Wheat-maize Rotation Research Articles

Sustainable high grain yield, nitrogen use efficiency and water productivity can be achieved in wheat-maize rotation system by changing irrigation and fertilization strategy

The winter wheat-summer maize rotation system is one of the most successful intensification agricultural systems in China, but low and unstable grain yield (GY) and high soil nitrate-N leaching caused by erratic precipitation and inefficient management of irrigation and fertilization have attracted wide attention. A two-year (2018–2020) field experiment was carried out to evaluate the effects of four water and nitrogen management strategies (a conventional irrigation and fertilization (CK) and three drip fertigation treatments (rain-fed: RF, deficit irrigation: DI and full irrigation: FI)) on soil water, soil nitrate-N residual, GY, water productivity (WP), nitrogen use efficiency (NUE) and net income in a winter wheat-summer maize rotation system. The results indicated that water and nitrogen management strategies had significant effects on soil water content in the 0–320 cm soil profile. More than 90 mm soil water in the 0–320 cm soil layer was consumed by winter wheat, and the soil water consumption followed the order of RF > DI > CK > FI. The soil water consumption can be replenished by irrigation and precipitation during the summer maize season, but the soil water in 180–260 cm under RF was significantly lower than that in the other treatments, which could not be fully replenished. There was no significant difference in the nitrate-N residual in the 0–180 cm soil layer among the treatments at harvest, but the nitrate-N residual rate of CK (less than 40% and 30% at winter wheat and summer maize harvest) was significantly lower than that of drip fertigation (more than 50% and 40% at winter wheat and summer maize harvest) in the 0–60 cm soil profile, but significantly higher than that in the 60–180 cm soil profile. These results indicate that drip fertigation had a lower risk of nitrate leaching compared with CK treatment. GY and NUE of DI and FI treatments were significantly higher than those of CK and RF treatments, but DI used 25% less irrigation water than FI, resulting in higher WP. The WP of DI was increased by 6.8–7.4% and 4.2–16.0% for winter wheat and summer maize compared with FI, respectively. From the perspective of winter wheat-summer maize rotation system, the two-year average net income of DI was increased by 2.8%, 37.9% and 59.9% compared with FI, RF and CK, respectively. Therefore, deficit irrigation with nitrogen fertigation was recommended as a sustainable fertigation strategy for achieving higher grain yield, nitrogen use efficiency, water productivity and net income and reducing the risk of soil nitrate-N leaching in the winter wheat-summer maize rotation system.

Long-term appropriate N management can continuously enhance gross N mineralization rates and crop yields in a maize-wheat rotation system

Long-term appropriate N management can continuously enhance gross N mineralization rates and crop yields in a maize-wheat rotation system

Vertical distribution of phosphorus fractions and the environmental critical phosphorus level in acidic red soil under long‐term fertilizer and lime application in southern China

AbstractBackgroundPhosphorus (P) deficiency in acidic red soil restricts crop yield. However, long‐term application of phosphate fertilizer can cause potential environmental risks due to the accumulation of P in the soil.AimsOur aim was to determine the distribution characteristics of P fractions in acidic red soil profiles and the environmental risk of soil P losses after application of organic fertilizer and lime, and analyze the key factors driving P distribution in the soil profile of acidic red soil.MethodsBased on the long‑term applicationof fertilizers and quicklime in the acidic soil under wheat–maize rotation system, contents of soil Olsen‐P and CaCl2‐P, as well as pH, at multiple soil layers between 0 and 50 cm depths were monitored. The environmental critical P levels were determined using a two‐segment linear model.ResultsDuring 1990–2010 and 2011–2014, application of phosphate fertilizer or quicklime on acidic red soil significantly (p < 0.05) increased the annual average aboveground biomass of wheat and maize and P recovery efficiency. Soil Olsen‐P and CaCl2‐P contents increased with the application of phosphate fertilizer, especially in combination with manure, and the increase mainly concentrated at the 0–20‐cm soil layer. The environmental critical Olsen‐P content was 99.7 mg kg−1. The Olsen‐P contents at different soil layers were mainly affected by cumulative P and organic P inputs, but were less affected by soil pH.ConclusionsThe application of organic fertilizer and lime can prevent the acidification of red soil, and the application of organic fertilizer should reduce the total phosphate fertilizer input to prevent rapid accumulation of P and risk of P loss in leachate while still improving the crop utilization rate of P fertilizer. Thus, this strategy should help achieve the concomitant goals of high crop yield and environmental protection.

