Paddy-upland Rotation Research Articles

Long-term experiments to identify response patterns of available soil nitrogen, rice, and soybeans to rice straw compost in a paddy-upland rotation field in Akita, Japan

ABSTRACT Compost application can enhance soil fertility and is consequently presumed to increase crop production in Japan’s paddy-upland rotation fields. This study aimed to evaluate the effects of rice straw compost (RSC) application on available soil nitrogen (Av-N) levels and rice and soybean plants in a paddy-upland rotation field using data obtained from a long-term field experiment. Data collected between 2005 and 2020 were analyzed from a long-term paddy rice – upland soybean rotation field. The experimental design employed a split-plot arrangement, with RSC application (with and without RSC) representing the whole plot, N fertilizer application (no nitrogen vs. standard fertilizer) representing the split-plot, and years representing the replication factor. The datasets included eight years of rice and soybean cultivation, and the chemical properties of postharvest soil spanned 16 years. The data was analyzed via analysis of variance. Applying RSC increased the Av-N concentration significantly by 63%–67%. The RSC application significantly increased the N concentration in rice shoots at the mature stage by 8%–12% but decreased it in soybean shoots after the seed emergence stage by 4%–8%. Consequently, the rice yield displayed clear responses to RSC application, whereas the soybean yield did not. The lack of soybean yield response might be due to an inhibitory effect of the Av-N gain attributable to the RSC application on biological nitrogen fixation. While applying compost can enhance Av-N content as well as rice productivity in paddy-upland rotation fields, its impact on soybean productivity requires careful evaluation.

Long-term straw return enhanced crop yield by improving ecosystem multifunctionality and soil quality under triple rotation system: An evidence from a 15 years study

ObjectiveRice-rice-oilseed rape rotation is a typical triple cropping system in Asia, and the development of rice-oilseed rape rotation plays an important role in ensuring global food and oil security. With the intensive cropping rotation and frequent changes between paddy and upland farming under anaerobic and aerobic conditions, whether tillage and straw return would be benefit for both agronomic and environmental perspectives remained to be tested. MethodTherefore, we used a long-term locational experiment (15 years) employing four treatments of conventional tillage without straw incorporation (CT); conventional tillage with straw incorporation (CTS); no-tillage without straw mulching (NT); no-tillage with straw mulching (NTS), to assess the relationships among soil quality, ecosystem multifunctionality, and crop yields under the straw-returning and tillage strategies, based on both agronomic and environmental perspectives. ResultThe results showed that long-term straw return to the field could increase the yield of early rice by 6.24–8.80%, late rice by 3.81–7.13%, and oilseed rape by 9.55–14.45%. Long-term straw return enhanced soil quality index (SQI) by 22.21–40.74% and ecosystem multifunctionality (EMF) by 104.19–141.14% in the 0–20 cm soil layer. Long-term conventional tillage (i.e., CT and CTS) showed higher SQI and EMF values especially in the oilseed rape season. Structural equation modelling (SEM) indicated that straw return and tillage mainly increased crop yield by increasing the SQI in the oilseed rape season. ConclusionIn conclusion, long-term straw return with conventional tillage would be more benefit for the improvement of soil quality and the multifunctionality of soil ecosystems under triple paddy-upland rotation system, offering an effective approach for sustainable soil management and crop production.

Improving soil organic carbon mapping in farmlands using machine learning models and complex cropping system information

Obtaining accurate spatial maps of soil organic carbon (SOC) in farmlands is crucial for assessing soil quality and achieving precision agriculture. The cropping system is an important factor that affects the soil carbon cycle in farmlands, and different agricultural managements under different cropping systems lead to spatial heterogeneity of SOC. However, current research often ignores differences in the main controlling factors of SOC under different cropping systems, especially when the cropping pattern is complex, which is not conducive to farmland zoning management. This study aims to (i) obtain the spatial distribution map of six cropping systems by using multi-phase HJ-CCD satellite images; (ii) explore the stratified heterogeneous relationship between SOC and environmental variables under different cropping systems by using the Cubist model; and (iii) predict the spatial map of SOC. The Xiantao, Tianmen, and Qianjiang cities, which are the core agricultural areas of the Jianghan Plain, were selected as the study area. Results showed that the SOC content in rice–wheat rotation was the highest among the six cropping systems. The Cubist model outperformed random forest, ordinary kriging, and multiple linear regression in SOC mapping. The results of the Cubist model showed that cropping system, climate, soil attributes, and vegetation index were important influencing factors of SOC in farmlands. The main controlling factors of SOC under different cropping systems were different. Specifically, summer crop types had a greater influence on spatial variations in SOC than winter crops. Paddy–upland rotation was more affected by river distance and NDVI, while upland–upland rotation was more affected by irrigation-related factors. This work highlights the differentiated main controlling factors of SOC under different cropping systems and provides data support for farmland zoning management. The Cubist model can improve the prediction accuracy of SOC under complex cropping systems.

