledgments Funding for this research was provided by USDA-CREES Grant #2009-34622-19970 “Renewable energy and products: Agronomic potential for fuel production in North Dakota”. I thank my technician, summer interns, and undergraduate and graduate student for their valuable collaboration on data collection and management of these experiments. References
Fig. 5. Regression models between biomass yield and plant density of switchgrass cultivar Dacotah and Forestburg averaged across two North Dakota environments, Fargo and Prosper, for the field experiment conducted in 2010.
biomass yield loss due to poor stand establishment (Bredja et al., 1989). 4. Conclusions Under controlled conditions (greenhouse experiment) soil type had an influence on PLSE and emergence index. Clay-type soil had a greater PLSE and EI than more coarse textured soils. Seeding depth did not seem to be a factor affecting seedling establishment except for the surface seeding where the lack of seed and soil contact reduced emergence. Regression models indicated that switchgrass maximum PLSE was when seeded at a 40 mm depth. In field conditions, the 13-mm depth had significantly higher PLSE and there was a strong interaction, mainly due to magnitude, between cultivar and seeding depth. The maximum biomass yield was achieved with 175 plant m−2 . The large differences in the results between greenhouse and field experiments indicate that in the field there are many other factors influencing seedling establishment besides depth, therefore greenhouse experiments results do not correlate well with switchgrass establishment in the field. As a general recommendation to growers switchgrass should be seeded no deeper than 13-mm depth. Testing the germination of the cultivar, without stratification is recommended in order to better predict field establishment success.
Aiken, G.E., Springer, T.L., 1995. Seed size distribution, germination, and emergence of six switchgrass cultivars. Journal of Range Management 48 (5), 455–458. Anfinrud, M.N., Schneiter, A.A., 1984. Relationship of sunflower germination and vigor tests to field performance. Crop Science 24, 341–344. AOSA, 2010. Handbook of the Association of Official Seed Analysts (AOSA). AOSA Rules for Testing Seeds. AOSA Inc., Ithaca, NY. Bredja, J.J., Moser, L.E., Waller, S.S.,1989. Rhizome and tiller development of three Nebraska sandhills warm-season grasses. In: Proceedings of the 11th North American Prairie Conference. Univ. of Nebraska, Lincoln, pp. 211–214. Carmer, S.G., Nyquist, W.E., Walker, W.M., 1989. Least significant differences for combined analyses of experiments with two- or three-factor treatment designs. Agronomy Journal 81, 665–672. Duclos, D.V., Ray, D.T., Taylor, A.G., 2009. Understanding the physiology and mechanism of seed dormancy in switchgrass (Panicum virgatum L.). In: Cermak, S.C., Berti, M.T. (Eds.), 21st Annual AAIC Meeting-The Next Generation of Industrial Crops, Processes, and Products. Termas de Chillan, Chillan, Chile, November 14–19, p. 30. Evers, G., Parsons, M.J., 2003. Soil type and moisture level influence on Alamo switchgrass emergence and seedling growth. Crop Science 43, 288–294. Hacisalihoglu, G., 2010. Response of switchgrass (Panicum virgatum L.) cultivars to seed priming and differential aging conditions. Acta Agriculturae Scanidavica, Section B: Plant and Soil Science 58 (3), 280–284. Mitchell, R.B., Vogel, K.P., 2012. Germination and emergence tests for predicting switchgrass field establishment. Agronomy Journal 104, 458–465. Newman, P.R., Moser, L.E., 1988. Grass seedling emergence, morphology, and establishment as affected by planting depth. Agronomy Journal 80, 383–387. SAS Insitute, 2009. SAS 9.1.2 Qualification Tools User’s Guide. SAS Institute Inc., Cary, NC. Sarath, G., Bethke, P.C., Jones, R., Baird, L.M., Hou, G., Mitchell, R.B., 2006. Nitric oxide accelerates germination in warm-season grasses. Planta 223, 1154–1164. Sarath, G., Hou, G., Baird, L.M., Mitchell, R.B., 2007. ABA, ROS, and NO are key players during switchgrass seed germination. Plant Signaling and Behavior 21 (6), 492–493. Sedivec, K., Tober, D.A., Duckwitz, W.L., Dewald, D.D., Printz, J.L., Craig, D.J., 2011. Grasses for the Northern Plains: Growth Patterns Forage Characteristics and Wildlife Values: Warm-season, vol. 2. North Dakota State Univ. Ext. Serv., Fargo (Bull. R-1390). Shen, Z.