CA1041788A

CA1041788A - Coated seeds

Info

Publication number: CA1041788A
Application number: CA193,890A
Authority: CA
Inventors: James J.A. Mclaughlin
Original assignee: FRUITGROWERS CHEMICAL Co Ltd
Current assignee: FRUITGROWERS CHEMICAL Co Ltd
Priority date: 1973-03-02
Filing date: 1974-03-01
Publication date: 1978-11-07
Also published as: GB1465979A; AU6626274A; ZA741357B

Abstract

ABSTRACT
It is known to coat seeds with various types of coatings to assist in plant development from the seed. It has been suggested to coat seeds with absorbent coatings which contain bacteria or agricultural chemicals. The utility of such processes is limited by the compatibility of the substance carried in the absorbent coating and the adhesive used to bind the coating to the seed, or the processing conditions to obtain proper adhesion between the absorbent carrier and the seed. The present invention seeks to overcome these drawbacks by providing a process for preparing coated seeds comprising mixing seeds with a biologically inert water soluble adhesive, feeding into the mixture a finely divided inert absorbent powder being of a particle size to pass a 150 mesh B.S.S. in which the absorbency is at least partially satisfied by pretreatment with water or a non aqueous liquid and forming on the said seeds a coating of powder bonded by the adhesive and drying the coated seeds to restore the powder to a liquid content of less than 0.5% by weight of coating.

Description

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~10~7~38 THIS INVENTION relates to modification of seeds.
Seeds have often been prepared with a desirable agricultural chemical added as a coating to each seed e.g.
fertilizers, fungicidesO Such chemicals have been added to the seed in the discontinuous state and where -the chemical is toxic the discontinuous s-tate crea-tes danger to workers due to the fine particle size of the powders involved In our British Patent Number 129937~ we have described and claimed a granule consisting of an inert core coated wi-th a finely divided absorbent powder bonded to the core with an adhesiveg where -the absorbent coating on the inert core can he used to absorb an agricultural chemical in a liquid state which avoids the handling of fine powders of toxic chemicals.
This invention provides for the use in such a granule, of a seed instead of the inert core therein pro-posed~
By the invention biologically active chemicals are placed in close proximity to the developing roo-t system of plantsO The invention has particular applicability to those chemicals which are absorbed by the root system and translocated within the plant to its aeril parts. Many of these l'systemic" chemicals are in a liquid form and the current method of applying such chemicals has been by direc-t placement in the seed row or by spraying to the plants foliage. By the invention the chemicals are placed mo~e effectively and efficiently to yield a beneficial effect on the growth and welfare of the plant e.g. by , ... . . .