Oilseed rape-rice rotation with recommended fertilization and straw returning enhances soil organic carbon sequestration through influencing macroaggregates and molecular complexity

The sequestration of soil organic carbon (SOC) is influenced by agricultural management practices. However, the mechanisms that underlie the impacts of diverse paddy-upland rotation systems and fertilization strategies on SOC sequestration remain to be elucidated. Within this study, we investigated the variations in SOC sequestration under oilseed rape-rice (OR) and wheat-rice (WR) rotations with various fertilization regimes (CK, without fertilization; EF, excessive fertilization; RF, recommended fertilization; and RF+S, recommended fertilization with straw returning) through a five-year field experiment. Crop C inputs, soil aggregate-associated organic C, SOC functional groups, and their importance in SOC sequestration were examined. The results revealed that both SOC stock and sequestration rate were significantly enhanced by the OR rotation and straw returning. Specifically, SOC stock and sequestration rates were 7.7–14.3% and 28.6–83.7% higher in the OR rotation compared to the WR rotation under the same fertilization treatment. In addition, SOC stocks and sequestration rates were 6.7–13.3% and 24.4–77.6% higher in the RF+S treatment compared to the RF treatment. However, excessive fertilization (EF) did not further promote SOC sequestration. The OR rotation also showed higher values of aggregate mean weight diameter (MWD) and large-macroaggregate C compared to the WR rotation, with increases of 7.7–14.1% and 4.7–33.8%, respectively. The nuclear magnetic resonance studies showed that the OR rotation exhibited an elevated abundance of aromatic C and a more intricate molecular configuration compared to the WR rotation. Furthermore, crop C input increased significantly with fertilization, and crop C input was the highest in the RF+S treatment. The aggregate MWD and large-macroaggregate C also significantly increased after fertilization. Partial least squares path modeling revealed that crop rotation affected SOC sequestration mainly through its effect on large-macroaggregate C and SOC molecular structure complexity, whereas fertilization mainly affected SOC sequestration though its effects on crop C inputs and large-macroaggregate C. We conclude that OR rotation combined with straw returning is an effective measure for enhancing SOC sequestration in paddy-upland rotation systems, contributing to mitigating climate change in agricultural systems.

Factors controlling available soil nitrogen in Japanese paddy fields

ABSTRACT Available soil nitrogen (Av-N) is an important indicator for understanding the soil fertility in paddy fields. Previous studies have reported a decline in Av-N resulting from paddy-upland rotation at a regional scale in Japan, while the factors influencing this phenomenon on a national scale are not well understood. This study aims to assess the effects of soil temperature, land use, soil type and soil texture on Av-N in paddy fields across Japan. Soil surveys were conducted in 13 prefectures in 2020 and 2021, involving the collection of soil samples from the plow layer in a total of 2,600 paddy fields. Our results revealed that soil temperature had the most significant influence on Av-N, followed by land use and soil type. Av-N exhibited a negative correlation with soil temperature, whereby the average Av-N in the thermic soil temperature regime (>15°C, Av-N: 107 ± 48 mg kg−1) significantly lower than that in the mesic soil temperature regime (≤15°C, Av-N: 166 ± 74 mg kg−1). Increased upland frequency in paddy fields led to a decrease in Av-N, particularly pronounced in the thermic soil temperature regime, while partially mitigated in the mesic soil temperature regime. In the thermic soil temperature regime, paddy fields with long-term upland usage (upland frequency of paddy fields was more than 50%) had an average Av-N of 50 mg kg−1, necessitating additional organic matter application. Furthermore, the results concerning soil type and soil texture indicated that Av-N was higher in wet soil compared to semi-wet soil, and fine-textured soil had higher Av-N than medium-course textured soil. These findings underscore the negative effect of accelerated drying in paddy fields due to the expanding practice of paddy-upland rotation, leading to decreased Av-N. In conclusion, our study proposes the importance of organic matter management practices, with a primary emphasis on soil temperature, further refined by considering land use and soil type, to ensure the maintenance of adequate Av-N levels in paddy fields in Japan.

