Promote Rice Growth Research Articles

Chitosan mitigates the adverse effects and improves photosynthetic activity in rice (Oryza sativa L.) seedlings under drought condition

ABSTRACT The ability of chitosan to promote rice growth, physiological traits, and photosynthetic performance in rice seedlings under drought stress was investigated. Rice seedlings (Oryza sativa L. cv. KDML105) were treated with 100 mg l−1 low and high molecular weight (MW) chitosan via a combination of seed priming and foliar spray. The seedlings were subjected to drought stress by withholding water for 4 days, which resulted in the U-shaped (scale 5) leaf rolling. The results showed that drought significantly decreased shoot and root growth. Chitosan application, particularly with high MW chitosan, improved shoot and root growth under drought stress. Chitosan treatment also alleviated the effects of drought stress by elevating relative water content, as well as reducing electrolyte leakage and malondialdehyde content. Antioxidant enzyme activities, including guaiacol peroxidase (GPX) and ascorbate peroxidase (APX), were increased in response to chitosan. Additionally, treating the plant with chitosan improved photosynthetic efficiency as evidenced by increased CO2 response, the maximum rate of Rubisco carboxylase activity (Vcmax), and photosynthetic rate. We conclude that the exogenous application of chitosan aids the plant in coping with the severity of drought stress. While both low and high MW chitosans were effective at alleviating the effect of drought on rice seedlings, high MW chitosan might have a slight advantage with respect to increased effective duration.

New insight to the use of oyster shell for removing phosphorus from aqueous solutions and fertilizing rice growth

The excess amount of phosphorus (P) in water bodies can cause eutrophication, while the lack of P in soil can limit plant growth. Therefore, this study proposes to recover P from eutrophic lakes and use the recovered P as a fertilizer for rice growth in soil. In order to recover P from water bodies, oyster shell wastes (OySh) were used to prepare an adsorbent for P removal. The P-adsorbed adsorbent can then be used as fertilizer to release P to the soil slowly. This study investigates the feasibility of the OySh as both the P adsorbent and fertilizer, and involves four major experiments: the characterization of the OySh, adsorption experiments, toxicity tests, and pot experiments for rice growth. The OySh was thermally treated to improve its adsorption capacity for P, and the OySh calcined at 800 °C (OySh-800) showed noticeably high P adsorption. The P adsorption to the OySh-800 was quantified in batch experiments under various conditions and column experiments using natural lake water. The potential use of P adsorbed OySh-800 (P-OySh-800) as a P fertilizer was assessed by its toxicity test using bioluminescent bacteria and earthworms and pot experiments for rice growth. X-ray diffraction and X-ray photoelectron spectroscopy analyses revealed that P adsorption by the OySh-800 was achieved by the reaction between P and the calcium in the OySh-800, which formed Ca(PO3)2 and Ca4.885(PO4)3(OH)0.654. The P adsorption on the OySh-800 took 72 h to reach the equilibrium, and the maximum P adsorption capacity was 228.15 mg/g, which was higher than that of other adsorbents used for P removal. In the column experiment, a breakthrough point was reached in 20 h, and 73.6% of the P in the lake water was removed. The toxic effects of the OySh-800 determined by Allivibrio fischeri (EC50 of 896 mg/L) decreased after P adsorption (EC50 of 28 300 mg/L for P-OySh-800). When the OySh-800 and P-OySh-800 were applied at 0%–0.42% in soil, the toxic effects of both adsorbents on earthworms were negligible. The application of the P-OySh-800 at the medium level (i.e., 0.1 g/kg-soil) significantly promoted rice growth (i.e., increased tiller number). The application of organic wastes (i.e., OySh-800) as value-added materials to remove P from water and subsequently supply P for rice cultivation can address two environmental issues with P, excess of P in water bodies causing eutrophication and lack of P in the soil.

