Paddy Field Soil Research Articles

Impact of Organic and Inorganic Fertilizers on Microbial Populations at Various Altitudes of Nepal in Paddy Field Soil Systems

Impact of Organic and Inorganic Fertilizers on Microbial Populations at Various Altitudes of Nepal in Paddy Field Soil Systems

Isolation and Growth Characterization of an Acrylamide-degrading E. cloacae strain UPM2021a Isolated from a Paddy Field

Acrylamide is a suspected carcinogen and a global pollutant. The presence of acrylamide in the soil is a major source of this chemical. Microbe-mediated acrylamide breakdown as a bioremediation technique is gaining popularity across the world. Several bacteria capable of digesting acrylamide have been identified in paddy field soils. The best isolate was a bacterium identified tentatively as E. cloacae strain UPM2021a based on cultural, colony morphology and biochemical tests. According to early studies, ideal growth parameters included a pH range of 6.5 and 7.5 and a temperature range of 25 to 35 degrees Celsius. Acrylamide dosages of up to 2500 mg/L were explored as a single nitrogen supply. The greatest growth occurs between 300 and 1000 mg/L of acrylamide, resulting in an approximate nett growth of 3 log CFU/mL when compared to the control. Growth was practically tolerated at 1700 mg/L, and growth stopped entirely at concentrations above 2000 mg/L. Toxic heavy metals such as mercury, copper, chromium, and cadmium hampered acrylamide development with mercury being the strongest inhibitor whilst other metal ions such as copper, cadmium, and chromium show from 30 to 50% inhibition whilst lead was the least inhibiting. The relatively high tolerant of acrylamide makes this bacterium suitable for remediation of soil contaminated with acrylamide whilst its sensitivity to heavy metals chiefly mercury means metal-chelating or sequestering compounds must be added to soil contaminated with both acrylamide and heavy metals.

A new record of Scedosporium dehoogii isolated from paddy field soil in Iran: Phylogeny and antifungal susceptibility profiles.

Scedosporium species are ubiquitous environmental fungi, which are considered emerging agents that trigger disease in humans and animals. The present study aimed to determine Scedosporium dehoogii strain isolated from paddy field soil samples using semi-selective media and evaluate its antifungal susceptibility profile. Three paddy field soil samples were collected during an investigation for the isolation of Scedosporium species in Mazandaran province, Iran. Morphological and molecular analyses based on ITS-rDNA sequencing were performed. Furthermore, in vitro antifungal susceptibility testing for conventional drugs and novel imidazole (luliconazole) was performed based on Clinical and Laboratory Standards Institute M38-A3 guidelines. In this study, S. dehoogii was isolated from the soil in paddy fields. Based on the results, itraconazole and luliconazole showed the least and most antifungal activity against this isolate, respectively. Based on the findings, molecular identification was essential for distinguishing the species of S. dehoogii. Remarkably, luliconazole showed potent activity against this strain.

Isolation and Characterization of Phosphate-solubilizing Bacteria from Rice Field of Odisha and Their Growth Promoting Effect on Agricultural-Sectors

Organic farming will be a significant approach for farmers in the coming decades due to improved production and the preservation of soil natural properties. Phosphorus is the second most macronutrient required for plants to survive. The primary goal of this research was to know the paddy field soil nutritional status and isolate potential PSB bacteria from soil samples, which may aid in the development of a potent biofertilizer for organic farming. 12 soil samples were collected from three districts of Odisha (Kendrapara, Cuttack, Khordha). A laboratory study was conducted to isolate, identify, and characterise phosphate solubilizing bacteria from rice field soil. The morphological and biochemical traits of the PSB strains were evaluated. Four potential PSB strains PR, PA, PD, PS were chosen based on solubilization zone production and abundance in sampling site. The isolates PR had maximum phosphate solubilization index of 2.72 in pikovskaya agar medium and were strongly predominant in all regions. Phosphate solubilization and enhanced germination potential were evident in all four species. When compared to controls, good plant height, dry weight, and fresh weight were confirmed in seed germination assays with all bacterial isolates. The PR strain had the highest rate of germination 96.03%.

Impacts of Rice-Rape Rotation on Major Soil Quality Indicators of Soil in the Karst Region.

