Rice Growth Stages Research Articles

ML-LME: A Plant Growth Situation Analysis Model Using the Hierarchical Effect of Fractal Dimension

Rice plays an essential role in agricultural production as the most significant food crop. Automated supervision in the process of crop growth is the future development direction of agriculture, and it is also a problem that needs to be solved urgently. Productive cultivation, production and research of crops are attributed to increased automation of supervision in the growth. In this article, for the first time, we propose the concept of rice fractal dimension heterogeneity and define it as rice varieties with different fractal dimension values having various correlations between their traits. To make a comprehensive prediction of the rice growth, Machine Learning and Linear Mixed Effect (ML-LME) model is proposed to model and analyze this heterogeneity, which is based on the existing automatic measurement system RAP and introduces statistical characteristics of fractal dimensions as novel features. Machine learning algorithms are applied to distinguish the rice growth stages with a high degree of accuracy and to excavate the heterogeneity of rice fractal dimensions with statistical meaning. According to the information of growth stage and fractal dimension heterogeneity, a precise prediction of key rice phenotype traits can be received by ML-LME using a Linear Mixed Effect model. In this process, the value of the fractal dimension is divided into groups and then rices of different levels are respectively fitted to improve the accuracy of the subsequent prediction, that is, the heterogeneity of the fractal dimension. Afterwards, we apply the model to analyze the rice pot image. The research results show that the ML-LME model, which possesses the hierarchical effect of fractal dimension, performs more excellently in predicting the growth situation of plants than the traditional regression model does. Further comparison confirmed that the model we proposed is the first to consider the hierarchy structure of plant fractal dimension, and that consideration obviously strengthens the model on the ability of variation interpretation and prediction precision.

Influence of Rhizobacteria on Soil Ion Concentration under Paddy Cultivation

Sustainable agriculture requires nutrient management options that can increase crop yields that are profitable for N nutrient availability and are environmentally friendly. However, N nutrient is dynamic and easy to lose, and excessive use of chemical N fertilizers has a negative impact on the environment. Biofertilizer by rhizobacteria is an effective way to maintain a reliable N-supply for rice growth. This study investigates the effect of a different combination of rhizobacterial fertilizers on nitrogen ion concentration in the soil and total rice production. The field experiment was conducted in two seasons. There were three treatments, including PGPR with 25% CF, PGPR with 50% CF, and 100% CF. The soil sample was taken from each treatment in six growth stages of rice i.e. 15, 36, 50, 72, 100, and 118 days after transplanting. Soil chemicals NH4+ and NO3- were analyzed by Ion Chromatography. The results showed that the uniformity of NH4+ and NO3- in the soil were the highest in fertilizer application with PGPR. The application of PGPR with 50% CF confirms that it can increase rice yields by 25.5% and 12.9%, respectively. The application of rhizobacteria can reduce the use of chemical fertilizers.

Methodology for studying nitrogen loss from paddy fields under alternate wetting and drying irrigation in the lower reaches of the Yangtze River in China

Nitrogen (N) loss from paddy fields is a major cause of water eutrophication. Alternate wetting and drying (AWD) irrigation is a promising measure for controlling nutrient loss. Nevertheless, quantifying N loss from paddy fields under AWD to water bodies is difficult because of 1) the sharp fluctuations in soil moisture and 2) the variation in runoff N concentrations caused by the probable first flush effect. Consequently, studies on N loss are usually confined to plot experiments. From June to November 2020, a 2.5 ha field-scale experiment was conducted in Shanghai during the rice growth stage. The proposed methodology included recording the water levels in a paddy field, quantification of runoff, and implementation of automatic sampling procedures. The electrical conductivity (EC) of runoff was applied to study the loss characteristics of nutrients. The antecedent field water level (AFWL) in paddies was used to evaluate the effect of soil moisture on the field water capacity, which was indicated by the runoff curve number (CN). It was found that AWD significantly altered the CN. When the AFWL dropped to 100 mm beneath the soil surface, the CN dropped to 40. The EC was closely related to the N concentration (adjusted R2 = 0.76, n = 176) when water samples with N concentrations ranging from 0.28 to 109.32 mg/L were analyzed. A hydrograph of EC versus runoff velocity during rainfall events indicated the significant effects of dilution caused by rainfall; therefore, the estimate of N loss should be based on high-frequency sampling. There was a more significant first flush effect on N loss during rainfall events than with artificial drainage. However, due to the high frequency of artificial drainage, N loss through artificial drainage should also be fully taken into account. In conclusion, the quantity and quality of N loss were significantly affected by wide fluctuations in soil moisture under AWD and the first flush effect of rainfall.