Multi-omics approaches explain the growth-promoting effect of the apocarotenoid growth regulator zaxinone in rice

The apocarotenoid zaxinone promotes growth and suppresses strigolactone biosynthesis in rice. To shed light on the mechanisms underlying its growth-promoting effect, we employed a combined omics approach integrating transcriptomics and metabolomics analysis of rice seedlings treated with zaxinone, and determined the resulting changes at the cellular and hormonal levels. Metabolites as well as transcripts analysis demonstrate that zaxinone application increased sugar content and triggered glycolysis, the tricarboxylic acid cycle and other sugar-related metabolic processes in rice roots. In addition, zaxinone treatment led to an increased root starch content and induced glycosylation of cytokinins. The transcriptomic, metabolic and hormonal changes were accompanied by striking alterations of roots at cellular level, which showed an increase in apex length, diameter, and the number of cells and cortex cell layers. Remarkably, zaxinone did not affect the metabolism of roots in a strigolactone deficient mutant, suggesting an essential role of strigolactone in the zaxinone growth-promoting activity. Taken together, our results unravel zaxinone as a global regulator of the transcriptome and metabolome, as well as of hormonal and cellular composition of rice roots. Moreover, they suggest that zaxinone promotes rice growth most likely by increasing sugar uptake and metabolism, and reinforce the potential of this compound in increasing rice performance.

The endophytic bacterium Bacillus koreensis 181-22 promotes rice growth and alleviates cadmium stress under cadmium exposure.

Recently, cadmium (Cd) contamination in paddy soils has become a highly concerning pollution problem. Endophytic microbes in rice not only affect the plant growth but also contribute to ion absorption by the roots. Therefore, they are a promising, ecologically sound means of reducing the Cd transport from soils to shoots and grains of the plant. In this study, a Cd-resistant endophytic bacterium, named 181-22, with high Cd absorption capacity (90.8%) was isolated from the roots of rice planting in heavily Cd-contaminated paddy soils and was identified as Bacillus koreensis CGMCC 19,468. The strain significantly increased fresh weight of roots and shoots (44.4% and 42.7%) and dry weight of roots and shoots (71.3% and 39.9%) and decreased Cd content in the rice roots (12.8%), shoots (34.3%), and grains (39.1%) under Cd stress compared to uninoculated plant by colonizing rice roots via seed inoculation. Moreover, colonization of 181-22 reprogrammed rice physiology to alleviate Cd stress by increasing pigment and total protein content, regulating Cd-induced oxidative stress enzymes such as superoxide dismutase and catalase and reducing malondialdehyde. Thus, B. koreensis 181-22 has the potential to protect rice against Cd stress and can be used as a biofertilizer to bioremediate paddy soils contaminated with Cd. KEY POINTS: • Bacillus koreensis 181-22 colonized the inside of rice roots at high numbers via seed inoculation. • B. koreensis 181-22 promoted rice growth and decreased Cd accumulation in grains. • B. koreensis 181-22 regulated the physiological response to alleviated Cd stress in rice.

Isolation, Screening, and Degradation Characteristics of a Quinclorac-Degrading Bacterium, Strain D, and Its Potential for Bioremediation of Rice Fields Polluted by Quinclorac.

ABSTRACTQuinclorac (QNC) is a persistent, highly selective, hormonal herbicide of low toxicity. QNC accumulates in soil and affects the growth and development of crops planted subsequent to its application. In this study, we isolated and screened a QNC-degrading bacterial strain, strain D, from rice paddy soil. Morphological analysis, physiological and biochemical tests, and 16S rRNA gene sequencing led us to identify strain D as a Cellulosimicrobium cellulans strain. We investigated the characteristics of strain D in relation to QNC degradation. Under optimal culture conditions, the QNC degradation rate was 45.9% after 21 days of culture. QNC degradation by strain D in the field was modeled and quantified by a pot experiment. The results show that strain D promotes rice growth and degrades QNC. This research has identified a new bacterial species that degrades QNC, providing a foundation for further research into QNC remediation.IMPORTANCE QNC-degrading bacteria have been isolated from different environments, but there are no reports of Cellulosimicrobium cellulans strains that degrade QNC. In this study, a previously unidentified bacterial strain that degrades QNC, strain D, was screened from paddy soil. The characteristics of strain D that relate to QNC degradation were investigated in detail. The results showed that strain D effectively degraded QNC. Two degradation products of QNC formed by strain D that have not been reported previously, i.e., 3-pyridylacetic acid (m/z 138.0548) and 3-ethylpyridine (m/z 108.0805), were identified using high-performance liquid chromatography–quadrupole time of flight mass spectrometry. Strain D has the capacity to degrade QNC in a QNC-polluted paddy.