Effects of Typical Cropping Patterns of Paddy-Upland Multiple Cropping Rotation on Rice Yield and Greenhouse Gas Emissions

In response to the limitations of traditional double rice cropping models, this study constructed five typical rice planting models in the middle reaches of the Yangtze River, namely “Chinese milk vetch-early rice-late rice (CK/CRR), Chinese milk vetch—early rice—sweet potato || late soybean (CRI), rapeseed—early rice—late rice (RRR), rapeseed—early rice—sweet potato || late soybean (RRI) and potato—early rice—late rice (PRR)” to study the annual emission characteristics of greenhouse gases under different planting models. The results showed the following: (1) From the perspective of total yield in two years, the CRI treatment reached its maximum, which was significantly higher than that of other treatments by 9.30~20.29% in 2019 (p < 0.05); in 2020, except for the treatment of RRI, it was significantly higher than other treatments by 20.46~30.23% (p < 0.05). (2) The cumulative emission of CH4 in the double rice treatment is generally higher than that in paddy-upland rotation treatment, while the cumulative emission of N2O in the paddy-upland rotation treatment is higher than that in the double rice treatment, but the total amount is much lower than the cumulative emission of CH4. Therefore, CH4 emissions from rice fields still occupy most of the GHGs. (3) The global warming potential (GWP) and greenhouse gas emission intensity (GHGI) of different planting patterns in rice fields in 2020 were higher than those in 2019, and the GWP and GHGI of double rice cropping treatment is higher than that of paddy-upland rotation treatments. During the two years, the GWP of CRR treatment reached its maximum and was significantly higher than that of other treatments by 48.28~448.90% and 34.43~278.33% (p < 0.05). The GHGI of CRR was significantly higher than that of CRI and RRI by 3.57~5.4 and 1.4~3.5 times (p < 0.05). Based on the comprehensive performance of greenhouse gas emissions over the two experimental years, RRI and CRI have shown good emission reduction effects, which can significantly reduce greenhouse gas emissions from paddy fields, are conducive to reducing global warming potential and greenhouse gas emission intensity and conform to the development trend of “carbon neutrality”. Therefore, considering high-yield, low-temperature chamber gas emissions, the Chinese milk vetch—early rice—sweet potato || late soybean model performs well and has the best comprehensive benefits. It is of great significance for optimizing the rice field planting mode in the middle reaches of the Yangtze River.

Analysis on Change in Soil Organic Carbon Content of Farmland in Yangtze River Economic Belt Under Different Fertilizing Measures

The literature from a long-term fertilization experiment in the Yangtze River Economic Belt from January 1992 to May 2022 was collected, and the data of farmland soil organic carbon were extracted and integrated. Using the normalization treatment and the analysis method of relative annual variation, the overall change in soil organic carbon content in farmland in the Yangtze River Economic Belt under different long-term fertilization measures was studied, and the change differences of soil organic carbon content under three tillage modes were compared so as to judge and analyze the influence of the duration of the experiment on soil organic carbon dynamics. The results showed that under different long-term fertilization measures, the organic carbon content of farmland soil in the Yangtze River Economic Belt in China showed an overall upward trend. The NP, NPK, O, and NPKO treatments all increased the organic carbon content of agricultural soils, with that of the NPKO treatment being the largest. The sole application of inorganic nitrogen fertilizer reduced the organic carbon content of the soil. The rates of change in soil organic carbon content were 0.22 g·(kg·a)-1, 0.24 g·(kg·a)-1, and 0.16 g·(kg·a)-1for dryland, paddy, and water-dry rotation farmland, respectively. Additionally, the relatively rapid increase effect of organic carbon brought by the O and NPKO treatments could last for no more than 28 years in dryland soil but could still last for more than 28 years in paddy field and paddy-upland rotation soil. There was some variation in the rate of change of soil organic carbon content between soil types. The average rate of change of organic carbon was 0.25 g·(kg·a)-1for red soils, 0.14 g·(kg·a)-1 for brown soils, 0.19 g·(kg·a)-1 for tidal soils, and 0.15 g·(kg·a)-1 for rice soils. The trend of NPKO>O>NPK>NPK>NP>N was basically maintained for the rate of change in soil organic carbon content. The NPKO treatments were all significantly higher than the chemical fertilizer (N, NP, and NPK) treatments alone. The N treatment showed a reduction in organic carbon content in both red soil and rice soils. Considering the carbon fixation of farmland soil, the combined application of organic and inorganic fertilizers is a more suitable fertilization method in this area.