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controlling pests or diseases of roots or aeril parts of the plant or by aiding its nutrition.
The term "Agricultural Chemical~s)" as used in the specification is meant any material(s) having an important influence on biological pro- -cesses, but the chemicals when used, shall not inhibi~ germination of the seed or markedly impair seedling vigour. In particular, the ~erm includes fertilizers, micro-organisms, fungicides, insecticides ~and other pest control chemicals) herbicides, trace elements and the like.
It is an object of this invention to provide a coated seed which, in manufacture, can be prepared with a known absorbency wherein the agri-cultural chemical can be applied to the coated seed in the continuous state.
According to this invention there is provided a seed coated with a finely divided absorbent powder which is bonded to the seed surface with a biologically inert adhesive.
Further according to this invention there is provided a process for preparing coated seeds comprising mixing seeds with a biologically inert water soluble adhesive, feeding into the mixture a finely divided inert absorbent powder being of a particle size to pass a 150 mesh B.S.S. in which the absorbency is at least partially satisfied by pretreatment with water or a non aqueous liquid and forming on the said seeds a coating of powder bonded by the adhesive and drying the coated seeds to restore the powder to a liquid content of less than 0.5% by weight of coating.
In a preferred embodiment the thus prepared dried coated seed is mixed wi~h an agricultural chemical in the liquid state whereby the chemical is absorbed by the coating on the seed.
Most preferably the dried coated seed is mixed wi~h an agricul~ural ;
chemical which is a plant growth regulating agent or systemic fungicide, ;;
insecticide, nematocide or acaricide.
Thus in accordance with the invention the seed surface is firstly coated with an adhesive acting as an agent to bond the powder to the seed.
Successive applications of adhesive and powder may be applied to produce a coating with a greater absorbency. The coated seed can now absorb : ' ' ~ _ 2 -agricultural chemicals such as fungicides, micro-organisms, fertilizers~ insecticides, herbicides and so consti-tute a readily controllable means of making such substances available to the seedling, mature plant, land or other 5. desired locusO
The seeds used for the process include those of all food and fodder crops and of such plants as may be used in horticulture and agricultureO
Finely divided absorbent powders used in accordance with this invention are powders which can absorb agricul-tural chemicals (when in a continuous state) and, the powders must be inert to the absorbed agricultural chemicalO
Such powders include finely ground mineral substances such as absorbent clays, attapulgite9 pumice, zeolite, diatomite, and modi-~ied diatomaceous materials (modified to improve B absorbency) such as Microcel E, fertilizers and finely ; ground organic substances such as peat, wood powder and combinations of finely ground mineral substances and/or finely ground organic substancesO
The adhesive used in accordance with this invention is preferably a water soluble adhesive in order that the adhesive bond between the finely-divided absorbent powder containing the agricultural chemical and the seed surface is dissolved when the coated seed is applied -to the soil surface or sown under, The solubili-ty of the adhesive in wa-ter can be high in order to obtain a rapid release of the agricultural chemicals absorbed in the finely divided absorbent powder or the solubility can be low in order to obtain a slow release of the agricultural chemical~ The ~ ~Rr~ 3 ' ~ .

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lq~8 adhesive shall ~lso be chosen to conform with the require-ments of -the agricul-tural chemical to be applied to the coated seed1 iOeO the agricultural chemical in its continuous state will not solubilise the adhesive of the seedO Furthermore the adhesive must be inert to the agricultural chemicals incorporated in the absorbent coating.
Sui-table water soluble adhesives are -those such as carboxymethyl cellulose, gum arabic and alginates.
The agricultural chemicals applied to the seed are in the continuous state, such as solutions in wa-ter or non-aqueous solvents or as liquids in their own right. These can be modified by admixture of two or more different kinds of agricultural chemicals and also by the addition of wetting agents, emulsifiers and stabilisersO
According to this invention the quantity of absorbent powder applied to the seed can vary depending on the parti-cular requirements. Addi-tional quantities of powder may be appliecl to permit the absorption of larger quantities of i agricultural chemicalO Alternatively additional quantities of powder may be applied to the seed in order to dilute a particular agricultural chemical, or to build up the seed to a size capable of being sown individual]y, by a single seed selecting machineO The powder is in a finely divided state preferably passing a 150 mesh BSS more preferably 2S having 95% of its particles passing a 300 mesh BSS.
`i In this invention the process of coating the seed with absorbent powder consists of conveying the seed to a suitable blender, adding the adhesive to form a mixture within the blender and feeding the finely divided absorbent i . !

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powder into the mix-ture to form an absorbent coating on the seed.
The finely divided absorbent powder material is preferably first intimately mixed with water or a non-aqueous liquid before appLication o~ the powder to the mixture of seed and adhesive. In this way the absorbency of the finely divided absorbent powder is satisfied and thus will not tend -to absorb excess quantities of the adhesive, and the amount of adhesive required is reduced to a minimum. After adding the damp absorbent powder to the mixture and causing formation of an absorbent coat, the coated seeds are -then dried to remove the water or non-aqueous liquid from the absorben-t coating to return to the original absorbency of the absorbent coatingO If a non-aqueous liquid is used then ' 15 a system of liquid recovery of the liquid is preferably in-r corporated in the drying apparatus.
The quantity of a-dhesive used depends on the quantity of powder to be applied to the seed. The maximum quantity of powder which can be e-ffectively applied in one applica~
tion depends partly on the nature of the powder, partly on the method of application of the powder to the adhesive coated or previously coated seed and partly on the size of the seed but in any particular circumstance can readily be determined.
Thus the coated seeds according to this invention are preformed with an absorben-t coa-t, and each coated seed produced in each batch will generally have a uniform amoun-t of absorbent powder on each seed. Each absorbent powder ! used in this invention has either a known water absorbency ~,, I .

