Study On The Rapid Determination Method And Instrument For Soil Nutrient

Nitrogen, phosphorus and potassium are the necessary nutriments for the plants. The appropriate amounts of N, P and K in the soil could be helpful for the growth of crops. At the same time, the excessive fertilizer will pollute the environment. So, it is very significant to develop a simple and rapid determination method for N, P and K in the soil.In this thesis, the methods and the instruments of determining N, P and K were reviewed, based on which, several novel spectrophotometric procedures were proposed to determine those three nutriments and the portable spectrophotometer was developed. The main contents of this study could be described as follows:1. Based on the investigation of the reaction mechanism of determining nitrate nitrogen in the soil by nitro indicator, the preparation of nitro indicator was improved. The amounts of a-naphthylamine and zinc powder were decreased, by which, the stabilized time of the reaction was extended and the accuracy of this reaction was elevated. The linear range and detection limit of the improved method were 0~3.6mg/L and 0.04mg/L, respectively. It has been successfully applied to analyze soil and environmental water sample.2. The optimum experimental conditions of using Nessler reagent to determine ammonia nitrogen were studied. Under pH 12.5, sodium tartrate was selected to conceal metal ions and the polyvinyl alcohol (PVA) was added to stabilize the determination solution. The linear range of the proposed method was 0~9mg/L. It has been used to detect ammonia nitrogen in the environmental water sample with satisfactory results.3. The effect of acidity for the determination of trace phosphate with the Molybdate (Mo) and Malachite green (MG) is investigated. An improved method is developed on the formation of the ternary complex among phosphate, Mo and MG in aqueous solution containing PVA as stabilizer. The absorbance of the complex at 649nm is linearly related to the concentration of phosphate in the range of 10~225ng/L and the limit of detection is 5fig/L. The method has been applied successfully to thedetermination of trace amount of soluble phosphate in river and soil samples.4. At pH 9, with tetraphenylboron as the precipitator, formaldehyde and EDTA as screening agent and polyvinyl pyrrolidon as the stabilizer, the content of K in the soil was successfully determined by turbidimetric method. Under the optimum experimental conditions, the linear range was 0.03~25|4.g/mL.5. A novel portable spectrophotometer was developed by using light-emitting diode (LED) as lamp-house. This instrument has been used to determine the soil and environmental samples and the experimental results were exact and reliable. The developed portable spectrophotometer maybe applied to simply, sensitively and in situ determine the contents of N, P and K in soil and environment water samples.