Chunyu Jiang

Discrepancy in Response of Rice Yield and Soil Fertility to Long-Term Chemical Fertilization and Organic Amendments in Paddy Soils Cultivated from Infertile Upland in Subtropical China

Abstract From 1990, over 17 years field experiment was carried out in paddy field cultivated from infertile upland to evaluate the response of rice productivity, soil organic carbon (SOC), and total N to long-term NPK fertilization or NPK combined with organic amendments. The field trials included NPK (N, P, K fertilizer), NPKRS (NPK combined with rice straw), NPK2RS (NPK combined with double amount of rice straw), NPKPM (NPK combined with pig manure) and NPKGM (NPK combined with green manure) and the cropping system was rice-rice ( Oryza sativa L.) rotation. Annual rice yield, straw biomass, and harvesting index increased steadily with cultivation time in all treatments. Average annual rice yield from 1991 to 2006 was ranged from 7 795 to 8 572 kg ha −1 among treatments. Rice yields in treatments with organic amendments were usually higher than that in treatment with NPK. Contents of SOC and total N also increased gradually in the cultivation years and reached the level of 7.82 to 9.45 and 0.85 to 1.03 g kg −1 , respectively, in 2006. Soil fertilities in treatments with chemical fertilization combined with organic amendments were relatively appropriate than those in treatment with NPK. There was obvious discrepancy between cumulative characters of rice yield and soil organic fertility in newly formed paddy field. Compared with relatively high rate of crop productivity improvement, cumulative rates of SOC and total N were much lower in our study. SOC and total N contents were still less than half of those in local highly productive paddy soils after 17 years cultivation in subtropical China. Present work helps to better understand the development of infertile paddy soils and to estimate the potential of yield improvement in this region.

Soil N transformation and microbial community structure as affected by adding biochar to a paddy soil of subtropical China

We have had little understanding on the effects of different types and quantities of biochar amendment on soil N transformation process and the microbial properties. In this study, various biochars were produced from straw residues and wood chips, and then added separately to a paddy soil at rates of 0.5, 1 and 2% (w/w). The effects of biochar application on soil net N mineralization and nitrification processes, chemical and microbial properties were examined in the laboratory experiment. After 135 d of incubation, addition of straw biochars increased soil pH to larger extent than wood biochars. The biochar-amended soils had 37.7, 7.3 and 227.6% more soil organic carbon (SOC), available P and K contents, respectively, than the control soil. The rates of net N mineralization and nitrification increased significantly as biochars quantity rose, and straw biochars had greater effect on N transformation rate than wood biochars. Soil microbial biomass carbon increased by 14.8, 45.5 and 62.5% relative to the control when 0.5, 1 and 2% biochars (both straw- and wood-derived biochars), respectively, were added. Moreover, biochars amendments significantly enhanced the concentrations of phospholipid fatty acids (PLFAs), as the general bacteria abundance increased by 161.0% on average. Multivariate analysis suggested that the three rice straw biochar (RB) application levels induced different changes in soil microbial community structure, but there was no significant difference between RB and masson pine biochar (MB) until the application rate reached 2%. Our results showed that biochars amendment can increase soil nutrient content, affect the N transformation process, and alter soil microbial properties, all of which are biochar type and quantity dependent. Therefore, addition of biochars to soil may be an appropriate way to disposal waste and improve soil quality, while the biochar type and addition rate should be taken into consideration before its large-scale application in agro-ecosystem.

