SEED PELLETS FOR IMPROVED SEED DISTRIBUTION OF SMALL SEEDED FORAGE CROPS

Association of Official Seed AnalystsSociety of Commercial Seed Technologists

SEED PELLETS FOR IMPROVED SEED DISTRIBUTION OF SMALL SEEDED FORAGE CROPSAuthor(s): Albert E. Smith and Richard MillerSource: Journal of Seed Technology, Vol. 11, No. 1 (1987), pp. 42-51Published by: Association of Official Seed Analysts and the Society of Commercial Seed TechnologistsStable URL: http://www.jstor.org/stable/23432935 .

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SEED PELLETS FOR IMPROVED SEED DISTRIBUTION OF SMALL SEEDED FORAGE CROPS1

Albert E. Smith and Richard Miller2

Abstract

Broadcast seeding of forage crops having small seed is difficult and often results in uneven stands due to the inability to consistently meter seed flow. Broadcast seeding of forage species into areas where ground equipment cannot operate is being accomplished with aircraft. The small

light seed of forage grass and legume species cannot be uniformly broadcast from an aircraft due to wind currents and packing of the seed in the aircraft container. The purpose of our research was to develop seed-pelleting methods for bermudagrass [Cynodon dactylon (L.) Pers.] and ladino clover (Trifolium repens L.) with improved metering and ballistic properties for increased precision and accuracy of seed distribu tion from aerial seeding. Seed pellets developed with kaolin clay and several binders were tested for pellet strength and destructability and

seedling establishment in greenhouse pots. Pellets made from formula tions containing polyvinyl alcohol binder resulted in strong pellets that had a low percentage of destruction when tumbled for one hour. These

pellets resulted in excellent seed germination (>85%) and seedling estab

lishment for both ladino clover and bermudagrass. The pellets could be stored for up to 6 months while maintaining good seed viability and

Rhizobium trifolii viability. The seed can be accurately distributed at low rates from an aircraft equipped with a Meterate™ applicator (Elanco

Products Co., Indianapolis, IN). Pellets sprayed with diammonium

phosphate (dap) produced the best bermudagrass seedling establishment. The dap, when sprayed on ladino clover seed pellets, damaged the clover

seedlings. The use of pelleted seed should increase precision and accuracy of seed distribution from an aircraft and should allow for the use of lower

seeding rates. Additional index words: Polyvinyl alcohol, kaolin clay, legumes,

grasses, aerial seeding, broadcast seeding.

Introduction

We have recently organized a research program to develop systems

for converting woodland-type vegetation to herbaceous vegetation for

grazing. An important criterium imposed on the resulting system is that it

'Supported by State and Hatch funds allocated to the Georgia Agrie. Exp. Stns. Mention

of a trademark or proprietary product does not constitute a guarantee or warranty of the

product by the University of Georgia and does not imply its approval to the exclusion of

other products that may also be suitable.

2Professor and Agricultural Res. Assist., Agronomy Dept., University of Georgia, Griffin, GA 30212-5099.

42



VOLUME 11, NUMBER 1, 1987 43

must conserve the ecosystem components (16). Chemical site preparation

has been shown to be less destructive of the soil system than mechanical

site preparation (11). Attention to the conservation of soil is especially

important in the Piedmont and upper Coastal regions of the humid

southeastern United States.

Our system for chemical-site preparation and crop establishment includes three phases. The first phase is the application of a herbicide. After the leaves have dropped from the woody species in response to the herbicide application, the site is burned in early fall for seeding with

cool-season forage species or in early spring for seeding to warm-season

species. The third phase of the system includes the aerial seeding of

forage species into the cooled ash. The majority of the trees on the treated site remain standing during the first two years; therefore, the use of aerial

applications of the herbicide, seed, and fertilizer is necessary. Aerial seeding of small-seeded species [i.e. ladino white clover (Tri

folium repens L.) and bermudagrass (Cynodon dactylon (L.) Pers.)] has

resulted in uneven stands across the treated site due to the inability to

consistently meter the seed (16). Similar problems have been resolved in

the application of dry formulations of pesticides through the develop ment of granule and pellet formulations. These formulations can be

aerially distributed at low rates across the site with accuracy and

precision. Similarly, it was hypothesized that pelleted seed could be

aerially distributed over large areas. Substantial interest exists in the development and use of seed coating

technology for inoculating legume seed with Rhizobium sp. (1, 2, 5, 15) and for treating agronomic and horticultural seed with fungicides (6, 7,

