•Soil microbial dynamics were evaluated after 41 years of variable fertilization in rice.•Nitrogen application without manure, limits the soil microbial biomass and activities.•Functional soil ...microbial community increased with application of nitrogen with manure.•Diversity index showed a positive correlation with soil carbon mineralisation.•Amino acid and polymer utilizing microbes were dominant, irrespective of treatments.
Soil microbial communities play an essential role in maintaining soil fertility and considered as ecological indicators to evaluate soil health. In the present study, long-term effects of organic and inorganic fertilizers on functional diversity of soil microbial communities, and their correlation with soil organic carbon, microbial biomass and activities, were observed under sub-humid tropical rice-rice cropping system. This experiment comprises six treatments viz. control (plots without application of chemical fertilizers and farm yard manure), nitrogen (N at the rate of 60 & 80kgha−1 in wet and dry seasons, respectively), nitrogen+phosphorus+potassium (NPK), farm yard manure (FYM), FYM+N and FYM+NPK. The results indicated that pH of the soil under the treatments decreased from its initial value, whereas total organic carbon increased in FYM-treated plots. Microbial biomass carbon and nitrogen in FYM+NPK were increased by 50.0 and 46.4%, respectively as compared to control treatment. Carbon and nitrogen mineralization; and soil enzyme activities were significantly (p≤0.05) higher in FYM+NPK over control. The average well color development (AWCD) values derived from Biolog® eco-plates followed the order of FYM+N>FYM>FYM+NPK>NPK>N>Control. Shannon index was greater (p≤0.05) in FYM-treated soil as compared to control and chemical treated soil. Principal component analysis (PCA) indicates a clear separation of the cluster of treatments with FYM application (FYM and FYM+NPK) and treatments without FYM (N and NPK). Shannon index was significantly correlated with available phosphorus (p≤0.002) and carbon mineralization (p≤0.015). Biplot analysis suggested that polymer and amino acid utilizing microbes were dominant, irrespective of all treatments. These results revealed that continuous application of nitrogen fertilizer alone has responded a shift in soil microbial community in the long run and decreased the functional diversity of microbes. However, application of FYM either alone, or in combination with chemical fertilizers, could restore soil fertility. Moreover, the information generated from this experiment though Biolog® may be the first particularly with reference to the dominance of polymer and amino acid utilizing microbes, irrespective of treatments under long-term fertilized paddy soil.
Rice straw burning is causing huge economic losses and environmental hazards. Microbial mediated
ex situ
composting could be a viable solution which would not only reduce the straw burning but also ...will enrich nutrition to the soil. Strains of
Trichoderma
isolated from tree bark were tested to decompose rice straw efficiently, and the
Trichoderma
-mediated rice straw compost was used subsequently to improve rice growth. Two isolates of
Trichoderma reesei
(NRRIT-26 and NRRIT-27) decomposed the straw by producing higher decomposing enzymes, like total cellulase (≥ 1.87 IU mL
−1
), endoglucanase (≥ 0.75 IU mL
−1
), xylanase (≥ 163.49 nkat mL
−1
), and laccase (≥ 11.75 IU mL
−1
).
Trichoderma
decomposed rice straw compost had higher nutrient contents (1.97% N, 2.04% K, and 0.88% P) and optimum C/N ratio (28:2) as compared to control. The
Trichoderma
decomposed rice straw as a nutrient reduced the mean germination time (2.2 days as compared to 4 days in control) and enhanced the seedling vigor and total chlorophyll content in rice. Expression of defense enzymes, like catalase (≥ 200% both in shoot and root), peroxidase (≥ 180% in root and ≥ 300% in shoot), and superoxide dismutase (≥ 160% in root and ≥ 90% in shoot), were higher in treated plants as compared to control indicating higher stress tolerance ability to crops. We conclude that the
Trichoderma
-mediated rice straw management is a viable option and has the potential to reduce straw burning, and at the same time, the compost could enrich soil fertility and impart intrinsic stress tolerance to rice.