Compensation of high nitrogen toxicity and nitrogen deficiency with biochar amendment through enhancement of soil fertility and nitrogen use efficiency promoted rice growth and yield

AbstractThe quality and nutritional status of agricultural soils are depleting gradually, and biochar is widely used in soil quality improvement. A sustainable approach of biochar application needs a better understanding of its interaction with nitrogen application and the final effect on crop growth. In our study, the effect of different biochar application levels (0, 15, 30, and 60 tons ha−1) in combination with nitrogen fertilizer levels (0, 150, 300, and 450 kg ha−1) on soil properties, rice growth, and nitrogen use efficiency were investigated. The results showed that sole application of biochar (B60) did not promote the rice growth except the soil organic carbon (SOC), total nitrogen, total phosphorous, and available potassium compared with no biochar addition, while a single application of 450 kg N ha−1 (N450) adversely affected the rice physiological and yield traits by destroying rice leaf ultrastructure and reducing the stomatal length by 13%, stomatal width 3% and density 12%, plant height 5%, dry biomass plant−1 4%, spike weight plant−1 8%, and grain weight plant−1 9% compared to N300 unless it was treated in combination with biochar. Biochar can significantly compensate the toxicity of excessive nitrogen and deficiency of low nitrogen fertilizer on rice growth. Compared to a single application of B0+N450 (450 kg N ha−1), combined application of biochar and nitrogen B30+N450 could elevate rice plant nitrogen content by 13%, plant height 30%, aboveground dry biomass plant−1 136%, spike weight plant−1 34%, and grain weight plant−1 36% while increments in total nitrogen accumulation (TNA 79%%) and nitrogen use efficiency (NUE 35%) were noted in B30+N300 treatment. These results suggest that biochar amendment combined with a proper amount of nitrogen fertilizer is an effective approach to promote soil conditions, manage nitrogen utilization, improve plant growth and increase crop yield on a sustainable basis.

Effects of Different Soil Conditioners on Rice Growth and Heavy Metal Uptake in Soil Contaminated with Copper and Cadmium

A rice pot experiment was conducted to study the effects of four soil conditioners, namely polyacrylic acid (PAA), polyacrylamide (PAM), polyvinyl alcohol (PVA), and humic acid (HA), on rice growth and heavy metal uptake from paddy soil contaminated with copper and cadmium. The results showed that the height and straw weight of rice in the conditioned soil treatments increased by 7.34%-22.0% and 10.0%-32.2%, respectively, compared to the control treatment. The increased height and straw weight was generally proportional to the amount of soil conditioners used in each treatment. Application of 0.4% soil conditioners led to a slight reduction in rice yield, with the grain weight decreasing by 6.70%-32.6% relative to the control treatment. Soil conditioners had no effect on soil pH, but significantly reduced the concentration of soil available Cu (5.38%-39.7%) and Cd (6.98%-59.6%). Similarly, concentrations of Cu in rice root, straw, and grain were decreased by 0.88%-27.2%, 8.50%-45.2%, and 3.41%-31.2%, respectively, while concentrations of Cd were decreased by 5.93%-20.5%, 10.0%-51.4%, and 3.12%-50.7%, respectively. The largest and smallest decreases occurred in the PAA and PVA treatments, respectively. Application of PAA, PAM, and HA significantly decreased the translocation factor of Cu from root to straw by 11.2%-27.1%, whereas the translocation factor of Cu from straw to grain increased by 17.9%-33.6%, respectively, compared with the control treatment. Application of PAA, PAM, and HA significantly decreased the translocation factor of Cd from root to straw by 15.2%-38.5%, compared with the control treatment, but with the exception of HA, had no effect on Cd translocation from straw to grain. In general, the application of soil conditioners promoted rice growth, inhibited the uptake of Cu and Cd by rice, and had a certain remediation effect on heavy metal contaminated soil.

