Paddy Soil Conditions Research Articles

Midseason draining of paddy water suppresses microbial arsenic methylation in soil and alleviates rice straighthead disease

Arsenic (As) methylation is an important component of As biogeochemical cycle. Microbial As methylation is enhanced under anoxic conditions in paddy soil, producing dimethylarsenate (DMA) which can cause physiological straighthead disease in rice. We conducted field experiments at two sites to test the effect of midseason draining of paddy water on microbial As methylation and the incidence of straighthead disease. Compared to continuous flooding, midseason draining increased soil Eh, decreased the abundances of microbial genes for arsenate reduction (arsC and arrA) and arsenite methylation (arsM), and lowered the concentrations of both inorganic As and DMA in soil porewater. Draining shifted microbial composition, resulting in decreases in the relative abundance of 17‐132 amplicon sequence variants. Draining decreased the accumulation of DMA in rice husk and of inorganic As and DMA in rice grain, decreased the incidence of straighthead disease, and increased grain yield by 20–45 %. Further experiments were conducted at eight field sites to assess the effect of midseason draining in a split field design. Draining decreased husk DMA concentration by 40–65 % and increased grain yield by 25–209 %. This study demonstrates that midseason draining can effectively suppress microbial As methylation and alleviate rice straighthead disease, benefiting both grain yield and safety.

Potential of biochar amendment as phosphorus source in tropical paddy soil

Phosphorus (P) is an essential element for crop production but its non-renewable natural sources are on the verge of depletion. The few remaining P sources may be depleted in the next 30–50 years. This calls for P recycling strategies with biochar application being an appealing approach. However, very limited information is available on the use of biochar as a P source and how it affects the various P fractions in tropical paddy soils. Therefore, the aim of this study was to establish whether biochar could potentially be used as a P source. A sample tropical paddy soil was treated with 1% biochar (derived from maize straw) and/or potassium dihydrogen phosphate, waterlogged and then incubated in airtight amber glass containers at 25 ℃, to mimic tropical paddy soil conditions. Soil aliquots were sampled periodically, followed by extraction and analysis of P fractions. The generated data was subjected to correlation analysis to explore the relationships among the P fractions. The study established that under anaerobic conditions, biochar amendment and P fertilization had no effect on aluminium bound P, calcium bound P, occluded P, moderately labile P and non-labile P. Additional P increased loosely sorbed P but biochar reduced it, even when combined with supplementary P fertilization. It was established that biochar increased iron bound P and to a greater extent with P fertilization. Additional P increased labile P while it was not affected by biochar. Apart from the effect on loosely sorbed P, biochar performed as well as the P fertilizer—or better in case of Fe-bound P. There is therefore promising potential for utilization of biochar as an alternative renewable P source.

Unveiling the significance of foliar-applied silicon, selenium and phosphorus for the management and remediation of arsenic in two different rice genotypes

Under paddy soil conditions, rice plants are vulnerable to arsenic (As) accumulation, thus causing potential threat to human health. Here we investigated the influence of foliar-applied phosphorus (P: 10 and 20 mg L−1), silicon (Si: 0.6 and 1.5 g L−1) and selenium (Se: 5 and 10 mg L−1) on As accumulation, morphological and physiological attributes of two contrasting rice genotypes (KSK-133 and Super Basmati) under As stress (25 mg kg−1 as arsenate). Silicon foliar dressing significantly (p < 0.05) reduced grain As uptake (up to 67%) and improved rice growth and chlorophyll content (28–66%) in both rice genotypes over their controls. Phosphorus foliar application resulted in a notable decrease (17%) in grain As uptake of coarse rice genotype (KSK-133), while it slightly increased grain As uptake in the fine one (Super Basmati; 6%) compared to controls. However, foliar-applied Se did not show significant effects on rice plants growth attributes and As uptake in both genotypes. Similarly, biochemical and enzymatic attributes (i.e., lipid peroxidation, electrolyte leakage, peroxidase and catalase) were improved with Si application in rice plants, except for P treatment that was only effective for coarse one. Foliar-applied Si also resulted in reduced cancer risk and hazard quotient (< 0.10) for both rice genotypes. This study advances our understanding on critical role of different foliar-applied nutrients and rice genotypes, which is imperative to develop effective As remediation and management strategies in coarse and fine rice genotypes and protect human health.