Biochar return in the rice season and straw mulching in the oilseed rape season achieve high nitrogen fertilizer use efficiency and low greenhouse gas emissions in paddy-upland rotations

Straw return can enhance crop yields and nitrogen fertilizer use efficiency (NFUE) in paddy-upland rotation systems. However, straw return in wetland rice systems can significantly increase CH4 emissions, which could be alleviated if the straw is converted to biochar before incorporation. This study investigated the effect of different crop residue management strategies on NFUE and greenhouse gas (GHG) emissions in a paddy-upland rotation over a four-year field experiment. We compared two treatments where all crop residues were removed (no N fertilizer (PK), recommended N fertilizer (NPK)) with three different methods of straw return. This included (i) direct straw return (NPK+S/S), where all crop residues were directly applied to the field after harvest; (ii) straw return as biochar (NPK+B/B), where all crop residues were converted into biochar before incorporation; (iii) straw return as biochar in the rice season and direct straw return in the oilseed rape season (NPK+B/S). Four-year crop yields, NFUE, two-year ammonia (NH3) volatilization, and GHG emissions were determined. The results showed that compared with the NPK treatment, straw and biochar return increased rice and oilseed rape yields by 0.41–0.80 t ha−1 and 0.24–0.33 t ha−1, respectively, and the annual NFUE by 4.3–6.9%. Direct straw return (NPK+S/S) did not significantly affect annual NH3 volatilization, but significantly increased cumulative N2O emissions (by 27.3%), CH4 (by 132.4%), global warming potential (GWP, by 75.2%) and greenhouse gas emissions intensity (GHGI, by 61.1%), respectively. In contrast, converting crop residues into biochar before incorporation significantly reduced annual NH3 volatilization and N2O and CH4 emissions. Compared with the NPK+S/S treatment, the NPK+B/B and NPK+B/S treatments reduced cumulative N2O by 20.5–26.7% and CH4 emissions by 56.5–65.9% with the corresponding reduction in GWP value (42.3–50.4%) and GHGI value (44.3–52.6%). Considering biochar production cost, we recommended straw return as biochar in the rice season and straw mulching in the upland season as a measure to increase crop yields and NFUE while reducing GHG emissions in the paddy-upland rotation.

Sustainability assessment on paddy-upland crop rotations by carbon, nitrogen and water footprint integrated analysis: A field scale investigation

Nutrients of carbon, nitrogen and water of farmland ecosystem are essential foundation to guarantee crop production, but also environmental flows associated greenhouse gas (GHG), reactive nitrogen (Nr) releases, and water consumption. Their flow characteristics serve as a crucial starting point for creating efficient management practices and mitigation measures. Therefore, the objectives of this study are to quantify the carbon footprint (CF), nitrogen footprint (NF), water footprint (WF), and comprehensive environmental footprint (ComF) of six paddy-upland rotation systems, including fallow-paddy rice (FA-PR), Chinese milk vetch-paddy rice (CMV-PR), wheat-paddy rice (WH-PR), rapeseed-paddy rice (RA-PR), green forage wheat-paddy rice (WF-PR), and vicia faba bean-paddy rice (FB-PR), as well as to analysis their relationships and define driving factors. Results showed that the lowest area-scaled CF of 3.74 t CO2-eq ha−1 were observed in the CMV-PR rotation, which were 41% lower than that for WH-PR (the highest CF, 9.13 t CO2-eq ha−1) when soil carbon change was taken into account. It is of importance that soil carbon sequestration in CMV-PR rotation could offset up to around 57% of its CF, while the WH-PR rotation only offset 25%. The RA-PR rotation had the highest area-scaled NF and WF, which was 1.8 and 1.9 times greater than those of the lowest rotation in FA-PR. In terms of comprehensive environmental effects, the six rotation systems showed the order of FA-PR < CMV-PR < FB-PR < RA-PR < WF-PR < WH-PR, with NH3 volatilization accounting 60.7%–66.7% and blue-green WF for 17.5%–26.6% of the total. Therefore, priority should be given to optimizing N fertilizer application and water consumption for paddy-upland rotation systems. The study also suggested that appropriate inter-annual adjustment of rotation system could contribute to achieving GHG mitigations and Nr losses.

Exploring antibiotic resistance load in paddy-upland rotation fields amended with commercial organic and chemical/slow release fertilizer.

