| The fast measurement for nutrient release rate of slow/controlled release fertilizers (SRFs/CRFs) and the correlated relationship and differences of nutrition release characteristics of SRFs/CRFs in different media of water and field soil have been a hot topic in SRFs/CRFs'study. Nine kinds of SRFs/CRFs were chosen for this study. Fast nutrient extraction and the colorimetry method of paradimethylaminobezaldehyde at 100℃for polymer coated urea (PCU) and method of fast extraction and electrical conductivity measurement at 100℃for polymer coated compound fertilizer (PCC) were introduced. The correlated analyses of measurement results between fast measurement methods and Kjeldahl measurement in water at 25℃were made, and the correlated equations of release longevity of SRFs/CRFs at the same nutrient release rate were established, validated and evaluated. The nitrogen release characteristics of different kinds of SRFs/CRFs in maize, paddy and wheat soil were evaluated too. The effects of soil temperature, soil moisture, urease activity and plants'root nitrogen assimilating on nitrogen release rate of SRFs/CRFs were discussed. Main results were summarized as follows:1. The nutrient release longevity and nutrient release rate of PCU could be measured accurately by the colorimetry method of paradimethylaminobezaldehyde at 100℃and this measurement was simple, highly active and fast. By using regression equation of this measurement, the errors of release longevity of studied sample S1 and S2 were only 0.10d and 1.75d respectively, and the relative errors were less than 2.3%.2. As a simple and fast method, electrical conductivity measurement could accurately measure the nutrient release longevity and nutrient release rate of coated compound fertilizers. By using the method of fast extraction and electrical conductivity measurement at 100℃, the errors of release longevity of studied sample S4, S5 and S6 were only 0.95d, 0.20d and 2.29d respectively, and the relative errors were less than 2.9%. 3. The curves of cumulative nitrogen release rate of sample S1, S4 and S7 in 25℃water were accordant generally with the curves in maize soil and paddy soil. However, as the nutrient dynamic release process was concerned, there were big differences for average nitrogen release rates in different media of water and soil. The nutrient release trends of SRFs/CRFs were more balanced and stable in water than in soil. The nutrient release of sulfur coated urea (SCU) S7 in water had a trend of nutrient"locking effect", but it had a better nitrogen release trend in maize soil and paddy soil than in water. The nitrogen release curve was identical completely with plants nitrogen assimilating curve, and the nitrogen supplying efficiency of S7 was higher than other fertilizers. So SCU S7 was very fitable for the planting of maize and paddy.4. The nutrient release rates of SRFs/CRFs in water were mainly affected by temperature. The cumulative nitrogen release rates of PCU S3 in water of different temperature at 25℃,15℃and 5℃had significant differences (p<0.01).5. Coated urea S3 and S8 were applied in planting wheat. There were peaks of cumulative nitrogen release rates of S3 and S8 when the soil temperature was high. In the wintering period of wheat, the soil temperature was under 0℃constantly and at this time the average nitrogen release rates of PCU S3 and SCU S8 reached zero and the minimum value respectively. The stated release time (Cumulative nitrogen release rate reached 80%. ) of S3 in water at 25℃was only 33d, but in wheat field soil it was 165d.6. The nutrient release trend of PCUs was affected by soil temperature, plants nitrogen assimilating and soil urease activity significantly, but the difference of media for water, soil had no effect on PCUs'nutrient release rate. Plants nitrogen assimilating and soil urease activity had no significant effects on the SCUs'nutrient release rate, but the effects of the difference of media for water, soil and the soil temperature were significant. Compared to SCUs, the PCUs'nutrient release trends were more controllable.
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