-X., Parrish, D.J., Wolf, D.D., Welbaum, G.E., 2001. Stratification in switchgrass, seeds is reversed and hastened by drying. Crop Science 41, 1546–1551. Smart, A.J., Moser, L.E., 1999. Switchgrass seedling development as affected by seed size. Agronomy Journal 91, 335–338. Steel, R.G.D., Torrie, J.H., 1980. Principles and Procedures of Statistics: A Biometrical Approach, 2nd ed. McGraw-Hill Inc., New York. Vassey, T.L., George, J.R., Mullen, R.E., 1985. Early-, mid-, and late-spring establishment of switchgrass at several seeding rates. Agronomy Journal 77, 253–257.
Contents lists available at SciVerse ScienceDirect
Industrial Crops and Products journal homepage: www.elsevier.com/locate/indcrop
Switchgrass establishment as affected by seeding depth and soil type Marisol T. Berti ∗ , Burton L. Johnson Department of Plant Sciences, North Dakota State University, NDSU Dept. 7670, Fargo, ND 58108-6050, USA
a r t i c l e
i n f o
Article history: Received 20 February 2012 Received in revised form 11 April 2012 Accepted 14 April 2012 Keywords: Pure live seed emergence Emergence index Soil texture Depth Dormancy
a b s t r a c t Switchgrass (Panicum virgatum L.) has been identified as a potential bioenergy crop for the North Central Region of the USA. One of the limitations to successful production of switchgrass is poor seedling establishment affected by the interaction between seeding depth and soil physical characteristics. The objective of this study was to determine the effect of seeding depth and soil types on switchgrass seedling establishment in a greenhouse and field experiment. The greenhouse experiment included seven seeding depths (0, 13-, 19-, 25-, 38-, 51-, and 64-mm deep), three soil types, and one cultivar, Dacotah. Soil types for the greenhouse experiment were brought in from three North Dakota State University research sites located at Fargo (silty-clay, 6.1% organic matter (OM)), Prosper (fine-silty, 3.3% OM), and Carrington (coarse loamy, 2.5% OM). The field experiment was conducted at Fargo and Prosper, ND, in 2010, and included four seeding depths (13-, 19-, 30-, and 38-mm deep) and two cultivars Dacotah and Forestburg. Results from the greenhouse experiment indicated pure live seed emergence (PLSE) differed among seeding depths and soil textures. Only the surface seeding (0-mm depth) had a significantly lower PLSE. Seeding depths from 13- to 64-mm depth were not significantly different and fluctuated between 64 and 74% PLSE. The silty-clay soil at Fargo had significantly higher PLSE (74%) across all seeding depths than the fine-silty soil at Prosper, and the coarse-loamy soil at Carrington (60% PLSE). In the field experiment, the Forestburg cultivar had very poor emergence at all seeding depths and environments. The PLSE for ‘Forestburg’ was 10%, from the 13-mm depth averaged across both locations. The PLSE for Dacotah across both locations was 80, 42, 18, and 5% for the 13-, 19-, 30-, and 38-mm depths, respectively. Under controlled conditions (greenhouse experiment), seeding depth was not a major factor affecting seedling establishment except for the surface seeding where the lack of seed and soil contact and surface dryness reduced emergence. Pure live seed emergence and emergence index were greater in the silty-clay soil at Fargo across all seeding depths, presumably due to a better seed–soil contact. Under field conditions, the 13-mm depth had significantly higher PLSE indicating other factors are interacting with the seeding depth. As a general recommendation to growers switchgrass should be seeded no deeper than 13-mm depth. Testing the germination of the seed lot, without stratification, before planting is recommended to better estimate field establishment success. © 2012 Elsevier B.V. All rights reserved.