Fungicidal activities of soil humic/fulvic acids as related to their chemical structures in greenhouse vegetable fields with cultivation chronosequence

In the background of rapid expansion of plastic greenhouse vegetable production in China, many environmental risks have emerged in recent years. In this study, the soils with a chronosequence in greenhouse vegetable fields were collected and the soil humic acids (HAs) and fluvic acids (FAs) were extracted and purified. The soil HAs and FAs were found to show inhibition activities against phytopathogenic fungi for the first time. Fourier transform infrared spectroscopy was performed to investigate the chemical structures of HAs and FAs. The variation of relative peak areas indicated the chemical structure of HAs become more complex and stable under continuous cultivation. The PCA analysis showed HAs and FAs could be distinctly separated from each other and cultivation years mainly determined the variation. Mantel test and RDA analysis indicated the active components (aliphatic peaks for HAs and COOH, OH peaks for FAs) had positive correlation with the inhibition rates of HAs and FAs against phytopathogenic fungi. According to our research, the active fungicidal components in soil HAs and FAs decreased along with the extension of cultivation years, which made the soil suffer more risk to phytopathogenic fugi. So we believe continuous cultivation too many years in PGVP systems is inadvisable.

Optimize nitrogen fertilization location in root-growing zone to increase grain yield and nitrogen use efficiency of transplanted rice in subtropical China

Abstract The optimized nitrogen fertilization location differs in different rice-growing regions. We optimized nitrogen deep-point application in root-growing zone (NARZ) for transplanted rice in subtropical China. Field plot experiments were conducted over two years (2014–2015) in a double-rice cropping system to evaluate the effects of nitrogen (N) fertilizer location on grain yield and N use efficiency (NUE). Four different nitrogen deep-point application methods (DN) were compared with traditional broadcast application (BN) using granular urea. The results showed that grain yield, recovery efficiency of N (RE N ), agronomic efficiency of N (AE N ), and partial factor productivity of N (PFP N ) significantly increased 10.3–63.4, 13.7–56.7, 24.7–201.9 and 10.2–63.4%, respectively, in DN treatment compared to BN, respectively. We also find that DN treatments increased grain yield as well as grain N content, and thus grain quality, in comparison with conventional BN treatment. Correlation analysis indicated that significant improvement in grain yield and NUE mainly resulted from increases in productive panicle number and grain N content. In our proposed NARZ method, granular urea should be placed 0 to 5 cm around the rice seeding at a 12-cm depth druing rice transplanting. In NARZ, balanced application of N, P and K further improved grain yield and NUE over treatments with a single N deep-point application. High N uptake by the rice plant did not cause significant soil fertility depletion, demonstrating that this method could guarantee sustainable rice production.

Effects of duckweed ( Spriodela polyrrhiza ) remediation on the composition of dissolved organic matter in effluent of scale pig farms

The swine effluent studied was collected from scale pig farms, located in Yujiang County of Jiangxi Province, China, and duckweed (Spriodela polyrrhiza) was selected to dispose the effluent. The purpose of this study was to elucidate the effects of duckweed growth on the dissolved organic matter composition in swine effluent. Throughout the experiment period, the concentrations of organic matter were determined regularly, and the excitation-emission matrix (3DEEM) spectroscopy was used to characterize the fluorescence component. Compared with no-duckweed treatments (controls), the specific ultra-violet absorbance at 254nm (SUVA254) was increased by a final average of 34.4% as the phytoremediation using duckweed, and the removal rate of DOC was increased by a final average of 28.0%. In swine effluent, four fluorescence components were identified, including two protein-like (tryptophan, tyrosine) and two humic-like (fulvic acids, humic acids) components. For all treatments, the concentrations of protein-like components decreased by a final average of 69.0%. As the growth of duckweed, the concentrations of humic-like components were increased by a final average of 123.5% than controls. Significant and positive correlations were observed between SUVA254 and humic-like components. Compared with the controls, the humification index (HIX) increased by a final average of 9.0% for duckweed treatments. Meanwhile, the duckweed growth leaded to a lower biological index (BIX) and a higher proportion of microbial-derived fulvic acids than controls. In conclusion, the duckweed remediation not only enhanced the removal rate of organic matter in swine effluent, but also increased the percent of humic substances.

