Effect Of Long-term Chemical Fertilizer On Content And Composition Of Soil Organic Matter

Soil organic matter(SOM) is one of the parameters to assess soil fertility as its concentration is closely related to soil fertility and crop growth. Long-term field experiment of fertilizer application on SOM is, constantly, a hot scientific topic. There is no substitute for chemical fertilizer in cereal production, however, few studies have focused on the effects of long-term chemical fertilizer on the changing composition of SOM. Based on previous researches, this paper studied the meadow chernozemic from a 29-year long experiment through field sampling and lab analysis. The effects of different fertilizer application(control, N, P, K, NP, NK, PK, NPK) on SOC, Active organic carbon(AOC), CPMI, the change of humic composition and combined states plus the difference in the composition of soil organic mineral complex and adhesive compound, the results are listed below:1. The SOC content of the 8 treatments ranged from 17.94 to 19.43 g/kg after 29 years fertilizer application. The control was the lowest in SOC content while NPK was the highest: 8.08 % higher when compared to control. The combination of NPK application was a better way to accumulate SOC than solo chemical fertilizer.2. The AOC content of the 8 treatments ranged from 3.36 to 4.91 g/kg. Compared to the samples which collected when the experiment was set, the AOC of the 8 treatments was decreased and the control decreased by 27.74 % and NP had the highest AOC among the 8 while the AOC content of solo N, P or K application was the lowest: 37.74-39.46 % lower when compared to the data when the experiment started.3. Compared to NPK, the CPMI decrement of control was the highest, namely 7.63 % while solo application of N, P or K decreased the CPMI by 4.58 %, 5.34 % and 5.34 %, respectively, no significant difference was observed among treatments. Dual fertilizer application, which contained NP, NK and PK, decreased the CPMI by 2.29 %, 1.52 % and 0.76 %, respectively. Compared to control, solo fertilizer application(N, P, K) dwindled the CPMI by 18.85 %, 17.28 % and 20.52 %, respectively, no significant difference was detected. The CPMI of mixed chemical fertilizer application(NP, NK, PK, NPK) ascended by 28.07 %, 27.80 %, 22.95% and 21.93 %, respectively and no significant difference among treatments.4. The composition of humus was refreshed after 29 years’ fertilizer application: both the free state and combined state humus was increased to some degrees while the humification degree was lowered. The ability of different adhesive compounds to absorb SOC was different: G2>G1>G0. Even though G1 was water stable, the absorbed SOC was slightly higher than G0, G2 was the best state for adhesive compounds. The organic mineral complex of meadow chernozemic was mainly consisted of silt, chemical fertilizer application could benefit the formation of silt and fine sand complex, increase the content of the 2 and decrease the content of clay complex. Different chemical fertilizer application could induce the varied distribution of SOC among different complex. Fertilizer application could increase the absolute amount of SOC in clay complex, however, the percentage of SOC tended to decrease.