GroEL protein from the potential biocontrol agent Rhodopseudomonas palustris enhances resistance to rice blast disease.

GroEL, which is a chaperone, plays a key role in maintaining protein homeostasis and, among other functions, serves to prevent protein misfolding and aggregation. In addition, the GroEL protein also has a significant effect on enhancing plant resistance and inhibiting plant diseases. However, the function of the GroEL protein in the inhibition of rice blast remains unknown. Field experiment results show that photosynthetic bacteria PSB-06 have a good control effect on Magnaporthe oryzae. PSB-06 also can promote rice growth and enhance stress resistance. A GroEL protein which was separated and purified from photosynthetic bacteria had a significant antagonistic effect on appressorial formation and pathogenicity of Magnaporthe oryzae, meanwhile transcriptional analysis demonstrated that the GroEL protein could improve the expression of defense gene of rice. Our results show that the photosynthetic bacteria Rhodopseudomonas palustris significantly controls rice blast disease. Its action involves an extracellular GroEL protein, which inhibits appressoria formation, antagonizes the pathogenicity of Magnaporthe oryzae and promotes a host defense response. The research results provide evidence of the potential of this photosynthetic bacterium as a biocontrol agent at least for rice blast control. © 2021 Society of Chemical Industry.

Identification of a plant endophytic growth-promoting bacteria capable of inhibiting cadmium uptake in rice.

The study aims to identify a novel plant growth-promoting bacteria (PGPB), which contributes to promoting growth and reducing cadmium (Cd) concentration in rice under Cd-contaminated conditions. Nine bacterial strains were isolated from plants grown in Cd-contaminated soil. These bacteria were tolerant to 1000μmol/L CdCl2 , capable of producing indole-3-acetic acid, fixing nitrogen and solubilizing phosphate. The result of hydroponic experiment showed that under the control and Cd stress conditions, the dry weight of the Tm02-inoculated rice seedlings increased significantly. Furthermore, under Cd stress, the concentration of Cd in the shoot of the Tm02-inoculated seedlings decreased significantly, while there was no significant difference in Cd concentration between treatment with other eight strains and noninoculated seedlings. The same results were observed in the pot experiment as well, where there was a significantly reduced Cd concentration in rice grains of the Tm02-inoculated rice plants. Tm02 was classified as Pantoea agglomerans through 16S rDNA sequencing. A novel PGPB strain Tm02 was identified and confirmed that it has the function of promoting rice growth and reducing Cd concentration in rice grain under Cd-contaminated conditions. This strain has the potential to improve rice yield in Cd-contaminated paddy fields. This study provides a new example of using PGPB to improve the tolerance of rice to Cd pollution.

Seed coating by biofertilizer containing spores of Bacillus pumilus TUAT1 strain enhanced initial growth of Oryza sativa L.