Effects of Long-Term Bare Fallow During the Winter-Wheat Growth Season on the Soil Chemical Properties, Fungal Community Composition, and the Occurrence of Maize Fungal Diseases in North China.

On the North China Plain, one of the most water-deficient regions in China, bare fallow has been implemented over a large-scale area to conserve water during the growth season of water-intensive winter wheat since 2015. However, the effects of this bare fallow on fungal community and the occurrence of crop diseases are poorly understood. Here we measured soil chemical properties, fungal community composition, and the occurrence of crop diseases after 15 years of long-term fallow (continuous maize or soybean) and non-fallow (maize-wheat rotation; soybean-wheat rotation) cropping systems. Bare fallow during the winter-wheat growth season significantly decreased soil organic matter, available nitrogen, and phosphorus. It also changed the composition of soil fungal communities, i.e., increased relative abundances of some potentially pathogenic species of Lectera, Fusarium, and Volutella but decreased beneficial Cladorrhium and Schizothecium. Meanwhile, the epidemic tendency of maize diseases changed correspondingly: the disease index of southern corn leaf blight and maize brown spot increased, but the incidence of stalk rot decreased compared with the non-fallow system. Soybean diseases were very mild regardless of the cropping system during the total experimental period. Network analysis demonstrated that the soil fungal diversity associated with maize diseases was affected by the decreased soil organic matter and available nitrogen and phosphorus. Our results suggest that bare fallow in the winter-wheat season affected the soil chemical properties, fungal community, and the occurrence of maize fungal diseases.

Pollution assessment, source identification, and health risks of heavy metals: a case study in a typical wheat-maize rotation area of eastern China.

Winter-wheat-summer-maize rotations are important cropping patterns in China, and the quality of the food produced from these systems can affect human health. However, the effects of heavy metal pollution on both crops remain unclear. We analyzed soil-wheat and soil-maize samples from eastern China for their Cd, Cu, Zn, Cr, Ni, and Pb contents. The concentrations of these metals in the soils analyzed were found to be lower than those recommended by the national guidelines, but the Cd, Cr, Cu, and Ni concentrations were higher than the natural soil background values in China. Quality indices showed that subpollution was predominant in wheat/maize (95.00%/81.25%) samples. Positive matrix factorization model data revealed that the contributions from natural sources, agricultural activities, and traffic to the heavy metal pollution levels were 30.40-43.07%, 34.67-26.63%, and 34.92-30.27%, respectively, in the wheat-maize rotations. Although the health hazard quotient values for wheat were higher than those for maize, there were no health risks for children or adults.

Soil organic and inorganic carbon pools as affected by straw return modes under a wheat-maize rotation system in the Guanzhong Plain, Northwest China

To understand the effects of straw return modes on soil carbon pools, we investigated total soil organic carbon (SOC), labile organic carbon fractions, and inorganic carbon (SIC) in different straw return modes at a depth of 0-40 cm under a maize-wheat cropping system in the Guanzhong Plain, Shaanxi, based on an 11-year field experiment. There were five straw return modes, i.e., no return of straw of both wheat and maize (CK), the retention of high wheat stubble plus the return of chopped maize straw (WH-MC), the return of both chopped wheat and maize straw (WC-MC), the retention of high wheat stubble and no return of maize straw (WH-MN), and the return of chopped wheat straw and no return of maize straw (WC-MN). The proportions of SOC storage were significantly higher under the WH-MC and WC-MC treatments than that under the CK by 28.1% and 22.2%, respectively. The proportions of SIC storage were increased by 20.4% and 17.3%, respectively. Compared with the initial value, the increases of sequestered SOC and SIC ranged from -0.84 t·hm-2 to 6.55 t·hm-2, respectively, and from -0.26 t·hm-2 to 8.61 t·hm-2, respectively. The efficiency of sequestration of SOC was 7.5%. To maintain the basic SOC level, the minimum carbon input from straw was 4.65 t·hm-2·a-1. The contents of labile carbon fractions at the 0-20 cm layer increased significantly under the WH-MC and WC-MC treatments compared with those of the control. Results of principal component analysis showed that the changes in soil carbon pools were primarily affected by the amount of straw return. Additionally, the increases in SIC storage could be ascribed to the Ca2+ and Mg2+ ions derived from irrigation water and plant residues that could coprecipitate with the CO2 from SOC mineralization to form CaCO3. In conclusion, our results indicated that the straw return mode that utilized the retention of high wheat stubble and chopped maize straw was sufficient to maintain soil carbon storage and would be the optimal straw-returning strategy for the region.