Metagenomic analysis of Fe(II)-oxidizing bacteria for Fe(III) mineral formation and carbon assimilation under microoxic conditions in paddy soil

Microbially mediated Fe(II) oxidation is prevalent and thought to be central to many biogeochemical processes in paddy soils. However, we have limited insights into the Fe(II) oxidation process in paddy fields, considered the world's largest engineered wetland, where microoxic conditions are ubiquitous. In this study, microaerophilic Fe(II) oxidizing bacteria (FeOB) from paddy soil were enriched in gradient tubes with FeS, FeCO3, and Fe3(PO4)2 as iron sources to investigate their capacity for Fe(II) oxidation and carbon assimilation. Results showed that the highest rate of Fe(II) oxidation (k = 0.836 mM d−1) was obtained in the FeCO3 tubes, and cells grown in the Fe3(PO4)2 tubes yielded maximum assimilation amounts of 13C-NaHCO3 of 1.74% on Day 15. Amorphous Fe(III) oxides were found in all the cell bands with iron substrates as a result of microbial Fe(II) oxidation. Metagenomics analysis of the enriched microbes targeted genes encoding iron oxidase Cyc2, oxygen-reducing terminal oxidase, and ribulose-bisphosphate carboxylase, with results indicated that the potential Fe(II) oxidizers include nitrate-reducing FeOB (Dechloromonas and Thiobacillus), Curvibacter, and Magnetospirillum. By combining cultivation-dependent and metagenomic approaches, our results found a number of FeOB from paddy soil under microoxic conditions, which provide insight into the complex biogeochemical interactions of iron and carbon within paddy fields. The contribution of the FeOB to the element cycling in rice-growing regions deserves further investigation.

The only constant is change: Endogenous circadian rhythms of soil microbial activities

Soil microbial community rhythms are a foundational mechanism that underpins soil microbial ecological processes, but evidence of endogenous circadian rhythms in these communities which are regulated by microbial molecular oscillations is lacking. In this study we used soil total and potentially active microbial communities to explore endogenous circadian rhythms excluded diurnal environmental fluctuations. Even though the communities were sampled from constantly dark, flooded paddy soil conditions, the potentially active microbial community structures were significantly different between the surface soil's ‘day’ and ‘night’. Seven taxa were identified as circadian indicators from the presence of circadian clock genes. The circadian indicators contributed to endogenous circadian rhythms by regulating community diversity, species interactions, and community assembly. These findings emphasize the importance of diurnal-scale perspective in understanding microbial ecological processes and, more practically, in the design of microbial ecology experiments.

The significance of eighteen rice genotypes on arsenic accumulation, physiological response and potential health risk

Rice is an important food crop that is susceptible to arsenic (As) contamination under paddy soil conditions depending on As uptake characteristics of the rice genotypes. Here we unveiled the significance of eighteen (fine and coarse) rice genotypes against As accumulation/tolerance, morphological and physiological response, and antioxidant enzymes-enabled defense pathways. Arsenic significantly affected rice plant morphological and physiological attributes, with relatively more impacts on fine compared to coarse genotypes. Grain, shoot, and root As uptake were lower in fine genotypes (0.002, 0.020, and 0.032 mg pot−1 DW, respectively) than that of coarse (0.031, 0.60, and 1.2 mg pot−1 DW, respectively). Various biochemical (pigment contents, hydrogen peroxide, lipid peroxidation) and defense (antioxidant enzymes) plant parameters indicated that the fine genotypes, notably Kainat and Basmati-385, possessed the highest As tolerance. Arsenic-induced risk indices exhibited greater hazard quotient (up to 1.47) and carcinogenic risk (up to 0.0066) for coarse genotypes compared to the fine ones, with the greatest risk for KSK-282. This study elaborates the pivotal role of genotypic variation among rice plants in As accumulation, which is crucial for mitigating the associated human health risk. Further research is required on molecular aspects, e.g., genetic sequencing, to examine rice genotypes variation in defense mechanisms to As contamination.

The role of various ameliorants on geochemical arsenic distribution and CO2-carbon efflux under paddy soil conditions.

