| [Objective] Nitrate is a dominant form of N in arid soil. Employing nitrification inhibitors is very conventional way to inhibit soil nitrification rate and control soil NH4+/NO3- supply ratio as well as improve N fertilizer use efficiency. In the present research, incubation and pot experiments were conducted to compare nitrification rate dose-dependent effects of 3 different types nitrification inhibitors on sandy, loamy and clayey soils condition. The aim of this paper is to find out the nitrification inhibitor reasonable amendment dosages, the biological effects of different nitrification inhibitors on pakchoi plant growth, nitrogen nutritional status. Furthermore, the response of soil key enzymes and soil microorganism communities which involved in soil nitrogen transformation was also studied by means of enzymological as well as soil microbial molecular method in this study. All knowledge about our research work is helpful to make further understand nitrification inhibitor occurred mechanisms and its biological effect in soil-plant system, meanwhile. Also, our research result will provide fundamental theoretical support for optimum soil NH4+/NO3- supply ratio and NI extend application under drip irrigation condition in Xinjiang.[Method] This study compared the effects of 3 different types nitrification inhibitors in 3 soils with different soil textures in Xinjiang by using laboratory simulation test to understand the impacts of different types and doses of nitrification inhibitors on soil inorganic nitrogen transformation (NH4+, NO3-) and on soil nitrification process and the rate of apparent soil nitrification, and select out the suitable nitrification inhibitor for different soil textures and the right dosage applied. Meanwhile, the optimum dosages of different nitrification inhibitors biological effect of on pakchoi plant were compared in pot experiments. Soil enzymological method and soil microbial molecular method(DNA-PCR-DGGE) was employed to measure soil biological reactions on different nitrification inhibitors.[Result]1) DCD exerted significant inhibitory effects on nitrification on all three types of soil texture tested (i.e. sandy, loamy and clayey soil). For instance, nitrification inhibition rates ranged from 96.5% to 99.3% on the loamy soil, from 34.0% to 85.6% on clayey soil and from 49.3% to 79.4% on the loamy soil. Among the three types of soil texture, the rates of nitrification inhibition by DCD were in the order of sandy soil> clayey soil> loamy soil. Soil nitrate concentration merely increased by 1.9～10.7 mg·kg-1 with DCD application rates elevated from 1% to 7%, indicating that DCD has no obvious dose effect on the sandy soil. However, soil nitrate concentration decreased sharply with increasing supply levels of DCD, and marked dose effect was observed on the loamy and clayey soils. Soil nitrification could be significantly inhibited through application of DCD on calcareous soils and the optimal recommended DCD application rates based on pure N were 6%,7% and 7% on sandy, clayey and loamy soil, respectively.2) DMPP exerted significant nitrification effects on all three types of soil texture (i.e. sandy, loamy and clayey soil). For instance, nitrification inhibition rates ranged from 96.2% to 99.7% on the sandy soil. Among the three types of soil texture, the rates of nitrification inhibition by DMPP were in the order of sandy soil> loamy soil> clayey soil. Nitrification inhibition of different doses of DMPP is significantly different, for example, nitrification inhibition rate on the sandy soil was more than 99% except for the treatments with 3%,3.5% and 6% DMPP added. The highest nitrification inhibition rates were found in the treatments with 2% and 3% DMPP added in loamy soil, and in the treatments with 3.5%,4% and 5% DMPP added in the clayey soil.3) Nitrapyrin (Type 1) exerted significant nitrification effects on all three types of soil texture. Nitrification inhibition rates ranged from 98.9% to 99.9% in the sandy soil, from 41.7% to 99.6% in the loamy soil, from 48.2% to 81.7% in the clayey soil. Among the three types of soil texture, the rates of nitrification inhibition by Type 1 were in the order of sandy soil> loamy soil> clayey soil. Type 1 nitrification inhibitor had no obvious dose effect on the sandy soil. However, soil nitrate concentration decreased sharply with increasing supply levels of Type 1, and marked dose effect was observed on the loamy and clayey soils. From our study, it can be concluded that soil nitrification could be significantly inhibited through application of Type 1 on calcareous