Arable land resources in karst regions are relatively scarce. The original crop rotation pattern can no longer meet the requirements of productivity development, while different crop rotation patterns have different impacts on the physicochemical properties of the soil. Through field experiments and laboratory analysis, the physicochemical properties and pollution characteristics of the soil during different crop growing stages in rice–rape rotation were investigated systematically. The main results are as follows. During the rice–rape rotation, fine sand in the topsoil experienced the greatest variation. During the rotation, pH variation in the subsoil was greater than that in the topsoil. The soil in paddy fields was poorly ventilated, and the rotation could reduce the redox potential of the soil. In the rotation process, the soil organic matter in the topsoil was higher than that in the subsoil, but the variation of soil organic matter in the topsoil was lower than that in the subsoil. The worst Cd pollution of the topsoil occurred in the seedling stage of rice, while that of the subsoil occurred in the flowering stage of rape; the comprehensive pollution index of Cr and Cd in the subsoil was higher than that in the topsoil. It is of great significance to investigate efficient crop rotation patterns under the conditions of the current productivity for promoting sustainable increases of rape and rice yield, maintaining soil fertility, and improving the soil.

Bio-efficacy of imidazolinones in weed control in a tropical paddy soil amended with optimized agrowaste-derived biochars.

Biochar is a black carbon sorbent that has the ability to stabilize organic substances in soil and, therefore, the potential to reduce their bio-availability. This sustainable material can be produced from locally-available agro wastes. The present study, for the first time, investigated the effects of biochars produced from oil palm empty fruit bunches (EFB) and rice husk (RH) on the efficiency of imazapic and imazapyr (two polar members of imidazolinone herbicides) as well as Onduty®, a mixture of them. It was executed in a Malaysian paddy field soil during a 30-day greenhouse experiment. The presence of optimized EFB and RH biochars in the heavy soil generally increases weed seeds germination and plants growth due to stabilization of the herbicides. The effect of EFB biochar was found higher than RH biochar having a higher affinity to the herbicides. An increase in the biochars application rates enhanced their effects as a soil modifier. Differences were more significant in the higher herbicides doses. Efficacies of all the herbicides were generally decreased in the biochar-amended soils. In the presence of 0.5% biochar in soil, the GR50 values for all herbicides were almost similar to biochar-free soil. In a 1.0% biochar-soil mixture, GR50 values of the herbicides increased by about 1.5 times. Bio-efficacies of the herbicides decreased by around 2.0 times as the biochar application rate enhanced to 2.0%. The greatest GR50 values were obtained in the presence of 4.0% biochar in the soils and were about 7.0-8.5 folds, indicating the high capability of amended soil in the stabilization of the herbicides. The findings of this study can help to reduce imidazolinones' pollution and, in this way, prevent the threats of their residues to the environment.

Protoptype Pengairan Sawah dan Monitoring Kualitas PH Tanah Berbasis IOT

Rice is a food crop commodity that produces rice which plays an important role in the economic life of Indonesia. Rice as a staple food is very difficult to replace by other staples. This study aims to determine the results of the design of the internet-based monitoring system for rice field irrigation and to determine the results of monitoring soil pH with Thinger.io. The tools used in the design of this system are Node MCU ESP8266, Ultrasonic Sensor HC-SR04, Soil pH Sensor, Servo Motor (MicroServo 9G – SG90), UTP Cable. Soil pH sensor can send soil acidity level data to NodeMCU and send data to thingger to display results, while ultrasonic sensor can read elevation value on surface if water level (11 cm) then servo will receive signal to open and when water level height value ( 6 cm) then the servo will receive a signal to close, the last process is to send data to the web server or thingger.io. The results of the pH test are that with a pH value equal to 7 then it is suitable for planting rice seeds and if the pH value is below 7 then it is not suitable for planting rice and dolomid lime will be added to neutralize the acidity level in the soil of paddy fields. The tests carried out are using the BlackBox method and the results of this test are the system runs as expected

Rice-crayfish pattern in irrigation-drainage unit increased N runoff losses and facilitated N enrichment in ditches

