Title Page

Group Title: Department of Soils mimeographed report
Title: Comparative accuracy of certain open-side and open-end fertilizer sampling tubes
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00091560/00001
 Material Information
Title: Comparative accuracy of certain open-side and open-end fertilizer sampling tubes
Alternate Title: Department of Soils mimeographed report 57-1 ; University of Florida
Physical Description: 7, 2 leaves : ; 28 cm.
Language: English
Creator: Volk, G. M ( Gaylord Monroe ), 1908-
Myers, J. Mostella ( Julian Mostella ), 1921-
University of Florida -- Dept. of Soils
University of Florida -- Agricultural Experiment Station
Publisher: University of Florida, Agricultural Experiment Station
Place of Publication: Gainesville, Fla.
Publication Date: July 2, 1956
Subject: Fertilizer equipment -- Testing -- Florida   ( lcsh )
Fertilizers -- Testing -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
Statement of Responsibility: by G.M. Volk and J.M. Myers.
General Note: Cover title.
General Note: "July 2, 1956."
 Record Information
Bibliographic ID: UF00091560
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 310116369

Table of Contents
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Full Text


July 2, 1956



G. M. Volk and J. M. Myers

University of Florida
Agricultural Experiment Station
J. R, Beckenbach, Director
Gainesville, Florida

Comparative Accuracy of Certain Open-Side and Open-End
Fertilizer Sampling Tubes

G. M. Volk and J. M. Myers1

Investigations under the general Fertilizer Control Research Project

indicated that the official Florida sampling tool used in collection of

control samples might be causing a negative bias in nitrogen recovery and

a corresponding positive bias in certain other ingredients in incomplete

mixtures deriving nitrogen largely from pelleted materials. The Florida

tube is a simple slotted open-side, closed-end tube 3/4 inch outside

diameter with 30 inch penetration depth.

To examine this source of bias, various sampling tools were devised

and tested by sampling a 10-0-10 fertilizer made up from pelleted ammonium

nitrate, fine crystal muriate of potash and builder's sand. The fertilizer

was placed in a box 6 x 6 x 30 inches, over one end of which was clamped a

section of standard 4-ply fertilizer bag through which the various tools

could be inserted. The cover of the box was inset so that compaction

pressure could be applied for certain of the tests.

A minimum of eight and a maximum of 24 replicate cores were drawn in

various tests. Each core was individually put into solution, and the

solution analyzed for ammoniacal nitrogen as a measure of pelleted ammonium

nitrate and for chlorine as a measure of muriate of potash recovered for a

given core. The fertilizer was placed in the box in four different ways:

1 Dry mixture in loose condition.
2 Dry mixture in compact condition.
3 Moist mixture in loose condition,
4 Moist mixture in compact condition,

Soils Chemist and Associate Agricultural Engineer, respectively.


Moisture was supplied to 3 and h by adding water to the builder's

sand before mixing. 'his amount of moisture in the mixture was barely

perceptible to the touch, but was enough to develop some adhesion of

materials without making them sticky. Compacted mixtures removed after

completion of a test were very friable.

The sample tubes tested were based on two principles. They were the

open-side closed-end tubes represented by the official Florida tube, and

open-end cone-shaped tubes developed by the writers. Tests with various

tubes indicated four possible sources of bias in recovery of pelleted


I Disproportionate entry of fine materials as compared to pelleted

materials in a loose dry mixture entering an open-side tube.

II Segregation of materials around the perimeter of a hole forced

into mixtures by a solid penetrating point. The geometry of

particle size distribution would tend to give a disproportionately

large amount of fines at the perimeter as a result of forcing

back of larger particles.

III Formation of a compression and shear zone ahead of a tube. The

process tends to develop segregation to the extent that the

compression cone most resistant to shearing differs from the

composition of the mixture.

IV The relation of curvature of the circumference of an open-end

tube to the diameter of the larger pellets in the mixture. As

greater curvature is introduced by decreasing diameter, the

tendency for larger pellets to move out instead of in becomes



The order of development of tubes resulted from the order of recog-

nition of possible sources of bias. This explains the non-orthogonal

nature of the tests. Statistical comparisons were made by using the

average standard deviation of 4.34, and making comparisons individually

to values obtained by the Florida tube for the comparable moisture and

compaction status, based on the standard error for the least number of

replicates in the pair of values being compared.