Advantages of an Orychophragmus violaceus-maize rotation in reducing greenhouse gas emissions and reactive nitrogen losses and increasing net ecosystem economic benefits on the North China Plain

Introducing cover crops into crop rotation systems is widely practiced to enhance the sustainability of agricultural production, but comprehensive evaluations of farmlands in cover crop-maize rotations on the North China Plain (NCP) from environmental, economic and net ecosystem economic benefits (NEEB) perspectives have rarely been performed. Therefore, a field experiment was conducted to compare economic benefits (EB), greenhouse gas (GHG) emissions, reactive nitrogen (Nr) losses, soil nutrient cycling values (SNV) and NEEB in three farming systems. The farming systems included a conventional wheat-maize (WM) rotation system, a government-promoted monoculture maize (MM) system and an innovative Orychophragmus violaceus (O. violaceus)-maize (OvM) rotation system. The OvM rotation system achieved more EBs from the maize season but lower annual profits than the WM system, with 68.29% lower GHG emissions and 39.33% lower Nr losses. In addition, the highest SNV was achieved in the OvM rotation system, which was 700.18% and 116.97% higher than those in the WM and MM systems, respectively. Furthermore, the NEEB of the OvM rotation system was 61.92% and 29.31% higher than those of the WM and MM systems, respectively. In conclusion, the OvM rotation is recommended as a sustainable and cleaner maize production farming system for the NCP and other regions with similar ecological conditions because it led to lower annual GHG emissions and Nr losses, as well as higher SNV and NEEB than the other farming systems.

Urease Inhibitors Effects on the Nitrogen Use Efficiency in a Maize–Wheat Rotation with or without Water Deficit

The use of urease inhibitors in irrigated systems decreases both soil ammonium (NH4+) and nitrate (NO3−) availability, and, thus, could be an easy tool to reduce N loss due to ammonia volatilization and NO3− leaching. The main goal of this experiment was to assess the effect of urease inhibitors on N use efficiency, N losses, and their economic impact in a maize-wheat field experiment. In this study, 10 treatments were compared, combining the urea fertilizer with or without urease inhibitor, applied in one or two dressings, and under optimal or sub-optimal irrigation. A single application of urease inhibitor (IN1d), coupled with the conventional urea, helped to reduce the nitrate leaching risk both during the maize period (even when compared to the two dressing treatment) and after harvest. In addition, this improvement was achieved together with an increase in economic benefit, even when compared with the application of the same amount of regular urea split into two dressings. Under low water availability systems, the benefits of applying urease inhibitors increased with respect to the application of regular urea, making this technique a very promising strategy for adaptation to climate change in arid and semiarid regions.

Effects of long-term phosphorus application on crop yield, phosphorus absorption, and soil phosphorus accumulation in maize-wheat rotation system.

In this study, we examined the effects of four phosphorus treatments on crop yields, and analyzed crop phosphorus uptake and phosphorus utilization efficiency, as well as changes in soil phosphorus deficit in maize-wheat rotation system, based on a 7-year field experiment in Baoding City, Hebei Province. The results showed that long-term phosphorus application significantly increased the yield and phosphorus uptake of maize and wheat. The yield and phosphorus uptake of maize and wheat showed a parabolic trend that first increased and then decreased with the increases of phosphorus application. The utilization efficiency of phosphorus fertilizer in the corn season was higher than that in the wheat season under various phosphorus application treatments. The cumulative utilization efficiency of phosphorus fertilizer in the wheat season showed a downward trend. The decline rate showed that optimized phosphorus application > 70% optimized phosphorus application >130% optimized phosphorus application. The cumulative utilization efficiency of phosphorus fertili-zer in the corn season showed an upward trend. For the rising rate, the optimized phosphorus application > 70% optimized phosphorus application > 130% optimized phosphorus application. Both the apparent phosphorus surplus and the accumulated phosphorus surplus of the soil without phosphorus application were under phosphorus deficiency. Under the treatment of phosphorus application, soil phosphorus showed a status of phosphorus surplus. The higher the phosphorus application rate, the longer the accumulation period, the higher the soil phosphorus surplus. Under the straw returning condition, phosphorus application rate for wheat of 105-150 kg·hm-2 and the phosphorus application rate for maize of 63-90 kg·hm-2 in Hebei fluvo-aquic soil could ensure the high crop yield, keep the phosphorus utilization efficiency at a high level, and reduce soil phosphorus accumulation and environmental risks.

Influence of Maize Residues in Shaping Soil Microbiota and Fusarium spp. Communities.

