Nitrogen is the most effective nutrient for plants and also presents more problems as a fertiliser than the other nutrients. In the case of phosphorus, ortho-phosphate is effective enough, but preferably the more soluble and mobile form is desirable in Japan to minimize the fixation. Pyrophosphate would become a matter of concern. With potassium, the elimination of the anions from potassium sulphate or chloride is desirable to avoid the soil acidification and concentration hazard. Potassium metaphosphate is regarded in Japan as a concentrated source of phosphorus and potassium and as a sulphate- or chloride-free potassium source rather than for slow release, and, when imported, it will be used as it is, or as monopotassium orthophosphate produced by hydrating it.
Returning to nitrogen, synthesized inorganic nitrogen materials and urea, are very good fertilisers being completely available but one defect is excessive water solubility which often causes the concentration hazard and leaching loss.
A fertiliser which will be mineralised in relation to the need of plant is required by many agronomists. And this goal is regarded as the ultimate goal which may never be reached. There are two methods of approach, one is the technique of coating inorganic nitrogen fertiliser, and the other is the synthesis of nitrogen compounds having only slight water solubility. Almost all of the latter compounds which have been studied are considered to be mineralised by soil microbial activity, but this mechanism would not work at the farmer’s will. In Dr. G. W. Cooke’s opinion, it will be impossible to control the mineralisation velocity at any specific rate by the biological mechanism.
Now, an alternative mechanism has been found to be possible which does not involve soil microbial action in the decomposition of the nitrogen compound. The studies on oxamide and IBDU show the mechanism. It is hydrolysis.
Generally, in the case of readily water soluble compounds, the suppression of dissolution of ingredients from the fertiliser granule by ‘granular effect’ would be very difficult. But, in the case of a slightly water soluble compound, the dissolution can be suppressed easily by ‘granular effect’ alone, as described in this paper.
By applying such mechanism and technique, IBDU was found to be very useful as a slow acting nitrogen fertiliser. Its long lasting effect could be controlled by adjusting the dissolution velocity by the ‘granular effect’, and the dissolved nitrogen is as effective as urea.
As is widely known, urea when applied heavily has some defects such as causing injury in the early stage of growth of young plants. Injury is caused by the urea itself or by ammonia from decomposition of the urea. The vaporisation loss of ammonia liberated from urea applied heavily is another defect. These defects are all caused by the rapid dissolution of urea when applied heavily. When urea is applied little by little these defects are avoidable, and urea becomes an excellent fertiliser. IBDU avoids these defects even when applied in one large dose. Briefly, IBDU could be described as ‘ the slightly water soluble urea’.
The author thinks that, for the purpose of obtaining a widely usable slow-acting nitrogen fertiliser, it is better to find a way of minimizing the dissolution velocity of available nitrogen than to expect slow mineralisation of initially non-available nitrogen by soil micro-organisms.
Lastly, the characteristics of IBDU as a fertiliser can be listed as follows
(1) IBDU can be obtained easily by the reaction between urea and isobutyraldehyde, the latter is a by-product of the manufacture of 2-ethyl-hexanol.
(2) As IBDU is sparingly soluble in water, it has less concentration hazard, less hygroscopicity and a lower caking tendency. It can be mixed with any other fertiliser ingredients excepting strongly acidic superphosphate.
(3) The duration of the fertilising effect of IBDU can be controlled by the ‘granular effect’.
(4) The nitrogen of dissolved IBDU is as effective as urea which can be used in any soil conditions such as paddy or upland fields, covering a wide range of microbial activity.
(5) There is no need to worry about liberated aldehyde except in the case of extraordinary heavy application, because aldehyde evaporates into the air and the remaining aldehyde changes to iso-butyric acid which is neutralized by soil bases and decomposed by soil microbes in the same way as other organic acids in the soil.
(6) It is considered that the fertilising properties of IBDU are quite similar to that of oxamide, and IBDU can be described as ‘a slightly water soluble urea’.
Masao Hamamoto, Central Research Laboratory, Mitsubishi Chemical Industries Ltd., Kawasaki City, Japan.
77 pages, 28 figures, 12 tables, 63 refs.