Soil treating method and composition for conserving nitrogen in soil

Certain metal salts of certain substituted pyrazole dithiocarbamates are employed as the active nitrification inhibitor in the presence of reduced nitrogen fertilizers. Compositions containing these salts can be applied to the surface of the soil and can remain on said soil surface for up to 3 days or more without mechanical incorporation into the soil and retain at least about 70 percent of the pyrazole as the salt in the composition.

BACKGROUND OF THE INVENTION 
The majority of plants obtain most or all of their nitrogen requirements 
from the soil. The adequate provision of nutrient nitrogen in soil for 
plant growth is one of the foremost agronomic problems. The nitrogen in 
the soil is found to occur primarily in three forms: organic nitrogen, 
ammonium nitrogen and nitrate nitrogen, of which ammonium nitrogen and 
nitrate nitrogen are the primary forms utilized by plants. This nitrogen 
is absorbed by plants in solution from the soil in the form of ammonium 
ions and nitrate ions. 
The ammonium nitrogen in the soil occurs principally as colloidal-bound 
nitrogen, only very small quantities of the ammonium form of soil nitrogen 
are lost from the feeding zone of the plants by leaching. 
The nitrate nitrogen in the soil is derived from the oxidation or 
nitrification of ammonium nitrogen by soil bacteria or by the addition of 
inorganic nitrate fertilizers such as ammonium nitrate, sodium nitrate, 
potassium nitrate and calcium nitrate. The inorganic nitrate compounds are 
readily soluble in water and the aqueous soil medium. When so dissolved, 
the nitrate nitrogen largely exists as the nitrate ion. 
The nitrogen contained in the nitrate, in contrast to ammonium nitrogen, is 
not adsorbed by the sorption carriers of the soil. A further discussion of 
the nature of this nitrogen problem in agriculture is set forth in U.S. 
Pat. No. 3,135,594. 
Because of the anionic nature of this nitrate ion, nitrate nitrogen is 
rapidly leached by rainfall and irrigation and readily lost from the 
feeding zone of the plants. Further, the nitrate nitrogen is reduced by 
many soil bacteria to nitrogen gas. The latter process is known as 
denitrification and accounts for an additional loss of large quantities of 
nitrate nitrogen from the soil. The yearly loss from leaching and 
denitrification amounts to from 20 to 80 percent of the nitrate nitrogen 
found in the soil. 
To overcome the loss of ammonium nitrogen in the soil by nitrification, it 
is the practice to add to the soil a nitrification inhibitor. 
Representative nitrification inhibitors and their use can be found in U.S. 
Pat. Nos. 3,135,594, 3,494,757 and 3,635,690 and British Pat. No. 
1,592,516. 
While the known inhibitors are effective in reducing nitrification, they, 
for the most part, have a major drawback in that they must be incorporated 
into the soil within a very short period of time, i.e., a few minutes to a 
few hours in order to avoid losses of the inhibitor to the air. This 
requirement for quick incorporation hinders and/or restricts the use of 
nitrification inhibitors in agronomic practices where no till or minimum 
till is employed and in those areas where fertilizers are added and 
incorporation is delayed. 
SUMMARY OF THE INVENTION 
The present invention is directed to methods and compositions useful in 
crop culture, and is particularly concerned with new agronomical practices 
and compositions for conserving nitrogen in soil by suppressing the 
nitrification of ammonium nitrogen therein. The active agent of the 
compositions employed in such methods is a metal salt of a 
bis(pyrazole-1-carbodithioate) corresponding to the formula 
##STR1## 
wherein M represents cobalt, copper, iron, manganese, nickel or zinc and X 
represents hydrogen, bromo, chloro or methyl. 
The pyrazole compounds which are a part of the 1-carbodithioate are 
3-methylpyrazole, 4-bromo-3-methylpyrazole, 4-chloro-3-methylpyrazole and 
3,4-dimethylpyrazole. 
While the active pyrazoles of the present invention are normally depicted 
as shown in Formula I, it is believed that these compounds also exist in 
two additional isomeric forms. These isomers can be depicted as follows: 
##STR2## 
wherein M and X are as above set forth. 