Agricultural fertilization caused the dissemination of antibiotic resistance genes (ARGs) in agro-ecological environment, which poses a global threat to crop-food safety and human health. However, few studies are known about the influence of different agricultural fertilization modes on antibiotic resistome in the paddy-upland rotation soils. Therefore, we conducted a field experiment to compare the effect of different fertilization (chemical fertilizer, slow release fertilizer and commercial organic fertilizer replacement at various rates) on soil antibiotic resistome in paddy-upland rotation fields. Results revealed that a total of 100 ARG subtypes and 9 mobile genetic elements (MGEs) occurred in paddy-upland rotation soil, among which MDR-ARGs, MLSB-ARGs and tet-ARGs were the dominant resistance determinants. Long-term agricultural fertilization remarkably facilitated the vertical accumulation of ARGs, in particular that bla ampC and tetO in relative abundance showed significant enrichment with increasing depth. It's worth noting that slow release fertilizer significantly increased soil ARGs, when comparable to manure with 20% replacing amount, but chemical fertilizer had only slight impact on soil ARGs. Fertilization modes affected soil microbial communities, mainly concentrated in the surface layer, while the proportion of Proteobacteria with the highest abundance decreased gradually with increasing depth. Furthermore, microbial community and MGEs were further proved to be essential factors in regulating the variability of ARGs of different fertilization modes by structural equation model, and had strong direct influence (λ = 0.61, p < 0.05; λ = 0. 55, p < 0.01). The results provided scientific guidance for reducing the spreading risk of ARGs and control ARG dissemination in agricultural fertilization.

Estimation models from soil pH with a solid-to-liquid ratio of 1:2.5 to pH measured by other methods using soils in Japan

ABSTRACT In Japan, soil pH is primarily measured using water with a solid-to-liquid (SL) ratio of 1:2.5, whereas soil pH measurement methods vary by country. Although some soil pH estimation models for each country have been developed to convert soil pH measured by other methods, suitable models for soils in Japan remain unidentified. Therefore, we propose models for estimating the various soil pH values from those measured by water with an SL ratio of 1:2.5. We collected a dataset of 192 topsoil properties in paddy-upland rotation fields in eastern Japan. The dataset comprised soil pH, electrical conductivity (EC, SL ratio of 1:5), particle density, silt and clay content, and total carbon. Soil pH was measured using distilled water (DW), 0.01 M calcium chloride (CaCl2), and 1 M potassium chloride (KCl) with an SL ratio of 1:1 (pH-1DW), 1:2.5 (pH-2.5DW, pH-2.5CaCl2, pH-2.5KCl), and 1:5 (pH-5DW, pH-5CaCl2, pH-5KCl). The comparison of linear regression models showed that the models comprising pH-2.5DW and intercept were sufficiently accurate to estimate pH-1DW and 5DW. However, to estimate pH-CaCl2 and pH-KCl, the models comprising pH-2.5DW, EC, and intercept were sufficiently accurate. From the study results, we proposed the following equations: pH-1DW = 1.10 × pH-2.5DW − 0.69 (R2 = 0.92, RMSE = 0.19); pH-5DW = 0.80 × pH-2.5DW + 1.32 (R2 = 0.86, RMSE = 0.16); pH-2.5CaCl2 = 0.93 × pH-2.5DW + 1.75 × EC − 0.44 (R2 = 0.94, RMSE = 0.14); pH-5CaCl2 = 0.83 × pH-2.5DW + 2.19 × EC + 0.29 (R2 = 0.88, RMSE = 0.20); pH-2.5KCl = 0.92 × pH-2.5DW + 2.86 × EC − 0.97 (R2 = 0.93, RMSE = 0.15); pH-5KCl = 0.88 × pH-2.5DW + 2.94 × EC − 0.57 (R2 = 0.93, RMSE = 0.15).

Diversity and function of soil microorganisms in response to paddy–upland rotation system in sustainable restoration of saline-sodic soils

Context Rapid desalination by planting rice in saline soil consumes large amounts of water, which is not environmentally friendly. Aims Herein, we propose rapid desalination by planting rice, then shifting to cultivating upland plants to attain substantial resource-saving and higher yield simultaneously with restoration of saline-sodic soil. Methods Field experiments were run for two consecutive years with five treatments: unreclaimed wasteland (WL) as control, rice cultivation followed by fallow (RF), rice–rice continuous cropping (RR), rice–ryegrass rotation (RG), and rice–sorghum rotation (RS). Physicochemical properties, including pH, electrical conductivity, and exchangeable sodium percentage were determined, and 16S rRNA sequences were used to evaluate soil microbial composition and stability. Key results The soil total organic carbon, total nitrogen, available phosphorus, and biomass in RR, RG, and RS treatments were all higher than RF and control. Notably, RR, RG, and RS increased the soil microbial biomass carbon and nitrogen, and significantly reshaped the soil communities of bacteria, fungi, and archaea relative to RF and WL. Conclusions Despite the lower efficiency of RG and RS in ameliorating saline-sodic soil, there were dramatic savings in irrigation water, and the improvements in microbial diversity and functionalities indicated that the paddy–upland crop rotation system had substantial influence on sustainability of soil quality. Implications Providing a balance between salt desalination performance with irrigation water input and yield, the paddy–upland rotation system is a robust, replicable, and environmentally friendly practice in saline-sodic soil remediation.