Temporal dynamics of the compositions and activities of soil microbial communities post-application of the insecticide chlorantraniliprole in paddy soils

Chlorantraniliprole (CAP) is a newly developed insecticide widely used in rice fields in China. There has been few studies evaluating the toxicological effects of CAP on soil-associated microbes. An 85-day microcosm experiment was performed to reveal the dissipation dynamics of CAP in three types of paddy soils in subtropical China. The effects of CAP on microbial activities (microbial biomass carbon-MBC, basal soil respiration-BSR, microbial metabolic quotient-qCO2, acid phosphatase and sucrose invertase activities) in the soils were periodically evaluated. Microbial phospholipid fatty acid (PLFA) analysis was used to evaluate the change of soil microbial community composition on day 14 and 50 of the experiment. CAP residues were extracted using the quick, easy, cheap, effective, rugged, and safe (QuChERS) method and quantification was measured by high performance liquid chromatography (HPLC). The half-lives (DT50) of CAP were in the range of 41.0-53.0 days in the three soils. The results showed that CAP did not impart negative effects on MBC during the incubation. CAP inhibited BSR, qCO2, acid phosphatase and sucrose invertase activities in the first 14 days of incubation in all the soils. After day 14, the soil microbial parameters of CAP-treated soils became statistically at par with their controls. Principal component analysis (PCA) determining abundance of biomarker PLFAs indicated that the application of CAP significantly changed the compositions of microbial communities in all three paddy soils on day 14 but the compositions of soil microbial communities recovered by day 50. This study indicates that CAP does not ultimately impair microbial activities and microbial compositions of these three paddy soil types.

Rational dose of insecticide chlorantraniliprole displays a transient impact on the microbial metabolic functions and bacterial community in a silty-loam paddy soil

Chlorantraniliprole (CAP) is a newly developed insecticide widely used in rice fields in China. There have been few studies regarding its effects on soil microbial functional diversity and bacterial community composition. An 85-day microcosm experiment was performed to reveal the dissipation dynamics of CAP under different application doses in a silty-loam paddy soil in subtropical China. The half-life of CAP was 51.3 and 62.5d for low (1mgkg-1) and high (10mgkg-1) application dose, respectively. We used a combination of community level physiological profile (CLPP) and 16S rRNA gene sequencing analysis to get insights into the soil microbial features responded to CAP during the experiment. Non-metric multidimensional scaling (NMDS) performed on CLPP and the sequence results indicated that the soil microbial functional diversity and bacterial community composition were significantly changed by CAP application at day 14, and recovered to the similar level as no CAP treatment (CK) under low dose of CAP at day 36. However, high dose of CAP imposed longer effect on these soil microbial features, and was still significantly different from CK at day 36. Mcrobial taxa analysis at phylum level showed that high dose of CAP decreased the relative abundance of Nitrospirae at day 14, while increased Bacteroidetes and decreased Actinobacteria, Nitrospirae, and Firmicutes at day 36 in relative to CK. Low dose of CAP only increased Crenarchaeota and decreased Nitrospirae at day 14. The response ratio (RR) analysis was used to quantify significant responses of OTUs to different doses of CAP and found that CAP significantly affected the microbes involving the N transformation. This study provides a basic information to aid in the development of application regulations regarding the safe use of CAP in soil and inspire us to apply CAP at rational dose to minimize its ecotoxicity on soil microbes.

Fungistatic Activity of Multiorigin Humic Acids in Relation to Their Chemical Structure