1. Introduction Switchgrass has been identified as one of the potential lignocellulosic biofuel feedstocks for the north central and southern regions of the USA. As a new crop to these regions development of management guidelines is recommended for successful production of switchgrass. Poor seedling establishment of switchgrass in North Dakota has been a limiting factor for large scale production. Establishment in grasses has two distinct phases: seedling emergence and seedling establishment (development of an adventitious root system) (Newman and Moser, 1988). Suboptimal temperatures when
∗ Corresponding author. Tel.: +1 701 231 6110; fax: +1 701 231 8474. E-mail addresses: [email protected], [email protected] (M.T. Berti). 0926-6690/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.indcrop.2012.04.023
seeded, excessive seeding depth, inadequate soil surface moisture, seed dormancy, small seed size, and low seedling vigor are factors that impact successful seedling establishment of grasses (Newman and Moser, 1988; Aiken and Springer, 1995; Smart and Moser, 1999). Extended or unpredictable seed dormancy in seed grasses is also detrimental for seedling establishment and agronomic success. Switchgrass seed dormancy has been studied extensively (Duclos et al., 2009; Sarath et al., 2006, 2007; Shen et al., 2001); however, reduced stand establishment due to seed dormancy still exists. The mechanisms of seed dormancy in switchgrass are not well understood. Duclos et al. (2009) examined the effect of seed covering layers: lemma, palea, and pericarp, and found that the pericarp was the major layer responsible for dormancy. These seed covering layers may act as a barrier for gas diffusion and/or for the diffusion of inhibitory compounds leaking into the environment.
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Several treatments have been proposed to overcome seed dormancy in switchgrass. A 2-week chilling (stratification) is the most commonly applied treatment to break dormancy in seed testing, followed by determining germination at an alternating 15/30 ◦ C for an additional 14 days (Association of Official Seed Analysts (AOSA), 2010). Unfortunately, laboratory germination test results do not always correlate with field performance since there are many factors that affect seed germination and emergence. Other studies indicate that nitric oxide from the donor sodium nitroprusside, promoted germination of switchgrass CV. Kanlow in alternating light and dark intervals at 25 ◦ C, across a broad range of concentrations (Sarath et al., 2006). Shen et al. (2001) indicated that short-term stratification treatments could successfully overcome dormancy if seeds were not dried and allowed to germinate. Mitchell and Vogel (2012) evaluated the ability of seed quality tests to predict field establishment. Of all test evaluated the best predictor of field establishment was emergence from 4 cm of sand, which had an establishment index that was 3.5 times greater than only using the pure live seed method. Proper seeding depth is also an important factor involved in successful establishment of switchgrass. Newman and Moser (1988) indicated seedling emergence decreased when depth exceeded 30mm. Aiken and Springer (1995) evaluated seeding depths of 5-, 10-, and 20-mm in a sandy and two silty-loam soils. They found no differences in seedling emergence at different depths in the silty-loam soils but a decline in emergence as planting depths increased in the sandy soil. The objective of this study was to determine the effect of seeding depth in different soil types on seedling establishment.