~4~788 or -this can be readily determined by trial. ~imilarly their absorbency in respect of various agricultural chemicals can be determined by trial. Thus the absorben-t c!oated seed generally provides a consistent ratio of weight of seed to weight of agricultural chemicalO When the agricultural chemical is applied to such coa-ted seed in the quantity caLculated to fully satisfy the absorbency of -the weight of coated seed concerned, it is consisten-tly found that the percentage by weight of agricul-tural chemicals carried by each coated seed is in the same order. Thus the coated seed according to this invention allow a selec-ted weight of agricultural chemicals to be absorbed uniformly amongst a selected weight of coated seed. Consequently when this weight of coated seed is applied -to a selected area, the ;
dose rate of the agricultural chemical per unit area of that chemlcal selected is uniform.
To the coated seed there may also be applied water soluble dyes of any required colour in order to distinguish different -types of produc-t. Dyes soluble in the agricul-tural chemical in its continuous state may also be employed.
The coated seed according to this invention may beprepared by the following production method.
~1) A ribbon blender of conventional design and of required capacity is equipped with spray noYzlesO The finely divided absorbent powder is first blended and then sprayed with water to produce a damp powder. Dye ma-terials, wetting or other modifying agents may be added at this stage to the water.

(2) The damp dust from the blender is passed through a .

~ 8 hammer mill and then packed off in weighed amounts in polythene bags.

(3) A ribbon blender of modified design is used to enable the ribbons to be locked in place and the drum and ribbons I 5 to be rotated as a single unit. One convenient size is a drum of 2' in diame-ter and 4' in leng-th which can be driven both clockwise and counter clockwise at a speed of about 27 r.p.m. A hinged lid is provided for filling and emptying~
(a) The required charge of seed is placed in the blender and adhesive solution poured or pumped in through a hose.
(b) The ribbons only are operated for a short period in both directions until the adhesive solution is evenly dis-tribu-ted through the mass of seed.
(c) The damp absorbent powder is then added. The ribbons I only are then turned for a short period. During this turning of the ribbons some of the absorben-t dust adheres to the seed with the result that individual seeds no longer adhere one to another. It is important tha-t this step is not taken too far otherwise abrasion can occur to the extent tha-t -the adhesive itself is lost wholly or partly from the seeds and the desired coating cannot be achieved. The ribbons are thenlocked and the drum rotated. This rotation provides the rolling motion necessary -to coat the remaining absorbent powder on to the seed.
(d) If additional powder is required to be applied to the seed coa-ted in step (l) the coated seed is removed from the blender and transferred to an exposed rotating bowl or enclosed rotating cylinder. The seed is rolled by the I
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rotation of the bowl or cylinder whilst adhesive is applied as finely dispersed droplets from spray nozzles, An applica-tion of powder to the adhesive sprayed seed follows and rolling is continued until the powder is suf-~iciently bonded~ This process may be repeated un-til a desired quantity of powder has been applied.

(4) Equipment for drying may be a vacuum dryer~ moving band or fluid bed. The seed coated wi-th absorbent powder ; is dried a-t a produc-t temperature which rises to about 110F
and is completed within ~0 mins when moisture content of the ~ -coat is at a maximum of 005%.

(5) The dried coated seed is screened to remove any over-size or loose dust and is then packed off in weighed amounts in polythene lined bags and stored ready for the next step of the addition of the agricultural chemical in its con--tinuous state.
- (6) Any -type or size of rotating drum open or closed may be used when applying the agricultural chemical. Provision - is made for pouring the agricultural chemical from a measure for small amounts directly on to the absorbent coating in an open con-tainer such as a concrete mixer, or as a coarse spray from a metering pump or other dispensing unit where coated seed are held in an enclosed drum. The drum is charged wi-th the required amount of the initially prepared coated seed from (5) above and an appropriate quantity of the agricul-tural chemical is poured or sprayed in. Rotation of the wet mass of coated seed is continued until all the agricultural chemical is ta~en up by the absorben~ coat and the products become free flowing.

