Soil Bacterial and Fungal Communities Response Differently to Bombax Ceiba (Malvaceae) in a Traditional Agroforestry System

Background Agroforestry system is one of promising directions for developing sustainable agriculture because the intercropping of crops and trees may facilitate resource cycling and avoid soil degradation. Bombax ceiba (Malvaceae), a tall tree with red flowers blooming in Spring, is traditionally planted in rice paddies in tropical Asia, while the roles of B. ceiba in the agroecosystem remain unexplored.Methods In this paper, we investigated and assessed spatiotemporal variations of soil nutrient contents and soil bacterial and fungal communities along the distance gradients to B. ceiba during three reproductive stages of rice, i.e. booting, heading, mature, in a typical Bombax-dominated rice paddy on Hainan Island, South China.Results B. ceiba in rice paddy could improve the soil nutrient conditions, particularly available K and soil organic carbons. The relative abundance of Chloroflexi and Ascomycota increased while Actinobacteria decreased along the distance gradient to B. ceiba. In addition, the relative abundance of Firmicutes was highest at harvesting stage of rice, while Acidobacteria was richer in the early reproductive stage of rice. Soil potassium content was the principal driver in shaping soil bacterial diversity and composition, while fungal community was mainly affected by soil nitrogen.Conclusions Our results provide evidences for positive influences of B. ceiba on biotic and abiotic traits of rice paddy soils and thus lend supports to the ecological basis of this tropical Asian endemic traditional Agroforestry system, which could increase resource cycling and paddy stability and have the potential to reduce carbon emission.

Main Controlling Factors and Empirical Models for Total Mercury and Methylmercury Accumulation in Rice (Oryza Sativa L.)

It has been reported that rice consumption is the main mercury (Hg) exposure pathway for humans, and soil properties could significantly affect the methylation and accumulation process of Hg in soil-rice system. In this study, 19 paddy soil with various properties were spiked with exogenous Hg(II) at three concentration levels to conduct a pot experiment after a 60-days aging period. Stepwise multiple linear regression was applied to determine the controlling soil factors and develop prediction models for the methylmercury (MeHg) concentration in soil and total Hg (THg) and MeHg in brown rice. The results showed that THg in brown rice was positively correlated with THg in soil, while it had a negative correlation with soil pH and clay content. Soil organic matter (OM) promoted Hg methylation and inhibited the accumulation of MeHg in brown rice. Soil pH and clay content were negative factors when soil MeHg was used to predict MeHg in brown rice. THg and MeHg in brown rice could be well predicted by soil THg, pH and clay content. These results may provide a theoretical basis for safe production of rice in Hg contaminated paddy field.

Soil bacterial community as impacted by addition of rice straw and biochar

The application of straw and biochar can effectively improve soil quality, but whether such application impacts paddy soil bacterial community development remains to be clarified. Herein, the impacts of three different field amendment strategies were assessed including control (CK) treatment, rice straw (RS) application (9000 kg ha−1), and biochar (BC) application (3150 kg ha−1). Soil samples were collected at five different stages of rice growth, and the bacterial communities therein were characterized via high-throughput 16S rDNA sequencing. The results of these analyses revealed that soil bacterial communities were dominated by three microbial groups (Chloroflexi, Proteobacteria and Acidobacteria). Compared with the CK samples, Chloroflexi, Actinobacteria, Nitrospirae and Gemmatimonadetes levels were dominated phyla in the RS treatment, and Acidobacteria, Actinobacteria, Nitrospirae and Patescibacteria were dominated phyla in the BC treatment. Compared with the RS samples, Chloroflexi, Acidobacteria, Actinobacteria, and Verrucomicrobia levels were increased, however, Proteobacteria, Gemmatimonadetes, Nitrospirae, and Firmicute levels were decreased in the BC samples. Rhizosphere soil bacterial diversity rose significantly following RS and BC amendment, and principal component analyses confirmed that there were significant differences in soil bacterial community composition among treatment groups when comparing all stages of rice growth other than the ripening stage. Relative to the CK treatment, Gemmatimonadaceae, Sphingomonadaceae, Thiovulaceae, Burkholderiaceae, and Clostridiaceae-1 families were dominant following the RS application, while Thiovulaceae and uncultured-bacterium-o-C0119 were dominant following the BC application. These findings suggest that RS and BC application can improve microbial diversity and richness in paddy rice soil in Northeast China.

Dynamics of Weedy Rice Soil Seedbank Under Differing Control Strategies in Italian Rice Fields: survey and model study

The abundance of weedy rice (Oryza sativa L.) in the soil seedbank was estimated in 2011 in Italian rice (Oryza sativa L.) fields with different histories of IMI-resistant Clearfield® rice varieties (CL), non-Clearfield® varieties (NCL) and planting methods. A model was used to predict weedy rice seedbank dynamics over time under different control strategies. Soil samples were taken from 50 rice fields cultivated with CL varieties consecutively for 0, 1, 2, or 3 years and weedy rice seedbank data were used in a model considering eight scenarios: A) rice monoculture with CL and NCL varieties in alternate years; B) two years of CL, followed by one year with NCL; C) three years of CL followed by one year of NCL; D) rice monoculture with only CL; E) rice monoculture with only NCL; F) two years of CL followed by one year of rotation with another crop (CR), and then by an additional year with NCL; G) one year of CR followed by two years of CL, and then by one year of NCL; H) two years of CR followed by two years of CL. Weedy rice seedbank exceeded 1,000 seeds m−2 in the surveyed fields with no significant differences between rice planting methods. Highest densities were found in fields cultivated for one year with CL varieties. Simulations indicated that where CL varieties were used in rice monoculture susceptible weedy rice seedbank reduced gradually, allowing a depletion after 17, 13, 11, and 9 years in scenarios A), B), C), and D), respectively. The weedy rice seedbank increased in NCL monoculture (E) and declined significantly in crop rotation scenarios (F, G, H). The simulations indicated that the introduction of crop rotation is crucial for obtaining a relatively fast reduction of weedy rice seedbank and delaying the evolution of herbicide-resistant populations.

Parametric and Non-Parametric Suitability Evaluations of Rice Soils of Asu River Group Parent Materials in Ohaozara, Nigeria

The study was carried out in Ohaozara Southern Ebonyi State in Southeastern Nigeria. Study area was identified in a rice soil of about 120 hectares used for FGN/IFAD Value Chain Development program (VCDP). Three profile pits were dug on a transect line of about 100 – 200m apart for suitability evaluation study. The aim of the study was to use parametric and non – parametric suitability evaluation to study the rice soils under Asu River Group parent material. Parametric method is where each limiting characteristic was rated using information provided on factor ratings of land use requirements for wetland ricetable. In Nonparametric method, pedons were placed in suitability classes by matching their land characteristics with the agronomic requirements of rice. The index of productivity (IP) (actual and potential) was calculated using the equation: IP= A x √(B/100 x C/100 x D/100xE/100). Suitability evaluation results show that climate, soil physical conditions and wetness were optimum S1(95%) and moderately suitable S2(85%) while,fertility and toxicity parameters made the soil marginally suitable S3(60%). Parametric and non – parametric suitability evaluation revealed that the soils were mostly marginally suitable both potentially and currently. Major limitations of the investigated soils bother on fertility and Al toxicity.