Responses of soil microbial community structure, potential ecological functions, and soil physicochemical properties to different cultivation patterns in cucumber

Changing crop cultivation patterns may alleviate the negative effects of continuous cropping by altering soil characteristics. But how soil properties and microbial states are specifically altered is largely unknown. In this study, soil properties and cucumber growth were investigated after nine years under six cultivation patterns. The results showed that the different cultivation patterns significantly altered the bacterial and fungal communities of the bulk soil, and bacteria appeared to be more sensitive to cultivation pattern than fungal communities. In pairwise comparisons of the six cultivation patterns at the phylum level, all 15 comparisons showed significant differences in bacterial phyla, and 6 showed significant differences in fungal phyla. The paddy upland rotation pattern (pattern 1) had the greatest effect on the types of soil microorganisms, with 5 unique OTUs for bacteria and 17 for fungi. The results of unweighted pair-group method with arithmetic mean (UPGMA) analysis between bulk soil and rhizosphere soil suggested that differences in bulk soil microbes led to differences in rhizosphere soil microbes. Bacterial and fungal genera (Serratia, Arachidicoccus, Penicillium, etc.) in the rhizosphere soil were significantly associated with cucumber agronomic traits. Compared with the other cultivation patterns, pattern 1 and the garlic rotation pattern (pattern 6) promoted the succession of soil microorganisms in a direction beneficial to plant growth through enrichment of more microbiota antagonistic to plant pathogens. Different cultivation patterns also changed the abundance of potential microbial functional genes. Pattern 1 had an increased abundance of microorganisms associated with functions such as N and P cycling, arsenic detoxification, and aromatic compound degradation. Pattern 1 also significantly weakened the trend of soil acidification and produced a significantly higher soil pH than the other five patterns. Therefore, paddy upland rotation and garlic rotation cultivation patterns may be considered as alternatives for sustainable cucumber production in the study area.

Effect of soil management systems on the rhizosphere bacterial community structure of tobacco: Continuous cropping vs. paddy-upland rotation

Rhizosphere bacteria play important role in soil nutrient cycling and plant growth, and their richness and diversity are influenced by soil management systems. However, the specific changes in tobacco rhizosphere bacterial community structure in continuous and tobacco-rice rotation cropping systems remain uninvestigated. In this study, soil properties and the composition of the rhizosphere bacterial community in tobacco monocropping and tobacco-rice rotation cropping systems were analyzed. Moreover, the comparison of rhizosphere bacterial community structure between tobacco continuous and tobacco-rice rotation cropping systems was performed via high-throughput sequencing. The changes in the composition of the rhizosphere bacterial community were investigated at different tobacco growth stages. The results showed that continuous tobacco cropping increased the soil soluble organic carbon (SOC), total nitrogen (TN), and the content of other nutrients (e.g., available phosphorus and available potassium) compared to tobacco-rice rotation cropping. However, monocropping decreased bacterial alpha-diversity and altered the community composition when compared to the rotation cropping system. At the phylum level, the relative abundance of Proteobacteria, Gemmatimonadetes, and Bacteroidetes increased in the continuous cropping soil, while that of Acidobacteria, Firmicutes, and Actinobacteria decreased. At the genera level, the average abundance of the dominant genus Bacillus varied from 12.96% in continuous cropping libraries to 6.33% in the rotation cropping libraries (p < 0.05). Additionally, several other taxa, such as o_Acidobacteriales and Candidatus_Solibacter decreased from 7.63 to 6.62% (p < 0.05) and 4.52 to 2.91% (p < 0.05), respectively. However, the relative abundance of f_Gemmatimonadaceae and c_Subgroup_6 showed an increase of 1.46% (p < 0.05) and 1.63% (p < 0.05) in the tobacco-rice rotation cropping system, respectively. The results of NMDS indicated that the rhizobacteria community structure differed in the two cropping systems. In tobacco, the rhizosphere bacterial community structure showed no significant changes in the prosperous long-term stage and topping stage, but the composition changed significantly in the mature stage.