2. Materials and methods 2.1. Greenhouse experiment The greenhouse experiment included six seeding depths (0, 13-, 25-, 38-, 51-, and 64-mm deep), one cultivar, and three soil types brought into the greenhouse from three experiment stations of North Dakota State University, from Fargo, Prosper, and Carrington. Soil texture and chemical composition of three soils were reported in Table 1. The cultivar Dacotah, released in North Dakota in 1989, was used for this experiment. Dacotah is an upland type, winter-hardy, leafy type with high plant vigor and seed yield and reaches anthesis earlier than most upland cultivars. It is shorter in height and has less coarse growth than most lowland types (Sedivec et al., 2011). The experimental design was a RCBD with a factorial arrangement with four replicates and two runs (repetition of the complete experiment). For each run, one hundred seeds of switchgrass were planted in 12-cm diameter pots at each of the desired seeding depths, with each of the three soil types, for each replicate. All pots were watered with the same amount every other day to replenish evaporated water. The pots had perforated bottoms to enable drainage and avoid saturated soil conditions. Seedling emergence was recorded every 3 days for 35 days after starting the experiment, in both runs. Run 1 and 2 were started on February 1 and February 23, respectively, in 2010. Seed germination for ‘Dacotah’ was 58%. This germination was obtained in our laboratory by germinating 100 seeds, replicated 3 times, in Petri dishes with a filter paper, at 20 ◦ C for 14 days without previous stratification. This germination was used to calculate pure live seed. Pure live seed emergence and was determined by the following formulas, seed purity used was 100% (AOSA, 2010): PLS (%) =
purity (%) × germ (%) 100
(1)
PLSE (%) =
nse × 100 (nsp × PLS (%))/100
(2)
PLS is the pure live seed; purity (%) the seed lot purity, 100% was used; germ (%) the percent germination of seeds planted; nse the number of seeds emerged; nsp the number of seeds planted and PLS planted is the number of pure live seed planted. The emergence index (EI) was determined for the germination period according to the formula: EI = a1
1 xi
+ · · · + ˛n
1 xn
(3)
where a is the number of seeds with exposed coleoptile each day, xi is the number of days after initial emergence of coleoptile, and xn is the last day of emergence (Anfinrud and Schneiter, 1984). 2.2. Field experiment The field experiment was conducted at Fargo and Prosper, ND, in 2010, and included four seeding depths (13-, 19-, 30-, and 38-mm deep) and two cultivars Dacotah and Forestburg. The Forestburg cultivar is an upland type released in 1987 in South Dakota. Forestburg has superior winter hardiness and persistence and is earlier maturing than most cultivars except for Dacotah. Biomass production is superior to Dacotah (Sedivec et al., 2011). Forestburg may have high levels of seed dormancy. Switchgrass seed marketed for commercial sale is tested in seed laboratories where the standard germination test is conducted after 2 weeks of cold stratification at 5 ◦ C (AOSA, 2010). Therefore the germination on the seed label may not predict stand establishment performance in the field. The Forestburg seed used in our study had 58% germination when stratified for 2 weeks at 5 ◦ C prior to the germination test, but only 2% germination without stratification. The tetrazolium viability test (TZ) as well as the germination test was performed according to the AOSA methods at the North Dakota State Seed Department. The TZ test value for the Forestburg seed indicated 64% viable seed which is close to the germination value after stratification. Seeding date was May 25 and May 28, 2010, at Fargo and Prosper, ND. The experimental design was a RCBD, with four replicates, in a split-plot arrangement where cultivar was the main plot and seeding depth the sub-plot. Each experimental unit had 6 rows 30-cm apart and 9-m in length. The same plot planter was used to adjust seeding depth to 13- and 25-mm deep. The planter was an Almaco1 plot seeder with six belt cones each delivering seed to a set of double disk openers with twin-V arranged press wheels. Seedlings emergence was determined from a 2-m section from each plot center row and expressed on a pure live seed basis. Pure live seed was calculated for both cultivars with 58% germination. Plant density was calculated from the plants emerged from a 2-m section from the two center rows in each plot. The 4-center rows of each plot were harvested with a Carter forage harvester on 19 and 25 August at Prosper and Fargo, respectively. A moisture sample was taken during harvest, dried and biomass yield for each experimental unit was calculated and expressed on a 10% moisture basis. 2.3. Statistical analysis The greenhouse and field experiments were analyzed separately. The two runs in the greenhouse experiment were considered fixed effects and analyzed as samples in a randomized complete block with a factorial arrangement using the GLM procedure of SAS (SAS Institute, 2009).