It is further believed that the product obtained in the preparation of 
Formula I is a mixture of the three isomers and the depiction of either 
one of the isomers should be taken as the inclusion of all three isomers. 
The method of the present invention comprises applying to soil a 
composition which contains, as the active nitrification inhibitor, a metal 
salt of a bis(pyrazole-1-carbodithioate) as defined above (hereinafter 
pyrazole compound). A further feature of the method of the present 
invention is that the pyrazole compound in admixture with a reduced 
nitrogen fertilizer can be applied to the surface of soil where it can 
remain without incorporation into the soil for a period of up to 3 days or 
more, with at least about 70 percent of the pyrazole remaining. After 
administration subsequent irrigation or rainfall can distribute the 
pyrazole compound throughout the soil. 
The expression "soil" is employed herein in its broadest sense to be 
inclusive of all conventional "soils", as defined in Webster's New 
International Dictionary, Second Edition, unabridged, published in 1937, 
G. C. Merriam Co., Springfield, Mass. Thus, the term refers to any 
substance or medium in which plants may take root and grow, and is 
intended to include not only earth, but also compost, manure, muck, sand, 
synthetic growth mediums such as vermiculite and pearlite and the like, 
adapted to support plant growth. 
By the practice of this invention, the nitrification of ammonium nitrogen 
in the soil to nitrate nitrogen is suppressed, thereby preventing the 
rapid loss of ammonium nitrogen from the soil. Furthermore, by proper 
distribution of the pyrazole compound this action of inhibiting the 
transformation of ammonium nitrogen to nitrate nitrogen is effective over 
a prolonged period of time. The ammonium nitrogen may arise from added 
ammonium nitrogen fertilizers or be formed in the soil by conversion of 
the organic nitrogen constituents found in soil or added thereto as 
components of organic fertilizers. 
The expression "reduced nitrogen fertilizers" as employed in the present 
specification and claims, is understood in the art, as embracing both 
inorganic and organic nitrogenous materials containing nitrogen in the 
reduced state. Examples of known reduced nitrogen fertilizers include 
anhydrous ammonia, aqueous ammonia, inorganic ammonium salts such as 
ammonium phosphate, ammonium nitrate and ammonium sulfate, ammonium salts 
of organic acids, urea, cyanamide, guanidine nitrate, dicyandiamide, 
thiourea, urea-form and other nitrogen-containing organic chemical 
fertilizers as well as protein mixtures, animal tankages, green manure, 
fish products, crop residues, and other natural materials known to be 
sources of ammonium ions in soil. 
The application of an effective, nitrification inhibiting, dosage of the 
pyrazole compound to the soil is essential for the practice of the present 
invention. In general, good results are obtained when the pyrazole 
compound is applied in the amount of from about 0.05 to about 10.0 pounds 
per acre of soil. The preferred amounts to be employed are dependent upon 
the particular situation. Thus, in determining the amount to be employed, 
consideration is necessary as to the soil pH, soil organic matter, 
temperature, soil type and time of application. By dispersing very large 
dosages to soil, a prolonged inhibition of nitrification can be obtained 
over a period of many months. The concentration of the active pyrazole 
compound is eventually reduced to a minimum by decomposition in the soil. 
In one method for carrying out the present invention, the pyrazole compound 
is distributed to the soil in a broadcast application such as by spraying, 
dusting, distributing in irrigation water, etc. In such application, the 
pyrazole compound is supplied in amounts of from about 0.05 to about 10.0 
pounds per acre. 
In another method for carrying out the present invention, the pyrazole 
compound is administered to the soil in a band or row application. In such 
application, administration is made with or without carrier in amounts 
sufficient to supply to the soil a concentration of the pyrazole compound 
which can be as high as 10 pounds per acre or more. 
In one embodiment of the present invention, the pyrazole compound is 
distributed throughout the soil prior to seeding or transplanting the 
desired crop plant. 
