Diazotrophic plant growth-promotion bacteria and sugarcane straw levels: Effects on sugarcane productivity and on soil enzymatic and microbiological activities

R.F. Vieira*, A.J.B. Luiz and N.P. Ramos

Embrapa Meio Ambiente, Soil Biogeochemical Departament, CP 69, CEP 13918-110, Jaguariúna, São Paulo, Brazil
*Corresponding author: rosana.vieira@embrapa.br

Abstract:

Due to the rising demand for bioenergy, a certain amount of sugarcane straw is often removed for ethanol production, but this practice may compromise health soil. In addition to the amount of straw, growing concern with the environment has made the use of diazotrophic plant-growth promotion bacteria (DPGPB) an alternative to the use of nitrogen fertilizers. A research was designed with the aim of evaluating the effect of different amounts of straw kept on the soil on soil microbial and enzymatic parameters and on sugarcane yield during the first ratoon. The field experiment was carried out in randomized blocks, using nitrogen fertilizer (NF) or DPGPB (BI), both with four straw levels. The parameters evaluated were: β-glucosidase (GA), urease (UR) and acid phosphatase (APA) activities, fluorescein diacetate activity, basal soil respiration, microbial biomass N, total C, total N and labile carbon. Responses were not obtained for various parameters with respect to the straw levels which was attributed to the short experimental period. In general, the evaluated parameters were always higher in the BI treatment, except for APA, which was lower in this treatment. This fact could be attributed to the greater capacity of the inoculated plants to make phosphorus available to the plants, which could reduce APA. The absence of a response for sugarcane yield between the NF and BI treatments demonstrates the beneficial effect of the bacteria in the inoculant in suppressing plants with adequate nitrogen contents. Greater yields were obtained for the L64 and L100 straw levels with no significant difference. This demonstrates the adequateness of removing part of the straw to produce second generation ethanol.

Key words:

Use of soil enzyme activity in assessing the effect of No-Till in the South of Russia

G. Mokrikov, T. Minnikova*, K. Kazeev and S. Kolesnikov

Southern Federal University, Academy of Biology and Biotechnology by D.I. Ivanovsky’s, Department of Ecology and Nature Management, av. Stachki 194/1, RU344090 Rostov on Done, Russia
*Correspondence: loko261008@yandex.ru

Abstract:

The activity of 11 enzymes (catalase, dehydrogenases, peroxydases, polyphenoloxidases, ascorbateoxidase, ferrireductase, β-fructofuranosidase, amylase, urease, phosphatase and protease) was assessed under conditions of steppe zone in the south of Russia when using different tillages. Winter wheat and sunflower are main crops in these soils. Moreover, chickpea, coriander, lint, barley, corn and some other crop are cultivated here in the crop rotation duration 6 years. Enzyme activity was compared in soils of 15 fields with long-term no-till (NT) versus to 15 fields with conventional tillage (CT). The researches were held along the whole Haplic Chernozem Loamic at a depth of 0–65 cm. Special attention was paid to top soil (0–10 cm), which is directly subject to the mechanical effect. The carbon cycle enzyme (β-fructofuranosidase) activity was the most sensitive indication for NT use. In top soil the enzyme activity was greater by 16–35% at NT versus to СТ. Activity of this enzyme reduces by 28–293% when soil depth increasing in both the tillages. Enzymes of different classes had different behaviours in soils depending on season, crops and tillage thanks to biochemical nature. Hydrolases and oxidoreductases were assessed by the indices characterizing soil condition and health. For this purpose geometric mean by hydrolase activity (GME_hd) and geometric mean by oxidoreductase (GME_ox), as well as integral index of biological soil condition (IIBC) were used. Index GME_ox in soil under sunflower reduced by 16% in summer versus to spring. Thereby, hydrolase index GME_hd reduced by 60%. At NT activity of oxidoreductase was lower by 10 and 13%, and activity of hydrolase was increased by 12 and 14% versus to СТ. Soil IIBS values at NT increased by 18–35% at average within three years (2016–2018). The use of NT technology contributes to an increase in the activity of hydrolases and soil quality due to the conservation of moisture in the soil.

Key words:

bioindicator, biological activity, no-till, soil enzymes, soil health indexes