Abstract
Organic and biological fertilizers are considered as a very important source of plant nutrients. A field experiment was conducted during 2017−2018 in paddy soil to investigate the effect of vermicomposting of cattle manure mixture with Azolla and rice straw on soil microbial activity, nutrient uptake, and grain yield under inoculation of N2-fixing bacteria. Experimental factors consisted of organic amendments at six levels (vermicomposts prepared from manure (VM); manure + rice straw (VRM); manure + Azolla mixture (VAM); manure + rice straw + Azolla mixture (VRAM); raw manure without vermicomposting (M), and a control) and N2-fixing bacteria at three levels (Azotobacter chroococcum, Azospirillum brasilence, and non−inoculation). The results showed that, vermicompost treatments compared to control and raw manure significantly increased the number and biomass−C of soil microorganisms, urease activity, number of tillers hill−1, phosphorus (P) and potassium (K) uptake, and grain and protein yield. Inoculation of plants with N2-fixing bacteria, especially Azotobacter increased the efficiency of organic amendments, so that the maximum urease activity, soil microbial activity, P and N uptake, and grain yield (4,667 (2017) and 5,081 (2018) kg/h) were observed in vermicompost treatments containing Azolla (VAM and VRAM) under inoculation with Azotobacter. The results of the study suggested that, using an organic source along with inoculation with appropriate N2-fixing bacteria for vermicompost has a great effect on enzyme activity, soil biology, nutrient uptake and grain yield has a synergistic interaction on agronomic traits under flooded conditions. Therefore, this nutrient method can be used as one of the nutrient management strategies in the sustainable rice production.
Highlights
The use of organic and biologic fertilizers in rice production is one of the most important methods used for soil fertility in a sustainable system (Wang et al, 2015; Amanullah, 2016; Chen et al, 2018)
Urease enzyme activity of soil increased up to stage T3 in most organic amendments in both years of the experiment, but its activity decreased, and under non-inoculation conditions (Figs. 2A and 2B), the urease activity trend lines of the control treatment collided with the urease activity trend lines of organic amendments while, such a collision was not seen under inoculation of Azotobacter (Figs. 2C and 2D) and Azospirillum (Figs. 2E and 2F)
The results of the present study showed that, vermicomposting of cow manure, rice straw and Azolla led to improvement of physicochemical properties of used materials
Summary
The use of organic and biologic fertilizers in rice production is one of the most important methods used for soil fertility in a sustainable system (Wang et al, 2015; Amanullah, 2016; Chen et al, 2018). Organic soil amendments using vermicomposts under inoculation of N2-fixing bacteria for sustainable rice production. Production of vermicompost as an easy and nature-friendly technology is a semi-aerobic process carried out by a specific group of earthworms (Eisenia fetida) and some soil microorganisms, especially bacteria and actinomists used for production of organic fertilizers from the waste and stabilization of these materials (Mahanta et al, 2012; Lim, Lee & Wu, 2016). Some composts and vermicomposts (especially those made from chaff of wheat or rice straw straw)with high value of carbon –to- nitrogen (C/N) may increase the time of bioconversion of the crop or stimulate N fertilization in the soil, and face the plant with N deficiency in some growth stages (Zhu et al, 2013; Li et al, 2015; Eo & Park, 2019)
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