| Abstract: | The effectiveness of nitrogen in slow-release synthetic-organic nitrogen fertilizer materials and mixed fertilizers containing a slow-release nitrogen component . In an incubation trial conducted for a period of 16 weeks at 30°C and 100% R.H. the release of nitrogen was studied from 20 slow-release nitrogen fertilizers and mixed fertilizers containing a slow-release nitrogen component on an urea-aldehyde basis. Amounts equivalent to 500 mg N per kg dry soil were added to a diluvial sandy soil having a pH-KCl of 5.44 and a moisture content of 55% of the maximum retentive capacity. On the average, 35% of the slow-release nitrogen was released, 60% of which during the first 4 weeks. The best measure of the amount of N released was the amount of cold-water soluble N in the fertilizers. The amount of N released exceeded the amount of applied cold-water soluble N on the average by about 4%, which was also the percentage of released cold-water insoluble nitrogen. The differences among the individual fertilizers were rather large. In a supplementary trial it was found that the various urea-aldehyde combinations do not react alike to pH and moisture content of the soil, and that they for that reason can hardly be lumped together with respect to their nitrogen effect. Each of these materials is more or less a special-purpose fertilizer, and as such less suited as a substitute for the conventional fast-acting fertilizers in agriculture. |