The rice-crayfish (RC) integrated pattern has been developed vigorously in China, but how it affects the nitrogen (N) runoff loss and distribution status during rice production is still poorly studied. Based on this, we selected two types of irrigation and drainage units (IDUs), which adopted the traditional rice-wheat (RW) rotation pattern and burgeoning RC rotation pattern separately, to investigate the effect of the RC pattern on N runoff loss, inorganic N distribution and N balance of the IDU. The results showed that there was a 241 kg ha−1 yr−1 and 135 kg ha−1 yr−1 N surplus achieved under RW and RC, respectively. Among these, the N surplus of RC was 53 % lower than that of RW during the rice growing season and was 37 % lower at other times. The NH4+-N contents of paddy field soils, rice yields and productive traits were not affected by rotation patterns. Nevertheless, the total nitrogen (TN), dissolved organic nitrogen (DON) and NH4+-N concentrations of RC field water were significantly higher (P < 0.01), and the N runoff losses of the RC pattern increased by 103 % to 855 % compared with the RW pattern. In addition, the NH4+-N reserved in RC ditch sediments substantially increased regardless of the dynamic changes during the rice growing season or from the vertical distribution at depths of 0–40 cm. Our results indicated that the RC pattern was beneficial for decreasing the N surplus without impacting the rice yield. However, larger N runoff losses and more available N flowing into crayfish farming ditches still pose great environmental risks. Therefore, more efficient and cleaner measures should be applied for the N management of IDU under the RC pattern.

Bacterial bio-mobilization and -sequestration of arsenic in contaminated paddy fields of West Bengal, India

One hundred and forty nine bacterial strains were isolated from arsenic contaminated paddy field soil of West Bengal following enrichment upon As(III), As(V) and control plates. The maximum tolerable concentration (MTC) of the bacterial population isolated towards As(V) and As(III) was found to be 600 mM and 10 mM, respectively. Eight isolates with varying MTC values were chosen to study their As ad-/ab-sorption abilities to form a consortium for bioremedial application to As contaminated soil. The As(III) or As(V) ab-/ad-sorption abilities of the chosen isolates positively correlated to their respective As(III) or As(V) MTC values. Phylogenetic analyses of the isolates affiliate them to be the members of genera Bacillus, Paenibacillus, Staphylococcus and Ralstonia. A consortium comprising the eight chosen isolates were incubated under eight microcosm conditions with combinations of flooded or non-flooded, sterile or non-sterile soils with low (6.1 mg/kg) or moderately high (19.5 mg/kg) As concentrations. The consortium revealed an overall appreciable activity of As mobilization and sequestration with best cellular As accumulation under non-flooded low As concentration soil incubation. While the microcosm with highly contaminated soil allowed best microbial As sequestration under flooded condition when incubated solely in sterile soil. Bacterial sequestration and removal of the toxic metalloid may find important implications in As bioremediation in agricultural fields hence, reducing the bioavailability of this toxic element for further translocation into the crop. The study, thereby, provides a novel insight for potential use of the consortia in bioremediating As contaminated soil through microbial biosequestration approach.

Application of an Ecotoxicological Battery Test to the Paddy Field Soils of the Albufera Natural Park.

Albufera Natural Park (ANP) (Valencia, Spain) is one of the most important wetland areas of the Mediterranean coast subject to high anthropogenic pressure, on whose soils a battery of bioassays has never been applied to evaluate the ecotoxicological risk. The present study determined available and water-soluble heavy metal content in four paddy soils used in the ANP, and the ecotoxicological effect on these soils was evaluated by performing the bioassays regulated in Spanish Royal Decree 9/2005. Soil properties and extractable Co, Cr, Cu, Ni, Pb and Zn (EDTA pH = 7) were analyzed in soils. These elements and macro- and micronutrients were also assessed in soil leachate. A test battery covering the following was needed: acute toxicity test in Eisenia foetida (OECD TG 207); mineralization tests of nitrogen (OECD TG 2016) and carbon (OECD TG 217); growth inhibition test in Raphidocelis subcapitata (OECD TG 201); mobility inhibition test in Daphnia magna (OECD TG 202). The soils found in the most anthropized areas to the north of the ANP (Massanassa and Alfafar) demonstrated a higher concentration of available heavy metals than in the southern ones (Sueca and Sollana). The aqueous leachate of the studied soils contained very low concentrations, which would be related to soil properties. Despite the high concentration of available potentially toxic elements (PTEs) in the Massanassa and Alfafar soils, the studied soils showed no toxicity during the performed battery bioassays. Therefore, soils can be considered non-toxic despite the obtained PTEs available concentration.