Inorganic fertilizers and manure application can alter the aggregate distribution as well as aggregate associated organic carbon and nitrogen. It is not fully understood how long term addition of ...carbon (C) and nitrogen (N) through biomass, farm yard manure (FYM) and inorganic fertilizers are distributed in soil aggregates in a tropical ricearice system. Therefore, the objectives of this study were to investigate the long-term effects of FYM and inorganic fertilizer in a ricearice system on (i) distribution of water stable aggregates in the soil, and (ii) amount of total soil organic carbon (TOC), total N and C/N ratio in different aggregate fractions. The total water stable aggregates (WSA) ranged from 71.6% under control to 91.1% under NPK + FYM in the surface soil (0-15 cm). The incorporation of FYM increased the macroaggregates (5-2 mm) by 165.3% and mesoaggregates by 130.7% (2-1 mm) and 282.8% (1-0.5 mm) over control in 0-15 cm soil layer. Mean weight diameter (MWD), varied from 0.43 to 0.78 in 0-15 cm and from 0.40 to 0.72 in 15-30 cm soil layer. MWD was higher under FYM treated plots than inorganic fertilizer alone and unfertilized control plots. Irrespective of treatment, macroaggregates (5-2 mm) had the highest (4.13-14.03 g kg/1) and microaggregate fraction (0.25-0.1 mm) had the least (3.70-8.89gkg/1) TOC content in the 0-15 cm soil layer. The application of FYM either alone or in combination with inorganic fertilizers significantly increased the accumulation of TOC in all aggregate fractions over control, however, the effect was more pronounced in macroaggregates fraction 5-2 mm and microaggregate fraction 0.1-0.053 mm. The combined application of inorganic fertilizers and FYM resulted in an increase in total N content which ranged from 0.43 to 1.0 g kg/1 in 5-2 mm and from 0.09 to 0.44 g kg/11 in 0.25-0.1 mm aggregate fractions. The highest C:N ratio was recorded in aggregate fraction of 0.1-0.053 mm irrespective of treatment, whereas aggregate fraction of 0.5-0.25 mm had the least C:N ratio. A higher C:N ratio was observed in 15-30 cm than 0-15 cm soil layer. Hence it was concluded that the long-term application of FYM resulted in C and N accumulation in bulk soil and aggregates, but the accumulation pattern was dependent on aggregate size.
•Urea briquette was applied in rice using mechanical applicator.•Use of briquette applicator yielded highest with highest agronomic use efficiency.•Use of briquette applicator recorded the lowest ...emission of nitrous oxide.•Ammonia volatilization was lower in mechanical than manual method of application.•Larger size of urea and placement by applicator are the most efficient N management.
Suitable method of application of urea briquette in flooded rice (Oryza sativa L.) not only increases nitrogen use efficiency, but at the same time sustain yield and reduce greenhouse gas emission in general and nitrous oxide emission in particular. Keeping this hypothesis, seven different treatments including manual and mechanical mode of application with two different type of applicators were tested in field in consecutive wet (2015) and dry (2016) seasons. Three row briquette applicator (TRBA) and top dressing applicator (TDA) were used in combination for basal and top dressing application along with prilled urea broadcasting and without application as well. It was observed the use of TRBA at basal with first top dressing by TDA and manual placement of urea briquette at second top dressing (TRBA+TDA) yielded highest @ 6.71tha−1 and 5.47tha−1 in the wet and dry seasons, respectively, with the highest agronomic use efficiency (36.3kgkg−1). Average emission of methane from all treatments were higher (19.2–27.1%) during wet season than the dry season and vice versa in case of nitrous oxide (3.6–11.8%). Among the treated plots, TRBA+TDA recorded the lowest emission of nitrous oxide. The largest amount of ammonia was lost through volatilization after basal application of urea, followed by top dressing at the end of maximum tillering stage and panicle initiation stage. As a whole, volatilization loss of N was lowest in control (3.3–3.4mgNH3-Nm−2d−1), followed by mechanical (27.6–33.9mgNH3-Nm−2d−1) and manual (49.1–55.3mg NH3-Nm−2d−1) method of urea briquette application. The population of nitrite oxidizers and heterotrophs were highest in prilled urea broadcasting. Soil dehydrogenase activity was the highest in urea briquette manual placement+top dressing applicator (UBMP+TDA, 148.0μg–160.0TPFg−1soild−1) treatment, while the urease activity was less was in urea applicator treated plots. Subsurface application of larger size urea (urea briquette) and applicator based precise placement of urea reduced the lossess of nitrogen through ammonia volatilization and nitrous oxide emission, thus enhanced nitrogen use efficiency. Apart from that, issue of adequate skilled labour for precise depth of application could be tackled by effectively adopting mechanical placement of urea briquette. The mechanical placement of briquette (relatively larger size particle) in tropical flooded rice is more precise and less labour intensive, hence this is an efficient environment friendly approach of N management.
Soil aggregates govern soil organic carbon (SOC) sequestration. But, sparse understanding about the process leads to inaccuracy in predicting potential of soil to stabilize C in warming world. We ...appraised effects of 43 years of fertilization on relative temperature sensitivity of SOC decomposition (Q₁₀) in soil aggregates to know whether SOC quality or quantity governs Q₁₀. Treatments were: fallow, control, 100% recommended dose of nitrogen (N), N and phosphorus (NP), N, P and potassium (NPK), and NPK + farmyard manure (FYM) (NPK + FYM). Macroaggregates, microaggregates and silt + clay (s + c) fractions were incubated for 16 weeks at 25, 35 and 45 °C, SOC quality (R₀) and Q₁₀ were computed. SOC mineralization from macro- and micro- aggregates were 34 and 28% higher than s + c across the treatments. The s + c fraction of NPK + FYM had ~ 41, 40 and 24% higher C decay rate than NPK plots at 25, 35 and 45 °C, respectively. For s + c fraction Q₁₀ increased over other aggregates. Mean Q₁₀ of s + c fraction was ~ 18.3 and 17.5% higher than macro and micro-aggregate-C, respectively. R₀ was the lowest for NPK + FYM, suggesting longterm manuring with balanced NPK significantly enhance recalcitrance of C. We observed Q₁₀ of macroaggregates and s + c fraction is controlled by C quality but C quantity governs Q₁₀ of microaggregates in Vertisol. Specifically, microaggregates of NPK + FYM were more temperature sensitive, and could be vulnerable to C loss. Hence, practices facilitating microaggregate formation should be avoided. Thus, we recommend manure application for facilitating C sequestration.
