No Fertilizer Research Articles

Contribution of distinct components in divergent organic amendments to long-term accumulation of soil organic matter in agricultural soils: evidence from thermally assisted hydrolysis and methylation-GC/MS.

Although maintaining/improving soil organic matter (SOM) quantity through utilizing organic amendments (OAs) is a productive practice, information on OA components contributing to long-term SOM accumulation in agricultural soils remains meager. Hence, we examined soil samples from a long-term experiment with different fertilizer managements, including no fertilizer (NF), chemical fertilizer (CF) only (CF), bark compost plus CF (BC + CF), coffee residue compost plus CF (CRC + CF), cattle manure compost plus CF (CMC + CF), and cattle manure compost (CMC) or sewage sludge compost (SSC) alone at a higher application rate. SOM in those samples was physically fractionated into free particulate form (fSOM), free form occluded in aggregates (oSOM), weakly bound form (wSOM), and strongly bound form (sSOM). Analysis of structural components in OAs and SOM fractions using thermally assisted hydrolysis and methylation combined with gas chromatography/mass spectrometry (THM-GC/MS) revealed OA components that have contributed to long-term SOM accumulation in each treatment. The SSC was characterized by higher proportions of short-chain fatty acids (FAs; 50%) and other aliphatic compounds (22%). Correlation analysis suggested that these characteristics may be effective for greater C accumulation in the bulk soil and wSOM fraction. The proportion of lignin-derived phenols, e.g., 3,4-dimethoxybenzaldehyde (Vh) and 1,2-dimethoxy-4-(1,2,3-trimethoxypropyl)benzene, was high in CMC (43%), presumably vital for promoting C accumulations in the oSOM, wSOM, and sSOM fractions in the CMC treatment. The short-chain FAs in CRC and aromatic components in BC are likely important for contributing fSOM accumulation.

Interactions between Sugarcane Leaf Return and Fertilizer Reduction in Soil Bacterial Network in Southern China Red Soil.

Microbes may play an important role in the sugarcane leaf degradation and nutrient conversion process. Soil bacterial communities are more or less involved in material transformation and nutrient turnover. In order to make better use of the vast sugarcane leaf straw resources and reduce the overuse of chemical fertilizers in the subtropical red soil region of Guangxi, a pot experiment, with three sugarcane leaf return (SLR) amounts [full SLR (FS), 120 g/pot; half SLR (HS), 60 g/pot; and no SLR (NS)] and three fertilizer reduction (FR) levels [full fertilizer (FF), 4.50 g N/pot, 3.00 g P2O5/pot, and 4.50 g K2O/pot; half fertilizer (HF), 2.25 g N/pot, 1.50 g P2O5/pot, and 2.25 g K2O/pot; and no fertilizer (NF)], was conducted to assess the interactions of different SLR amounts and chemical FR levels in the soil bacterial network and the relationship between the soil properties and bacterial network by using Illumina Miseq high-throughput sequencing technology. According to the results of the soil bacterial community compositions and diversity, the soil bacterial network was changed during maize growth. SLR exerted a stronger effect on soil bacterial function than FR. Returning the sugarcane leaf to the field increased the diversity of the soil bacteria network. The bacterial communities were consistently dominated by Acidobacteria, Actinobacteria, and Bacteroidetes across all treatments, among which Actinobacteria was the most abundant bacteria type by almost 50% at the phylum level. The analysis results of the experimental factor on maize growth showed that the effect of SLR was lower than that of FR; however, this was opposite in the soil bacterial community structure and diversity. The soil bacterial network was significantly correlated with the soil total K, available N and organic matter contents, and EC. The soil bacteria community showed different responses to SLR and FR, and the FF in combination with FS partly increased the complexity of the soil bacteria network, which can further benefit crop production and soil health in the red soil region.

Long-term fermented organic fertilizer application reduce urea nitrogen-15 loss from plastic shed agricultural soils