Nitrous oxide and carbon dioxide emissions from two soils amended with different manure composts in aerobic incubation tests

ABSTRACT Identification of nitrous oxide (N2O) and carbon dioxide (CO2) emissions from soils amended with different types of compost is needed for appropriate use of manure in agriculture. This study aimed at investigating the interaction effects of compost type and soil properties and effects of moisture contents on N2O and CO2 emissions, with identification of relative abundances of functional ammonia-oxidizing genes. Laboratory tests were conducted using cattle manure compost (CC) or mixed compost (MC) (cattle, poultry, and swine manure) amended Kochi (from a greenhouse) or Ushimado (from a paddy field) soils (3% by weight) with controls (no compost). Initial moisture contents were adjusted to 60% water-holding capacity (WHC) for Kochi soil and 70% WHC for both soils. The samples were aerobically incubated at 25°C. Emissions of N2O and CO2 and contents of ammonium N (NH4 +-N) and nitrate N in soils were measured continuously until day 42. The abundances of ammonia-oxidizing bacteria (AOB) and archaea genes were estimated to evaluate nitrifying activities. Cumulative N2O and CO2 emissions were significantly higher (p < 0.05) in MC than those in CC treatments probably due to higher NH4 +-N content and lower C/N ratio, which facilitated faster N mineralization and C decomposition. Emissions of N2O and CO2 were higher in compost-amended Kochi soil (70% WHC) with high total C and N, mineral N, and clay contents than those in less fertile Ushimado soil. Interestingly, interactions of compost type and soil properties on N2O emissions were significant (p < 0.05) only in Kochi soil because the addition of decomposition resistant CC increased N2O emissions only from this soil with high C and N contents. Higher soil moisture contents increased N2O and CO2 emissions significantly (p < 0.05) in Kochi soil. Emissions of N2O until day 15 were mainly due to activities of AOB amoA genes (R2 = 0.91). This study suggests that N2O emissions are increased by high NH4 +-N contents and a low C/N ratio in compost and high total C and N, mineral N, and clay contents in soil. The application of compost with less decomposable C increases N2O emissions only from nutrient-rich soil.

Study on the potential of silica-available based on types of soil on the productivity of paddy field in West Java Province, Indonesia

The Si-available (Siap) content in the soil of paddy fields is decreasing, so it will affect decreasing the productivity of paddy fields. Soil type maps can be used to estimate the potential Siap content in paddy fields. The purpose of this study was to assess the productivity of the paddy field in West Java Province based on the Siap potential in each region using maps of soil types and paddy productivity data. This research was conducted in West Java Province. The research was carried out from February 2021 to March 2021. The research method used was the descriptive research method. This research is secondary data analysis so that no field test is carried out. The validation of the data from the analysis was based on the literature from the previous researchers. The parameters measured in this study were: the distribution of paddy fields, the percentage of soil types in each paddy field, the average productivity of paddy field on each type of soil, the distribution of paddy productivity levels, the potential for Siap to paddy productivity and map of the potential distribution of Siap in West Java Province. Secondary data obtained were then analyzed using spatial analysis and descriptive analysis. The results of the spatial analysis show that 77% of paddy fields in West Java have medium Siap potential, 17% low and 7% high. The results of the correlation analysis show that the productivity of paddy plants has a strong correlation (r = 0.99) to the Siap of paddy soil. The soil maps can be used to estimate the potential of Siap and the productivity of paddy plants. The Si application was recommended in paddy fields in the southern region of West Java Province.

Evaluation of first and second rice cultivation based on diazinon pesticide concentration in water and soil of paddy fields of Mazandaran province