In another embodiment, the soil in the root zone of growing plants is 
treated with the pyrazole compound in an amount effective to inhibit 
nitrification but sublethal to plant growth. 
In a further embodiment, the pyrazole compound can be applied following 
harvest or after following to prevent rapid loss of ammonium nitrogen and 
to build up the ammonium nitrogen formed by conversion of organic nitrogen 
compounds. Such practice conserves the soil nitrogen for the following 
growing season. In such application the upper limit is primarily an 
economic consideration. 
Additionally, the pyrazole compound can be applied prior to, subsequent to 
or simultaneous with the application of a reduced nitrogen fertilizer. 
Such practice prevents the rapid loss of the ammonium nitrogen added as 
fertilizer and the ammonium nitrogen formed from the organic reduced 
nitrogen in fertilizers by the action of soil bacteria. In a preferred 
procedure, the pyrazole compound is employed as a solid or liquid 
composition comprising a reduced nitrogen fertilizer in intimate admixture 
with the pyrazole compound. 
As indicated above, the present method embraces distributing the pyrazole 
compound as a constituent in liquid or solid fertilizer compositions. In 
such practice, the pyrazole compound is admixed with the fertilizer and 
such mixture can be modified with one or more additaments or soil treating 
adjuvants to formulate the mixtures employing conventional procedures as 
wettable powders, emulsifiable concentrates, dust, granular formulations 
or oil or water flowable emulsion concentrates. In preparing such 
formulations, the pyrazole compound/fertilizer mixture is extended with 
adjuvants including water, petroleum distillates or other liquid carriers, 
surface-active dispersing agents and inert finely-divided solids. 
Preferred adjuvants are surface-active dispersing agents and inert 
finely-divided solids; these adjuvants cooperate with the pyrazole 
compound so as to facilitate the practice of the present invention and to 
obtain an improved result. These compositions may also contain as 
additional adjuvants one or more other biologically active materials such 
as herbicides, insecticides, fungicides, miticides, bactericides, 
nematocides, and the like. The only requirement for these added materials 
is that they be both chemically and biologically compatible with the 
pyrazole compound. 
The concentration of the pyrazole compound in the compositions can vary 
considerably provided the required nitrification inhibition dosage of the 
effective agent is supplied to the soil. In general, good results are 
obtained when employing liquid compositions containing from about 0.05 to 
about 5.0 percent by weight of the pyrazole compound; in some operations, 
however, compositions containing amounts of pyrazole compound in excess of 
5.0 percent, such as from 5 to 98 percent of the active pyrazole compound 
by weight of composition are conveniently employed, as for example, in row 
or band application. With solids, good results are usually obtained with 
compositions containing from 0.05 to 5.0 percent or more by weight of 
pyrazole compound. In some circumstances, such as in high-intensity 
application, however, it is preferred to employ solid compositions 
containing as much as from 5 to 98 percent or more by weight of the 
pyrazole compound. Liquid or solid compositions in which the pyrazole 
compound is present in higher concentration can be utilized as such or can 
be employed as concentrate compositions to be diluted to prepare actual 
treating compositions. 
The liquid compositions containing active agent, i.e., the pyrazole 
compound, can be prepared by admixing one or more of the active agents 
with water or an organic solvent, with or without the aid of a suitable 
surface-active dispersing agent or emulsifying agent, and admixing this 
mixture in an aqueous solution of the desired fertilizer. 
Suitable organic solvents include acetone, diisobutylketone, methanol, 
ethanol, isopropyl alcohol, diethyl ether, toluene, methylene chloride, 
chlorobenzene and the petroleum distillates. The preferred organic 
solvents are those which are of such volatility that they leave little 
permanent residue in the growth media. 
Dispersing and emulsifying agents which can be employed in liquid 
compositions include condensation products of alkylene oxides with phenols 
and organic acids, alkyl aryl sulfonates, polyoxyalkylene derivatives of 
sorbitan esters, complex ether alcohols, mahogany soaps and the like. The 
surface-active agents are generally employed in the amount of from 1 to 20 
percent by weight of the pyrazole compound. 
