摘要:
以采自于黄土高原差异较大的25个农田耕层石灰性土壤为供试土样,以淋洗和未淋洗土壤起始NO3--N小麦和玉米两季盆栽试验作物累积吸氮量为参比,对8种反映旱地土壤供氮能力的化学方法进行比较研究。结果表明,在一定程度上,可用有密切关系的土壤全氮或有机质,反映有机氮或全氮存在较大差异的土壤供氮能力,但其灵敏性较差。石灰性土壤矿质氮,特别是NO3--N与未淋洗土壤起始NO3--N作物吸氮量之间有较高相关性(r=0.884,P0.01),而与淋洗土壤起始NO3--N作物吸氮量间相关系数仅为0.472(P0.05),说明矿质氮可反映土壤当前供氮水平,而不能反映土壤潜在供氮能力;石灰性土壤起始NO3--N对各化学方法与作物吸氮量之间相关性影响较大。酸性高锰酸钾法既可反映土壤潜在供氮能力,也可反映土壤总供氮能力;酸性高锰酸钾法的修订方法,即硫酸高锰酸钾法提取出的NH4+-N值接近于KCl水浴法提取出的NH4+-N值,该方法在反映土壤总供氮能力方面与酸性高锰酸钾法相当,但在反映土壤潜在供氮能力方面不及酸性高锰酸钾法优越。KCl水浴法在评价石灰性土壤供氮能力方面,与酸性高锰酸钾法的效果基本相同;沸水浸取法和NaHCO3-UV法在评价石灰性土壤供氮能力方面效果较差。总结以上发现,在以盐类溶液提取法中,酸性高锰酸钾法、硫酸高锰酸钾法和KCl水浴法可作为反映石灰性土壤供氮能力的化学方法,其中以酸性高锰酸钾法最优,其次为KCl水浴法和硫酸高锰酸钾法。这3种方法在不包括起始NO3--N时,可反映石灰性土壤潜在供氮能力;包括起始NO3--N后,可反映土壤总供氮能力(当前供氮能力+潜在供氮能力)。
Abstract:
Soil N-supplying capacity is an important parameter to determine the nitrogen application rate.Based on the results from pot experiments treated with leaching soil initial nitrate and native soil,we compared the 8 chemical methods which reflecting soil nitrogen supplying capacity and nitrogen uptake by wheat and maize.25 different types of calcareous soils with big differentia collected from in ploughing layer in the Loess Plateau were used as tested soils.Among the 8 chemical methods,the H2SO4-KMnO4 method was a modified acid KMnO4 method.The results indicated that soil organic matter and total nitrogen can reflect soil nitrogen supplying capacity to a certain extent.However,the sensitivity of these two methods was low.The initial mineral nitrogen,especially soil nitrate,in those calcareous soils,significantly correlated with crop uptake nitrogen with native soil(r=0.884,P0.01),but did not significant with leaching soil initial nitrate(r=0.472,P0.05).The results showed that initial mineral nitrogen could reflect soil nitrogen supplying capacity,but insufficiently reflect soil potential nitrogen supplying capacity.The high content of initial soil nitrate affected the correlations between the chemical methods and crop uptake nitrogen.The acid KMnO4 method reflected both soil potential and total nitrogen supplying capacity.The amount of ammonia-N released by H2SO4-KMnO4 method was similar to that extracted by hot KCl water bath method.The H2SO4-KMnO4 method was similar to acid KMnO4 method in reflecting soil total nitrogen supplying capacity,but it was inferior to acid KMnO4 method in reflecting soil potential nitrogen supplying capacity.Hot KCl water bath method was similar to the acid KMnO4 method in reflecting calcareous soil nitrogen supplying capacity.The boiling water method and NaHCO3 UV method were not suitable for reflecting calcareous soil nitrogen supplying capacity.We could concluded that the acid KMnO4 method was the best one in reflecting calcareous soil nitrogen supplying capacity.The hot KCl water bath method and H2SO4KMnO4 method were also superior to other chemical methods in reflecting soil total nitrogen supplying capacity(with control soil) and soil potential nitrogen supplying capacity(without including soil initial nitrate).
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