سابقه و هدف: مصرف آفت کش های ارگانوفسفره در کشاورزی، مشکلات عدیده محیط زیستی در پی دارد. آلودگی آب و خاک و بر هم خوردن تعادل‌ اکوسیستم های طبیعی، ظهور آفات و بیماری های جدید، وجود بقایای آفت کش ها در محصولات کشاورزی و عوارض بهداشتی حاصله موجب شده است که مدیریت مصرف آفت کش های آلی فسفره به عنوان یک ضرورت اجتناب ناپذیر مطرح شود. با وجود پایین بودن سرانه مصرف آفت کش ها درکشور در مقیاس جهانی، کاربرد نامطلوب آفت کش های ارگانوفسفره در برخی مناطق کشور از جمله استانهای شمالی و آلودگی های ناشی از آن، از مسائل مهم محیط زیستی کشور می باشد. در این تحقیق، با توجه به مصرف گسترده آفت کش فسفره دیازینون برای کنترل کرم ساقه خوار برنج در استان مازندران و با امعان نظر به شاخص تاثیر زیست محیطی (Environmental Impact Quotient) این آفت کش از حیث مخاطره آمیز بودن برای محیط زیست منطقه، غلظت دیازینون در آب و خاک مزارع برنج مورد بررسی قرار گرفت.مواد و روش ها: شناسایی آفت کش دیازینون در آب و خاک مزارع برنج استان مازندران با تعیین ایستگاههای ثابت برای نمونه برداری صورت گرفت. در مجموع 50 نمونه آب و خاک برای کشت اول و 30 نمونه آب و خاک در کشت دوم نمونه برداری گردید و پس از انتقال به آزمایشگاه توسط دستگاه گاز کروماتوگرافی (Gas Chromatography) مورد اندازه گیری قرار گرفت. نمونه برداری در سه فصل بهار، تابستان (قبل از نشا یا درحین برداشت محصول) و اوایل پاییز (برای کشت دوم برنج) انجام شد.نتایج و بحث: نتایج اندازه گیری انجام شده حاکی از تفاوت معنی‌دار در مقدار دیازینون در آب کشت اول در مقایسه با کشت دوم و خاک کشت اول در مقایسه با کشت دوم داشت. همچنین میانگین دیازینون در نمونه‌های آب کشت دوم نسبت به کشت اول، 7.8 برابر و در نمونه‌های خاک کشت دوم نسبت به کشت اول 1.66 برابر بود که بیانگر مقادیر بالا و هشداردهنده مصرف آفت کش دیازینون در کشت دوم برنج است. پایداری و حلالیت دیازینون و شرایط محیطی استان مازندران به ویژه بالابودن سطح آب های زیرزمینی، موجب افزایش ماندگاری این آفت کش و به تبع آن مخاطرات جدی محیط زیستی می شود. نتیجه گیری: با توجه به مقادیر غلظتی بالای آفت کش دیازینون در کشت دوم برنج، موضوع مدیریت مصرف سموم ارگانوفسفره و بهره برداری پایدار از اراضی تحت کشت با تمرکز بر ارتقای بهره وری تولید و افزایش راندمان محصول، توسعه آموزش های عمومی و تخصصی برای گروههای ذی نفع در تولید، عرضه و مصرف آفت کش های فسفره، ثبت و کاربرد این سموم بر مبنای ضریب اثر محیطی، استفاده از روش ها و فناوری های نوین برای مقابله با آفات مهم برنج، حذف و جایگزینی آفت کش پرخطر دیازینون از اهم مواردی هست که می بایست به عنوان راهبردها و سیاست های اجرایی حاصل از تحقیق مدنظر قرار گیرد.

KARAKTERISTIK SIFAT KIMIA DAN FISIKA TANAH PADI SAWAH PASCA BANJIR BANDANG DI KECAMATAN SILIMA PUNGGA – PUNGGA KABUPATEN DAIRI

Rice (Oryza sativa L.) is the main food crop commodity that has a strategic function, namely as a staple food, so that domestic rice production plays a role in food security and self-sufficiency. The Ministry of Agriculture has made various efforts and breakthroughs in the midst of the COVID-19 pandemic on food security, including the acceleration of rice planting, development of swamp land, diversification of local food, strengthening of government rice reserves and community food barns. Dairi Regency is one of the rice producers in North Sumatra Province. However, the productivity of rice plants has decreased in Longkotan Village and Bonkaras Village, Silima Pungga - Pungga District, Dairi Regency, due to the flash flood that caused material and land damage. One form of land damage caused is rice fields that have been covered with mud. Based on data from the Dairi Regency agriculture office, after the flash flood in December 2018 resulted in damage to rice fields in Longkotan Village, which was 112 hectares and Bongkaras Village was approximately 40 hectares. The real impact of banjir bandang in addition to reducing rice fields that can be used by farmers, decreasing soil fertility due to environmental damage to rice fields such as loss of top soil which has chemical and physical properties of soil in the availability of nutrients so that it directly causes a decrease in soil productivity and rice plants. Therefore, it is studied to overcome the limited supply of national food, especially rice, through increasing the productivity of paddy fields, especially the chemical and physical characteristics of lowland rice soil after the flash flood so that it can analyze its management efforts to support rice demand in Dairi Regency. The study was to determine the chemical and physical characteristics of the soil of paddy fields after banjir bandang and its management techniques. The research was carried out from April to August 2021 in Longkotan Village and Bonkaras Village. Soil testing was carried out at the Research and Development Center Laboratory of PT. Nusa Pusaka Kencana Analytical &amp; Qc. Laboratory of Bailang High Cliff Gardens, North Sumatra. Soil laboratory tests were conducted to determine the chemical and physical characteristics of the soil. Data analysis was carried out using a descriptive method, namely explaining a situation in the field based on the characteristics of the paddy field soil after the flash flood in the affected village. The results of this study are the clay content and organic matter contained in the soil of the Land Not Affected by Flash Floods. However, the soil pH in the Land Affected by Flash Floods is lower, this is due to the high sand fraction. Soil pH in Land Not Affected by Flash Floods is higher than soil pH in Land Affected by Flash Floods due to the higher organic matter content in Land Not Affected by Flash Floods. Based on the results of the research that the soil that has lower organic C is on the Land Affected by Flash Floods, namely 1.70% which includes low criteria. This is due to the loss of the top soil layer due to flash floods along with the Nitrogen and C-Organic content of the soil in the top soil layer. Because the rate of weathering and Ultisol formation runs faster, the wet climate with high temperature and rainfall causes Ultisols to be poor in organic matter.