Climate change is a global challenge that is accelerated by contamination with hazardous substances like arsenic (As), posing threat to the agriculture, ecosystem and human health. Here, we explored the impact of various ameliorants on geochemical distribution of As in two soils with contrasting textures (sandy clay loam (Khudpur Village) and clay loam (Mattital Village)) under paddy soil conditions and their influence on the CO2-carbon efflux. The exchangeable As pool in clay loam soil increased as: lignite (0.4%) < biogas slurry (6%) < cow dung (9%), and < biochar (20%). However, in the sandy clay loam soilexchangeable soil As pool was found to be maximum with farmyard manure followed by biogas slurry, biochar and cow dung (17%, 14%, 13% and 7%, respectively). Interestingly, in the sandy clay loam soil the percentage As distribution in organic fraction was: biochar (38%) > cow dung (33%) > biogas slurry (23%) > sugarcane bagasse (22%) > farmyard manure (21%) that was higher compared to the clay loam soil (< 6% for all the amendments). In addition to the highest As immobilization by biochar in sandy clay loam soil, it also led to the lowest CO2-carbon efflux (1470 CO2-C mg kg-1) among all the organic/inorganic amendments. Overall, the current study advances our understanding on the pivotal role of organic amendments, notably biochar, in immobilizing As under paddy soil conditions with low (CO2) carbon loss, albeit it is dependent on soil and ameliorant types.

Decomposition of rice straw residues and the emission of CO&lt;sub&gt;2&lt;/sub&gt;, CH&lt;sub&gt;4&lt;/sub&gt; under paddy rice and crop rotation in the Vietnamese Mekong Delta region - A microcosm study

This study investigated the influence of soil undergoing different crop rotations on the CH&lt;sub&gt;4&lt;/sub&gt;, CO&lt;sub&gt;2&lt;/sub&gt; emissions, and decomposition of rice straw. The studied soil undergoing crop rotation systems were rice-rice-rice (SR) and baby corn-rice-mungbean (SB). Two main microcosm set-ups: anaerobic (SR-AN, SB-AN) and aerobic (SR-AE, SB-AE) conditions. Litter bags containing rice stems were inserted into the soil and recollected at different time points for chemical analysing and the gas sampling was collected to measure the CO&lt;sub&gt;2&lt;/sub&gt; and CH&lt;sub&gt;4&lt;/sub&gt; emissions. The results indicated that the total carbon (TC) decreased around 30%, and the TC removal in anaerobic was significantly higher than in aerobic conditions. The residue cellulose content varied in a range from 68.2% to 78.6%, while the hemicellulose content varied from 57.4% to 69.3% at day 50 after incorporation. There were no significant differences in the total nitrogen removal, cellulose, hemicellulose, and lignin contents among the microcosm set-ups. CO&lt;sub&gt;2&lt;/sub&gt; emission increased in all the microcosm set-ups with the treatments without rice straw (CTSR, CTSB) in both aerobic and anaerobic conditions. CH&lt;sub&gt;4&lt;/sub&gt; release in the SR-AN treatments did not differ significantly compared with the SB-AN treatments. This study confirmed that the decomposition of rice straw residues is faster in the anaerobic paddy soil condition compared to the aerobic crop rotation condition.

Modeling paddy field soil conditions in East Java, Indonesia

Knowledge of soil conditions is a critical factor of effective land management to achieve optimum ecosystem services in agriculture. Digital soil modeling that incorporates soil spectral data has become a cost-efficient method compared to traditional wet-chemical soil analysis to produce high quality soil management data at the regional level. This research objective was to develop soil property prediction models to assess the characteristics of paddy field soil conditions in East Java, Indonesia. This study examined the utilization of a hybrid two-step regression (2Step-R) soil modeling approach that incorporates categorical soil-environmental variables and continuous visible-near-infrared (VNIR) spectral data. The integrative 2Step-R method was implemented in two modes—Partial Least Square Regression, PLSRmod, and Sparse Bayesian Infinite Factor, SBIFmod—with ‘mod’ referring to the fusion of important categorical soil-environmental parameters and soil VNIR spectral data. This research successfully developed reliable prediction models for soil organic carbon, nitrogen (N), pH, sum of bases (SB), and cation exchange capacity in the study area, with acceptable model performance (performance to interquartile ratio or RPIQ 1.77 to 2.54; performance to deviation ratio or RPD 1.45 to 1.89; and coefficient of determination or R2 0.53 to 0.72). The fused soil-environmental and VNIR spectral data approach (2Step-R) showed markedly improved model performances when compared to models that solely used VNIR spectra data (PLSR) for all modeled soil properties. This research underpins the utilization of cost-effective soil modeling to reveal existing soil conditions in securing soil ecosystem services for intensive agriculture in data sparse regions such as Indonesia.