Continuous application of fermented organic fertilizer can improve soil quality, while the performance of nitrogen (N) in the improved soils is rarely investigated. To investigate the fate of applied N in the soils with organic management history, the 15NH2CO15NH2 (15N abundance of 19.6 %) was employed as the exogenous N source to conduct an experiment in the Chinese cabbage and tomato rotation system under plastic shed condition. The cultivated soils have received 15-year of effective microorganism (EM) fermented organic fertilizer (EM-OF), N, P, K inorganic fertilizer (NPK-IF) and no fertilizer (NoF). The 15N use by cabbage and tomato, the soil 15N forms, as well as the 15N distribution were observed. Results showed that the 15N use efficiency of cabbage in the EM-OF, NPK-IF and NoF soils were 55.1 %, 37.3 % and 26.6 % respectively, showing significant (p ≤ 0.05) differences. The succeeding crop tomato could take up the soil residual 15N, and the highest 15N reuse efficiency was 7.1 % that detected in the NoF soil. The total 15N loss (6.0 %) from the rotation system was the lowest in the EM-OF soil, compared to that in the NPK-IF and NoF soils. It was concluded that the long-term fermented organic fertilizer applied soils can reduce urea 15N loss from plastic shed agriculture, mainly through improving the in-season crop 15N use efficiency.

Effects of Organic Liquid Waste Derived from Bioethanol Fermentation on Corn Production

The liquid waste (LW) discharged during bioethanol production needs treatment. In this study, LW was applied to corn, and its effects on corn growth, yield, and nitrogen (N) content, as well as on soil chemical properties, were evaluated. Five treatments were applied during corn cultivation: no fertilizer (NF), chemical fertilizer (CF), LW at a standard application rate (LW1.0), LW at 1.7 times the rate of LW1.0 (LW1.7), and split application of LW1.7 (S-LW1.7) in six replications. The amount of N applied was 30 kg 10a−1 for CF and LW1.0, and 51 kg 10a−1 for LW1.7 and S-LW1.7. N was applied separately three times in CF, LW1.0, and LW1.7 and six times in S-LW1.7. A higher corn yield, corn ear weight, and number of leaves was observed in LW treatments than in CF. N content of the corn plant top was higher in S-LW1.7 than in LW1.7; N availability was 56.9% and 40.5% higher, respectively, indicating that split application improved N availability. Soil total N content increased significantly in LW treatments, and soil total carbon content tended to increase in S-LW1.7. Therefore, application of LW could increase corn yield and soil fertility, and its effect could be enhanced by split application.

Cropping rotation improved the bacterial diversity and N-cycling genes in tobacco fields through a 19-year long-term experiment

Soil microorganisms play crucial roles in various processes within the soil ecosystem, such as nutrient cycling, organic matter decomposition, and maintenance of soil structure. However, their responses to fertilization and different cropping systems in tobacco soils remain poorly understood. In this study, we conducted a 19-year-long field experiment on rice-tobacco rotation cropping (R) and continuous tobacco cropping (C), with three fertilization treatments: no fertilizer (NF), chemical NPK fertilizer (NPK), and composted pig manure (OM). The composition, co-occurrence patterns, N-cycling genes (nifH, AOA-amoA, AOB-amoA, nirS, nirK, and nosZ) of the bacterial communities as well as the soil properties were analyzed in the soils after tobacco was harvested. The pH and available potassium (AK) in the rotation cropping soil were significantly lower than those in continuous cropping soil, while the α-diversity index, and the abundance of nifH, nirS, nirK, and nosZ genes were opposite. The phyla Chloroflexi, Desulfobacterota, MBNT15, and Nitrospinota, as well as number of low-abundance genera, were significantly enriched in rice-tobacco rotation cropping. Partial least squares path model (PLSPM) indicated that cropping systems had a greater influence on the variations in bacterial communities compared to fertilization practices. These findings enhance our understanding of the significance of land management and fertilization in shaping the soil bacteria of tobacco. The rice-tobacco rotation cropping system demonstrated greater benefits to soil microorganisms and N-cycling genes compared to continuous cropping system.

Temporal dynamics of density separated soil organic carbon pools as revealed by δ13C changes under 17 years of straw return