Pool size of microbial biomass potassium in various farmland soils

ABSTRACT Potassium (K) is the major intracellular cation in all kinds of organisms including soil microorganisms. This study for the first time presented the potassium pool size in microbial cells in various farmland soils and the effect of land use and organic matter application on the contents. Microbial biomass potassium was determined for several paddy field soils under various managements in different areas, together with some upland, orchard, and pasture field soils, to estimate the potassium pool size in microbial cells in the farmland soils. The contents of microbial biomass potassium ranged from 9 to 65 mg K kg−1 soil in the paddy field soils and showed no difference among soil groups of the paddy fields. The biomass potassium content was higher in the pasture field (183–187 mg K kg−1 soil) than that in the paddy, upland (8–51 mg K kg−1 soil) and orchard (25–50 mg K kg−1 soil) field soils. The average ratio of microbial biomass potassium to exchangeable potassium was 0.25 for all the soils and the average values for paddy field (0.31) and pasture field (0.53) soils were higher than those for upland field (0.06) and orchard field (0.08) soils. Positive correlations were found between the contents of microbial biomass potassium and microbial biomass carbon and nitrogen. Application of organic matter significantly increased microbial biomass potassium in the farmland soils. These findings indicate that microbial biomass potassium plays an important role in potassium supply to crops as a reservoir of potassium and also suggest that the contribution of microbial biomass potassium to the potassium source for crops could be relatively higher in paddy field and pasture field soils than upland field and orchard field soils.

Ecological and Quantitative Analysis of Blue Green Algae from Paddy Fields of Patan and Karad Tehsil, Satara District, Maharashtra

Paddy fields are best studied aquatic ecosystems on earth. Blue green algae are the important components of paddy field soils expressively contribute to its fertilization. Present investigation was carried out to study the Ecological and quantitative analysisof blue green algae and correlate them with diversity of blue green algal flora in paddy field soils of Patan and Karad tehsil. Ecological and quantitative analysisof BGA showed that there is bit difference found in Simpsons diversity index (H) and Shannon’s diversity index (SDI) as well as species richness and evenness from both tehsil. This showed that blue green algal flora from paddy field soils of both tehsil is considerably correlated (0.776).

Estimation of turnover time of microbial biomass potassium in paddy field soil

ABSTRACT Soil microbial biomass (microbial biomass) contains substantial amounts of potassium (K) as a reservoir of K in soils. However, information about K dynamics and K flux through the microbial biomass are lacking. In the present study, the turnover time of microbial biomass K was estimated for the first time using paddy field soils. The paddy field soils, either amended with substrates of carbon, nitrogen, and phosphorus, or not, were aerobically incubated for 60 days, during which the amounts of microbial biomass K were periodically determined by the chloroform fumigation-extraction procedure. Microbial biomass K increased to twice (51.4–72.3 mg K kg−1 soil) of that in the unamended control 5 days after addition of the substrates and gradually decreased to the values in the control (25.2–44.0 mg K kg−1 soil) until 60 days of the incubation. The turnover time of microbial biomass K was estimated from the declines in the substrate amended soils. The turnover time of microbial biomass K ranged from 80.4 to 98.5 days, which roughly corresponded to the cultivation period of rice (about 100 days). These results indicated that microbial biomass K plays important roles in the supply of K source as well as the reservoir of K in paddy field soil.