Impact of organic and inorganic amendments on arsenic accumulation by rice genotypes under paddy soil conditions: A pilot-scale investigation to assess health risk

In this study, we investigated the distinct effects of organic (farmyard manure (FYM), cow dung (CD), biogas slurry (BGS), sugarcane bagasse (SCB)) and inorganic (gypsum and lignite) amendments on arsenic (As) accumulation by two rice genotypes, Kainat (fine) and Basmati-385 (coarse), under As stress. Results showed that shoot As concentration was ~2-time greater in Kainat compared to Basmati-385 (3.1–28 vs. 1.7–16 mg kg−1 DW, respectively), with the minimum shoot As content observed with CD and SCB. In contrast to gypsum and lignite, grain As concentration was significantly reduced with CD and SCB for Kainat (0.29 and 0.24 mg kg−1 DW) and Basmati-385 (0.04 and 0.09 mg kg−1 DW). Data indicated that the CD and SCB also improved chlorophyll a and b contents, reduced lipid peroxidation and hydrogen peroxide production in both rice genotypes. Significantly, the CD and SCB decreased grain As concentration below the FAO safe As limit in rice grain (0.2 mg kg−1 DW), especially in coarse rice genotype (Basmati-385), resulting in negligible As-induced human health risk. This study highlights the significance of amendments and rice genotypes controlling As accumulation in rice grain, which should be considered prior to As remediation program of paddy soils for limiting exposure of humans to As via rice grain.

Rice rhizodeposition promotes the build-up of organic carbon in soil via fungal necromass

Rice rhizodeposition plays an important role in carbon sequestration in paddy soils. However, the pathways through which rice rhizodeposits contribute to soil organic C (SOC) formation are poorly understood because of specific paddy soil conditions. Furthermore, microbial necromass has been largely ignored in studies examining the contribution of rhizodeposits to C sequestration during plant growth. To evaluate the contribution of microbial necromass to SOC formation via rhizodeposition, rice (Oryza sativa L.) plants were continuously labeled with 13CO2 for 38 days under ambient (aCO2, 400 μL L−1) or elevated CO2 (eCO2, 800 μL L−1) in a paddy field at two levels of N fertilization. The distributions of photosynthetic-13C in the shoots and roots, microbial communities, and SOC fractions were quantified. eCO2 increased plant growth and, consequently, the total 13C incorporated into the shoots, roots, and SOC compared to aCO2, while N fertilization (100 kg N ha−1) decreased root biomass and rhizodeposits in the soil and microbial pools, including living biomass (phospholipid fatty acids, PLFA) and microbial necromass (amino sugars). Rhizodeposits were initially immobilized mainly by bacteria and preferentially recovered in fungal necromass (glucosamine). While 13C incorporation into PLFAs was slightly increased during plant growth, 13C in microbial necromass increased greatly between the tillering and booting stages. Fungal necromass, which is less decomposable compared to bacterial residues, was the largest contributor to C sequestration with rhizodeposits via the mineral-associated SOC fraction, particularly under elevated CO2 without N fertilization. This study reveals the significance of the C pathways from rhizodeposits through fungal necromass and organo-mineral associations for the build up of SOC in paddy fields.

Rice straw biochar mitigates N2O emissions under alternate wetting and drying conditions in paddy soil