The effect of phosphorus split application on use efficiency and dynamic of phosphorus and zinc at the soil, aerial parts, and grain, and Zinc biofortification of two rice varieties (Oryza sativa L.) (Hashemi and Guilaneh)

Introduction: Despite the P vitality for rice cultivation, its recovery index in paddy soils is very low and less than 25% of added P, and the rest goes out of reach of rice plant through the P fixation by soil particles at different fractions. Also, despite abundant studies on the effect of basal soil P application, we face a lack of knowledge on research findings of the P splitting application and its effect on soil Zn concentration and tissues Zn content. Thus, the current research project was done to explore the effect of P splitting application at flooded conditions on the soil and rice plant tissues P and Zn variation trend at the different rice growth stages of two more common varieties (Hashemi and Guilaneh varieties). Materials and methods: The outdoor pot experiment was conducted on a three factors factorial experiment in a randomized complete block design with three replications in 2017 at the research farm of the rice research institute of Iran, Rasht. The experimental treatments were: phosphorus fertilizer split application at five levels, soil at two levels, and rice varieties at two levels (Hashemi (local variety) and Guilaneh(improved variety)), The P application treatments were: control (no added P), 100% basal, P split application at 50% basal and 50% at 20 days after transplanting (DAT), P split application at 50% basal and 50% at 60 days after transplanting (DAT), P split application at 50% basal, 25% at 20 days after transplanting, and 25% at 60 days after transplanting. Results: The results indicated that the highest soil available P and Zn concentrations were recorded at the flowering stage about 95.3 and 90.10, and 8.6 and 8.7 mgkg-1by two and three P split for Hashemi and Guilaneh, respectively. Also, the maximum P of rice grain was obtained about 0.17 and 0.20 mgkg-1 for Hashemi and Guilaneh, respectively. The Zn content of rice grain at P split pots was significantly more than control and 100% basal application. The highest agricultural recovery (13.31 and 12.72), physiological (693.19 and 740.10) and physiological-agricultural efficiency (482.00 and 753.00), P use efficiency (5.34 and 5.66), and apparent recovery (1998 and 1272.22 kg kg-1) were found for Hashemi and Guilaneh, respectively, in the two and three P split application. Furthermore, stepwise multiple regression analysis revealed that the soil available P concentration at ripening stage, Zn content of the grain, and Zn concentration at rice aerial parts can explain 52% of grain yield variations for studied rice cultivars. Conclusion: The three-stage P splitting (50% soil basal, 25% 20 DAT, and 25% 60 DAT) increased the Zn content of the Hashemi variety by about 54.72% at slit loam soil, whereas the Guilaneh rice variety was received a 37.5% increase in Zn content of grain in silty clay through two-stage P splitting (50% soil basal and 50% 20 DAT) compare to control (100 % basal). It can be concluded both three and two-stage P splitting might be positively significantly effective on rice grain nutritional quality.

Dynamics and influencing factors of soluble organic nitrogen in paddy soil under different long-term fertilization treatments