Analysis and evaluation of paddy-upland rotation of Gastrodia elata- Oryza sativa in Dabie Mountains

Gastrodia elata, as the valuable Chinese medicinal material, has been used for more than 2 000 years in China. With the increasing market demand for G. elata, the traditional wild resources have been unable to transform into commodities. At present, local authorities give full play to the advantages of natural resources and vigorously cultivate G. elata to form the cultivation mode and technical system with local characteristics. Huanggang Comprehensive Experimental Station of National Technical System of Chinese Medicinal Materials Industry has optimized and summarized the paddy-upland rotation of G. elata-Oryza sativa in Dabie Mountains of Hubei province through field visits and guidance for four consecutive years. Based on the ecological adaptability and planting characteristics of G. elata and O. sativa, and the actual production experience of farmers, analyzed the principle of paddy-upland rotation from production environment selection and fungus treatment, and evaluated the paddy-upland rotation of G. elata-O. sativa from production status, ecological benefits, and economic benefits. The paddy-upland rotation of G. elata-O. sativa has achieved efficient cultivation of G. elata and produced considerable economic benefits. Through the summary, analysis, and evaluation of the paddy-upland rotation mode of G. elata-O. sativa in Dabie Mountains, the present study put forward the optimization strategy of cultivation technology for G. elata in low-altitude areas, i.e., to use artificial Armillaria sticks instead of traditional cut-log for substitute cultivation of G. elata, which can effectively alleviate the &quot;bacteria-forest contradiction&quot; arising from the cultivation of G. elata. It can also improve the ecological environment and production status of the Dabie Mountains and even the G. elata producing areas at the same altitude.

Straw returning mediates soil microbial biomass carbon and phosphorus turnover to enhance soil phosphorus availability in a rice-oilseed rape rotation with different soil phosphorus levels

The alleviation of phosphorus (P) limitation by increasing carbon (C) input is an effective strategy for improving crop production and P uptake efficiency. However, the effects of straw returning on soil microbial biomass P (MBP) turnover and P fractions in paddy-upland rotation remain poorly understood. Soil MBP turnover involves the mineralization and immobilization of organic P (Po), potentially altering P fractions and reducing the risk of P loss. The effects of straw returning on soil MBP turnover, P fractions and crop P utilization during the rice-oilseed rape rotation were evaluated in two field experiments with different soil Po levels. The treatments included no P fertilizer (-P), P fertilizer (+P) and P fertilizer plus straw returning (+P + S). The crop P uptake and cumulative P utilization efficiency were increased by straw returning. Straw addition promoted microbial biomass, decreased the MBC:MBP ratio in Po-high soil, increased the MBC:MBP ratio in Po-low soil, and increased the MBP turnover rates and fluxes in both soils. According to structural equation modeling (SEM), soil MBC and MBP had significant effects on crop P uptake directly or via P fractions. In Po-high soil, straw addition increased inorganic P (Pi) (NaHCO3 and NaOH) and decreased Po content by increasing the MBP turnover, while the Po-low soil mainly increased Po content. Among multiple observed variables, MBP was the most important driving factor controlling P uptake in Po-high soil, while MBC and NaOH-Pi were the best driving factors in Po-low soil. Additionally, the soil MBC, MBP and MBC:MBP ratios were higher in the oilseed rape season than in the rice season. Consequently, straw returning improves soil P availability by increasing MBP turnover, which is beneficial for improving P utilization.

Ecological circular agriculture: A case study evaluating biogas slurry applied to rice in two soils

In the context of carbon peak, neutrality, and circular agricultural economy, the use of renewable resources from agricultural processing for plant cultivation still needs to be explored to clarify material flow and its ecological effects. Paddy-upland rotation is an effective agricultural strategy to improve soil quality. This study evaluated the effects of biogas slurry application against those of chemical fertilisers in these two typical Chinese cropping soils. The application of biogas slurry increased total carbon content in paddy soil by 73.4%, and that in upland soil by 65.8%. Conversely, application of chemical fertiliser reduced total carbon in both soil types. There were significant positive correlations between total carbon and Zn, Cu, and Pb in rice husks grown in paddy soil (R2 = 0.95, 0.996, 0.95; p < 0.05). The content of amylose in biogas slurry treatment of paddy soil increased by 35.9%, while that in upland soil decreased by 19.2%. After biogas slurry was applied, the contents of fulvic acid- and humic acid-like substances in paddy soil average increased by 40.9% and 45.6%, while the contents of protein-like components were enhanced by 46.8% in upland soil. This result was consistent with predictions of microbial community function. Microorganisms in paddy soil generally preferred carbon fixation, while those in upland soil preferred hydrocarbon degradation and chemoheterotrophy. Understanding the changes in soil carbon stock and microbial function after biogas slurry application will contribute to sustainable agricultural development and food security.