12) and herbicides (4). Pelleting seed of horticultural crops was popular as

an aid for more efficient planting (13, 17). The most extensive study on the use of pelleted seed for improved

seed distribution of forage species was reported by Hull et al. (10). This

research was conducted over a period of 16 years on more than 70,000 ha

of rangeland seeded with several species of grasses. Generally, no

advantages for use of pelleted seed occurred under dryland conditions for

stand establishment. However, the southeastern United States has a

climate that would be more favorable to aerial seeding when compared to

the western rangeland.

The purpose of our research was to develop pelleted seed of bermuda

grass and ladino clover with improved metering and ballistic properties to

increase the precision and accuracy of seed distribution during aerial

seeding. Materials and Methods

Hulled bermudagrass and ladino clover seed used in this research

were obtained from the 1984 seed crop and the seed lots had a percentage

germination of 93 and 96$, respectively. Nine formulations of both



44 JOURNAL OF SEED TECHNOLOGY

bermudagrass seed (Table 1) and clover seed (Table 2) were formed into a paste having a consistency for easy extrusion. Polyvinyl alcohol resins

(PVA) (PVA 205S, 523S, and 540S) were purchased from Air Products and Chemicals, Inc. (Allentown, PA 18001) and the kaolin clay (RC 32-air

float) was purchased from Thiele Kaolin Co. (Wrens, GA 30833). Aqueous solutions of PVA were formed by slowly heating with continuous stirring. The seed, kaolin, calcium sulfate and inoculum (for clover seed) were combined and thoroughly mixed before adding the aqueous solution.

Table 1. Composition of pellets, containing bermudagrass seed, used in this investigation.

Component

Formulation

kaolin clay 60.0 58.5 58.5 58.5 80.0 52.0 59.5 52.4 57.5 seed 1.0 1.0 1.0 1.0 1.0 1.0 1.0 0.8 2.0 PVA 205S 1.5 0.5 1.2 PVA 523S 1.5 PVA 540S 1.5 sodium silicate 0.8 calcium sulfate 8.0

dap1

water 39.0 39.0 39.0 39.0 18.2 39.0 39.0 30.9 38.0

'dap: diammonium phosphate. 2sop: sprayed dried pellet with saturated-aqueous solution of dap (100 ml solution/200 g

pellets).

Table 2. Composition of pellets, containing clover seed, used in this

investigation. Formulation

Component l 2 3 4 5 6 7 8 9

%

kaolin clay 59.0 57.5 57.5 57.5 75.0 51.0 58.5 52.0 57.5 seed 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 inoculum 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 PVA 205S 1.0 0.5 1.0 PVA 523S 1.0 1.0 PVA 540S 1.0 sodium silicate 0.8

calcium sulfate 8.0

dap1 15.0 sop2

water 38.0 38.5 38.0 38.0 21.2 38.0 38.0 39.0 38.0

'dap: diammonium phosphate. 2sop: sprayed dried pellet with saturated-aqueous solution of dap (100 ml solution/200 g

pellets).




Sodium silicate was added to the paste when included in the formulation. Clover seed were inoculated with R. trifolii using the pelgel method (14) prior to mixing with the kaolin and in addition to the one-percent (w/w) inoculum addition to the dry mixture. The consistency of the paste was

adjusted by adding small quantities of water or kaolin. Uniform pellets (Figure 1) were cut from a dried ribbon (2.5 mm diam.) that was formed

by extruding the formulation paste from a mechanical extruder (Figure

2).

Tffjt|Tfppjr ijrpji 'IT, TO 7^

- Figure 1. Extruded pellets used for laboratory and greenhouse studies.

Figure 2. Mechanical extruding device used to develop pellets containing ladino clover and

bermudagrass seed.




The longitudinal and diametric strengths were determined on 5 pellets for each formulation using an Instron Compression Model A1020M Tester

(Instron Corp., Canton, MA). A single pellet was used for each positional strength measurement and pellets from two extrusions for both species were analyzed. Pellets of uniform size were selected and data are

presented in grams required to fracture the pellet. Pellet destructability was determined by tumbling 5 grams of clover pellets in a closed flask for one hour. The powder was screened from the pellets and pellet destruc

tion was determined by the loss in pellet weight and expressed as

percentage loss. Determinations for each formulation were replicated 4 times and the formulated pellets were extruded twice.