soils and the optimal doses recommended for Type 1 were 0.1%,0.25% and 0.3%(based on amount of Urea)on the sandy, clayey and loamy soil, respectively.4) Nitrapyrin (Type 2) exerted significant nitrification effects on all three types of soil texture. Nitrification inhibition rates ranged from 97.9% to 99.7% in the sandy soil,40.2% to 95.5% in the loamy soil, and 38.9% to 92.2% in the clayey soil. Among the three types of soil texture, the rates of nitrification inhibition by Type 2 were in the order of sandy soil> loamy soil> clayey soil. Type 2 nitrification inhibitor had no obvious dose effect on the sandy soil. However, soil nitrate concentration decreased sharply with increasing supply levels of Type 2, and marked dose effect was observed on the loamy and clayey soils. From our study, it can be concluded that soil nitrification could be significantly inhibited through application of Type 2 on calcareous soils and the optimal Type 2 doses recommended were 0.1%,0.4% and 0.45%(based on amount of Urea)on the sandy, clayey and loamy soil, respectively.5) There was no significant inhibitory effect on nitrification on the sandy soil between any two of the 4 kinds of nitrification inhibitors tested (7%DCD,1%DMPP,0.25%Type 1, and 0.1%Type 2). The effect of nitrification inhibitors was in the order of 0.5%Type 1> 1%DMPP> 0.4%Type 2> 7%DCD in the loamy soil and 1%DMPP> 0.45%Type 2> 7%DCD> 0.3%Type 1 in the clayey soil.6) The process of soil NH4+ transferred into NO3- was significantly inhibited, and the nitrification inhibitory effect was in the order of DMPP> Nitrapyrin> DCD based on the application rate recommended, no matter the N fertilizer applied is urea or ammonia sulphate.7) Application of nitrification inhibitors could improve the activities of soil catalase, protease, nitrate reductase, hydroxyl proposed reductase, amine reduction enzyme and reduce the activity of soil urease. The microbial structural diversity of ammonia-oxidizing bacteria and archaea amoA affected by application of nitrification inhibitors.8) Compared with Urea or ammonia sulphate, application of nitrification inhibitors with N fertilizers could increase the yield and quality of pakchoi, improve root activity and leaf SPAD value, but reduce nitrate content in leaves and leafstalks. For example, at the early stage (15 days) nitrate content in leaves of packoi was 10.8%,17.8% and 1.6% lower in treatments with Urea+DCD, Urea+DMPP and Urea+Nitrapyrin than in the treatment with equal amount of Urea only, compared to 3.7%,14.3% and 1.0% in nitrate content of leafstalk. Nitrate content in leaves of packoi was 11.2%,22.6% and 8.9% lower in the treatments with ASN (ammonia sulphate)+DCD, ASN+DMPP and ASN+Nitrapyrin than in the treatment with equal amount of ammonia sulphate only, compared to 24.0%,22.6%,14.8% in leafstalk. Compared with Urea, the yield and biomass dry weight of packoi plant significantly enhanced with nitrification inhibitors (DCD, DMPP and Nitrapyrin) application treatment.[Conclusion]1) Application of nitrification inhibitors (DCD, DMPP and Nitrapyrin) could inhibit nitrification in soil. Among the three types of soil texture, the effects of nitrification inhibition by DCD were in the order of sandy soil> clayey soil> loamy soil, when that were sandy soil> loamy soil> clayey soil by Nitrapyrin and DMPP. The effects of nitrification inhibition by different types of NI were DCD< Nitrapyrin<DMPP in the same does.2) Within the NI concentration range of 1%～7%for DCD(based on pure N) and of 0.1%～0.5% for nitrapyrin (based on amount of Urea), a marked nitrification inhabitation dosage effect was observed on the loamy and clayey soil. DMPP application rates elevated from 1% to 7%, indicating that DMPP has no obvious dose effect on the three types of soil texture. There has marked dose effect on loamy and clayey soil only in low application rates of Nitrapyrin (Type 1,0.1% to 0.25%), when there has no obvious dose effect on high rates (higher than 0.25%). From our study, it can be concluded that the optimal doses recommended for Nitrapyrin (Type 1) were 0.25%(based on amount of Urea).3) Application of nitrification inhibitors (DCD, DMPP and Nitrapyrin) could reduce NO3- content in leaves and leafstalks, but increase the yield and quality of pakchoi, improve root activity and leaf SPAD value.4) Application of nitrification inhibitors could significantly affect the enzyme activity of soil nitrogen transformation and the ammonia-oxidizing bacteria and ammonia-oxidizing archaea community structure and genetic diversity. |
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