~1 r~ ,,, ~0~a1788 (7) Where the coating material is required to dilute -the agricul-tural chemical and the absorbency of the coating is greater than that required to absorb the quanti-ty of agricultural chemical applied; then application of the chemical should take place in an enclosed revolving cylinder.
In this method -rinely dispersed droplets of the chemical are applied evenly to the surface of the coating material on -the seed from a nozzle directed onto the rolling coated seed inside the cylinder.
(8) The finished product is screened to remove any over-size and packed off.
The quantity and composition of the absorbent powder used is determined by the physical nature and active chemical content of the agricultural chemical -to be used.
The objec-tive is to produce an absorbent coating which takes up the required quanti-ty of agricultural chemical, in its continuous state, slowly, thereby allowing sufficien-t time for even distribution throughout the mass of coated seed but which has sufficien-t absorbency to ensure that within a few minutes any excess liquid is completely absorbed and the coated seed become fxee flowing. There are several variables which can be adjusted to achieve these objectives:
(i) The nature of the absorbent powder mixture. Use B of ~icrocel E increases absorbency but when used alone gives ~5 rise to difficulties o-f p:coducing a stable absorbent seedcoat. Additions of clay, pumicite9 and diatomiteg in vary~
; ing proportlons improves stability and serves to adjust absorbency to required levels.
(ii) The proportion of water added to the absorbent powder.

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It is necessary to satisfy most of the absorbent capacity of the powder by addition of water to enable effective coat-ing of the seed. The least amount of water ls used to reduce cost of drying. If wa-ter is increased loss of absor~ency occurs through excess compaction of the coat.
(iii) The quantity of the adhesive used on the seed. This has to be sufficient to produce a stable coa-t but not an excess which causes undue compac-tion o-f the coat and leads to loss of absorbencyO
(iv) The weight of absorbent powder to seedO The absorb-ency of the coated seed can be adjusted to greater or lesser amount according to the proportion of powder used.
~v) Prolongation of the time of rolling causes increased compaction of the coat resulting in a reduced absorbency of the finished product.
(vi) The physical nature of the agricultural chemical.
The percentage of active chemical which can be -taken up depends on the density of the agricultural chemical, on the active conten-t of the technical chemical and on the use of additives. If absorbency of the coated seed is in excess then distribution may be uneven with some of the seeds carrying reduced amounts and others carrying excess amounts of active chemical. This can be corrected by dilu-tion of the agricultural chemical with a suitable liquid but the ;- 25 preferred method is to adjust the absorbent character of the seed coat itself at time of manufacture, or as per method ou-tlined under (7)~
Agricultural chemicals such as herbicides~ insect~
icides, and fungicides can be readily incorporated within ,. ', ' ! . . . . ~, ~ ' . .