Soil soluble organic nitrogen (SON) plays an important role in nitrogen cycling. However, the dynamic and influencing factors of SON in paddy soil are largely unknown. In this study, 36-year fertilization experiments with different fertilized (control (CK), chemical fertilizer (NPK), chemical fertilizer combined with cow manure (NPKM) and chemical fertilizer combined with straw (NPKS)) paddy soils were selected to investigate the dynamic changes and influencing factors of the SON content during the whole rice growth stage. We found that NPK, NPKM and NPKS increased the soil SON content by 20.61 %, 51.33 % and 52.50 %, respectively, compared with CK. Compared with the NPK treatment, the average SON contents in the NPKM and NPKS treatments were significantly increased by 25.46 % and 26.44 %, respectively, but there was no significant difference between the NPKM and NPKS treatments. Soil SON contents in different growth stages under the same fertilization treatments showed maturity stage > tillering stage > flowering stage > jointing stage > seedling stage. Structural equation model (SEM) analysis showed that bacterial biomass was an important factor affecting soil SON content, with a total path coefficient of 0.92, including direct path coefficients of 0.24 for soil SON and indirect path coefficients of 0.68 for soluble organic carbon, microbial biomass nitrogen and protease activity. Redundancy sequencing analysis showed that SON contents during different rice growth stages were significantly affected by the bacterial community, i.e., Chloroflexi in the early growth stage and Proteobacteria and Bacteroidetes in the later stage contributed 5.33 %, 37.40 %, and 2.17 % to the SON content variation, respectively. Conclusively, the dynamics of SON in paddy soil under long-term fertilization treatments are closely related to both fertilization treatments and the rice growth stage and are mainly affected by the bacterial community.

Long-term straw return with N addition alters reactive nitrogen runoff loss and the bacterial community during rice growth stages

Crop residue return is an effective, eco-friendly tillage method for decreasing reactive nitrogen (Nr) losses via surface runoff. However, the associated variation in Nr characteristics and its prospective mechanisms are not well understood. We systematically evaluated the response of Nr runoff loss and N variation in standing water to the abiotic and biotic parameters of soil in a paddy field after 6 years of straw return. Five experimental treatments of different fertilization strategies in combination with straw return were tested during the rice growth season. The results indicated that under equivalent fertilizer input, long-term straw return significantly reduced Nr runoff loss by 11.5% (P < 0.05), even though the loss increased with N fertilizer addition. We report that variations in abiotic soil properties (P < 0.05) and bacterial communities (P < 0.01) were both responsible for Nr loss differences between the rice growth stages and among the tested fertilizing patterns. Soil inorganic nitrogen (r = 0.18) had a significant positive influence on Nr runoff loss, but this effect was surpassed by the overall negative influence of soil organic carbon (r = −0.43), soil pH, (r = −0.40), and bacterial community composition (r = −0.14), which was especially apparent during the tillering stage. Our results emphasize the importance of jointly considering biotic and abiotic factors in soil and standing water when characterizing the effects of long-term straw return and N addition on Nr runoff loss, which will aid in mitigating N-based agricultural non-point pollution.

Determining nitrogen status and quantifying nitrogen fertilizer requirement using a critical nitrogen dilution curve for hybrid indica rice under mechanical pot-seedling transplanting pattern

Field experiments of nitrogen (N) treatment at five different application rates (0, 75, 150, 225, and 300 kg ha−1) were conducted under pot-seedling mechanical transplanting (PMT) in 2018 and 2019. Two high-quality and high-yielding hybrids of indica rice, Huiliangyou 898 and Y Liangyou 900, were used in this study. The N nutrition index (NNI) and accumulated N deficit (Nand), used to assess the N nutrition status in real-time, were calculated for the indica cultivars under PMT with a critical nitrogen concentration (Nc) dilution model based on shoot dry matter (DM) during the whole rice growth stage. The relationships between NNI and Nand with relative yield (RY) were determined, and accurate N application schemes were developed for hybrids indica rice under PMT. The results indicated that high application rate of N-fertilizer significantly increased the concentrations of shoot DM and N in aboveground organs during the observed stages in the two cultivars for two years (P<0.05). The Nc dilution model of hybrid indica cultivars was Nc=4.02DM−0.42 (R2=0.97) combining the two cultivars under PMT. Root-mean-square error and normalized root-mean-square error of the curve verification were 0.23 and 10.61%, respectively. The NNI and Nand ranged from 0.58 to 1.31 and 109 to –55 kg ha−1, respectively, in the two cultivars for all N treatments. NNI showed a linear relationship with Nand during the entire growth stage (0.53<R2<0.99, P<0.01). In addition, NNI showed a linear-plateau relationship with RY (0.73<R2<0.92, P<0.01) throughout the observed stages. These results suggest that the models can accurately diagnose the N-nutrition status and support effective N-fertilizer management in real-time for hybrid indica rice under PMT.