AbstractIn rice production, early growth is often slow in direct‐seeded system. Techniques to overcome this barrier are needed. This study evaluated the effectiveness of Kikuichi—a biofertilizer containing Bacillus pumilus TUAT1 spore—in promoting rice growth in a direct‐sowing system. Oxygen, iron, and molybdenum as coating materials were also evaluated to combine with biofertilizer. The seeds were coated with powdered Kikuichi with polyvinyl alcohol followed by a coating with calcium peroxide (CALPER), molybdenum (Benmoly), and iron powder. Double coating with the biofertilizer and Benmoly promoted plant growth. We applied amounts of Kikuichi equivalent to one, two and a half, and five times the weight of the seeds and found that the growth‐promoting effect was dependent on the amount applied. The best timing of application of the coating, specifically during sprouting, was before the coleoptile emerged. Bacillus pumilus TUAT1 can enhance the growth of rice when it exists in high concentration on the spermosphere by coating with molybdenum, but double coating with neither calcium peroxide nor iron powder contributed to the initial growth of the seeds. Kikuichi coating with Benmoly has positive effects on the rice growth. This coating method is suitable to apply biofertilizer for direct sowing cultivation of rice.

Isolation and evaluation of the biocontrol potential of Talaromyces spp. against rice sheath blight guided by soil microbiome.

Rice sheath blight caused by Rhizoctonia solani is the major disease of rice that seriously threatens food security worldwide. Efficient and eco-friendly biological approaches are urgently needed since no resistant cultivars are available. In this study, fallow and paddy soils were initially subjected to microbiome analyses, and the results showed that Talaromyces spp. were significantly more abundant in the paddy soil, while Trichoderma spp. were more abundant in the fallow soil, suggesting that Talaromyces spp. could live and survive better in the paddy soil. Five Talaromyces isolates, namely, TF-04, TF-03, TF-02, TF-01 and TA-02, were isolated from the paddy soil using sclerotia of R. solani as baits and were further evaluated for their activity against rice sheath blight. These isolates efficiently parasitized the hyphae and rotted the sclerotia even at higher water contents in the sterilized sand and the soil. Isolate TF-04 significantly promoted rice growth, reduced the severity of rice sheath blight and increased the rice yield under outdoor conditions. Defence-related genes were upregulated and enzyme activities were enhanced in rice treated with isolate TF-04. Our research supplies a microbiome-guided approach to screen biological control agents and provides Talaromyces isolates to biologically control rice sheath blight.

The combination of different nitrogen fertilizer types could promote rice growth by alleviating the inhibition of straw decomposition

AbstractStraw return plays an important role in the improvement of farmland ecological environments, increasing soil fertility, crop quality, and yield. However, in the early growth of rice (Oryza sativa L.), straw decomposition and rice growth may be inhibited by suboptimal carbon/nitrogen (C/N) ratios. We, therefore, explored methods that could alleviate the inhibition of straw decomposition using different combinations of ammonium bicarbonate and compound fertilizer. No fertilizer (CK) and compound fertilizer (S0) were used as the control. The ratios of added ammonium bicarbonate were 10% (S1), 20% (S2), 30% (S3), and 40% (S4), respectively. Compared with the S0 treatment, the S2 treatment accelerated straw decomposition, promoted the early growth of tillers and roots, and improved the leaf area index, dry matter accumulation, and N use efficiency (apparent N utilization, agronomic N utilization, and partial factor productivity increased by 4.05‒19.48% in two years). Moreover, panicle number, filled‐grain percentage, and 1000‐grain weight were significantly higher in the S2 treatment than other treatments. The grain yield of S2 treatment was significantly higher than that of S0 treatment by 4.06% (2019) and 5.66% (2020). Regression analysis revealed that the optimal ratios of ammonium bicarbonate for increasing straw decomposition and grain yield were relatively close, 16.27% and 14.60%, respectively. These results suggest that compared with conventional fertilization method (S0), the 20% treatment is a more effective fertilization method that prevents inhibition of straw decomposition, promoting rice growth and yield, and improving nitrogen (N) use efficiency.