Straw return is widely recommended as an effective measure to increase the amount of soil organic carbon (SOC) and improve soil fertility in agroecosystems. However, the temporal dynamics of the original and newly derived SOC during long-term straw return remain uncertain. This study aimed to (i) determine the temporal dynamics of original and newly derived SOC in various soil organic matter (SOM) fractions during cultivation and (ii) evaluate the effect of continuous straw return on the contents of original and newly derived SOC. These aims were achieved by analyzing topsoil samples (0–20 cm) in a 17-year field experiment using a continuous maize (Zea mays L.) cropping system. Three fertilizer treatments were tested: no fertilizer (NF), mineral fertilizer (NPK), and mineral fertilizer with straw return (NPKS). The SOC was physically separated into three density fractions: the free light fraction (fLFOC), occluded light fraction (oLFOC), and heavy fraction (HFOC), and their δ13C values were determined. The original and newly derived SOC of each fraction and the rate of conversion of exogenous C inputs were evaluated. The SOC content in the bulk soil and C fractions generally increased continually with cultivation time in the NPKS, indicating that the soil had not reached maximum C sequestration. NPKS significantly increased the C contents of fLFOC, oLFOC, and HFOC by 38.6%, 43.0%, and 11.6%, respectively, relative to the initial soil after the 17-year experiment. The newly derived SOC content was significantly higher in NPKS than in NF and NPK, and the rate of conversion of exogenous C inputs to SOC was the lowest in NPKS. The annual rate of loss of original SOC in NPKS was lowest for the light fractions (fLFOC and oLFOC) and highest for HFOC, implying that the return of straw moderated the mineralization of original SOC in the light fractions but increased the decomposition of original SOC in the heavy fraction via the priming effect (PE). The average rate of conversion of exogenous C inputs remained the highest in HFOC (23.5%), lowest in oLFOC (0.6%), and intermediate in fLFOC (4.1%) throughout the study. Thus, the stable HFOC pool retained more straw C, despite the stronger PE. Our results demonstrated that long-term straw return continuously increased the proportion of new SOC in the bulk soil and density fractions and increased the decomposition of the original SOC in the stable SOC fractions. These findings provide further detailed insights into the mechanisms of SOC stabilization in agricultural soils.

Long-term mineral combined with organic fertilizer supports crop production by increasing microbial community complexity

Soil microbial communities play a critical role in agroecosystem productivity. Most previous studies focused on changes in community composition and diversity, yet the association between microbial community complexity and crop production is poorly understood. In this study, a 26-year fertilization experiment was conducted to analyze effects of soil microbial complexity on maize (Zea mays L.) yield. Compared with no-fertilizer (NF) and mineral fertilizer (MF), the maize yield under the treatment of mineral combined with organic fertilizer (MO) was significantly increased 68.01 % and 27.76 %, respectively. The different fertilization profoundly changed soil chemical properties and microbial community composition. Meanwhile, the bacterial and fungal network of MO have the maximum complexity (edges of network). When 50 % nodes were removed, the network of MO exhibited the strongest robustness. Meanwhile, MO also had the highest degree of functional redundancy. Compared with NF and MF, the relative abundance of bacterial functional groups (carbon, nitrogen, sulfur cycling) was significantly increased by 1.88 %, 0.86 %, and the relative abundance of saprophytic fungi by 13.76 %, 10.54 % in MO, respectively. Most importantly, the results of variance partitioning analysis and RandomForest regression demonstrated that community complexity had the most contribution to maize yield compared to soil chemical properties and microbial community composition. Finally, the results of null model showed that deterministic processes driven bacterial and fungal community assembly processes under all treatments. Overall, our study suggests that microbial community complexity is a key factor in maintaining the sustainability of crop production.

Effects of Sugarcane Leaf Return and Fertilizer Reduction on Maize Growth, Yield and Soil Properties in Red Soil.

In order to make better use of the vast sugarcane leaf straw resources and reduce the overuse of chemical fertilizers in the subtropical red soil region of Guangxi, this study aimed to determine the effects of sugarcane leaf return (SLR) and fertilizer reduction (FR) on maize growth, yield component and yield, and soil properties. A pot experiment with three SLR amounts (full SLR (FS), 120 g/pot; half SLR (HS), 60 g/pot; and no SLR (NS) with three FR levels including full fertilizer (FF), 4.50 g N/pot, 3.00 g P2O5/pot, and 4.50 g K2O/pot; half fertilizer (HF), 2.25 g N/pot, 1.50 g P2O5/pot, and 2.25 g K2O/pot; and no fertilizer (NF)), without nitrogen, phosphorous, and potassium added, was conducted to assess the effects of different SLR amounts and chemical FR levels on maize growth, yield, and soil properties. Compared with no sugarcane leaf return and the no-fertilizer treatment (CK), SLR and FR could increase maize plant height, stalk diameter, number of fully developed maize plant leaves, total leaf area and chlorophyll content, soil alkali-hydrolyzable nitrogen (AN), available phosphorus (AP), available potassium (AK), soil organic matter (SOM), and electrical conductivity (EC). The maize yield component factors of FS and HS were higher in NF treatment than those in NS treatment. The relative increase rate of treatments retained FF/NF and HF/NF under FS or HS condition on 1000 kernel weight, ear diameter, plant air-dried weight, ear height, and yield than that under NS condition. FSHF had not only the largest plant air-dried weight but also the highest maize yield (3225.08 kg/hm2) among nine treatment combinations. The effects of SLR on maize growth and yield and soil properties were lower than those of FR. SLR and FR combined treatment did not affect maize growth but affected maize yield significantly. Soil properties improved more with SLR + FR treatment than with SLR or FR application alone. The plant height, stalk diameter, number of fully developed maize plant leaves, and total leaf area, as well as AN, AP, AK, SOM, and EC levels in soil, were enhanced by SLR and FR incorporation. The experimental results indicated that applying reasonable FR combined with SLR increased AN, AP, AK, SOM, and EC, which improved maize growth and yield and enhanced soil properties in red soil. Hence, FSHF might be a suitable combination of SLR and FR.