Changes in bacterial community and abundance of functional genes in paddy soil with cry1Ab transgenic rice

A field experiment involving cry1Ab transgenic rice (GM) and its parental non-cry1Ab rice (M) has been on-going since 2014. The diversity of the bacterial communities and the abundance of the microbial functional genes which drive the conversion of nitrogen in paddy soil were analyzed during the growth period of rice in the fifth year of the experiment, using 16S rRNA-based Illumina MiSeq and real-time PCR on the amoA, nirS and nirK genes. The results showed no differences in the alpha diversity indexes of the bacterial communities, including Chao1, Shannon and Simpson, between the fields cultivated with line GM and cultivar M at any of the growth stages of rice. However, the bacterial communities in the paddy soil with line GM were separated from those of paddy soil with cultivar M at each of the growth stages of rice, based on the unweighted UniFrac NMDS or PCoA. In addition, the analyses of ADONIS and ANOSIM, based on the unweighted UniFrac distance, indicated that the above separations between line GM and cultivar M were statistically significant (P<0.05) during the growth season of rice. The increases in the relative abundances of Acidobacteria or Bacteroidetes, in the paddy soils with line GM or cultivar M, respectively, led to the differences in the bacterial communities between them. At the same time, functional gene prediction based on Illumina MiSeq data suggested that the abundance of many functional genes increased in the paddy soil with line GM at the maturity stage of rice, such as genes related to the metabolism of starch, amino acids and nitrogen. Otherwise, the copies of bacterial amoA gene, archaeal amoA gene and denitrifying bacterial nirK gene significantly increased (P<0.05 or 0.01) in the paddy soil with line GM. In summary, the release of cry1Ab transgenic rice had effects on either the composition of bacterial communities or the abundance of microbial functional genes in the paddy soil.

Direct and Residual Effect of Integrated Nitrogen Management on Physico-Chemical Properties of Soil

Aim: To find out the direct and residual effect of integrated nitrogen management on physico-chemical properties of soil under rice – maize cropping system.&#x0D; Study Design: The experiment was laid out in randomized block design during kharif season and in split plot design during rabi crop.&#x0D; Place and Duration of Study: At Agricultural college farm, Bapatla during 2018-19 and 2019-20 in Kharif and rabi seasons.&#x0D; Methodology: After the preliminary layout, paddy was sown in kharif and maize was sown in rabi season. Vermicompost and green leaf manure were applied two weeks before sowing of paddy. Treatments applied for paddy were considered as main plots and each one divided into two sub plots during rabi.&#x0D; Results: Applications of different treatments did not show any significant difference in physico-chemical properties of soil (pH and EC) at all the growth stages of rice and maize during both the years of study. Application of 75% RDN through green leaf manure + 25% RDN through inorganics (T5) to rice during kharif significantly improved organic carbon in both kharif and rabi seasons whereas different levels of fertilizers applied have not shown an significant influence on soil organic carbon content.&#x0D; Conclusion: Application of inorganic fertilizers, organic manures and their combination didn’t show marked difference on physico-chemical properties of soil like pH and EC. However substitution of 75% N through GLM in kharif season significantly improved OC content in soil during both kharif and rabi and organic carbon content was not influenced by the level of fertilizers from 50% RDF (S1) to100% RDF (S2).

Agronomic Management and Interventions to Increase Rice Yield in Bangladesh

Avenues of agronomic manipulation need to be explored critically for getting potential rice yield in a given environment. Increasing population, decreasing resources and increasing climate vulnerability such as salinity, drought, submergence, early flash flood in haor areas can interrupt achieving the target of rice yield. Location specific variety, profitable cropping sequences, innovative and smart cultural management, and appropriate agronomic management with smart dissemination using multiple means would maximize rice yield and decrease the production barriers of rice. Appropriate variety and location- specific crop management systems should be formulated for rice yield maximization to reduce yield gap in farmers’ field. A number of approaches can be undertaken for maximizing rice yield by adopting location-specific crop production e.g., manipulating sowing and planting times, appropriate weed management technology in proper time, suitable variety selection for improving cropping intensity, Judicious and balance application of organic and inorganic fertilizer application etc. Nitrogen application before panicle primordia is crucial because at this stage panicle primordia determined the spikelet number of the panicle and the absorbed nitrogen is efficiently used to increase spikelet number, accumulated photosynthates to leaf sheath and culm and, hence, increases panicle size and grain yield. Farmers should have a plan and should follow different steps of rice production to get higher yield and sustain productivity. Rice growth stage- wise agronomic management should be followed to get maximum yield. Choice of appropriate variety in a specific location or ecosystem is a major concern that contributed about 20% to the grain yield. Whereas management is a big issues which contributed about 60% for obtaining higher grain yield.The difference of environment × management explained the largest variations ( 80%) in explaining the yield. The bridging of knowledge gaps can bridge yield gaps. New paradigms need to be added to transfer and use new high yielding varieties and knowledge based technologies under new policy settings. Bangladesh Rice J. 24 (2): 161-181, 2021