Data are summarized in Table 1. The individual standard deviations

are included because they have certain indicative value over and above

their use in determining significance.

Descriptive names and letters for the various tubes have the

following meaning;

Official Florida This is the tube exactly as used for the collection

of official samples.

Florida F The official tube with a I inch fin welded the length of the

tube on one side of the slot so as to give a deeper "bite" as the tube

is turned in filling.

Florida PDF The official tube with longer and sharper point and fitted

with a finned sleeve thus making a double wall tube that would permit

closure during penetration and withdrawal. The long point was intended

to reduce the compression cone, the fin to give deeper "bite", and the

closure system to prevent rakeoff of surface pellets during withdrawal.

VM This refers to the open-end cone principle embodied in a series of

tubes. The tube was constructed of stainless steel sheet welded into a

cone 1 1/8 inch diameter at the large end and decreasing in diameter at

- inch per foot toward the cutting or insertion end. The associated

-4 -

figure in inches refers to the insertion depth measured from the large

end, after allowing 2- inches projection for a handle.

VM 20" S Cut at 45 slant with inside diameter of 0.60" at cutting end.

VM 15" Cut vertical. 0.75 inside diameter.

VM 15"SC Cut at 780 slant. 0.75" inside diameter except the heel of

slant depressed to reduce diameter to 0.63" and provide additional con-

striction at the opening into the tube. It was intended that the long

point of the slant would separate the mixture without bias before a

pressure cone developed, and that the depressed heel would allow rapid

release of pressure within the tube end to aid unbiased entry.

VM 15"C Vertical cut but constricted perimeter to give 0.65" inside

diameter of cutting edge.

VM 10" Cut vertical. 0.85 inside diameter.

VM 10"C Constricted like VM 15"C to give 0.77" inside diameter.

VM 10"B Cut vertical with ring inserted to give blunt with 0.69" inside

diameter and marked constriction.

The Florida type tubes were inserted with gradual even pressure in

inverted position, and then turned to place the slots upright for with-

drawal. The VM type tubes did not obtain the amount of sample to be

expected when used with gradual pressure. Driving these tubes with sharp

blows with a light ballpeen hammer proved to be the best procedure. This

took advantage of the inertia of the material to move it into the tube

with least bias.

Data in Table 1, fourth column, show first that the Florida tube

introduced a definite negative bias in recovery of pelleted ammonium

nitrate in dry mixtures. Modifying the Florida tube gave no improvement.

The best recovery with this tube was from moist loose mixtures where dry

segregation of fines, of Type I bias did not occur, and where there was

not sufficient resistance to penetration to develop much segretation of

Type II. VM tubes did not improve on accuracy with this mixture. This

agrees with results from complete mixtures sampled under the general

Fertilizer Control Research Project.

The VM tubes improved accuracy in practically all instances where

the Florida tube was grossly in error. The 15 inch tube gave significantly

increased recovery of ammonium nitrate in all instances, except when a tube

with constriction around the entire perimeter was used; or with the loose

moist mixture where the Florida tube itself gave little bias. The improved

accuracy amounted to reduction of the bias by 50 to 60 percent.. Apparently

the slant cut and partial constriction of VM15"SC is not necessary. A tube

of greater diameter would reduce bias still more, and such a tube may be

practical provided damage to the bag is not a limiting factor. Constriction

around the complete circumference of the tube appears to be undesirable,

probably because of greater development of a compression cone.

Figure 1 shows the type of positive bias usually occurring for muriate

of potash when a negative bias of pelleted ammonium nitrate exists. This

is a summary of all samples analyzed for Table 1. If the pelleted nitrogen

does not enter the tube in proper proportion, then it must be substituted

with fines to take its place. The degree to which this negative correlation

occurred is shown by the graph, The fact that the regression lime passes

through the 100 percent recovery intersection indicates the accuracy of the

investigational procedure.