Effect of Organic Material Amendments on Soil Respiration in Tobacco Fields of Central Henan

A field experiment was conducted to study the effects of different organic material amendments on soil respiration in a flue-cured tobacco field. Five treatments were set up:no fertilizer (NF), chemical fertilizer (NPK), chemical fertilizer+ryegrass (NPKG), chemical fertilizer+wheat straw (NPKS), and chemical fertilizer+tobacco straw biochar (NPKB). The results showed that:① Compared with that under NPK, NPKG and NPKS decreased the temperature sensitivity (Q10) of total soil respiration and heterotrophic respiration, whereas NPKB increased the Q10 of heterotrophic respiration. The two-factor fitting model of soil respiration and soil hydrothermal factors accounted for 50%-80% of the variation in soil respiration. ② The addition of organic materials significantly increased the content of soil soluble organic carbon (DOC) and root dry matter. Soil heterotrophic respiration(Rh) was significantly positively correlated with DOC content, and soil autotrophic respiration(Ra) was significantly parabolically correlated with root biomass, with an R2 of 0.327-0.634. ③ Soil respiration increased first and then decreased during the tobacco growth period. Compared with that under the NF treatment, the NPK treatment significantly promoted soil respiration and its components. Compared with those of the NPK treatment, Rsrates were significantly increased by 20.08%, 10.32%, and 9.88% under the NPKG, NPKS, and NPKB treatments, respectively; Rh rate increased by 24.21%, 16.51%, and 11.68% respectively, and Ra rate was increased by 15.12% in the NPKG treatment. In summary, straw returning and biochar addition significantly increased Rh by increasing soil DOC, thereby promoting Rs. Incorporation of ryegrass not only increased the Rh but also increased Ra by promoting the growth and development of roots and therefore the Rs.

Macroaggregates Serve as Micro-Hotspots Enriched With Functional and Networked Microbial Communities and Enhanced Under Organic/Inorganic Fertilization in a Paddy Topsoil From Southeastern China.

Microbial communities of soil aggregate-size fractions were explored with molecular and networking assays for topsoil samples from a clayey rice paddy under long-term fertilization treatments. The treatments included no fertilizer (NF) as control, chemical fertilizer only (CF), chemical fertilizer with swine manure (CFM), and chemical fertilizer with rice straw return (CFS). Following a wet-sieving protocol, water-stable aggregates were separated into size fractions of large macroaggregates (L-MacA, >2,000 μm), macroaggregates (MacA, 2,000–250 μm), microaggregates (MicA, 250–53 μm), fine microaggregates (F-MicA, 53–2 μm), and fine clay (F-Clay, <2 μm). Mass proportion was 32.3–38.2% for F-MicA, 23.0–31.5% for MacA, 19.0–23.1% for MicA, 9.1–12.0% for L-MacA, and 4.9–7.5% for F-Clay, respectively. The proportion of MacA was increased, but F-Clay was reduced by fertilization, whereas the mean weight diameter was increased by 8.0–16.2% from 534.8 μm under NF to 621.5 μm under CFM. Fertilization affected bacterial 16S rRNA and fungal 18S rRNA gene abundance in F-MicA and F-Clay but not in aggregates in size larger than 53 μm. However, bacterial and fungal community α-diversities and community structures were quite more divergent among the fertilization treatments in all size fractions. Organic carbon and gene abundance of bacteria and fungi were enriched in both L-MacA and MacA but depleted in F-Clay, whereas microbial Shannon diversity was rarely changed by fraction size under the four treatments. L-MacA and MacA contained more bacteria of r-strategists and copiotrophs, whereas F-MicA and F-Clay were demonstrated with a higher abundance of K-strategists and oligotrophs. Guilds of parasitic and litter saprotrophic fungi were enriched in F-MicA but depleted in L-MacA. Furthermore, most of bacterial and fungal operational taxonomic units were strongly interacted in L-MacA and MacA rather than in MicA and F-Clay. Thus, MacA acted as micro-hotspots enriched with functional and networked microbial communities, which were enhanced with organic/inorganic fertilization in the rice paddy.