Fe(II) Addition Drives Soil Bacterial Co-Ocurrence Patterns and Functions Mediated by Anaerobic and Chemoautotrophic Taxa.

Iron is among the most abundant elements in the soil of paddy fields, and its valence state and partitioning can be transformed by flooding and drainage alternations. However, little is known about the function of soil microbes that interact with Fe(II). In this study, sandy and loamy soils originating from rice fields were treated with Fe(II) at low and high concentrations. The findings demonstrate that additional Fe(II) has various effects on the soil’s microbial community structure and metabolic pathways. We conclude that Fe(II) at high concentrations reduced bacterial abundance and diversity in two textured paddy soils, yet the abundance in loamy soils was higher than it was in sandy soil. Additionally, in environments with high Fe(II) levels, the relative abundance of both anaerobic and chemoautotrophic bacteria increased. The Fe(II) concentration was positively correlated with total reduced substances but negatively correlated with redox potential and pH. Co-occurrence networks revealed that Fe(II) significantly promoted interactions with the most anaerobic and chemoautotrophic bacteria. In addition, adding Fe(II) greatly increased the number of more complex bacterial networks, and an increase in the number of mutually beneficial taxa occurred. We found that Fe(II) promoted the methane pathway, the Calvin cycle, and nitrate reduction to small but significant extents. These pathways involve the growth and interrelation of autotrophic and anaerobic bacteria. These results suggest that changes in the bacterial community structure occur in many dry–wet alternating environments.

Effects of Organic Amendment on Heavy Metal and Macronutrient Contents in Paddy Soil

The enormous use of chemical fertilizers recently has contributed to negative impacts on soil quality for agriculture purposes. However, if we use the fertilizer along with the organic amendment, it would offer a good approach for sustainable agriculture practice. Therefore, this study examined the effects of HT Organic Compound (HTOC) application on heavy metal and macronutrient content of the soil in a 2-season cultivated paddy field from 2016 to 2017. The sampling period was carried out after the harvest period and this study included three treatments: Chemical fertilizer or NPK (CF), chemical fertilizer and 250 kg organic amendment (CF+HTOC250), and chemical fertilizer and 500 kg organic amendment (CF+HTOC500). Several soil parameters were analyzed for this study such as soil organic matter content, pH, available P, available K, total N, and some heavy metals like As, Cd, Cr, Cu, Pb, and Zn. The results showed that the treated soil (CF+HTOC treatment) showed significantly higher soil organic matter content, pH, available P, available K, and total N than the chemical fertilizer treatment (CF). In the long-term application, the treated soils with HTOC tended to have lower Cd, Cr, Cu and Pb concentrations as compared with the chemical fertilizer treatment (CF). As a whole, this study concluded the application of chemical fertilizer along with HTOC could be an alternative method to improving soil quality in a paddy field area.

Dissipation of oxaziclomefone residues from rice, soil, and paddy field water using carbon nanotube-based QuEChERS and HPLC-MS analysis

Oxaziclomefone is an organic heterocyclic herbicide widely used in the control of rice weeds but its residues in the environment may pose risks to ecological security. This study established a method for the detection of oxaziclomefone residues in paddy field water, soil, rice plants, rice husks and brown rice using QuEChERS, purification with multi-walled carbon nanotubes, and high-performance liquid chromatography-mass spectrometry, and carried out a field trial. The method showed excellent linearity between oxaziclomefone peak area and concentration in the range 0.01–5 mg/L. The method detection limit were found to be 0.002 mg/kg in water, soil and rice plants and 0.003 mg/kg in brown rice and rice husks. Relative recovery of oxaziclomefone (0.01, 0.1 and 1 mg/kg) from the various matrices was 95.92–108.20% with relative standard deviations of 1.07–9.37%, indicating excellent accuracy and precision. The half-life of oxaziclomefone in rice plants and soil was 3.2–3.5 d and 37.9–41.0 d, respectively (a moderately degraded pesticide). Final oxaziclomefone residue concentrations were significantly below the method limit of quantification in water, plants, rice husks and brown rice, and below the limit of detection in soil, so oxaziclomefone does not pose a risk to the environment or rice consumers. This analytical method has the advantages of simple operation, high sensitivity, quick analysis time and good reproducibility, and is suitable for detection of oxaziclomefone residues in paddy water, paddy soil, rice plants, rice husks, and brown rice.