Influences of tobacco straw return with lime on microbial community structure of tobacco-planting soil and tobacco leaf quality.

Soil amendment is an important strategy for improving soil quality and crop yield. From 2014 to 2019, we conducted a study to investigate the effects of tobacco straw return with lime on soil nutrients, soil microbial community structure, tobacco leaf yield, and quality in southern Anhui, China. A field experiment was conducted with four treatments: straw removed (CK), straw return (St), straw return with dolomite (St + D), and straw return with lime (St + L). Results showed that after 5 years of application, the St + L significantly increased the soil pH by 16.9%, and the contents of soil alkaline nitrogen (N) and available potassium (K) by 17.2% and 23.0%, respectively, compared with the CK. Moreover, the St + L significantly increased tobacco leaf yield (24.0%) and the appearance (9.1%) and sensory (5.9%) quality of flue-cured tobacco leaves. The addition of soil conditioners (straw, dolomite, and lime) increased both the total reads and effective sequences of soil microorganisms. Bacterial diversity was more sensitive to changes in the external environment compared to soil fungi. The application of soil amendments (lime and straw) promoted the growth of beneficial microorganisms in the soil. Additionally, bacterial species had greater competition and limited availability of resources for survival compared to fungi. The results showed that soil microorganisms were significantly influenced by the presence of AK, AN, and pH contents. These findings can provide an effective method for improving the quality of flue-cured tobacco leaves and guiding the amelioration of acidic soil in regions where tobacco-rice rotation is practiced.

Root-zone fertilization improves crop yields and minimizes nitrogen loss in summer maize in China.

It is urgently to minimize nitrogen (N) loss while simultaneously ensuring high yield for maize in China. A two-year field experiment was conducted to determine the effects of root-zone fertilization (RZF) and split-surface broadcasting (SSB) on grain yield, N use efficiency (NUE), and urea-15N fate under different N rates (135, 180 and 225 kg ha-1). Results showed that RZF increased grain yield by 11.5%, and the N derived from fertilizer (Ndff%) by 13.1-19.6%, compared with SSB. The percentage of residual 15N in the 0-80 cm soil was 37.2-47.4% after harvest; most 15N (64.4-67.4%) was retained in the top 20 cm. RZF significantly increased the N apparent recovery efficiency (NARE) and 15N recovery in maize by 14.3-37.8% and 21.9-30.0%, respectively; while decreased N losses by 11.2-24.2%, compared with SSB. The RZF of urea can be considered a slow-release fertilizer, which better matches maize N demand and effectively reduces N losses. Overall, RZF achieved yields as high as the SSB, but with a 20-25% reduction in N application. These results help improve our understanding of N fate in the maize cropping system, and may help guide recommendations for N management in southeastern China.

One-time root-zone N fertilization increases maize yield, NUE and reduces soil N losses in lime concretion black soil.

Excess N-fertilizer application and inappropriate fertilization methods have led to low N use efficiency (NUE) and high N leaching. A field experiment was performed in a typical lime concretion black soil area to compare N application methods: split surface broadcasting (SSB) and one-time root-zone fertilization (RZF) on grain yield, NUE, the fate of 15N urea and soil N loss during the 2015 and 2016 maize growing seasons. Each application method was tested at N rates of 135 and 180 kg N ha-1, and a control (CK) with no N fertilizer. The RZF treatment remarkably increased grain yield by 7.0% compared with SSB treatment under 180 kg N ha-1, and significantly increased N derived from fertilizer by 28.5%. The residual 15N in the 0-80 cm soil layer was 40.6-47.6% after harvest, 61.8-70.9% of which was retained in 0-20 cm. The RZF remarkably increased the 15N recovery in maize by 28.7%, while significantly decreased the potential N losses by 30.2% compared with SSB in both seasons. In conclusion, one-time RZF of urea is recommended for obtaining high yields, increasing NUE, and minimizing N losses in maize, which deserves more attention for developing and applying in the future.

Impact of tillage practices on soil bacterial diversity and composition under the tobacco-rice rotation in China.