Effects on the root morphology and mircostructure of young pear (Pyrus pyrifolia) tree by split-root supply of bioorganic and chemical fertilizer

Bioorganic fertilizers are widely used in fruit orchards to improve soil properties and increase productivity. To investigate the effects of bioorganic fertilizer (BIO) and chemical fertilizer (CF) on the root system architecture and above-ground growth of pear trees, a split-root experiment was conducted. To this end, six soil amendment combinations were investigated: NF–NF (no fertilizer), NF-CF, NF-BIO, CF-CF, BIO-BIO, and BIO-CF. Roots of 1-year old ‘Cuiguan’ pear trees were distributed as evenly as possible into split-root chambers containing the aforementioned amendment combinations and maintained for 210 days after budding. Results showed that in boxes containing the same fertilizer in both chambers (NF–NF, CF-CF and BIO-BIO), the BIO chambers had an improved soil pH, by 0.6–0.8 units, and 23%–65.5% greater SOM than the soils in the NF and CF chambers. We also found that in these BIO chambers the lateral root number was 2.1–3.5 times greater than in NF and CF chambers and the maximum order of lateral roots was greater than 9. BIO application promoted lateral root growth in the paired NF and CF chambers, increasing specific root length and reducing root tissue density. In BIO-CF boxes, the 4th to 6th lateral root number and length accounted for the largest proportion of total lateral root number and length respectively. Moreover, compared with trees grown in CF-CF, those grown in BIO-BIO and BIO-CF had greater mean xylem, phloem, and cork layer thicknesses, as well as greater mean vessel density and number. BIO-CF treated soils had significantly reduced (50%) available phosphorus content compared to CF-CF treated soils, and consistently, BIO-CF resulted in the greatest growth of trunk girth (by 5–29%) among all the treatments. Soil organic matter and nitrate nitrogen concentration had significantly positive effects on root growth and activity, while branching intensity was significantly related to available phosphorus content and total nitrogen, followed by available potassium content and ammonia nitrogen content. In conclusion, local application of bioorganic fertilizer is a promising technique to sustainably maintain pear tree productivity because it accelerates the root proliferation and activity in either nutrient-deficient or -sufficient soil.

Distinguishing N2O and N2 ratio and their microbial source in soil fertilized for vegetable production using a stable isotope method

Vegetable production systems with excessive nitrogen fertilizer result in severe N2O emission. It is pivotal to identify the source of N2O for reducing N2O emission, but estimating microbial pathways of N2O production is very difficult due to the existence of N2O reduction. A promising tool can address this problem by using δ18O and δ15NSP of N2O to construct a dual isotopocule plot. For ascertaining the microbial pathways of N2O production and consumption in soil fertilized for vegetable production, four treatments were set up: urea (U), half urea and half organic fertilizer (UO), organic fertilizer (O) and no fertilizer (NF), and the experiment was carried out continuously for two years. The δ18O vs. δ15NSP plot method indicated that the nitrification/fungal denitrification was a dominant in N2O emission, and the U treatment was the highest, followed by OU, O and NF in the both years. Among the different treatments, furthermore, the N2O flux had the same trend, whereas the extent of N2O reduction showed an opposite trend. Overall, inorganic fertilizer enhances nitrification/fungal denitrification and hinders reduction of N2O to N2, resulting in a larger amount of N2O emission. However, organic fertilizer increases the contribution of denitrification and greatly improves the extent of N2O reduction, which helps to reduce N2O emission. Therefore, organic fertilizer is crucial to reducing N2O emission by enhancing N2O reduction and should be properly applied in production practice.