This study is a unique report of the utilization of
strains collected from even tree barks for rice plant growth, its health management, and paddy straw degradation. Seven different spp. of
were ...characterized according to morphological and molecular tools. Two of the isolated strains, namely
and
, outperformed the other strains. Both of the strains controlled four important rice pathogens, i.e.,
(100%),
(84.17%),
(66.67%), and
(76.25%). Seed bio-priming with respective
strains reduced the mean germination time, enhanced the seedling vigor and total chlorophyll content which could be related to the higher yield observed in two rice varieties; Annapurna and Satabdi. All the seven strains accelerated the decomposition of rice straw by producing higher straw degrading enzymes like total cellulase (0.97-2.59 IU/mL), endoglucanase (0.53-0.75 IU/mL), xylanase (145.35-201.35 nkat/mL), and laccase (2.48-12.60 IU/mL). They also produced higher quantities of indole acetic acid (19.19-46.28 μg/mL), soluble phosphate (297.49-435.42 μg/mL), and prussic acid (0.01-0.37 μg/mL) which are responsible for plant growth promotion and the inhibition of rice pathogen populations. Higher expression of defense enzymes like catalase (≥250% both in shoot and root), peroxidase (≥150% in root and ≥100% in shoot), superoxide dismutase (≥ 150% in root and ≥100% in shoot), polyphenol oxidase (≥160% in shoot and ≥120% in shoot), and total phenolics (≥200% in root and ≥250% in shoot) as compared to the control indicates stress tolerance ability to rice crop. The expression of the aforementioned enzymes were confirmed by the expression of corresponding defense genes like PAL (>3-fold), DEFENSIN (>1-fold), POX (>1.5-fold), LOX (>1-fold), and PR-3 (>2-fold) as compared to the non-treated control plants. This investigation demonstrates that
strains obtained from tree bark could be considered to be utilized for the sustainable health management of rice crop.
We hypothesized that lignin decomposition microbial consortium would make rice-straw decomposition faster as straw contain around 15–24% lignin. In this study, we isolated aerobic lignin degrading ...microbes from four natural sources and based on their ability towards lignin degradation four microbial strains and their combination (2 bacteria (LB 8, LB 18) and 2 fungi (LF 3, LF 9) were selected for rice straw decomposition. The greenhouse gases emission, enzymatic activities (β-glucosidase, cellulase, laccase), reduction in lignin content, weight loss and carbon nitrogen ratio (C:N) were quantified during the process of decomposition. The β-glucosidase, cellulase and laccase activities were higher in compost where LB 18 + LF 3 consortium was applied as compared to others. The lignin content was also decreased (8.9–9.5 to 6.6–7.9%) gradually from initial to 28th days of composting under LB 18 + LF 3. We found the microbial consortium LB 18 + LF 3 decomposed the rice straw relatively faster than other strains/consortium tested as indicated by lowering of C:N ratio and reduction of lignin, hemicellulose, and cellulose contents of 60, 19.2, 41.5 and 10.3%, respectively at 28th day of composting compared to initial values. However, higher, methane and carbon dioxide fluxes were also observed at 28th days of composting (1.36 and 200.7 mg m
−2
h
−1
) with no significant trend in nitrous oxide fluxes. Further, the consortium identified could be tested for
in-situ
straw decomposition with proper moisture management to evaluate its potential in field condition. Therefore, we conclude that use of lignin decomposing microbial consortium has the potential to hasten the composting of rice straw in large scale.
Graphic abstract
Soil phosphorus (P) fractionation, adsorption, and desorption isotherm, and rice yield and P uptake were investigated in flooded tropical rice (Oryza sativa L.) following 42-year fertilizer and ...manure application. The treatments included low-input unfertilized control without N, P, or K (C0N0), farmyard manure (FYM) (C1N0), NP (C0NP), NPK (C0NPK), FYM+NP (C1NP), and high-input treatment, FYM+NPK (C1NPK). Grain yield was increased significantly by 74% over the control under the combined application of FYM+NPK. However, under low- and high-input treatments, yield as well as P uptake was maintained at constant levels for 35years. During the same period, high yield levels and P uptake were maintained under the C0NP, C0NPK, and C1NPK treatments. These are unique characteristics of a tropical flooded ecosystem, which is a self-sustaining system for rice production. The Fe–P fraction was highest compared to the Ca–P and Al–P fractions after 42years of fertilizer application and was significantly higher under FYM+NPK treatment. The P adsorption capacity of soil was highest under the low-input treatment and lowest under long-term balanced fertilization (FYM+NPK). In contrast, P desorption capacity was highest under NPK and lowest in the control treatment. Long-term balanced fertilization in the form of FYM+NPK for 42years lowered the bonding energy and adsorption capacity for P in soil but increased its desorption potential, increasing P availability to the plant and leading to higher P uptake and yield maintenance.
PDF