Alternate wetting and drying (AWD) is an important strategy that saves water and reduces greenhouse gases emission (GHG). Moreover, biochar (BC) has been also emerged as a promising approach to reduce GHG emissions. Hitherto, the mechanism lying behind reduction in nitrous oxide (N2O) emissions following the addition of BC are not clearly understood. Therefore, this field study was performed to assess the effects of different rates of rice straw biochar (RSB), i.e., control (0 RSB), 20 t RSB ha−1, and 40 t RSB ha−1 with no nitrogen (N) fertilizer (-N) and with N fertilizer (180 kg ha−1: +N) on soil pH, soil N dynamics, microbial genes abundance, N2O emissions and performance of paddy. The experiment was conducted in two factors factorial design with three replications. Application of RSB enhanced the soil pH and NH4+ and decreased NO3– therefore led to a significant reduction in the N2O emissions. However, the application of RSB (40 t ha−1) significantly decreased the N2O emissions by +59% and +62% in comparison to control under -N and +N conditions. The increased soil pH augmented the abundance ofnosZandnirKgenes, more following addition of 40 t RSB ha−1 and therefore, leads to an appreciable reduction in the N2O compared to 20 t RSB and control under both -N and +N conditions. Additionally, 40 t RSB ha−1 significantly enhanced the tillers production, kernel weight, paddy, and dry matter yield compared to control and 20 t RSB ha−1 under -N and +N conditions. Conclusively, RSB application at the rate of 40 t ha−1 could be a promising approach to reduce N2O emissions and increase the paddy yield.

Wetting-drying cycles during a rice-wheat crop rotation rapidly (im)mobilize recalcitrant soil phosphorus

The residual phosphorus (P) in Hedley’s sequential fractionation procedure is considered to be a relatively stable soil P pool and unavailable for plant uptake. In the present study, we investigated the effect of wetting-drying events on the dynamics of the residual soil P fraction in a flooded rice and aerobic wheat rotation. Soils were taken from a long-term field trial after flooded (rice), and aerobic (wheat) crops were harvested. Hedley’s sequential fractionation method was used to assess the distribution of various P fractions. These changes in these P fractions were then related to Fe cycling in the soil. The residual P (H2SO4-H2O2 digested) was the dominant P fraction (37–51% of total P) in the aerobic soil under wheat, while it was decreased by 18–27% in flooded soil under rice cultivation. In contrast, the sparingly soluble Ca-bound P (HCl-Pi) increased from 25–31% under wheat cultivation to 41–50% under flooded rice (paddy) cultivation where reducing conditions are expected to prevail under submerged paddy soil conditions. The crop rotation not only altered the sparingly available P fraction but also influenced soil labile P, especially the organic P form. Compared with the rice soil, a 4-fold increase in the labile P fraction (NaHCO3-Po) was observed in wheat soil. The moderately labile P fraction (NaOH-extractable) showed a similar trend to that of labile P pool, but the increased NaOH-Po in wheat soil was relatively small. The relatively rapid change in the residual P fraction was attributed to oxidation-reduction cycles of Fe oxides between flooded (rice) and aerobic (wheat) soil conditions. Wetting and drying cycles associated with a rice-wheat crop rotation promoted the transformation of the sparingly soluble soil P fraction between crops, which was attributed to changes in soil redox conditions, particularly Fe cycling. This indicated that the rice-wheat crop rotation can draw upon the sparingly soluble P fraction for crop production, thus relying less on fertilizer-applied P.

A high activity zinc transporter OsZIP9 mediates zinc uptake in rice.

Zinc (Zn) is an essential micronutrient for most organisms including humans, and Zn deficiency is widespread in human populations, particularly in underdeveloped regions. Cereals such as rice (Oryza sativa) are the major dietary source of Zn for most people. However, the molecular mechanism underlying Zn uptake in rice is still not fully understood. Here, we report that a member of the ZIP (ZRT, IRT-like protein) family, OsZIP9, contributes to Zn uptake in rice. It was expressed in the epidermal and exodermal cells of lateral roots, localized in the plasma membrane and induced during Zn deficiency. Yeast-expressed OsZIP9 showed much higher Zn influx transport activity than other rice ZIP proteins in a wide range of Zn concentrations. OsZIP9 knockout rice plants showed a significant reduction in growth at low Zn concentrations, but could be rescued by a high Zn supply. Compared with the wild type, accumulation of Zn in root, shoot and grain was much lower in knockout lines, particularly with a low supply of Zn under both hydroponic and paddy soil conditions. OsZIP9 also showed Co uptake activity. Natural variation of OsZIP9 expression level is highly associated with Zn content in milled grain among rice varieties in the germplasm collection. Taken together, these results show that OsZIP9 is an important influx transporter responsible for the take up of Zn and Co from external media into root cells.

Inverse modeling of laboratory experiment to assess parameter transferability of pesticide environmental fate into outdoor experiments under paddy test systems.