Solid compositions containing the active agent can be prepared by admixing 
the pyrazole compound, dispersed in a volatile organic solvent, with the 
solid fertilizer. In another procedure, the solid fertilizer can be 
mechanically ground with a dispersion of the pyrazole compound in a 
solvent and the resulting mixture prilled, granulated or otherwise formed 
into the desired form. After coating the solvent is vaporized off. In an 
additional procedure, solid granules of the fertilizer are treated with a 
sticking agent such as mineral oil and then coated with a dispersion of 
the pyrazole compound in a solvent. 
These solid compositions may, if desired also contain an alkyl aryl 
sulfonate or other surface-active dispersing agent. Depending upon the 
proportions of ingredients, these compositions can be employed without 
further modification or be considered as concentrates and subsequently 
further diluted with conventional solid carriers such as talc, chalk, 
gypsum, clays, or the like to obtain the desired treating composition. 
Furthermore, such concentrate compositions can be dispersed in water with 
or without added dispersing agent or agents to prepare aqueous soil 
treating compositions. 
In these fertilizer compositions, it is desirable that the pyrazole 
compound be present in an amount of at least about 0.05 percent by weight 
based on the weight of the nitrogen present in the fertilizer as reduced 
nitrogen and can be present in amounts as high as 95 percent by weight of 
the reduced nitrogen in the fertilizer. Generally, though, amounts of 
pyrazole compound in excess of about 5.0 percent yield no greater 
advantage and are therefore seldom used. Thus, when a fertilizer 
composition contains both reduced nitrogen and other forms of nitrogen, 
such as in the case of ammonium nitrate fertilizer compositions, the 
amount of pyrazole compound is based on the weight of nitrogen present in 
the ammonium component. 
The novel pyrazole compounds employed in the practice of the present 
invention can be prepared employing procedures similar to those taught in 
Trofimenko, The Journal of Organic Chemistry, Volume 33, No. 2, February 
1968, pages 890-892 wherein an aqueous solution of an alkali metal 
pyrazole-1-carbodithioate is mixed with the appropriate metal ion.

The following examples illustrate the invention but should not be construed 
as limiting the scope of the invention. 
EXAMPLE I 
Zinc bis (3-methylpyrazole-1-carbodithioate) 
##STR3## 
To a solution of 7.6 grams of zinc chloride in 100 milliliters of deionized 
water was added at once a solution of 20 grams of the sodium salt of 
3-methylpyrazole-1-carbodithioate in 150 milliliters of deionized water 
with vigorous stirring. The product precipitated immediately as a yellow 
solid. The product was collected by filtration, dried and recovered in a 
yield of 14.5 grams (70 percent of theoretical). The product melted at 
151.degree.-153.degree. C., with decomposition. Upon analysis, the product 
was found to have carbon, hydrogen and nitrogen contents of 31.39, 2.60 
and 14.62 percent, respectively, as compared with the theoretical contents 
of 31.62, 2.65 and 14.75 percent, respectively, as calculated for the 
above-named compound. 
EXAMPLE II 
Sodium salt of 3-methylpyrazole-1-carbodithioate 
##STR4## 
A slurry was prepared by admixing 1.5 grams of sodium hydride with 200 
milliliters of dry tetrahydrofuran. To this slurry was slowly added, with 
stirring, 5.0 grams of 3-methylpyrazole. The solution thus formed was 
filtered and then an excess of carbon disulfide (4.65 grams) was added, at 
once with stirring. After 5 minutes, a yellow precipitate formed. Half of 
the solvent was removed in vacuo and the product was recovered by 
filtration. The product was washed with dry ether and dried. The desired 
product was recovered in a yield of 6.8 grams (62 percent of theoretical). 
The product melted at 254.degree.-255.degree. C., with decomposition. Upon 
analysis, the product was found to have carbon, hydrogen and nitrogen 
contents of 33.13, 2.71 and 15.39 percent, respectively, as compared with 
the theoretical contents of 33.32, 2.80 and 15.55 percent, respectively, 
calculated for the above-named compound. 