English

Enhancing soil fertility and reducing the devastative effect of weed competition in rice is increasingly important and critical for ensuring a sustainable increase in rice production and secure food supply. Field experiment was conducted at Bontanga in the Northern Region of Ghana to investigate the effect of soil amendments and weeding regimes on growth and yield of rice under different moisture sources. The experiment was a three-factor experiment laid in a split plot design with three replications. The factors were water source (irrigation and rainfed), four levels of soil amendments [no fertilizer (NF), poultry fertilizer (PF), mineral fertilizer (MF), cow dung (CD)] at the same N rate (60kg N ha-1) and four levels of weeding regime (weedy check (W1), weed free (W2), one hand weeding + twice herbicides application (W3) and twice hand weeding + one time herbicides spray (W4). Parameters measured were tiller count, weed biomass, weed control efficiency, grain yield and cost analysis. Results showed that water source, soil amendments and weeding regimes had influenced rice yield. Irrigation increased rice grain yield by 49% compared to rainfed. Application of CD, MF and PL at the same N quantity increased grain yield by 5.4, 28 and 8%, respectively compared to NF. Among weeding regime, weed free reduced weed density and biomass, this translated to greater tiller counts and increased grain yield. Weed interference in weedy check reduced grain yield by 48, 30 and 26% compared to W2, W3 and W4, respectively. Irrigation increased cost of production by 7%, however, cost:benefit ratio increased by 44% compared to rain fed conditions. Key words: Soil amendments, weed control, irrigation, rain fed, yield, rice.

Nutrient loss from slope cropland to water in the riparian zone of the Three Gorges Reservoir: Process, pathway, and flux

Eutrophication of the surface water in the Three Gorges Reservoir (TGR) area in response to anthropogenically derived nutrients is a serious concern. Widespread cultivation in the riparian zone could lead to a large amount of nitrogen and phosphorus being transported via runoff during the cropland cultivation period or being released during the submerging period into the water of the TGR. However, little is known about the nutrient release fluxes from slope cropland into water during the submerging period. It is also not clear which process is critical. The experimental site in this study is representative of arable land on slopes in the riparian zone in the TGR area. Free-drainage lysimeters were constructed on a block of intact sandstone at a water level of 165 m in the riparian zone in the TGR area. The treatments were as follows: (1) no fertilizer (NF), (2) reduced nitrogen fertilizer treatment (RFT), and (3) conventional fertilizer treatment (CFT). The experimental plots were cropped conventionally with summer maize (Zea mays L.) from March to early September, and the experimental plots were submerged in water from October to March of the next year. Runoff water samples were collected during the 3-year experimental period (March 2016-October 2018). The results from this study indicate that nitrogen losses via interflow and phosphorus losses via overland flow are the dominant processes in the slope cropland in the riparian zone in the TGR area during the cropland cultivation period. In the CFT treatment, the average annual total nitrogen (TN) loss fluxes were 4.28 ± 0.10 kg hm−2 via overland flow and 26.17 ± 3.68 kg hm−2 via interflow. Additionally, the average annual total phosphorus (TP) loss fluxes in the conventional fertilizer treatment were 0.83 ± 0.43 kg hm−2 via overland flow and 0.15 ± 0.02 kg hm−2 via interflow. Before submerging, there were significant seasonal changes in the nutrient loss flux in every treatment. During the submerging period, the NO3--N, NH4+-N, and available phosphorus release fluxes from soil to water in the CFT treatment were 5.40 ± 0.75 kg hm−2, 4.38 ± 3.30 kg hm−2, and 12.09 ± 11.08 kg hm−2, respectively. The NO3--N release fluxes during the submerging period were higher than the NO3--N loss fluxes via overland flow, but they were lower than the NO3--N loss fluxes via interflow. Different from the pattern of NO3--N, the NH4+-N and available phosphorus release fluxes in the three treatments were much higher than the sum of the NH4+-N and available phosphorus loss fluxes via overland flow and interflow. Based on these findings, our results suggest that efforts to avoid further eutrophication of the reservoir water should take into account nutrient release from the soil of arable croplands in the riparian zone during the submerging period.

Effect of Nitrogen Fertilizer on Soil CO2 Emission Depends on Crop Rotation Strategy

Developing environmentally friendly and sustainable nitrogen (N) fertilizer management strategies is crucial in mitigating carbon dioxide (CO2) emission from soil. How N fertilizer management practices influence soil CO2 emission rates under different crop rotations remains unclear. The aim of this study was to assess the impact on soil CO2 emission and soil physicochemical properties of three N fertilizer treatments including traditional rate (TF), optimized rate (0.8TF), and no fertilizer (NF) under three different crop rotation treatments: wheat-fallow (WF), wheat-soybean (WS), and wheat-maize (WM) over two years in a field experiment in northwest China. The rates were 5.51, 5.60, and 5.97 μmol·m−2·s−1 of mean soil CO2 emission under the TF, 0.8TF, and NF treatments, respectively. Mean soil CO2 emission rates were 21.33 and 26.99% higher under the WM rotation compared with the WF and WS rotations, respectively. The WS rotation showed higher soil nutrient content and lower soil CO2 emissions, and reduced fertilizer application. Importantly, soil organic carbon (SOC) concentration in the topsoil can be maximized by including either a summer legume or a summer maize crop in winter wheat rotations, and by applying N fertilizer at the optimal rate. This may be particularly beneficial in the dryland cropping systems of northern China.

