دانلود رایگان مقاله واکنش تابعی جوامع میکروبی خاک به گیاهان پوششی و نیتروژن

Abstract

Agricultural practices such as tillage, cover crops, and nitrogen (N) fertilization affect physico-chemical and biological soil parameters. However, these factors were often studied separately and their combined effects remain unclear, especially with respect to soil microbial functional diversity and carbon (C) and N content. Thereafter, we aim to assess the links between cropping systems and functional response of microbial communities by using a large range of soil chemical and biological measurements. A 5-yr field experiment was conducted in Northern France using a combination of three factors: i) no-till (NT) vs. conventional tillage (CT); ii) with or without winter cover crops (bare fallow; cover crops with a low prevalence of legumes; cover crop with a high prevalence of legumes); and iii) with or without N fertilization. C and N inputs from cover crops and crop residues, C and N content, enzyme activities, and microbial functional diversity in the topsoil (0–10 cm) were measured over an industrial crop rotation: wheat, pea, corn, wheat, flax. No-till combined with any of the cover crops was characterized by increased total soil organic C and N contents by more than 20% between 2010 and 2015. Dehydrogenase and urease activities were significantly greatest under NT, irrespective of the presence of cover crops. Cover crops without N fertilization under no-till led to higher microbial functional activity (faster carbohydrate and phenolic compound degradation) and diversity. Bare fallow had lower soil microbial functional diversity and C and N contents compared with soil under NT and cover crops. On the other hand, NT associated with cover crops allowed to maintain the soil in both C and N, and to promote microbial activities without N fertilization. In conclusion, winter cover crops and/or NT are sustainable agricultural practices resulting in a greater soil quality index. These results demonstrate that NT and use of standard cover crops or cover crops with legumes for 5 years under a low biomass return in industrial crop production have a positive effect on: i) upper soil C content and microbial enzymes, irrespective of N fertilization regime; ii) soil microbial functional diversity in the absence of N fertilization.

5. Conclusions

In summary, without N fertilization, conventional tillage plus standard cover crops strongly decreased the soil CN content and markedly increased potential soil polymer degradation. Under the same N fertilization, no-tillage with standard and legume-enriched cover crops improved degradation activity of soil microorganisms (AWCD, carbohydrates and phenolic compounds degradation) and their functional diversity. These results indicate that, without N fertilization, cover crops are required to prevent C and N depletion and to maintain microbial functional activities and diversity. Irrespectively of N fertilization, cover crops enriched with legumes prevented the strong decrease of C and N content caused by plowing. No-till combined with cover crops increases enzyme activities. Thereby, under a crop rotation characterized by a low organic C input, a gradual reduction of synthetic N fertilizers is compensated with an increase of cover crop N input must be encouraged to reduce the risk of soil fertility depletion associated with conventional farming practices. However, it is known that soil microbial functional responses may vary seasonally, so, studies including sampling collections throughout seasons and years are required to investigate further the links between cropping systems and microbial communities’ behavior at long term.