Effect of atmospheric H2O2 on arsenic methylation and volatilization from rice plants and paddy soil

Studies focusing on arsenic methylation and volatilization in paddy soil, aiming to limit bioaccumulation of arsenic (As) in rice grains, have attracted global attention. In this study, we explored three aspects of these topics. First, rainwater and trace H2O2 were compared for their influence on the arsenic methylation and volatilization of paddy soil in different rice growth stages. Second, the arsenic accumulation in different parts of rice was affected by rainwater and trace H2O2. Third, we determined whether rice fields were affected by rainwater and trace H2O2. The result showed that the rainwater or trace H2O2 irrigation caused As(III) to significantly decrease and As(V) to significantly increase in soil. A similar consequence occurred in the filling stage and mature stage of rice. The arsenic volatilization rates of the rainwater and trace H2O2 irrigation were significantly higher than the control, and the arsenic volatilization of rainwater irrigation was the highest (51.0 μg m−2 d−1) in the filling stage. Compared to the control, the total arsenic and iAs of treatments decreased by 14–41% and 12–32% respectively. Finally, we found that rainwater and trace H2O2 irrigation likely increased rice fields.

Elevated Atmospheric CO2 and Nitrogen Fertilization Affect the Abundance and Community Structure of Rice Root-Associated Nitrogen-Fixing Bacteria.

Elevated atmospheric CO2 (eCO2) results in plant growth and N limitation, yet how root-associated nitrogen-fixing bacterial communities respond to increasing atmospheric CO2 and nitrogen fertilization (eN) during the growth stages of rice is unclear. Using the nifH gene as a molecular marker, we studied the combined effect of eCO2 and eN on the diazotrophic community and abundance at two growth stages in rice (tillering, TI and heading, HI). Quantitative polymerase chain reaction (qPCR) showed that eN had no obvious effect on nifH abundance in rice roots under either ambient CO2 (aCO2) or eCO2 treatment at the TI stage; in contrast, at the HI, nifH copy numbers were increased under eCO2 and decreased under aCO2. For rhizosphere soils, eN significantly reduced the abundance of nifH under both aCO2 and eCO2 treatment at the HI stage. Elevated CO2 significantly increased the nifH abundance in rice roots and rhizosphere soils with nitrogen fertilization, but had no obvious effect without N addition at the HI stage. There was a significant interaction [CO2 × N fertilization] effect on nifH abundance in root zone at the HI stage. In addition, the nifH copy numbers in rice roots were significantly higher at the HI stage than at the TI stage. Sequencing analysis indicated that the root-associated diazotrophic community structure tended to cluster according to the nitrogen fertilization treatment and that Rhizobiales were the dominant diazotrophs in all root samples at the HI stage. Additionally, nitrogen fertilization significantly increased the relative abundance of Methylosinus (Methylocystaceae) under eCO2 treatment, but significantly decreased the relative abundance of Rhizobium (Rhizobiaceae) under aCO2 treatment. Overall, the combined effect of eN and eCO2 stimulates root-associated diazotrophic methane-oxidizing bacteria while inhibits heterotrophic diazotrophs.

