不同耕作处理下大豆生物固N能力及对系统N素的贡献

The biological N fixation ability of soybean and its contribution to a maize-winter wheat-soybean rotation system under different tillage treatments

2002年至2003年在黄土高原研究了4个耕作处理,传统耕作(t)、传统耕作+秸秆覆盖(ts)、免耕(nt)和免耕+秸秆覆盖(nts)下大豆的生物固N百分率(%Ndfa)、固N数量及其对春玉米-冬小麦-夏大豆轮作系统中N素的贡献。结果表明,在tt、s、nt和nts处理下2002年的生物固N百分率为17.6%、34.3%、22.4%和19.3%,2003年则为58.5%、62.4%、54.9%和43.8%,其中2003年的生物固N百分率比2002年分别高出69.9%、45.0%、59.3%和56.1%,固N数量高出56.2%、33.8%、49.5%和43.1%。大豆生物固N百分率、生物固N数量与生物量呈正相关关系,在ts处理下显著相关。土壤NO3-N含量和大豆固N数量呈负相关,大豆植株吸N量占土壤NO3-N的百分比在2002年为:t(88.1)>ts(84.6)>nts(78.7)>nt(63.6),2003年为:t(115.5)>ts(104.2)>nts(99.8)>nt(95.8)。2002年大豆对该轮作系统的N素贡献分别为6.6(t)、11.6(ts)6、.5(nt)和6.1(nts)kg/hm2,生物固N量占总N输入量的百分比为14.6(t)、21.5(ts)、14.9(nt)和12.9(nts);2003年大豆对系统的N素贡献分别为14.9(t)1、7.6(ts)、12.9(nt)和10.7(nts)kg/hm2,生物固N量占总N输入的百分比为63.2%(t)、58.5%(nt)、47.7%(ts)和39.9%(nts)。年际变异造成了大豆生物固N的年际差异,秸杆覆盖+耕作因改善水分状况,而促进了大豆的生物固N作用。

One major reason legumes are utilized in farming systems is for their ability to maintain the soil nitrogen balance when incorporated into crop rotations. As such legumes can play an important role in both maintaining and improving crop yields, h is therefore important to quantify the total amount of nitrogen fixated through the biological nitrogen fixation （BNF） process used by legumes and to determine how much of this fixated N is available to the following crop. In doing so, this will enable greater precision in terms of appropriate fertilizer application rates and can increase fertilizer use efficiency. In 2002 and 2003, the 15 N natural abundance technique was used to record the percentage of biological nitrogen fixation （ % Ndfa） fixated by soybeans and the soybeans N contribution to a spring maize-winter wheat-summer soybean rotation system. The field experiment which was located in the Gansu Loess Plateau used four tillage treatments. These were： conventional tillage （T）, conventional tillage with stubble retention （TS）, no-tillage （NT）, and no-tillage with stubble retention （NTS）. In general the % Ndfa by soybean was higher in 2003 than in 2002, related to 2003 receiving a significantly more rainfall. The % Ndfa by soybean in the TS treatment was significantly higher than in the other three treatments. The TS treatment benefited from a higher N fixing enzyme activity which improved the soybeans BNF ability and as a consequence resulted in a higher yield. A negative relationship between the amount of N fixed by soybean and the amount of NO3-N in the 0-30cm soil profiles was found. A soil NO3-N concentration of 40 kgN/hm^2 was thought to be the critical value above which BNF activity was reduced. Soybean obtained its N requirements from beth soil N and BNF. When there was no BNF activity recorded, N was supplied wholly by soil N, which led to soil N depletion and soil N scarcity. The abeveground biomass of soybeans increased with increases in % Ndfa, however this finding was most evident in the TS treatment. A positive relationship between the amount of N fixed by soybean and its above-ground biomass was also found. In 2002, the treatment effects on the proportion of soybean BNF to total N input ranged from 13 - 22%, with the highest proportion recorded under the TS treatment. In 2003, the % Ndfa ranged from 43.8 % - 62.4%, with the amount of fixated N ranging from 10.7 - 17.6kgN/hm^2 and the proportion total N contributed by N fixation ranging from 40% -63%.