石灰性土壤供氮能力几种生物测定方法的评价研究

Estimation of the Biological Methods on Assessing Soil Nitrogen-Supplying Capacity in Calcareous Soil

【目的】目前测定土壤供氮能力的生物方法较多,但基于土壤氮素形态的复杂性、土壤和微生物的高度变异以及生态条件的差异,不同土壤及不同测定方法结果之间仍然存在一定差异,对石灰性土壤采用哪些生物培养方法较好,目前仍无明确结论。【方法】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吸氮量为参比,对可反映土壤供氮能力的淹水培养法、通气培养2周法、通气培养4周法、干湿交替通气培养2周法、间歇淋洗长期通气培养法、短期淋洗通气培养法、微生物量碳和微生物量氮等8种生物方法进行了比较研究,其中干湿交替通气培养法和通气培养4周法,是我们对通气培养2周的修订方法。【结果】在不包含起始矿质氮条件下,以上8种生物培养方法与淋洗土壤起始NO3--N盆栽试验作物吸氮量的相关系数依次为0.530,0.700,0.777,0.768,0.764,0.650,0.555和0.465(r0.05=0.369,r0.01=0.505),其中间歇淋洗长期通气培养法确定的氮素矿化势与作物吸氮量的相关系数为0.790;在包括起始矿质氮后(起始矿质氮+矿化氮),以上8种生物方法与未淋洗土壤起始NO3--N盆栽试验作物吸氮量相关系数依次为0.351,0.963,0.962,0.959,0.825,0.963,0.289和0.095(r0.05=0.369,r0.01=0.505),其中氮素矿化势与作物吸氮量的相关系数为0.812。【结论】在排除起始矿质氮,特别是硝态氮的影响后,在反映旱地石灰性土壤可矿化氮量上,以氮素矿化势最佳;其次为通气培养4周、干湿交替通气培养2周和间歇淋洗长期通气培养法。包括起始矿质氮后,即在反映土壤供氮能力方面,各种通气培养法与未淋洗土壤起始NO3--N作物吸氮量相关性均大幅度提高,其中通气培养2周、通气培养4周、干湿交替通气培养2周和短期淋洗通气培养法相关系数均在0.950以上。而淹水培养法和微生物量碳、氮在表征石灰性土壤供氮能力上均比其它通气培养法逊色。综合考虑各方法在反映土壤可矿化氮和土壤供氮能力上的优劣,以及考虑到间歇淋洗长期通气培养法和以此获得氮素矿化势需培养时间较长,不适于作为实验室常规分析和快速测定土壤供氮能力的方法。根据本研究结果,可将干湿交替通气培养2周作为旱地石灰性土壤供氮指标,该方法不仅更加符合旱地土壤实际水分变化特征,而且既可反映土壤可矿化氮,也可用于评价土壤供氮能力。

[Objective] Although many biological methods are used to determine the soil nitrogen supplying capacity, there are certain differences among the results for different types of soils and various ways of measurement due to the complexity of soil N conformation, the high variance of soil and microorganism, and the difference of environments. Therefore, the conclusion is not clear as to which biological incubation method is better for calcareous soil. [Method] In this study, pot experiments were made, using 25 different calcareous surface soil samples from the Loess Plateau. Soils were tested to note the nitrogen uptake of wheat and corn. Pot experiments were used as control. The experiment was used to investigate the difference of eight biological incubation methods reflecting soil nitrogen supplying capacity. Various methods include waterlogged incubation, aerobic incubation for two weeks and four weeks, dry-wet alternation aerobic incubation for two weeks, long-term alternate leaching aerobic incubation （and N mineralization potential, No）, short-term leaching aerobic incubation, microbial biomass carbon （Bc） and microbial biomass nitrogen （BN） method. Among these methods, the dry-wet alternation aerobic incubation and aerobic incubation for four weeks were modified. They were adaptations of the aerobic incubation for two weeks method according to the actual farmland moisturs. [Result] The results showed that the correlation coefficients between various methods and crop uptake nitrogen with leaching soil initial nitrate ware 0.530, 0.700, 0.777, 0.768, 0.764 （0.790 for No）, 0.650, 0.555 and 0.465, respectively （r0.05=0.369, r0.01=0.505）, while without leaching soil initial nitrate their coefficient was 0.351, 0.963, 0.962, 0.959, 0.825 （0.812 for No）, 0.963, 0.289 and 0.095, respectively （r0.05=0.369, r0.01=0.505）. [Conclusion] In conclusion, without the soil initial nitrate, the correlation coefficients between the eight methods and crop uptake nitrogen were, from high to low, No, aerobic incubation for four weeks, dry-wet alternation aerobic incubation for two weeks and long-term alternate leaching aerobic incubation. The soil initial nitrate the correlation coefficients between the aerobic methods increased significantly and the values were all beyond 0.950 for these four methods, including aerobic incubation for two weeks and for four weeks, dry-wet alternation aerobic incubation for two weeks and short-term leaching aerobic incubation. The waterlogged incubation method, Bc and BN in reflecting calcareous soil nitrogen supplying capacity had lower correlation coefficient compared with other methods. Thus, dry-wet alternation aerobic incubation for two weeks was chosen as better index for evaluating calcareous soil nitrogen supplying capacity due to some methods having disadvantages and not suitable for the actual farmland character.