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Table 1 Soil classification, texture, and chemical characteristics of soils from Carrington, Prosper, and Fargo, ND. Location
Chemical characteristicsa
Soil classification Soil texture
Mineral class
Sub group
pH
OM (%)
Greenhouse experiment Heimdahl loam Carrington Fargo-Ryan Fargo Prosper Perella-Bearden
Soil type
Coarse-loamy Silty-clay Fine-silty
Mixed Montmorillonitic Mixed
Calcic Hapludoll Vertic Haplaquoll Typic Endoaquolls-Aeric Calciaquolls
7.7 7.1 6.4
2.5 6.1 3.3
– – –
– – –
– – –
Field experiment Fargo-Ryan Fargo Perella-Bearden Prosper
Silty-clay Fine-silty
Montmorillonitic Mixed
Vertic Haplaquoll Typic Endoaquolls-Aeric Calciaquolls
7.6 7.2
5.9 2.9
166 83
15 20
400 355
a
N-NO3 (mg/kg)
P (mg/kg)
K (mg/kg)
pH, organic matter (OM), P, K for 0–15 cm depth, N-NO3 from 0 to 60 cm depth.
Statistical analysis was conducted by using standard procedures for a randomized complete-block design (Steel and Torrie, 1980). Each location-year combination was defined as an “environment” and was considered a random effect in the statistical analysis. Seeding depth and cultivar treatments were considered fixed effects. Environments were analyzed individually by ANOVA. Trait mean square errors were tested for homogeneity before analysis was performed across environments. To separate treatment means, F-protected LSD comparisons with P ≤ 0.05 was applied. The estimated variance of pairwise mean differences and the corresponding degrees of freedom was calculated to estimate the correct LSD values for comparison of significant interactions (Carmer et al., 1989). The SAS System was used to analyze the data (SAS Institute, 2009). Regression analysis was considered for trait responses when there was a significant main effect or interaction for any of the fixed effects. Linear and polynomial regression models were tested.
maximum PLSE and emergence index occurred at 41- and 29-mm depth, respectively, this was calculated by deriving the models to obtain the maximum (Fig. 2). Similar results were found by Aiken and Springer (1995) who evaluated seeding depths of 5, 10, and 20 mm in one sandy and two silty-loam soils also in a greenhouse experiment. They did not find differences in seedling emergence at different depths in silty-loam soils, but a decline in emergence as planting depths increased in the sandy soil.
3. Results and discussion 3.1. Greenhouse experiment Seeding depth by soil type interaction was not significant for any of the variables evaluated (Table 2). Pure live seed emergence and emergence index differed among soil types (Fig. 1). The PLSE and emergence index were higher for the silty-clay soil across all seeding depths. Coarser soil textures had a lower average PLSE mainly because the PLSE at the surface seeding depth was lower in those textures and it was observed that the soil surface dried between waterings. Evers and Parsons (2003) also determine that seedling emergence and survival was greater on clay soils at all watering intervals in a greenhouse experiment conducted with several soil types from southern Texas. Only the surface seeding (0-mm depth) had a significantly lower PLSE and emergence index across soil types (Fig. 2). Seeding depths from 13- to 64-mm depth were not significantly different and fluctuated between 64 and 74% PLSE. Based on the regression models, PLSE = 42.7 + 1.6x − 0.0196x2 , r2 = 0.91, and EI = 11.7 + 0.8x − 0.014x2 , r2 = 0.89 (x = seeding depth in mm), the
Fig. 1. Effect of soil texture on mean pure live seed emergence (PLSE) and emergence index (EI) of Dacotah switchgrass averaged across seven seeding depths and two experiment runs for the greenhouse experiment.