Impact of long-term chemical fertilizer and organic amendment to Fusarium root rot of soybean

Soil suppressiveness to Fusarium root rot of soybean had been observed in a black soil field after a long-term fertilization with nitrogen (N) and phosphorus (P) fertilizer combined with pig manure as organic amendment (NPM), rather than that with only nitrogen and phosphorus fertilizer (NP) or no fertilizer (NF). To determine the microbial role on this suppressiveness, fungal and bacterial community characteristics in NPM, NP and NF treatments were investigated by qPCR and DGGE. Compared with the similar bacterial community characteristics among 3 treatments, fungal community, especially Fusarium population size and community composition in NPM treatment were different with those of NP and NF groups. Based on the isolation and pathogenicity test, pathogenic F. oxysporum, F. graminearum, F. verticillioide and F. lateritium absolutely dominated Fusarium community in NF and NP groups. Nonpathogenic F. avenaceum, F. equiseti, F. culmorum, F. redolens, F. solani and F. tricinctum dominated Fusarium community in NPM group. Isolation rate of pathogenic Fusarium in NPM reduced from 100% to 38% in NF. These results suggested that the dominance of soil non-pathogenic Fusarium population induced by organic amendment might play an important role on suppressing Fusarium root rot in the tested field.

Chronic effects of different fertilization regimes on nirS-type denitrifier communities across the black soil region of Northeast China

Denitrification is one of the major processes causing nitrogen loss from arable soils. This study aimed to investigate the responses of nirS-type denitrifier communities to different chronic fertilization regimes across the black soil region of Northeast China. Soil samples were collected from sites located in the north (NB), middle (MB), and south (SB) of the black soil region of Northeast China, each with four chronic fertilization regimes: no fertilizer (NoF), chemical fertilizer (CF), manure (M), and chemical fertilizer plus manure (CFM). Methods of quantitative polymerase chain reaction (qPCR) and Illumina MiSeq sequencing were applied to assess the abundance and composition of denitrifier communities by targeting the nirS gene. The results showed that the M and CFM regimes significantly increased the abundances of nirS-type denitrifiers compared with NoF at the three locations. The majority of nirS sequences were grouped as unclassified denitrifiers, and the different fertilizers induced little variation in the relative abundance of known nirS-type denitrifier taxa. Over 90% of the sequences were shared among the four fertilization regimes at each location, but none of the abundant operational taxonomic units (OTUs) were shared among the three locations. Principal coordinate analysis (PCoA) revealed that the communities of nirS-type denitrifier were separated into three groups that corresponded with their locations. Although similar fertilization regimes did not induce consistent changes in the nirS-type denitrifier communities, soil pH and NO−3-N content simultaneously and significantly influenced the structure of nirS-type denitrifier communities at the three locations. Our results highlight that geographical separation rather than chronic fertilization was the dominant factor determining the nirS-type denitrifier community structures, and similar chronic fertilization regimes did not induce consistent shifts of nirS-type denitrifier communities in the black soils.

Effects of Wood-derived Biochar Application on Soil Chemical Properties and Growth of Lettuce (Lactuca sativa L.)

Biochar is an amendment that can be used for reducing odors, enhancing crop productivity and soil fertility to revitalize the urban agriculture. The objective of this study was to evaluate the effects of biochar from the pyrolysis pine on the soil chemical properties, nutrient uptake, and growth of lettuce plants (Lactuca sativa L.) in an upland field. Lettuce was planted in an silt loam soil amended with four rates of biochar 0 (CFB1), 60 (CFB2), 120 (CFB3), and 240 kg 10a-1 (CFB4) with chemical fertilizer (14.3 kg 10a-1 N, 15.7 kg 10a-1 P2O5, and 12.1 kg 10a-1 K2O), no fertilizer (NF), and animal compost 440 kg 10a-1 with chemical fertilizer (CFC). Leaf number and fresh weight of lettuce plant were higher in CFB4 treatment than in the other treatments. Increasing rates of biochar caused a significant increase in lettuce yield, amount of nutrient uptake, and soil pH. The economically optimum application rate of fertilizer biochar was 200 kg 10a-1 on the basis of the regression curve. The electrical conductivity of the CFB1 soil was significantly higher than in the other treatments, whereas the soil pH was significantly lower in the CFB1 soil than those in the biochar treatments and NF soils. These results showed that biochar amendment increased yield of crops as well as improving soil properties. A regression curve between yield of lettuce and application rate of wood-derived biochar.