Seed germination and seedling establishment for the formulation

pellets, including both bermudagrass and ladino clover, were conducted in greenhouse containers (10 x 10 x 12 cm deep) filled with a soil mix.

Components of the potting mixture were 2 parts Cecil sandy loam, a

clayey, kaolinitic thermic Hapludult to one part of Professional Growing Medium 400S (Pro-Gro Products, Inc., Elizabeth City, NC). Ten pellets were evenly spaced on the surface of the potting mixture in a container. Five pots for each formulation were analyzed for each of two pellet extrusions containing bermudagrass and clover seed. The containers were

randomly located on a greenhouse bench. The temperature in the

greenhouse was maintained between 22-31 C. Supplemental light was

used to extend photoperiod to 14 hr. Percentage seed germination was determined 21 days after planting of the ladino clover and bermudagrass pellets. Seedling establishment was observed for an additional 6 months. A second planting of pellets for each extrusion was accomplished 6 months after extrusion to determine the influence of storage at room

temperature (20-26 C) on seed viability. The effectiveness of the inoculum in the ladino clover seed pellets was

determined under asceptic conditions. Cylindrical containers (2.5 cm diam x 5 cm deep) previously soaked in aqueous sodium hyperchlorite solution (2% for 30 min) were filled with sand. The sand had been autoclaved at 110 C and 12 psi for 15 min. One ladino clover pellet for each formulation was planted in each container. The containers were watered daily with half-strength low-nitrogen nutrient solution (9). Seven weeks after planting, the plants were removed from the containers and

presence or absence of nodules was determined under a dissecting microscope. Each formulation was planted in 5 replications. In order to

test the inoculum viability in response to pellet storage, this process was

repeated 6 months after extruding the pellets. The pellets were stored in

closed containers at room temperature (20-26 C). Results and Discussion

The pellets used in this research contained an average of 3 bermuda

grass or 2.4 ladino clover seed per pellet (data not included) and the pellet




weights averaged 71 mg for both species. The establishment of 12 to 15

plants m~2 is considered adequate for a good stand of forage. Generally, the uniform distribution of small seed, such as bermudagrass or ladino

clover, is difficult to achieve especially when broadcast seeding is

necessary. Therefore, the recommended rates for seeding these species (4.8 kg/ha1) (8) allows for 420 and 250 seed m~2 for bermudagrass ladino

clover, and respectively. The 20-fold difference fctetween the recom mended seeding rates and the desired density of established plants of these species is costly to the land manager.

Pellet conformation (Figure 1) resulted from working with a Meterate™

(Elanco Chemical Co., Indianapolis, IN) applicator attached to a fixed

wing aircraft. This applicator allows for even distribution of pellets at a low density (as low as 4 pellets m~2). Cylindrical pellets (2.5 mm diam. x 7 mm long) containing herbicide have been broadcast over large areas with

great precision using this applicator (data not included). Data for each formulation were not significantly different for the two

extrusions, therefore, the data for both extrusions were combined for

analyses. The pellet strength was greatest for pellets containing the PVA's

(i.e. formulations 2,3,4, 7, and 9) (Tables 3 & 4). The PVA's increased the

pellet strength 10-30 fold compared to clay alone (treatment 1). Polyvinyl alcohol is a polyhydroxy polymer that is water soluble. The wide range of chemical and physical properties of PVA resins has led to their broad

Table 3. Percentage germination of ladino clover-seed pellets at 21 days after planting, pellet strength, and pellet destructability. Pellets were

planted immediately after drying (Planting 1) and after 6 months

storage at room temperature (Planting 2).

Seedlings Germination pellet"1

Planting Planting Pellet strength Pellet 1 2 1 2 longitudinal diametrical destructability'

—m — (no.) ■ (g) —(%)— 1 85 86 1.6 2.3 270 293 3.3 2 82 89 2.0 2.5 3573 2363 0.8 3 89 91 1.9 2.6 6882 7061 0.4 4 82 80 1.9 2.1 6772 6200 0.4 5 74°2 62 2.0 1.8 795 776 1.2 6 58 52 1.7 1.5 362 442 1.2 7 82 89 1.8 2.2 2520 2974 1.0 8 1 1 0.1 0.1 1846 1515 1.8 9 48° 16 1.4* 0.7 4879 4988 0.8

LSD 10 10 0.3 0.5 751 825 0.8

'Pellet destructability was determined by weight lost when tumbled for 1 hr.