Exogenous IAA Alleviates Arsenic Toxicity to Rice and Reduces Arsenic Accumulation in Rice Grains

Arsenic (As) contamination in paddy soil reduces rice production and quality. It is important to increase the As tolerance of rice and reduce As accumulation in rice using exogenous methods. We examined the effects of exogenous plant hormones on the growth of and As accumulation in rice exposed to As. Under hydroponic conditions, 10 μmol L−1 As inhibited the growth of rice seedling. However, pretreatments with indole-3-acetic acid (IAA), salicylic acid (SA), and gibberellins (GA) rescued this inhibition, as evidenced by changes in plant morphology (root and shoot elongation, biomass, total root length, root surface area, root volume, and root tip number) and root activities, especially with the application of IAA. The As concentration in rice seedlings was significantly reduced. With soil culture, 20 mg L−1 IAA application significantly increased the grain biomass of both rice varieties, the 1000-grain weight and plant biomass of Mo Wang Gu Nei (MWGN), while decreased the As concentration in rice grains and total As accumulation in grains per plant. Furthermore, exogenous IAA reduced As translocation, as evidenced by lower As concentrations in upper leaves and internodes, but higher levels in lower leaves and internodes in Dong Ting Wan Xian (DTWX) after spraying with IAA compared to the control treatments. In conclusion, exogenous IAA can significantly promote rice growth and reduce As accumulation in rice grains.

Acclimation of CH4 emissions from paddy soil to atmospheric CO2 enrichment in a growth chamber experiment

Elevated levels of atmospheric CO2 (eCO2) promote rice growth and increase methane (CH4) emissions from rice paddies, because increased input of plant photosynthate to soil stimulates methanogenic archae. However, temporal trends in the effects of eCO2 on rice growth and CH4 emissions are still unclear. To investigate changes in the effects of eCO2 over time, we conducted a two-season pot experiment in a walk-in growth chamber. Positive effects of eCO2 on rice leaf photosynthetic rate, biomass, and grain yield were similar between growing seasons. However, the effects of eCO2 on CH4 emissions decreased over time. Elevated CO2 increased CH4 emissions by 48%–101% in the first growing season, but only by 28%–30% in the second growing season. We also identified the microbial process underlying the acclimation of CH4 emissions to atmospheric CO2 enrichment: eCO2 stimulated the abundance of methanotrophs more strongly in soils that had been previously exposed to eCO2 than in soils that had not been. These results emphasize the need for long-term eCO2 experiments for accurate predictions of terrestrial feedbacks.

The effect of integrated rice–frog ecosystem on rice morphological traits and methane emission from paddy fields

Integrated Rice–frog Ecosystem (IRFE) has the potential to reduce methane (CH4) emission and maintain yields from paddy fields. However, the quantitative relationship between rice morphological traits and CH4 emission remains to be explored. In this study, a 2-year field experiment was conducted to evaluate the effect of IRFE on rice morphological traits and CH4 emission from paddy fields and the ecological mechanisms. This study was conducted to analyze twelve aboveground and eight underground rice morphological traits, rice yields, and CH4 flux and emission from the paddy fields with six frog densities (0, 3750, 7500, 15,000, 30,000, and 60,000 frogs ha−1). The results showed that IRFE reduced CH4 emission by 24.70%–41.75% and 21.68%–51.21% in the 2018 and 2019 rice growth seasons, respectively. Moreover, CH4 emission decreased with the increase of frogs. Frogs also increased the diameter, biomass, and volume of rice roots, thus promoting rice growth. Root biomass, thousand-grain weight, and harvest index were also closely related to the yield. Root porosity and oxygen secretion capacity were negatively correlated with CH4 flux. Frogs increased root porosity and oxygen secretion, thereby reducing CH4 emission. The present study demonstrated that reducing CH4 emission and improving rice yields could be simultaneously achieved by altering rice morphological traits in IRFE.

Beneficial effects of endophytic Pantoea ananatis with ability to promote rice growth under saline stress.

