1.  Field of the Invention
This invention relates to the preservation of stored crops including animal feedstuffs, and more particularly to the storage of such materials by treating the material to be stored with a slow release microorganism growth-inhibiting composition. 
2.  Description of the Present Art
The growth of microorganisms causes serious problems in the storage of grains and forages.  In past years, a primary method for preserving such stored materials has been the reduction of moisture content to a level below about 13 percent by weight.  This was formerly accomplished by permitting the mature plants to dry naturally in the field before harvesting, but more commonly now involves artificial drying procedures which remove moisture after harvesting. 
Artificial drying procedures have encouraged earlier harvesting, which minimize exposure to field losses from adverse weather conditions.  In addition, excessive field drying is not desirable for cereal grains which are to be harvested by modern mechanical devices, since serious losses due to separation of the kernels from the stalk are more likely to result.  However, the continually increasing costs of fuel materials, which must be burned to effect the drying of harvested plants, have had a severe impact upon the economics of agricultural operations. 
Spoilage of stored feedstuffs is primarily caused by pathogenic microorganisms, many of which are classified as molds.  Lapore et al.,  in U.S. Pat.  No.  3,806,600, have identified some of the offensive molds as Sclerotium rolfsii, Rhizoctionia solani, Fusarium, Pythium, Penicillium, and Aspergillus species.  Molds and fungi are well known to produce poisons (mycotoxins), causing sicknesses and even deaths among animals ingesting feedstuffs which carry the mold or fungus. 
A variety of treatments have been proposed or used to control mold growth on high-moisture (over 13 percent by weight) grains and forage.  Huitson et al.  show the use of acetic acid, formic acid or binary and ternary mixtures of acetic, propionic and formic acids as mold growth-inhibitors for crops and animal feedstuffs in U.S. Pat.  No.  3,595,665.  In U.S. Pat.  No.  3,806,600, Lapore et al.  describe the use of ammonium and potassium isobutyrates to inhibit the growth of organisms.  U.S. Pat.  No.  3,899,588 to Skov et al.  is directed to a composition for preserving silage or seeds, comprising an aqueous solution of the product from ammoniating an alkanoic acid having 2 to 10 carbon atoms.  A comparison of the effectiveness of sodium chloride, sodium propionate, propionic acid, a mixture of acetic and propionic acids, and ammonium isobutyrate was reported by H. K. Goering and C. H. Gordon in Journal of Dairy Science, Vol.  56, No.  10 at pages 1346-1351 (1973). 
R. J. Bothast et al.,  in Journal of Dairy Science, Vol.  56, No.  2, at pages 241-245 (1973) demonstrate the elimination of molds and yeasts from corn which contained 26 percent moisture by treating the corn with 2 percent (based upon dry weight) of ammonia.  A subsequent paper by Bothast et al.  in Journal of Dairy Science, Vol.  58, No.  3, pages 386-391 (1975) compared the performance of ammonia, ammonium isobutyrate, isobutyric acid, and propionic-acetic acid in the preservation of freshly harvested, 27 percent moisture corn, stored in bins. 
Ammonia and propionic acid solutions were also tested and compared as preservatives by Vandergraft et al.,  as reported in Cereal Chemistry, Vol.  52, pages 79-84 (1975). 
East German Patent 117,171, as abstracted in Chemical Abstracts, Vol.  85, 45207u (1976), discloses the use of urea as a preservative for high-moisture grain to be used for feed, attributing the preservative effect to the generation of ammonia through hydrolysis of the urea. 
In United Kingdom Pat.  No.  1,514,835, the treatment of grass silage with mixtures of urea and propionic acid is described.  Treatment with the mixtures was found to yield a better stored product than if only a urea treatment was used. 
Several other chemical treatments have been utilized for preserving animal feedstuffs during storage, including aldehydes, sulfur, metal salts, guanidine and others, but without notable success.  A need remains for an inexpensive preservation treatment which is easily applied to undried crop materials prior to storage, and which remains effective during the entire storage period, even though the exact storage duration is normally not known when a treatment is applied. 
Accordingly, it is an object of the present invention to provide a treatment for inhibiting the growth of harmful microorganisms during the storage of crop materials. 
Another object of the invention is to provide a treatment which is relatively inexpensive, and can be safely applied by an unskilled worker. 
It is a further object to provide a treatment which remains effective over prolonged periods of storage, but which will not adversely affect the usefulness of treated materials is storage is unexpectedly shortened. 
These and other objects will appear more clearly from consideration of the following description and examples.