2Means for plantings 1 and 2 are significantly different (P = .05) for each formulation as

determined by student's T test.




Table 4. Seed germination of bermudagrass-seed pellets at 21 days after

planting, pellet strength, and pellet destructability. Pellets were planted immediately after drying (Planting 1) and after 6 months storage at room temperature (Planting 2).

Seedlings Germination pellet

1

Planting Planting Pellet strength

1 2 1 2 longitudinal diametrical

—m — (no.) - (k) 1 84"' 64 2.7° 1.3 254 286 2 82 71 2.1 1.6 3783 3184 3 95" 75 3.2° 1.7 6776 5225 4 96° 64 3.2° 1.5 7800 7207 5 90° 57 2.8 1.7 560 584 6 95° 54 3.1° 1.6 343 404 7 87 76 2.3 1.7 4715 3425 8 82 90 2.3 2.0 1921 1360 9 84 91 2.4 2.3 6737 6964

LSD 13 12 0.5 0.3 728 802

'Means for plantings 1 and 2 are significantly different (P = .05) for each formulation as determined by student's T Test.

industrial use. They are excellent adhesives and highly resistant to

solvents, oil and grease (3). Pellets made of formulation 2 had the least

longitudinal and diametrical strengths of the formulations that included the three PVA formulations. The percent germination for each pellet and the seedlings per pellet were not influenced by the PVA formulation. All

pellet formulations readily absorbed water from wet soil (data not

included). Also, the pellets from all PVA formulations remained in contact with the seedling during the initial stages of root and shoot formation. This characteristic would help retain moisture for seedling use

during short, dry periods. A major loss of seedlings from seed that are broadcast on the soil surface results from desiccation. Other pellet formulations crumbled during germination. The ladino clover pellet destruction was inversely associated to the pellet strength (Table 3). The coefficient of linear correlation was -0.81. The strongest pellets were least

disintegrated by tumbling in a flask. This characteristic is important when

considering handling the pellets, especially during aerial seeding. Pellet formulations 2,3, and 4 resulted in less than 1.0$ disintegration during the

tumbling treatments. Formulations that included calcium sulfate (formulation 6), sodium

silicate (formulation 5), or dap (formulations 8 and 9) adversely affected ladino clover seedling development (Table 3). The bermudagrass pellets were not influenced by these salts (Table 4) and the seedlings from pellets containing dap (formulations 8 and 9) were much more vigorous than




seedlings from other formulations. The "starter" nitrogen apparently is beneficial to the bermudagrass seedling establishment and destructive to

the clover seedlings. The storage of the pellets for 6 months at room temperature (dif

ference between planting 1 and 2) did not greatly influence the germina tion of seed in ladino clover pellets except for formulations 5 and 9 (Table 3). These formulations included sodium silicate and dap. However, the

6-month storage period decreased germination for formulations of all

bermudagrass pellets by 10-20$, except formulations 8 and 9 (Table 4). These formulations included dap. The number of seedlings per pellet were similarly influenced. The decrease in germination could have been

due to normal loss in seed viability under these storage conditions. Excellent nodulation was noted for ladino clover pellets of all formu

lations, except formulations 8 and 9, which included the dap (Table 5). The nodulation for formulations 1 through 7 was good following 6 months

storage at room temperature (planting 2). After storage, only 60$ of the

plants from pellets of formulation 5 had nodules indicating that sodium silicate in the formulation influenced the viability of the inoculum during storage.

These data indicate that pellets including ladino clover and bermuda

grass seed can be manufactured. Formulations 3 and 9 would appear to

be most desirable for ladino clover and bermudagrass, respectively. Both

formulations would result in strong pellets with limited destruction during

Table 5. Percentage of ladino clover plants having nodules in response to inoculum added to pellets. Pellets were planted immediately after

drying (Planting 1) and 6 months after extrusion (Planting 2).