Soil salinization severely inhibits plant growth, leading to a low crop yield. The aim of the current study was to isolate endophytic bacteria with the ability to promote rice growth under saline conditions. We isolated eight salt-tolerant endophytic bacteria from rice roots. An isolated strain D1 was selected due to its ability to stimulate rice seed germination in the presence of NaCl, which was identified as Pantoea ananatis D1. It exhibited multiple plant growth-promoting traits including phosphate solubilization, production of indole-3-acetic acid, 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase and siderophore. Inoculation of P. ananatis D1 obviously enhanced the rice root and shoot growth under normal and saline conditions. It also significantly increased the contents of chlorophyll, total soluble protein, and proline in salt-stressed rice seedlings. Moreover P. ananatis D1 could ameliorate the oxidative stress in rice induced by NaCl and Na2 CO3 treatment. The malondialdehyde content and various antioxidant enzyme activities were decreased by P. ananatis D1 inoculation in salt-affected rice. In addition, P. ananatis D1 showed a positive potential for limiting the Na+ accumulation and enhancing the K+ uptake, leading to an increase of 1·2-1·7 fold in K+ /Na+ ratio under saline environment. Pantoea ananatis D1 has the ability to improve the salt tolerance of rice seedlings. The application of plant growth-promoting bacteria (PGPB) is an eco-friendly strategy to improve plant tolerance towards abiotic stresses. We demonstrated that P. ananatis D1 could be used as an effective halotolerant PGPB to enhance rice growth in different salt-affected soils.

Rice intercropping with water mimosa (Neptunia oleracea Lour.) can facilitate soil N utilization and alleviate apparent N loss

Legume/non-legume intercropping is a widely applied agricultural practice worldwide and is very important for the development of sustainable agriculture, especially for improving soil nitrogen (N) nutrients and reducing N application via biological N fixation by legumes. However, research on intercropping between rice and aquatic legumes has rarely been undertaken. To address this issue, a field experiment was conducted to investigate the apparent N balance in rice and water mimosa (Neptunia oleracea Lour.) intercropping systems. Planting pattern treatments, including rice monocropping and rice/water mimosa intercropping, were employed in the paddy field, and three N fertilizer application levels, zero N (ZN, 0 kg ha−1 N), reduced N (RN, 140 kg ha−1 N), and conventional N (CN, 180 kg ha−1 N), were applied for the two planting patterns. The results showed that compared with rice monocropping, the growth indicators of rice were higher in the rice/water mimosa intercropping system. N fertilizer facilitated rice growth, and water mimosa grew better but reduced the partial factor productivity of rice. Notably, the biological N fixation efficiency of water mimosa was the highest in the reduced N treatment. In addition, the soil N nutrients in the rice/water mimosa intercropping treatments were higher than those in the rice monocropping treatments. In contrast, apparent N loss in the monocropping treatments was higher than that in the intercropping treatments, and it also increased with more N fertilizer applied. Thus, intercropping with water mimosa could promote rice growth, enhance N input, improve soil N nutrients, and reduce N loss. Furthermore, based on the performance of rice monocropping treatment under the conventional N level and rice/water mimosa intercropping treatment under the reduced N level on crop growth, N fixation, soil N nutrients, N mineralization and loss, we suggest thatrice/water mimosa intercropping with a reduced N application level is a much better choice. Taken together, rice/water mimosa intercropping is an environmentally friendly practice that could decrease N fertilizer application, and may alleviate nonpoint source pollution in paddy fields.

Organic fertilizer enhances rice growth in severe saline–alkali soil by increasing soil bacterial diversity