Aerial Nitrogen Fluxes and Soil Nitrate in response to Fall-Applied Manure and Fertilizer Applications in Eastern South Dakota

Manure and inorganic fertilizer help to meet crop nitrogen demand by supplementing soil nitrogen (N). However, excessive N losses reduce soil fertility and crop yield and can impair water and air quality. The objectives of the research were to compare different forms of fall-applied N for (1) the change in soil nitrate (NO3-N) over the growing season and (2) the aerial ammonia (NH3) and nitrous oxide (N2O) fluxes during the fall and early growing season. Treatments included solid beef cattle manure with bedding (BM), solid beef cattle manure only (SM), urea (UO), and no fertilizer (NF). The two-year plot-scale study took place in Brookings County, South Dakota, under rain-fed conditions in a silty clay loam. Manure and urea were applied at equal plant-available N rates of 130 and 184 kg·N·ha−1in Y1 and Y2, respectively, according to the South Dakota nutrient management planning process. The average total (i.e., 0–0.60 m soil depth) soil NO3-N for Y1 (83 kg·ha−1) was significantly higher than Y2 (67 kg·ha−1), whereas surface (i.e., 0–0.15 m soil depth) soil NO3-N was not significantly different between years. The average surface soil NO3-N (33.5 kg·ha−1) and total soil NO3-N (105.0 kg·ha−1) for UO were significantly higher than the remaining treatments (P&lt;0.05). Soil water NO3-N concentrations, leaf-N, corn-grain-N, and yield measurements did not indicate any significant differences between treatments. Based on the two-year average, the highest NH3-N flux occurred from the BM (3.4 g·ha−1·h−1); however, this flux was only significantly higher than NF (1.4 g·ha−1·h−1). The NH3-N fluxes from UO (2.2 g·ha−1·h−1) and SM (1.7 g·ha−1·h−1) were similar to both BM and NF. The N2O-N flux from UO (0.79 g·ha−1·h−1) was significantly greater than NF (0.25 g·ha−1·h−1), while BM- (0.49 g·ha−1·h−1) and SM-produced (0.33 g·ha−1·h−1) N2O-N fluxes were not significantly different than neither UO nor NF. The three fall-applied N sources had similar aerial-N fluxes even though urea application resulted in significantly higher soil nitrate.

Rice plant growth and nutrient leaching under different patterns of split chemical fertilization on sandy soil using a pot

Savannakhet Province has 25% of the total lowland rice cultivation area of Lao People’s Democratic Republic (Laos). However, most of the fields are rainfed, with highly permeable sandy soil, which has low water and nutrient availability. In such sandy rainfed fields, high leaching loss of nutrients from applied fertilizer is expected, and rice yield is also decreased. Therefore, an efficient fertilization scheme is required to improve rice yield in this area. We conducted a pot experiment to evaluate rice plant growth and nutrient leaching under different split chemical fertilizer application patterns. Sandy soil collected in a village in Savannakhet Province was placed in test pots. Four treatments, viz., standard fertilization (control: C, three splits), subdivided fertilization (SF, six splits), intensive fertilization (IF, once at the time of transplanting), and no fertilizer (NF) were tested. Irrigation was done every 3 days during the initial 3 months and every 10 days in the final month with reference to the rainfall pattern recorded in the rainy season of 2016. Although the maximum number of tillers in C and IF was higher than that of SF, they ultimately decreased to a smaller number than that of SF. The yield of SF was higher than that of the other three treatments. NF showed the lowest growth and yield. The six-split fertilization might supplement nitrogen (N) at the late growing stage. IF showed the largest N leaching loss among treatments. Because of low phosphorus (P) leaching loss, split P fertilization was ineffective. K leaching was completed by 39 days after transplanting, suggesting that all of the K applied by fertilizer and irrigation was consumed by rice plants or lost through leaching before panicle initiation. The proposed split fertilization is advantageous in that it supplies N for panicle initiation and maturing stages in sandy paddy fields, but the timing and amount of P application must be considered.