Mapping a Cloud-Free Rice Growth Stages Using the Integration of PROBA-V and Sentinel-1 and Its Temporal Correlation with Sub-District Statistics

Monitoring rice production is essential for securing food security against climate change threats, such as drought and flood events becoming more intense and frequent. The current practice to survey an area of rice production manually and in near real-time is expensive and involves a high workload for local statisticians. Remote sensing technology with satellite-based sensors has grown in popularity in recent decades as an alternative approach, reducing the cost and time required for spatial analysis over a wide area. However, cloud-free pixels of optical imagery are required to produce accurate outputs for agriculture applications. Thus, in this study, we propose an integration of optical (PROBA-V) and radar (Sentinel-1) imagery for temporal mapping of rice growth stages, including bare land, vegetative, reproductive, and ripening stages. We have built classification models for both sensors and combined them into 12-day periodical rice growth-stage maps from January 2017 to September 2018 at the sub-district level over Java Island, the top rice production area in Indonesia. The accuracy measurement was based on the test dataset and the predicted cross-correlated with monthly local statistics. The overall accuracy of the rice growth-stage model of PROBA-V was 83.87%, and the Sentinel-1 model was 71.74% with the Support Vector Machine classifier. The temporal maps were comparable with local statistics, with an average correlation between the vegetative area (remote sensing) and harvested area (local statistics) is 0.50, and lag time 89.5 days (n = 91). This result was similar to local statistics data, which correlate planting and the harvested area at 0.61, and the lag time as 90.4 days, respectively. Moreover, the cross-correlation between the predicted rice growth stage was also consistent with rice development in the area (r &gt; 0.52, p &lt; 0.01). This novel method is straightforward, easy to replicate and apply to other areas, and can be scaled up to the national and regional level to be used by stakeholders to support improved agricultural policies for sustainable rice production.

Fe-Mn Plaque Formation Mechanism Underlying the Inhibition of Cadmium Absorption by Rice Under Oxygation Conditions.

Oxygation (O) is a water-saving and energy-saving irrigation method that can also influence the absorption of cadmium (Cd) by rice, but the related mechanism is still unclear. In this study, the relationship between O method and Fe-Mn plaque formation was tested through pot experiments. The Fe-Mn plaque content and Cd concentration were measured during different rice growth periods, and the fitted models based on their correlation were established. The results show that, Fe-Mn plaque formation was the most significant factor affecting Cd accumulation in rice under O conditions. The content of rice root Fe-Mn plaque was higher after the application of O during the filling and maturity stages of rice growth, and Fe-Mn plaque inhibited Cd accumulation in the rice roots and grains and reduced the translocation factors (TFs) from the rice dithionite-citrate-bicarbonate extract (DCB) to the roots (TFDCB-R) and from the roots to the straw (TFStraw-G). O may influence the Fe-Mn plaque formation on the root surface to impede Cd absorption by rice. This research provides theoretical support for the Cd absorption under O conditions.

Developing a multivariable lookup table function for estimating flood damages of rice crop in Vietnam using a secondary research approach

It is increasingly important to evaluate the economic flood damage toward agricultural crops to further improve decision-making and mitigate flood impacts in developing countries. In this study, we derive a multivariable lookup table function for estimating flood damages to rice crops based on a secondary research approach, which involves collecting and integrating fragmented secondary information sources of rice damage caused by inundation and event data observed in southern rural areas of the Ca River Basin, Central Vietnam. The derived lookup table function includes the effects of the rice growth stages on the damage caused, in addition to flooding parameters such as inundation level and inundation duration. This indicates that the rice crops are generally the most vulnerable and robust to inundation in the ripening and the reproductive stages. The yield loss in the ripening stage dramatically increases from 50% to 90% when the complete inundation lasts 5–8 days. Even after 7 days of 75% inundation, the yield hardly decreased at the reproductive stage and was reduced by almost half for 7 days of complete inundation. Four–five days of complete inundation at the ripening and vegetation stages are likely to cause almost the same damage to rice crops as that caused by 7 days of inundation at the reproductive stage. Utilization of the function to estimate rice damage in four flood events reveals that the derived multivariable function captures flood damages well and outperforms the univariable damage functions for the target area.