Extraction of environmental fate parameters for pesticides by inverse modeling in laboratory experiments has evolved to become a common practice in higher tier exposure modeling. This study focuses on flooded paddy soil conditions using a simple container test system. Four active ingredients of paddy herbicide were tested. The results were parameterized and transferred to analyze the effect of formulation types on the outdoor experimental data via inverse analyses of two structurally-compatible mathematical models, namely: pesticide concentration in paddy field for laboratory (PCPF-LR) and PCPF for outdoors (PCPF-1Rv1.1 ). After in-laboratory calibration, the PCPF-LR model revealed statistically acceptable or ideal simulations of pesticide concentrations in both the aqueous and soil phases (e.g. Nash-Sutcliffe efficiency > 0.7), in addition to determining the apparent sorption from the laboratory data. The extracted persistence indicators (degradation half-life, DegT50 ) in the aqueous phase were 1.4-38.7 times higher than those of the dissipation (DT50 ) due to the exclusion of partitioning and phase transfer processes (diffusion and sorption). In the outdoor experiment, 72% of the outdoor-calibrated simulations of the PCPF-1Rv1.1 model, showed statistically acceptable representations of the concentrations in paddy water. Furthermore, the DegT50 as 'bulk' degradation in paddy water was statistically insignificant between the formulation types; however, the DT50 demonstrated statistically different results. The laboratory/outdoor data interconnections using proposed modeling approach facilitate the data-specific model calibration and analysis. These can be useful in the exposure modeling of paddy pesticide by manipulating the parameter uncertainties associated with the experimental constraints. © 2020 Society of Chemical Industry.

Evaluation of Flooding Tolerance of Soybean (Glycine max L. Merr.) in Greenhouse under Upland and Paddy Soil Conditions

Domestic rice production has exceeded the demand in Korea and cultivation of upland crops like soybean has been increased in converted paddy fields. The objective of this study was to investigate the effect of two soil types, upland and paddy, on flooding tolerance of three tolerant and three susceptible soybean cultivars under greenhouse conditions. The flooding tolerance of soybean cultivars was evaluated based on chlorophyll content (CC), plant height (PH), and shoot dry weight (DW) measured under unflooded control and flooded treatments for 14 days. These three parameters were significantly (P < 0.01) affected by the soil type during the flooding and flood recovery periods of 14 days. Mean flooding tolerance index (FTI) of susceptible cultivars was higher than that of tolerant cultivars in upland soil. However, the FTI of tolerant cultivars was greater than that of susceptible cultivars in paddy soil at 14 days after flooding (DAF). A non-significant negative correlation between CC and DW and a significant (P < 0.01) positive correlation between PH and DW were found in both soils, whereas the negative correlation between CC and PH was non-significant in upland soil and was significant (P < 0.01) in paddy soil at 14 DAF. The results suggested that the flooding tolerance level of soybean cultivars could be influenced by soil type hence, it could be useful to consider designing flooding tolerance studies in different soil types. Also, field experiments could be designed to observe data until harvest to verify that with vegetative parameters of tolerant soybean varieties.

A paddy field study of arsenic and cadmium pollution control by using iron-modified biochar and silica sol together.

Under flooded conditions in paddy soil, the mobility of As increases while the mobility of Cd decreases. The opposite geochemical behavior of As and Cd makes it difficult to reduce their mobilities simultaneously. Our recent study found that combined applications of biochar and zero-valent iron successfully reduced the mobilities of As and Cd simultaneously. On this basis, in the present study, an iron-modified biochar (Fe-BC) was developed, and its effect on decreasing the accumulations of As and Cd in rice was verified in a 2-year field trial. In addition, previous studies indicated that silicon fertilizer can also reduce As and Cd accumulation in rice grain. Hence, the effect of the combined or separate application of Fe-BC and silica sol on As and Cd accumulation in rice grain was investigated. Over the 2-year field trial, the grain yields decreased in the following order: iron-modified biochar plus silica sol (Fe-BC plus Si) > silica sol (Si) > Fe-BC > control (CK). Concentrations of As and Cd in brown rice were in the order: Fe-BC plus Si < Si ≈ Fe-BC < CK. The treatments of Fe-BC and Fe-BC plus Si significantly increased the soil pH and thus decreased available As and available Cd in the soil. In addition, significantly positive correlations between available As and As in brown rice and between available Cd and Cd in brown rice were found. In conclusion, co-application of iron-modified biochar and silica sol should be a recommended strategy to reduce the accumulation of As and Cd in rice grains.