Table 2 Mean squares for pure live seed emergence (PLSE) and emergence index (EI) for seven seeding depths and three soil types in the greenhouse experiment. SOV
df
PLSE
EI
Rep Soil Depth Soil × depth Error CV, %
2 2 6 12 73
27 2559*** 1561*** 204 188 21
151 1051*** 531*** 78 59 21
***
Significant at 0.001.
Fig. 2. Effect of seeding depth on mean pure live seed emergence (PLSE) and emergence index (EI) of Dacotah switchgrass averaged across three soil types and two experiment runs for the greenhouse experiment.
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Table 3 Mean squares of pure live seed emergence (PLSE), plant density, and dry matter biomass yield for the combined analysis from the field experiment at Fargo and Prosper, ND. SOV
df
PLSE
Plant density
Biomass yield
Environmenta Rep (Env) Cultivar C × Env Rep × C × Env Seeding depth SD × Env SD × C SD × C × Env Error CV, %
1 6 1 1 6 3 3 3 3 36
63 459 17,997* 38 430 5373* 309 3289* 350 127 58
552 4002 159,201* 324 3887 45,214* 2686 29,552* 3028 1092 58
44.4 9.3 247.8 24.1 8.4 53.5** 1.2 8.0* 0.8 1.8 41.0
* ** a
Significant at 0.05. Significant at 0.01. Environment (Env), seeding depth (SD), cultivar (C).
3.2. Field experiments The combined analysis of variance for the field experiments indicated a significant interaction for cultivar by seeding depth for PLSE, plant density, and biomass yield (Table 3). There was no significant interaction between environment and seeding depth or cultivar for PLSE, plant density, or biomass yield. The Forestburg cultivar had very poor emergence at all seeding depths, 10, 2, 0.5, and 0.2% PLSE at 13-, 19-, 30-, and 38-mm seeding depths, respectively, with highest PLSE (10%) from the 13-mm depth when averaged across environments (Fig. 3). The low percent emergence is largely explained by the high seed dormancy in this seed lot with a germination of 2% without stratification. In a seed with high levels of dormancy shallow seeding is even more important than in a seed with low dormancy because the few non dormant seeds will emerge easier from shallower seeding depths. Seed priming may help ensure growers a successful establishment especially with those seed lots that have high levels of dormancy (Hacisalihoglu, 2010). Also testing the seed lot for seedling emergence from 4 cm of sand resulted in a better predictor of field establishment (Mitchell and Vogel, 2012). The PLSE for Dacotah averaged across environments was 80, 42, 18, and 5% for the 13-, 19-, 30-, and 38-mm seeding depths, respectively (Fig. 3). Decline in PLSE as seeding depth increased does not appear to be caused by soil moisture limitations since moisture levels among the sampled depths were generally not different (data not shown). The 13-mm seeding depth actually had higher PLSE than other seeding depths when averaged across environments (Fig. 3). Newman and Moser (1988) indicated switchgrass seedling
Fig. 3. Effect of seeding depth and cultivar on mean pure live seed emergence (PLSE) averaged across two North Dakota environments, Fargo and Prosper, for the field experiment conducted in 2010. Regression models are for PLSE.
Fig. 4. Effect of seeding depth and cultivar on mean biomass yield and plant density averaged across two North Dakota environments, Fargo and Prosper, for the field experiment conducted in 2010.