Insufficient Zn uptake reduces rice grain yield in integrated rice-crayfish culture – a case study in the Jianghan Plain, China

ABSTRACT China has recently seen a substantial increase in integrated rice-crayfish (Procambarus clarkii) culture (IRCC). However, grain yield reductions (GYR) with rice plants having normal vegetative growth but failed filling are becoming common in IRCC, and the driving factors remain unclear. Here, we tried to identify the mechanisms behind this GYR mode in the Jianghan Plain, China, by investigating the soil properties, grain yield parameters, and plant mineral content in five IRCC plots experiencing GYR and an adjacent paddy-upland rotation plot (CK). The results showed slight to extreme GYR (11–82%) in the IRCC plots compared to those in CK. The translocation of phosphorus from shoot to grain during the productive stage of rice plants was inhibited in IRCC plots (26–71%) compared to CK (75%). The grain yield and phosphorus translocation coefficient correlated strongly (r > 0.95) with zinc uptake in aboveground rice organs which was significantly lower in IRCC than in CK. We conclude that this GYR in IRCC plots is not due to decreased macronutrients availability or heavy metals toxicity in IRCC soils, but the insufficient uptake of zinc by IRCC rice plants. We recommend Zn foliar spray or introducing Zn efficient rice cultivars as potential mitigation measures.

The mass water content of paddy soil after harvest is strongly associated with the accumulation of organic matter as the source of available nitrogen

ABSTRACT Paddy soils are the dominant source of nitrogen for rice via mineralization, and knowledge about the available nitrogen (AN) in paddy soil is important for rice cultivation. Although the relationship between AN and soil physicochemical parameters has been studied, no systematic studies of the relationships between AN and the soil moisture content of various soil types in Japan have been studied. Therefore, we examined the impacts of soil types and treatment of organic matter application or paddy–upland rotation on these relationships. We sampled topsoils from 30 paddy fields throughout Japan. We compared the relationships between AN and soil physicochemical properties, such as total nitrogen (TN), cation exchange capacity, soil water-holding capacity (WHC), mass water content after harvest (MWH), and water content after harvest (WCH). The scatter diagram revealed that AN and either MWH or WCH (p < 0.01) had the highest positive linear correlation coefficient; the pattern became clearer after separating Andosols and non-Andosols. We analyzed the relationship between AN and either TN or MWH in 100 topsoils, including soils from treatment plots with successive organic matter application or paddy-upland rotation. A significantly positive correlation between AN and TN was observed, although the regression slopes for volcanic or non-volcanic soils differed. The decrease in AN due to frequent paddy–upland rotation was greater than that for TN. On the other hand, a highly positive correlation between AN and MWH was observed, and the coefficient of determination was higher than that for AN and TN. TN and the WHC increased when the accumulation of organic matter in paddy soil was greater. As there was a positive correlation between WHC and MWH, a positive correlation was also observed between AN and MWH. Additionally, we investigated year-to-year variation in MWH using topsoil samples collected before autumn tillage, for 3–5 consecutive years in 24 plots, for various soil types throughout Japan. In order to eliminate the effects of precipitation and to minimize the fluctuation of MWH in paddy topsoil, it was desirable to collect topsoil samples within 24–96 hours of the last precipitation of 1 mm h−1 or more, for the measurement of moisture content.

Differences in responses of ammonia volatilization and greenhouse gas emissions to straw return and paddy-upland rotations.

Paddy-upland rotation and/or straw return could improve soil structure and soil nutrient availability. Different previous crops (wheat and/or oilseed rape) and straw return methods (straw mulching and/or returning) might increase soil organic carbon (C) and total nitrogen (N) content, and further affected the ammonia (NH3) volatilization, nitrous oxide (N2O), and methane (CH4) emissions. A comparison study was carried out in a located field experiment started from 2014 in Central China, aiming to exam seasonal and annual NH3, N2O, and CH4 emissions under the wheat-rice (WR) and oilseed rape-rice (OR) rotations. Three treatments were chosen, i.e., (i) no chemical N fertilizer application (PK), (ii) chemical nitrogen-phosphorus-potassium combination (NPK), and (iii) chemical NPK with straw returning (NPK+St). We found that after 3years of cultivation, treatment with straw return increased soil total N content and organic C by 15.57% and 17.11% on average as compared with the NPK treatment, respectively. Straw return did not generate additional NH3 and N2O losses during the rice season after improving soil fertility. However, CH4 emissions increased by 45.35% on average after straw return in summer. In winter, straw return increased NH3, N2O, and CH4 emissions by 70.12-85.23%, 16.93-22.97%, and 7.18-9.17%, respectively. The stimulation of NH3 volatilization mainly occurred in the topdressing stage. Compared with WR rotation, OR rotation had no significant effect on NH3 and CH4 emissions, and the change of N2O emission might be related to the increase of soil C and N pools. The retention of residues in the process of straw decomposition may be the main factor leading to the difference of gas emission between the paddy-upland rotation and straw return.