Response of denitrification in paddy soils with different nitrification rates to soil moisture and glucose addition

Denitrification is one of the most important N loss pathways in paddy soil. The nitrification rate is a key natural feature for controlling denitrification N loss in paddy soil. However, the relationship between nitrification and denitrification under different conditions in paddy soil remains unknown. By using 15N tracing, we investigated the response of denitrification loss to soil moisture and glucose addition in six paddy soils, whose net nitrification rates ranged from 0.36 mg N kg−1 day−1 to 5.72 mg N kg−1 day−1. The soils were amended with or without glucose to simulate root exudates at rates of 100 mg kg−1 of soil and incubated under either 60% water holding capacity (WHC) or flooded (2 cm depth) at 25 °C for 15 days. Denitrification loss was calculated by the unrecovered 15NH4+. The results showed that the soil nitrification rate significantly affected the N recovery form and denitrification loss of the applied 15N. NH4+ was the main recovered N form of the applied 15N in soil with a low nitrification rates. Denitrification losses were higher in the high nitrification rate soil than soil with low nitrification rate in all treatments. The correlation between denitrification and nitrification rates was well fit by Michaelis-Menten kinetics during the incubation, irrespective of soil moisture and glucose addition, and the R2 ranged from 0.801 to 0.977 (P < 0.05). Glucose addition did not stimulate denitrification under either 60% WHC or flooded conditions. The results showed that nitrification rate, rather than labile organic supply, controlled denitrification in paddy soil.

Ethanol extract of Nandina domestica Thunb. leafs: effect on Pomacea canaliculata and growth of Orzya sativa seedlings

Alien species may adversely affect not only human health, agriculture, and fisheries but also the native ecosystem. Pomacea canaliculata is one of alien harmful species (IUCN). Forest residues are a kind of renewable, cheap and secure source of primary energy. Nandina domestica Thunb. is a commonly and widely cultivated plant for city landscape construction in China. After being pruned, a large of N. domestica leaves are usually abandoned. In this work, extracts of ethanol Soxhlet (SE), ethanol immerse (EE), and water immerse (WE) were obtained from leaves of N. domestica Thunb. cv. Firepower. The molluscicidal effects of the three extracts from the leaves were evaluated against black P. canaliculata. In sand pot culture condition and pot culture with paddy soil condition, SE at concentration of 4000 mg L-1 did not affect seedlings normal growth. Plant height, seedling fresh weight (SFW), seedling dry weight (SDW) and Chlorophyll content of SE (4000 mg L-1) were not significantly different from that in DS (distilled water + seedlings). Besides, in pot culture with paddy soil condition, the SE treatment at concentration of 4000 mg L-1 inhibited P. canaliculata chewing rice seedlings effectively, which was not statistically different from the positive control {NSP, niclosamide (according to field dosage, 0.086 g m-2 ) + seedlings + P. canaliculata)}. Results from this study indicated that SE has molluscicidal effect against P. canaliculata and SE did not affect the normal growth of rice seedlings. Thus, we suggest further chemical and toxicological studies of SE.

PENGARUH PEMBERIAN BAHAN ORGANIK TERHADAP SIFAT KIMIA PADA TANAH SAWAH TERDEGRADASI DI KECAMATAN PANTAI LABU KABUPATEN DELI SERDANG

Organic fertilizers provide an advantage in increasing the growth and yield and can reduce the use of inorganic fertilizers. The study aims to analyze the land rehabilitation efforts relegated to improve the properties of the fields of chemistry, physics, and biology of the soil, with compare paddy soil conditions before and after rehabilitation. thereby increasing the productivity of rice in the District of Pantai Labu. The research was conducted in Durian, District, Pantai Labu, Deli Serdang, North Sumatra in April 2017 to July 2017. The study was arranged in a randomized block design (RAK) non-factorial experiment with five treatments and four replications. The treatments used are B0 = Control, B1 = 1.5%, B2 = 3%, B3 = 4.5%, B4 = 6%. The results showed that organic fertilizer can increase plant growth indicated by an increase in plant height. Organic fertilizers also increase the number of productive tillers, panicle length. Organic fertilizers also increase the number of grains per panicle and filled the grain.