Humic acid (HA) has an inhibitory effect on phytopathogenic fungi, but the structure-activity relationship remains unclear. HAs were extracted from 14 different materials, and their fungistatic activities and elemental C, N, S, and O contents were measured. Cross-polarization magic-angle spinning 13C nuclear magnetic resonance (CPMAS 13C NMR) was used to measure the organic carbon composition. The results showed that all HAs suppressed phytopathogenic fungi growth, with Yunnan lignite HAs showing the highest inhibition (85.3%) against Physalospora piricola. The soil and compost HA aromaticity (ARO) was <50%, except for black soil HAs, while the ARO of all coal HAs was >60%. The ARO of meadow and moss peat HAs was <50%, while the ARO of woody peat HAs was 50.61%. Mantel test and redundancy analysis (RDA) were applied to evaluate the structure-activity relationship. The Mantel test revealed that the N, S, O, N/O, carbonyl C, aromatic C-O, and anomeric C contents were significantly correlated with fungistatic activity. The RDA analysis showed that the S content was positively correlated with fungistatic activity, while the O content was negatively correlated. The carbonyl C content had a positive correlation with fungistatic activity, while the anomeric C and aromatic C-O content had a negative correlation. A high S content and an active composition (carbonyl C) in HAs would lead to a high degree of fungistatic activity. Phytotoxicity test indicated all HAs were beneficial to plant growth. This work identified the basic properties of HAs from various raw materials that control their fungistatic activities.

Nitrogen Fertilizer Deep Placement for Increased Grain Yield and Nitrogen Recovery Efficiency in Rice Grown in Subtropical China

Field plot experiments were conducted over 3 years (from April 2014 to November 2016) in a double-rice (Oryza sativa L.) cropping system in subtropical China to evaluate the effects of N fertilizer placement on grain yield and N recovery efficiency (NRE). Different N application methods included: no N application (CK); N broadcast application (NBP); N and NPK deep placement (NDP and NPKDP, respectively). Results showed that grain yield and apparent NRE significantly increased for NDP and NPKDP as compared to NBP. The main reason was that N deep placement (NDP) increased the number of productive panicle per m-2. To further evaluate the increase, a pot experiment was conducted to understand the N supply in different soil layers in NDP during the whole rice growing stage and a 15N tracing technique was used in a field experiment to investigate the fate of urea-15N in the rice–soil system during rice growth and at maturity. The pot experiment indicated that NDP could maintain a higher N supply in deep soil layers than N broadcast for 52 days during rice growth. The 15N tracing study showed that NDP could maintain much higher fertilizer N in the 5–20 cm soil layer during rice growth and could induce plant to absorb more N from fertilizer and soil than NBP, which led to higher NRE. One important finding was that NDP and NPKDP significantly increased fertilizer NRE but did not lead to N declined in soil compared to NBP. Compared to NPK, NPKDP induced rice plants to absorb more fertilizer N rather than soil N.

Change in water extractable organic carbon and microbial PLFAs of biochar during incubation with an acidic paddy soil

Biochar has been considered to affect the transformation of soil organic carbon, soil microbial activity and diversity when applied to soil. However, the changes in chemical and biological properties of biochar itself in soil have not been fully determined. In this study, various biochar samples were obtained from three crop straws (rice, peanut and corn) and two wood chips (bamboo and pine), and incubated with an acidic paddy soil. We examined the changes of biochar water extractable organic carbon (WEOC) content and its ultraviolet (UV) absorbance at 280 nm during incubation period, and also investigated the microbial phospholipid fatty acids (PLFAs) profile of biochar after 75 days of incubation. The WEOC content of biochars decreased at the end of incubation, except for the biochar pyrolysed from bamboo chips at 400°C. An average reduction rate of 61.2% in WEOC concentration for straw biochars occurred within the first 15 days, while no significant change was observed for all biochars between day 15 and 45, and a slight increase in WEOC occurred for all biochars in the last 30 days. There was a positive relationship between biochar WEOC content and its UV absorbance properties. The microbial PLFAs concentrations of biochars varied from 15.56 to 60.35 nmol g–1, and there was a greater abundance in content and species for corn straw biochars than for the other types of biochars. General bacteria were the dominant microbial group that colonised biochar sample, while gram-positive bacterial and fungi were less in abundance. The chemical properties of fresh biochar were well correlated with total PLFAs concentrations, and significantly related to the composition of microbial community. We concluded that the WEOC component of most biochars change within such short-term application to soil, and the WEOC in combined with the pH and nutrient status of biochar, can alter the type and abundance of microorganisms that colonised biochar.