q88 the absorbent coat when the agricultural chemical is in a continuous state. When i-t is desired to incorporate micro-organisms such as Rhizobia within the absorben-t coat of the seed then it is desirable to convert the micro-organisms ` from its inert state when freeze dried or such like into a suitable continuous and viable state. Thus -the micro-organism may be incorporated in a nutrient broth and this nutrient broth containing the micro organism can then be -applied to the absorben-t seed. The absorbent coat will preferably be of such a type to support the micro-organism in a viable state and, where conditions require, to provide a medium wi-thin which the organism can multiply. Nutrient materials may be added to the absorbent coat to support the growth of the micro-organism and also other chemicals may be added to the absorbent coat to protect the micro-organism against other effects such as that of ultra violet light The adhesive bound absorbent coat according to this inverltion can be provided-such that the coat contalning -the agricul-tural chemicals will rapidly disperse and release the agricultural chemicals in the presence of water or where the desired use of the chemical requires a slower rate of release of the agricultural chemical to the soil area, then the adhesive can be such tha-t it will be resistant to the effects of water and the absorben-t coat will release the absorbed chemicals slowly by leaching or by vola-tilisation.
In a further aspect of this invention -the seed can be mixed wi-th an initially water soluble adhesive compound of such a type that a-fter addition of the absorbent powder material and formation of coat, on removal of the water, ~ o~
the water soluble adhesive becomes insoluble in water e.g.
using an acrylic emulsion polymer as the adhesive.
In a further aspect of -the inven-tion the seed can be mixed with an adhesive of such a type -that af-ter addition of the absorbent powder and formation o-~ the coat, the further addition by spraying of an agent or additive causes the adhesive to reac-t chemically to form an insoluble adhesive.
In a further aspect of this invention there can be added a chemical wh~ch adjus-ts the pH of the absorbent coat to suit the agricultural chemical to be applied which chemical will be inert to the agricultural chemical, or to provide a suitable pH medium for the micro-organism.
Af-ter dispersing the agricultural chemical into the absorbent coat of the seed and separa-tion of the coated seed as free flowing it is desirable to add a lubricant such as talc to the coated seed to improve the ~ree flowing pro-perties of the coated seed and thus improve the rate and area of distribution of the coated seed in application by any suitable meansO
Furthermore, various other formula-tions can be added in small amoun-ts as -trace elemen-ts to assist in biological `
function.
The following non~limi-tative examples are given by way of explanation~
Percentages are given by weight.

_ To coat white clover seed with finely divided fertilizer and from i-t formulate a product containing chlorobromopropane 1~4 ~
equal -to 20% of the weight o~ the actual seed.
For -this product the fertilizer is not dampened before application to the seed.
Fertilizer Formula - Rock phosphate - 80%
Dolomite - 20%
(1) ~lend fertilizer as described in production methods 1 and 2 but do not add water.
(2) Coat seed with powder by production method 3 steps (A) to (C).
(A) Charge the blender with 200 lbs white clover seed and pour or pump in 40 lbs of 25% Gum Arabic solution.
(B) Deposit 150 lbs of the fertilizer on to the adhesive coated seed and rotate blenders 10 seconds in each direction or until seed has ! been separated by the fertilizer.
(C) Lock ribbons and rotate blender for 5 mins in each direction to compact the fertilizer on to the seed.
20 (3) Transfer the coated seed on to a fluid bed or band drier through which air not exceeding 110F is passed.
- Continue drying until moisture of the coat is 0.5% or lessO
~; Dried prGduc-t is screened to remove oversize and fine dust.
(4) ~pplication of chlorobromopropane.
Transfer 200 lbs of dry coated seed to a rotating bowl or drum and apply 23 lbs chlorobromopropane as described in production methods (6) and (~).

The application of absorbent powder to swede seed in two _ 13 -:

stages to provide substantially more absorbent capacity -than required -to hold the insecticide trichloronate when applied at 3% of actual seed weight~ The excess coating material ~ Gr,~/uen~ :
3L~ in this example acts as a ~*~ for the trichlorona-te~ -thus reducing -the concentration of the chemical near the actual seed. By this method greater quantities of chemical may be carried without harming the seed.
Powder formula - 31.6% micro Cel E
5.3% china clay 63.1% water Adhesive formula 1st stage - 25% Gum Arabic 3% Sodium Alginate 72~ water (Dissolve sodium alginate in ho-t water before adding gum -arabic) Adhesive formula 2nd stage - 25% Gum Arabic ` 75% water l. Blend powder as described in production me-thods l and 2.
2. (a~ (lst Stage). Charge blender with 100 lbs seed and pour or pump in 30 lbs adhesive (lst stage formula).
(b) Operate the ribbons 60 seconds in each direction to blend adhesive.
(c) Deposit 60 lbs of the prepared powder and rotate ribbons 10 seconds in each direction or until seed has been separated by powderO
(d) Transfer seed to a separate rolling drum, and rotate until powder has compacted on the seed.
(e) Apply 30 lbs adhesive (2nd Stage formula) by means _ 14 -~tr~e ~rk - ~)4~7~ :
of fine jet nozzles in the drum whilst coated seed is rolling.
(f) Stop drum, add 60 1bs more prepared powder and commence rolling whilst applying a further 30 lbs of ad-hesive (2nd stage formula) by spray.
3. Transfer coated seed on to a band or fluid bed drier - through which air not exceeding 110F is passedO Continue drying until moisture of the coating material is 0.5% or less.
Dried product is screened to remove oversize and fine dust.
4. Application of TrichloronateO
(A) Find the exact ratio of coating material to seed~
(B) Transfer a quantity of coated seed representing 75 lbs actual seed to an enclosed rotary cylinder and apply .25 lbs AI-trichloronate by means of a very fine lS spray as described in step (7) and finish as described in step (~)0 ; The coating of carrot seed with a mixture of finely divided absorbent peat and dolomite and from it formulate a product 20 containing cells of Bacillus subtilis suspended in a nutrient broth.
Coating material formula:-Finely divided peat - 64%
Finely divided dolomite - 16%
Water - 20%
tThe peat used contains approx. 53% organic matter as determined by loss on ignition and provides a suitable environment for maintaining -the viability of the micro-organ-isms ~vhen they are absorbed in a continuous state).

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1. Blend coating materials as described in production methods 1 and 2.
2. Coat seed by production method 3, Steps (A) to (D) ..
(A) Charge the blender with 200 lbs carrot seed and pour or pump in 80 lbs of adhesive solution consisting of 25% Gum Arabic, 75%
water~
(B) Operate the ribbons, 60 seconds in each direction to mix seed and adhesive3 (C) Deposit 250 lbs coating material on to seed adhesive mixture, and rotate ribbons 20 seconds in each direction or until seed has been separated by the coating material.
(D) Lock ribbons and rotate drum 5 minutes in each direction until the coating material is compacted on to the seed.
; 3. Transfer the coated seed on to a band or fluid bed, drie~ through which air not exceeding 110F is passed.
Continue drying until moisture content of this coat is 0~5%
or less. Dried seed is screened to remove any oversize or surplus dust and stored in airtight containers until treated ~ith a broth suspension of Bacillus subtilis just before sowing~
4. Application of nutrient broth containing Bacillus subtilis.
Coated seed to be treated is transferred to an enclosed revolving cylinder and Bacillus subtilis broth applied at the rate of 10 lbs per 100 lbs coated seed as described in pro-duction step 7.

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1(~41788 : The quantity of wa-ter in the broth is no-t sufficient to ; dissolve the adhesive, and stability of the coating material is not markedly impaired thus permitting sowing of the coated seed by normal means.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for preparing coated seeds comprising mixing seeds with a biologically inert water soluble adhesive, feeding into the mixture a finely divided inert absorbent powder being of a particle size to pass a 150 mesh B.S.S. in which the absorbency is at least partially satisfied by pretreatment with water or a non aqueous liquid and forming on the said seeds a coating of powder bonded by the adhesive and drying the coated seeds to restore the powder to a liquid content of less than 0.5% by weight of coating.

2. A process as claimed in claim 1 wherein the liquid removed in the drying step is recovered.

3. A process as claimed in claim 1 wherein the initially water-soluble adhesive is converted after the drying step into a water-insoluble compound.

4. A process as claimed in claim 3 wherein the initially water-soluble adhesive is an acrylic emulsion polymer.

5. A process according to claim 1 further including the step of mixing the dryed coated seed with an agricultural chemical in the liquid state whereby the chemical is absorbed by the coating on the seed.

6. A process as claimed in claim 5 wherein the chemical is a plant growth regulating agent or systemic fungicide, insecticide, nematocide or acaricide.

7. A process as claimed in claim 1, 4 or 5 wherein the finely divided absorbent powder is an absorbent clay, modified diatomaceous material, fertilizer, finely ground organic powder, or mixtures thereof.

8. A process as claimed in claim 1 wherein the adhesive is carboxy-methylcellulose, gum arabic or an alginate.