EXAMPLE III 
Zinc bis (3,4-dimethylpyrazole-1-carbodithioate) 
##STR5## 
A mixture is prepared by admixing 7.9 grams of the sodium salt of 
3,4-dimethylpyrazole-1-carbodithioate in 50 milliliters of deionized 
water. This mixture is added to a mixture of 2.6 grams of zinc chloride in 
250 milliliters of deionized water. A precipitate formed immediately and 
the product was recovered by filtration and dried. The product was 
recovered in a yield of 6.2 grams (75 percent of theoretical). The product 
decomposed above 210.degree. C. Upon analysis, the product was found to 
have carbon, hydrogen and nitrogen contents of 35.00, 3.42 and 13.85 
percent, respectively as compared with the theoretical contents of 35.33, 
3.46 and 13.74 percent, respectively, as calculated for the above-named 
compound. 
EXAMPLE IV 
Sodium salt of 3,4-dimethylpyrazole-1-carbodithioate 
##STR6## 
A slurry was prepared by admixing 2.2 grams of 60 percent sodium hydride 
(after washing, this amounts to 1.32 grams) with 75 milliliters of dry 
tetrahydrofuran. To this slurry was slowly added, with stirring, 5.0 grams 
of 3,4-dimethylpyrazole. The solution thus formed was filtered and then an 
excess of carbon disulfide (7.0 grams) was added, with stirring. After 10 
minutes, a yellow precipitate formed. The product was recovered by 
filtration and washed with dry ether and dried. The desired product was 
recovered in a yield of 7.9 grams (78 percent of theoretical). The product 
decomposed at 275.degree.-278.degree. C. Upon analysis, the product was 
found to have carbon, hydrogen and nitrogen contents of 36.88, 3.54 and 
14.31 percent, respectively, as compared with the theoretical contents of 
37.10, 3.63 and 14.42 percent, respectively, as calculated for the 
above-named compound. 
The reactions in the above Examples were carried out employing room 
temperatures and atmospheric pressures. 
EXAMPLE V 
A study was conducted to determine the stability of the zinc salt of 
bis(-3-methylpyrazole-1-carbodithioate) when coated onto urea prills. 
One hundred gram portions of urea prills were placed into 600 milliliter 
(ml) beakers and rotated at a 45.degree. angle. The zinc salt of 
bis(-3-methyl-pyrazole-1-carbodithioate) was dissolved in methylene 
chloride and sprayed as a fine mist onto the rotating urea prills. After 
the prills were evenly coated, the solvent was evaporated off with the aid 
of a hot air gun. 
Two different formulations were prepared, one in which the coated prills 
contained about 0.05 percent (%) and the other about 0.1% of the pyrazole 
by weight based on the weight of nitrogen in the urea. Each formulation 
contained a different percentage of the base pyrazole compound. In one, 
the solution contained 59.4 milligrams (mg) and the other 118.8 mg of the 
pyrazole compound was present on the urea prills. 
Two gram samples of each formulation were weighed into 1 inch 
diameter.times.1/4 inch deep round steel planchetts and placed into a 
35.degree. C..+-.1.degree. C. circulating oven. Samples of each 
formulation were removed for assay each week for three weeks to determine 
the amount of pyrazole loss from the surface of the urea. This loss was 
determined employing standard high pressure liquid chromatograph analysis 
techniques. The results of this analysis are set forth below in Table I. 
TABLE I 
______________________________________ 
Stability at 35.degree. C. 
% Pyrazole remaining per gram of 
Zinc Bis(3-methylpyrazole- 
ammonium nitrogen at 
1-carbodithioate 
following time in weeks.sup.(a) 
Formulation Tested 
0 1 2 3 
______________________________________ 
0.05 0.052 0.047 0.042 
0.036 
(100) (90) (81) (69) 
0.10 0.106 0.095 0.092 
0.076 
(100) (89) (86) (71) 
______________________________________ 
.sup.(a) figure in () is percent (%) of pyrazole remaining based on 0 day 
amount.