Soil enzymatic activities response to long-term fertilization during key growth stages of early rice

ABSTRACT This long-term fertilization experiment was conducted since 1981, included non-fertilization (NF), chemical fertilizer (CF), double chemical fertilizer (DCF) and chemicals with organic fertilizer (COF). In 2017, soil samples were collected at the tillering, heading and maturity stages of early-season rice (Oryza sativa L.). The activities of urease (UR), α-glucosidase (AG), glucosaminidase (NAG), β-1,4 glucosidase (BG), β-cellobiosidase (CBH), β-xylosidase (BXYL), acid phosphatase (ACP), phenoloxidase (POX) and peroxidase (PER) were measured. The activities of AG, NAG, BG, CBH, BXYL, ACP and POX in the maturity stage were significantly higher than in the tillering stage by 343.0%, 153.4%, 55.0%, 8.5%, 1791.5%, 1237.7% and 1179.4%, respectively. Compared with the CF treatment, the activities of UR, AG, BG, and POX in the COF treatment increased by 33.5%, 23.3%, 19.5% and 40.1%, respectively. Meanwhile, both CBH and ACP in the COF treatment were higher than in the DCF treatment by 33.4% and 66.7%, respectively. A significant relationship was identified between UR/PER activities and soil available nitrogen, phosphorus, potassium/rice biomass using the redundancy analysis method. Therefore, the application of organic and chemical fertilizers could increase most enzymatic activities and soil productivity. UR and PER were key factors indicating soil nutrient turnover and rice growth.

Effect of water and fertilization management on Cd immobilization and bioavailability in Cd-polluted paddy soil

The field trial was conducted to investigate remediation effects of two alkaline fertilizers and three water management techniques on Cd contaminated paddy soil. The results revealed downward trend of soil pH and EC during growth period of rice. The treatment of organic fertilizer has indicated high pH and organic matter than treatment of calcium magnesium phosphate fertilizer. The integrated effect of organic fertilizer and continuous flooding (COF) has significantly (p < 0.05) reduced soil Eh to −180 mv at booting stage. The exchangeable Cd of soil decreased with growth of rice in all treatments. The continuous flooding has showed lowest content of soil exchangeable Cd at every stage of rice growth than other treatments. The organic fertilizer, calcium magnesium and phosphorus have promoted growth of rice. The treatments of continuous flooding were most effective in reducing Cd content in rice grain by 12.6–51.9%. The treatments of continuous flooding have lowest TFhusk-rice, and TFshoot-husk. The BCF of continuous flooding was 0.13, 0.35 and 0.13. According to Pearson correlation coefficients, soil exchangeable Cd concentration has significantly (P < 0.05) negative correlation with soil pH and EC, but has significantly (P < 0.05) positive correlation with soil Eh. The Cd concentration of rice grain has significantly (P < 0.05) positive correlation with Cd of leaf, and negative correlation with Cd of husk. It is concluded that organic fertilizer combined with continuous flooding was most effective management strategy for Cd remediation in paddy soil.

Remediation potential of spent mushroom substrate on Cd pollution in a paddy soil.

To investigate the remediation potential of spent mushroom substrate (SMS) on Cd pollution in a paddy soil, a rice pot experiment was conducted to study the effects of SMS addition on the availability of Cd in soil and the uptake of Cd in rice tissues. Five percent of SMS from Pleurotus eryngii (SMS-A, treatment: A), SMS from Agaricus bisporus (SMS-B, treatment: B), or SMS-A plus SMS-B (1:1, treatment: A+B) were added into a Cd-contaminated paddy soil before planting, respectively. The treatment of no SMS amendment was set up as the control (CK). At the four main growth stages of rice, the soils and plant samples were collected to detect the soil properties, Cd concentration in soils and rice tissues, and Cd fractions in soils. Results indicated that the application of SMS-A, SMS-B, and A+B significantly increased soil pH by 14.0-22.9, 23.9-32.9, and 22.7-30%, organic matter (OM) contents by 12.9-31.5, 22.1-34.5, and 26.1-36.9% comparing with CK. While cation exchange capacities (CECs) were increased by 3.6-8.5, 4.9-13.1, and 0.4-10.0% in A, B, and A+B treatments, respectively, except those at the maturation stage in A and B treatments. However, the CaCl2-Cd concentrations in soils were significantly decreased by 64.8-77.9, 76.1-98.9, 73.2-98.9% in A, B, and A+B treatments, respectively, comparing with CK. The reduced availability of Cd was attributed to the changes of Cd from soluble to insoluble fractions in soils amended with SMS and resulted in the decreased Cd uptake in rice tissues. The Cd concentrations in roots significantly decreased by 22.8-36.9, 28.6-36.6, and 26.8-42.6%, while the Cd concentrations in straw decreased by 20.1-46.4, 9.3-41.6, and 16.0-49.1% in A, B, and A+B treatments, respectively. At the maturation stage, the Cd concentrations in brown rice were reduced by 17.7, 15.9, and 19.4% in A, B, and A+B treatments, respectively. Correlation analysis revealed that the Cd concentrations in rice roots, straws, and brown rice were all positively correlated with CaCl2-Cd concentrations of soils. Moreover, soil pH and OM were significantly negatively correlated with the Cd concentration in rice tissues, except that between soil pH and the Cd concentration in rice straws. Therefore, the reduced Cd availability in soil and uptake in rice plant tissues together with better soil nutrient conditions by SMS application improved the biomass of root and straw at heading, filling, and maturation stages and the rice production by 32.9-38.8% at the maturation stage. The combined application of SMS-A and SMS-B can be used as a potential method for remediation of Cd-contaminated paddy soil.