Planting

(%)

1 97°2 80 2 93 100 3 100° 80

4 89 80

5 88° 60

6 91 100

7 93 100

8 0 0

9 0 40°

Check1 0 0

LSD 12 20

'Check are plants grown in sterile sand from seed not receiving inoculum.

2Means for plantings 1 and 2 are significantly different (P = .05) for each formulation as

determined by student's T test.




handling (less than 0.5% loss). The pellets could be stored for up to 6 months at room temperature without excessive loss of seed viability. The

dap appears to result in more vigorous bermudagrass seedlings. Small

quantities of insecticides or fungicides could be formulated into the

pellets to decrease seedling loss from insects and diseases as shown by other researchers (6, 7, 12).

The pellets can be manufactured very inexpensively. The kaolin, PVA, and seed would cost approximately 13C kg"1 which would be adequate to seed an area of 1000 m2. The increased accuracy in seed distribution

during aerial application and the lowered cost for seeding because of the reduced rate should make pelleted seed desirable for broadcast seeding small seeded crops.

Literature Cited

1. Brockwell, J. 1962. Studies on seed pelleting as an aid to legume seed inoculation. 1) coating materials, adhesives, and methods of inocula tion. Australian J. of Agrie. Res. 13:638-642.

2. Brockwell, J. and L. J. Phillips. 1970. Studies on seed pelleting as an aid to legume seed inoculation. 3) Survival of rhizobium applied to seed sown into hot, dry soil. Aust. J. of Experimental Agrie, and An. Hus. 10:739-744.

3. Cincera, D. L. 1983. Vinyl-polymers (polyvinyl alcohol). Kuk-athmer:

Encyclopedia of Chemical Technology. John Wiley and Sons, Inc. 23:848-865.

4. Dawson, J. H. 1981. Selective weed control with EPTC-treated seed of alfalfa (Medicago sativa). Weed Science 29:105-110.

5. Elkins, D. M., F. J. Olsen, and E. Grover. 1976. Effects of lime and

lime-pelleted seed on legume establishment and growth in south Brazil. Expl. Agrie. 12:201-206.

6. Fletcher, B. 1983. The seed scene (sugarbeets, pellets, performance, fungus disease control). British Sugar Beet Rev. 51:51-52.

7. Gibson, I.A.S. 1969. Pelleting of pine seeds with Rhizoctol and other

fungicides for control of damping-off in Kenya highland nurseries. East African Agrie, and For. J. 35:98-102.

8. Heath, M. E., R. F. Barnes, and D. S. Metcalfe. 1985. Forages, the science of grassland agriculture. Iowa State University Press, Ames,

Iowa. 643 pp. 9. Hoagland, D. R. and D. I. Arnon. 1950. The water culture method for

growing plants without soil. Calif. Agrie. Exp. Stn. Cir. 347. 32 pp. 10. Hull, A. C., R. C. Holmgren, W. H. Berry, and J. A. Wagner. 1963.

Pellet seeding on western rangelands. U. S. Dep. Agrie. Misc. Pubis. 922. 27 pp.




11. Johnson, J. J. 1975. New developments in seed pelleting and seed

coating with special reference to rangeland improvement. Outlook on

Agriculture. 9:281-283.

12. Kakenhoff, E. 1982. Pelleting seed to control damping-off and rodents (Pythium, Rhizoctonia). The Plant Propagator 28:1-3.

13. Millier, W. F. and C. Sooter. 1967. Improving emergence of pelleted vegetable seed. Transactions of the ASAE 10(5):658-666.

14. Nitragin Co. 1975. The Pelgel method of inoculation. Inf. Bui. No. 1622. The Nitragin Co. 2 pp.

15. Norris, D. 0. 1973. Seed pelleting to improve nodulation of tropical and subtropical legumes. 5.. The contrasting response to lime pelleting of two rhizobium strains on Leucaena leucocephala. Aust. J. of

Experimental Agrie, and An. Hus. 13:98-101.

16. Smith, A. E., J. J. Silvoy, and L. L. Goodroad. 1986. A system for

converting woodland to pasture. J. of Soil and Water Conserv. In Press.

17. Sooter, C. A. and W. F. Millier. 1978. The effect of pellet coatings on the seedling emergence from lettuce seeds. Transactions of the ASAE 21 (6): 1034-1039.



Documents

SEED PELLETS FOR IMPROVED SEED DISTRIBUTION OF SMALL SEEDED FORAGE CROPS