Tobacco-rice rotation is a common farming system in south China, and many tillage practices such as straw mulching, dolomite dust, and quicklime application have been adopted to improve crop production. These agricultural management practices alter soil physical and chemical properties and affect microbial life environment and community composition. In this research, six tillage practices including no tobacco and rice straw mulching (CK), tobacco and rice straw mulching (TrSr), rice straw returning fire (TrSc), tobacco and rice straw mulching with dolomite dust (TSD), rice straw returning fire and quicklime (TSQ), and rice straw returning fire, quicklime and reduced fertilizer (TSQf) were conducted to detect changes in soil bacterial diversity and composition using Illumina sequencing. The results showed that the total number of operational taxonomic units (OTUs) from the six treatments was 2030, and the number of mutual OTUs among all samples was 550. The TrSc treatment had the highest diversity and richness, while TSQf had the lowest. Soil physio-chemical properties and microbial diversity can influence each other. Proteobacteria and Actinobacteria had the greatest proportion in all treatments. The abundance of Nitrospirae was the highest in the TrSc treatment. The TSQf treatment had the highest abundance of Firmicutes. The abundance of Nitrospira in the TrSc treatment was 2.29-fold over CK. Streptomyces affiliated with Firmicutes improved by 37.33% in TSQf compared to TSQ. TSQf treatment was considered to be the most important factor in determining the relative abundance at the genus level.

Effect of exogenous selenium supply on photosynthesis, Na+ accumulation and antioxidative capacity of maize (Zea mays L.) under salinity stress.

The mechanism of selenium-mediated salt tolerance has not been fully clarified. This study investigated the possible role of selenium (Se) in regulating maize salt tolerance. A pot experiment was conducted to investigate the role of Se (0, 1, 5 and 25 µM Na2SeO3) in photosynthesis, antioxidative capacity and ion homeostasis in maize under salinity. The results showed that Se (1 µM) relieved the salt-induced inhibitory effects on the plant growth and development of 15-day-old maize plants. Se application (1 µM) also increased the net photosynthetic rate and alleviated the damage to chloroplast ultrastructure induced by NaCl. The superoxide dismutase (SOD) and ascorbate peroxidase (APX) activities were increased, and ZmMPK5, ZmMPK7 and ZmCPK11 were markedly up-regulated in the roots of Se-treated plants, likely contributing to the improvement of antioxidant defence systems under salinity. Moreover, 1 µM Se increased K+ in the shoots while decreasing Na+ in the roots, indicating that Se up-regulates ZmNHX1 in the roots, which may be involved in Na+ compartmentalisation under salinity. The findings from this single experiment require repetition together with measurement of reactive oxygen species (ROS), but nevertheless suggest that exogenous Se alleviates salt stress in maize via the improvement of photosynthetic capacity, the activities of antioxidant enzymes and the regulation of Na+ homeostasis.

[Selenium uptake and transport of rice under different Se-enriched natural soils].

In this study, a pot experiment was conducted with "Wandao 205" as test materials to investigate Se uptake and translocation in rice under different Se concentrations (0.5, 1.0, and 1.5 mg . kg-1). Results showed that there was no significant change in rice yield when Se concentration in soil was lower than 1.5 mg . kg-1. Significant linear correlations existed between Se concentration in soil and different rice plant tissues. Se concentration in rice plant followed the order of root > straw > grain. Se concentration in different rice grain fractions followed the order of bran > polished rice > hull. The root absorption index of Se was more than 1.86, suggest that the rice could absorpt Se from soil effectively. However, the transport and accumulation of Se in seeds from Se-enriched soil was relatively constant. The Se transport index in seeds was between 0.53 and 0.59. Soil Se concentration within the range of 0.5 to 1.0 mg . kg-1 could produce Se-enriched rice, which might be enough for human requirement of 60-80 µg . d-1 Se. However, polished rice at high-Se treatment (1.5 mg . kg-1) exceeded the maximum standard limit of Se (0.3 mg . kg-1) for cereals in China. These results suggested that we could produce Se-enriched rice under soil Se concentration in the range of 0.5 to 1.0 mg . kg-1 without spraying Se fertilizer, thus reducing the cost and avoiding soil and water pollution caused by exogenous Se.