AbstractThe northeast region of China is an important grain‐growing area. However, severe soil salinization in the region impairs plant production. In the present study, organic fertilizer application (composted poultry manure) was evaluated as a potential strategy for remediating saline–alkali soil and promoting rice growth. Following continuous organic fertilizer application for 4 years, the contents of basic cations, including sodium (Na+) and chlorine cations (Cl−), decreased significantly (p < .05) (soil Na + decreased from 24.3 mg kg−1 to 21.8 mg kg−1 and soil Cl‐ decreased from 570.4 mg kg−1 to 38.5 mg kg−1), while soil organic matter (SOM), total nitrogen (TN), total phosphorus (TP), available nitrogen (AN) and available potassium (AK) were markedly increased (especially for soil AK, which increased from 85.8 mg kg−1 to 141.7 mg kg−1) compared to the treatment without organic fertilizer application. In addition, the relative abundance of plant growth‐promoting bacteria such as Thiobacillius, Methylobacter, Rhodoferax, Lysobacter and Flavobacterium increased significantly, whereas halophilic genera (Nitriliruptor, Mongoliicoccus, Litoribacter, Halomonas and Aliidiomarina) decreased markedly. Bacterial diversity also increased significantly, with data analysis suggesting that such shifts translated into more abundant plant‐growth‐related gene functions. According to structural equation modelling results, soil bacterial diversity was a key factor driving the maintenance of healthy plant growth in saline–alkali soil. These results suggested that organic fertilizers could improve the physicochemical properties of saline–alkali soil by altering interactions between rice plants and bacteria, for example, via the recruitment of specific beneficial microbial communities to increase their salinity–alkali stress tolerance, and, in turn, promote their growth.

Effect of Water Management on Rice Growth and Rhizosphere Priming Effect in Paddy Soils

The rhizosphere priming effect (RPE) caused by carbon inputs from crop rhizodeposits plays a key role in regulating the carbon emission flux and carbon balance of farmland soils. Due to frequent alternations between dry and wet conditions, CO2 and CH4 emissions and the RPE in paddy field ecosystems are significantly different to those of other ecosystems. Therefore, it is of great significance to determine the direction and intensity of the rice RPE under alternations of dry and wet to limit greenhouse gas emissions. In this study, using a 13C-CO2 continuous labeling method combined with a pot-based experiment, the response of rice growth and the RPE under alternating dry and wet and continuous flooding conditions was examined. The results showed that, compared with the continuous flooding treatment, the alternating dry and wet treatments significantly increased aboveground and root biomass and the root-to-root ratio, and also increased soil microbial biomass. Under continuous flooding conditions, fluxes of 13CO2 and 13CH4 increased with rice growth from 10.2 μg·(kg·h)-1 and 2.8 μg·(kg·h)-1 (63 d) to 16.0 μg·(kg·h)-1 and 3.2 μg·(kg·h)-1 (75 d), respectively. During the 12-day drying process, the emissions of 13CO2 and 13CH4 derived from rhizosphere deposited C decreased by 57.5% and 88.1%. Under continuous flooding conditions, the RPE for CO2 and CH4 were positive and increased with the growth of rice. Under the alternating dry and wet treatment, after 12 days of drying, the RPE for CO2 and CH4 was reduced from 0.29 mg·(kg·h)-1 and 12.3 μg·(kg·h)-1 (63 d) to -0.39 mg·(kg·h)-1 and 0.07 μg·(kg·h)-1 (75 d). Thus, alternating wet and dry treatment can effectively promote rice growth and reduce the cumulative emissions of CH4. Therefore, adopting appropriate field water management is of great significance for increasing rice yields and mitigating greenhouse gas emissions.

Magnesium and silicon fertilizer application to promote rice growth and production

The global demand for rice continues to increase due to population growth. In Indonesia, various innovations have been implemented for improving rice production, while magnesium silicate fertilizer application is still limited. The study was undertaken to investigate the effect of Mg and Si (MgSi Fert) on rice growth and productivity. This study was conducted at Luhur Jaya Village, Cipanas District, Lebak Regency, Banten Province in a rainy season. A randomized complete block design with ten treatments and three replications was set. The treatment was MgSi Fert with multiple dosages. Results showed that NPK fertilizer combined with 100 kg ha−1 MgSi fertilizer gave the highest yield. Based on the quadratic equation y = - 0.1301x2 + 28.812x + 5,474.2, it was known that highest slope on the equation was reached at dosage less than 150 kg ha−1 of MgSi Fert. The optimum dosage of MgSi Fert for Ciherang rice variety was achieved at 110 kg ha−1 with yield as 7.07 t ha−1. This present study showed that MgSi Fert application improved rice growth and yield.