Co-application of nitrogen and straw-decomposing microbial inoculant enhanced wheat straw decomposition and rice yield in a paddy soil

Straw returning is a promising approach to improve soil fertility and to mitigate the negative effects of chemical fertilizers on soil quality. However, straw degradation is a slow and multifactorial-controlled process. Herein, a field experiment (June 2010–September 2013) was carried out to examine the effects of concurrent application of chemical nitrogen (N) and straw-decomposing microbial inoculant (SDMI) on wheat straw decomposition and rice yield in a paddy soil, Anhui Province, East China. To do so, four treatments were selected with basal N fertilization rates of 0 (CN105), 67.5 (CN24), 97.5 (CN18), and 150 (CN12) kg ha-1. For all treatments, wheat straw and SDMI were applied at the equal rates of 6000 and 30 kg ha-1, respectively. To assess wheat straw decomposition, straw samples were taken at tillering, elongation, heading, and maturity stages of rice growth. Results indicated that straw decomposition substantially increased two to over 15 times with rice growth. In tillering stage, N amended straws had 7.5 to almost 21% higher decomposition than CN105 due to the stimulation of soil microbes with higher N requirement. After this stage, all treatments had rather similar decomposition rates. This might attribute to SDMI application that, in turn, significantly increased soil microbial respiration (P < 0.05). Generally, N addition increased grain yield 0.4–13.6% higher than CN105. This can be due the accelerated straw decomposition caused by boosting soil microbial activity/respiration. Overall, our results suggested that CN18 was the most favorable C/N ratio for both microbial straw decomposition and rice productivity in the study paddy soil. Although we found that co-application of N and SDMI is an efficient/inexpensive approach to improve soil fertility and crop productivity through acceleration of straw degradation, full documentation of straw degradation in relation to the soil properties/agricultural management practices still requires long-term field trials.

Effects of biochar on methane emission, grain yield, and soil in rice cultivation in Thailand

Biochar has been recommended as a soil amendment to improve soil fertility and mitigate methane (CH4) emissions from rice cultivation. Its effects, however, vary depending on soil type, biochar characteristics, and application rate. This study was aimed to evaluate the potential of mangrove biochar on CH4 mitigation, soil properties, and the productivity of rice cultivated in a clay loam soil in Thailand. Biochar was used at a rate equivalent to 10 t ha−1 season−1, both with (biochar + fertilizer: BF) and without (biochar alone: BI) fertilizer, for two cultivation seasons. BI reduced CH4 flux at most stages of rice growth. Relative to control soil (no biochar, no fertilizer: CT), BI significantly decreased cumulative CH4 emissions by 21.1% in the first season and 24.9% in the second season. CH4 emissions from BF soil were also less than those from the use of fertilizer alone (FE). Rice grain yield in BI was 7.85% and 14.4% greater than in CT, and in BF by 1.47% and 3.72% greater than FE, in the first and second seasons, respectively. The decrease in CH4 emissions and increase in rice grain yield decreased CH4 emission intensity under biochar treatments. Soil pH, organic carbon, cation exchange capacity, and available nutrients in the soil increased with biochar addition. The soil organic carbon stock was significantly increased by 32.6% in BI and 27.5% in BF after the first season, and by 43.5% in BI and 39.6% in BF after the second season.