emergence decreased when depth exceeded 30-mm depth in a field study conducted on a Kennebec silt–loam in Lincoln, NE. models for both cultivars: Dacotah, Regression PLSE = 196 − 11.1x + 0.164x2 , r2 = 0.99 and Forestburg, PLSE = 26.4 − 1.7x + 0.028x2 , r2 = 0.91, indicate that whether the cultivar has high or low dormancy the best recommendation is to seed shallow at 13-mm depth (Fig. 3). Growers should test seed germination without stratification before planting to have a better estimate of field establishment success. Also as indicated by Mitchell and Vogel (2012), testing the seed lot for seedling emergence from sand 4 cm of sand proved to be the best predictor of field establishment. The seeding depth by cultivar interaction is predominately magnitude related and shows biomass yield decreasing as seeding depth increased for both cultivars, but the yield levels where the response occurs are much higher for the cultivar Dacotah than Forestburg (Fig. 4). As seeding depth increased from 13-, 19-, 30-, to 38-mm, stand density decreased from 236-, 124-, 37-, to 32-plants m−2 , respectively for the cultivar Dacotah (Fig. 4). The cultivar Dacotah biomass yield was greatest, 7.5 Mg ha−1 , at the highest plant density of 236 plants m−2 and decreased linearly to 2.7 Mg ha−1 at the lowest plant density 32 plants m−2 . The cultivar Forestburg exhibited much lower PLSE values than Dacotah resulting in stand densities of 23, 4, 2, and 1 plant m−2 from seeding depths of 13-, 19-, 30-, and 38-mm, respectively. Consequently, biomass yield was limited because of low stand densities and decreased from 3.5 Mg ha−1 at the highest plant density (23 plants m−2 ) to 0.2 Mg ha−1 at the lowest plant density (1 plant m−2 ). Interestingly, biomass yield performance for Forestburg (3.5 Mg ha−1 ) and Dacotah (2.7 Mg ha−1 ) were generally similar when their plant densities were comparable. This occurred for Dacotah at the deepest seeding depth (32 plants m−2 ) and Forestburg at the shallowest seeding depth (23 plants m−2 ). Maximum biomass yield, in the seeding year, for the cultivar Dacotah was obtained with 175 plants m−2 by deriving the regression model, biomass yield = 1.13 + 0.07x − 0.0002x2 , r2 = 0.98 to obtain the plant density that maximizes biomass yield (Fig. 5). Vassey et al. (1985) obtained biomass yield of 4.6–8.9 Mg ha−1 , in the seeding year, with a plant density of 245 and 55 plants m−2 , respectively, with ‘Cave-in-Rock’ switchgrass in Ames, IA; however; in this study biomass yield depended more on seasonal rainfall than plant density. Switchgrass can compensate for biomass yield in the seeding year by producing more tillers or vertical rhizomes from the stem base. In the following years, switchgrass tillers develop from vertically and horizontally oriented rhizomes that colonize areas not established in the seeding year compensating for any possible
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Acknowledgments Funding for this research was provided by USDA-CREES Grant #2009-34622-19970 “Renewable energy and products: Agronomic potential for fuel production in North Dakota”. I thank my technician, summer interns, and undergraduate and graduate student for their valuable collaboration on data collection and management of these experiments. References
Fig. 5. Regression models between biomass yield and plant density of switchgrass cultivar Dacotah and Forestburg averaged across two North Dakota environments, Fargo and Prosper, for the field experiment conducted in 2010.
biomass yield loss due to poor stand establishment (Bredja et al., 1989). 4. Conclusions Under controlled conditions (greenhouse experiment) soil type had an influence on PLSE and emergence index. Clay-type soil had a greater PLSE and EI than more coarse textured soils. Seeding depth did not seem to be a factor affecting seedling establishment except for the surface seeding where the lack of seed and soil contact reduced emergence. Regression models indicated that switchgrass maximum PLSE was when seeded at a 40 mm depth. In field conditions, the 13-mm depth had significantly higher PLSE and there was a strong interaction, mainly due to magnitude, between cultivar and seeding depth. The maximum biomass yield was achieved with 175 plant m−2 . The large differences in the results between greenhouse and field experiments indicate that in the field there are many other factors influencing seedling establishment besides depth, therefore greenhouse experiments results do not correlate well with switchgrass establishment in the field. As a general recommendation to growers switchgrass should be seeded no deeper than 13-mm depth. Testing the germination of the cultivar, without stratification is recommended in order to better predict field establishment success.
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