The Florida tube collects from 100 to 150 grams of sample per probe,

while the VM15" tube collects 100 to 130 grams per probe depending on

dryness and compaction of mixtures. The best construction for the VM15"

tube and protective driving head to withstand field usage is yet to be

decided. The head used for the laboratory tests was a 2 x 2 inch piece

of oak flooring to the reverse side of which was nailed a rubber stopper

of proper size to center it and hold it to the tube end. There was no

evidence of clinging or compaction in the cone shaped tube. A simple

cylindrical tube was not considered because experience with soil tubes

indicates that jamming sufficient to increase the compression cone would

result even if constriction at the cutting edge were included.

Depth of penetration of a tube is important in obtaining a long cross

section of material, and to properly sample bagged mixtures without con-

sistently introducing the bias resulting from segregation within bags.

The official tool with 30 inch penetration is intended to be used diagonally

from corner to corner of a sack lying on its side. The principle is sound,

but in practice the most biased area probably lies next to the sack wall

and may not be properly sampled because of danger of double puncture of

the bag at extreme penetration. A substitute would be 2 penetration,

assuming sacks are sampled from either end with equal frequency. This

would eliminate one serious objection to the VM sampler the large

diameter and resulting bag damage necessary to give penetration depth

equal to the Florida tube, yet retain the cone shape essential to free entry

of the sample. A sampler of 15 inches penetration depth appears to be

within reason.


The primary contribution of these tests is the principle of the cone-

shaped open-end tube, and the use of sharp, light driving blows rather

than pressure as the method of insertion. The value of moisture or a

similar factor to increase cohesion is indicated. It is suggested that

further testing must now be done under actual field conditions. The

most promising tube to compare to the official Florida tube would be VM1N"

without slant or constriction.

In using this tube it is necessary first to make a hole in the bag

with a pointed probe so that the point of the tube can be inserted without

carrying a wedge of paper and restricting freedom of entry of the sample.

The weight of the driving hammer will be determined by the weight of the

tube plus head, and by resistance to penetration encountered in routine

use. Its weight should be such that a sharp blow will move the tube

between one-half and one inch.

250 copies Soils Department 7/5/56

Table 1. Percentage Recovery of Nitrogen from 10-0-10
Made up From Pelleted Ammonium Nitrate
Fine Crystal Muriate of Potash and Builder's Sand.

S: : : Statistical :
: : No, of : Standard : Percentage : Significance :
: Tube : Samples : Deviation : Recovery of : over Off. :
: Type : Drawn : (Av. 4.34) : Nitrogen : Florida Tube :
: Dry Mixture in Loose Condition
: Off.Florida : 16 : 6,02 : 908 :
: VM 20" S : 8 : 3.36 : 93.4 : No
: VM 15" : 8 : 3.29 : 96.7 : Yes (.01)
: VM 15" SC : 16 : 6.45 : 94.6 : Yes (.01)
: VM 15" C 8 : 2.97 : 91.8 : No

: Dry Iisture in Compact Condition
:Off.Florida : 24 : 4.40 : 90.2
: Florida F : 8 : 3.21 : 90.3 No
: Florida PDF : 8 : 5.7 : 87.2 :No
:VM 15" 9 : 3.60 : 9.8 : Yes (.05)
SVM 15" SC 16 : 7.71 : 95.8 Yes (.01)
: VM 15" C 8 2.61 : 90.3 :No
: VM 10" 8 : 6.83 : 100.9 : Yes (.01)

: Moist Mixture (0.44% water) in Loose Condition
: Off.Florida : 24 : 5.78 : 97.2* :
:Florida F : 8 : 3.6 : 95. No
SV 20" S : 16 : 2.81 : 95.6 No
:V 15" 8 : 2.59 : 97.1 : No

: Moist Mixture (0.h44 water) in Compact Condition
: Off.Florida : 18 : 5.38 : 93.2- :
: V 15" : 16 : 2.79 : 97.7 : Yes (.01)
: VM 15" SC : 22 : 4.79 : 97.6 : Yes (.01)
:VM 10" : 8 : 4.20 : 9.1 : No
:VM O" B : 8 : 3.2 : 96.5 : No

* Official Florida tube gave significantly greater recovery (.01)
from moist mixturesthan from dry mixtures under similar compaction.

Percentage Potash Recovery


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