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材料与方法土壤及其分析:供试土壤及性状见表1。土壤以pH4.8的1M NH_4OAc缓冲液提取后分别以比色法、火焰光度法和原子吸收法测定P、K和Mg。Giffordtown土壤所有营养元素浓度都很高,施肥不会有增产效应,但其它两种土壤的有效K,以及Hexpath土壤的有效Mg处于缺乏临界点。土壤有机碳按修改的Tinsley法测定(用0.5克粒度为0.2mm的风干土样)。将有机C％乘以1.72得有机质含量。全N以标准凯氏法测定。
Materials and Methods Soil and its analysis: The test soil and its properties are shown in Table 1. The soil was extracted with 1M NH 4 OA buffer at pH 4.8 and then determined by spectrophotometry, flame photometry and atomic absorption spectrometry for P, K and Mg, respectively. All Giffordtown soils have high concentrations of all nutrients and fertilization does not yield an effect, but the available K in the other two soils and the effective Mg in the Hexpath soils are at a critical point. Soil organic carbon was determined by the modified Tinsley method (0.5 grams of air-dried soil with a particle size of 0.2 mm). Multiply organic C by 1.72 to give organic matter content. All N is measured by standard Kjeldahl method.