Fusarium head blight (FHB) is a devastating fungal disease of small grain cereals including wheat. Causal fungal agents colonize various components of the field during their life cycle including previous crop residues, soil, and grains. Although soil and residues constitute the main inoculum source, these components have received much less attention than grains. This study aimed at disentangling the role of previous crop residues in shaping soil microbiota, including Fusarium spp. communities, in fields under wheat-maize rotation. Such knowledge may contribute to better understand the complex interactions between Fusarium spp. and soil microbiota. Dynamics of bacterial and fungal communities, with a special focus on Fusarium spp., were monitored in soils at 3 time points: during wheat cultivation (April 2015 and 2017) and after maize harvest (November 2016) and in maize residues taken from fields after harvest. Shifts in microbiota were also evaluated under mesocosm experiments using soils amended with maize residues. Fusarium graminearum and F. avenaceum were predominant on maize residues but did not remain in soils during wheat cultivation. Differences in soil bacterial diversity and compositions among years were much lower than variation between fields, suggesting that bacterial communities are field-specific and more conserved over time. In contrast, soil fungal diversity and compositions were more influenced by sampling time. Maize residues, left after harvest, led to a soil enrichment with several fungal genera, including Epicoccum, Fusarium, Vishniacozyma, Papiliotrema, Sarocladium, Xenobotryosphaeria, Ramularia, Cladosporium, Cryptococcus, and Bullera, but not with bacterial genera. Likewise, under mesocosm conditions, the addition of maize residues had a stronger influence on fungal communities than on bacterial communities. In particular, addition of maize significantly increased soil fungal richness, while bacteria were much less prone to changes. Based on co-occurrence networks, OTUs negatively correlated to Fusarium spp. were identified, such as those assigned to Epicoccum and Vishniacozyma. Altogether, our results allowed to gain a deeper insight into the complex microbiota interactions in soils, with bacteria and fungi responding differently to environmental disturbances.

The agronomic and economic viability of innovative cropping systems to reduce Fusarium head blight and related mycotoxins in wheat

CONTEXTThe effective control of Fusarium head blight (FHB) in wheat, mainly caused by the toxigenic fungus Fusarium graminearum, has a significant impact on food safety worldwide. As maize is one of the main hosts of F. graminearum, the risk of infection by this plant pathogen is highest when wheat is grown after maize and infected crop residues are not buried through ploughing. OBJECTIVESThis study aimed to investigate the agronomic and economic viability of two innovative cropping systems with the goal to reduce the risk of FHB and mycotoxins in subsequent wheat. These systems were maize-intercropping and cover cropping with different plant species before the wheat growing season under reduced tillage practices. METHODSFor the maize-intercropping study, red clover, sudangrass, phacelia, white mustard and Indian mustard were used as intercrops with grain maize and compared with a sole maize crop in a grain maize-winter wheat rotation under no-tillage or reduced tillage. For the cover cropping study, white mustard, Indian mustard and winter pea were used as interval cover crops in a silage maize-spring wheat rotation under no-tillage and compared with treatments without a cover crop, i.e. herbicide or plough applied after silage maize. The incidence of Fusarium head blight causing species and the accumulation of mycotoxins in grains of wheat as well as the crop yield were monitored. In addition, an economic assessment was conducted by calculating the receipts, operating costs and gross margin for each cropping system. RESULTS AND CONCLUSIONSGrowing intercrops with maize or interval cover crops in a maize-wheat rotation under reduced tillage decreased mycotoxins in wheat while maintaining wheat yield. The use of white mustard or Indian mustard as intercrops reduced deoxynivalenol in winter wheat by up to 52% compared with maize grown as a sole crop. The use of white mustard, Indian mustard or winter pea as interval cover crops also reduced deoxynivalenol and improved yield in spring wheat by up to 85% and 25%, respectively. Remarkably, the toxin reduction through these cover crops was comparable with that obtained by ploughing. However, due to increased operating costs, we observed economic trade-offs in these innovative cropping systems, i.e. 7–25% reduced gross margin over the entire rotation. SIGNIFICANCEBoth cereal growers and consumers can benefit from the recommended practices, which considerably lower the risk of mycotoxin contamination in harvest products while maintaining crop yield. To address the economic trade-offs, policy makers should support innovation in cropping systems, enhancing food safety while also ensuring the economic viability of cereal production systems.

Partitioning nocturnal respirations and their respective δ13C signatures in a wheat–maize rotation

We conducted a four-year in situ experiment using chamber, eddy covariance, and mass spectrometry methods to partition nocturnal respiratory components (Fr, ecosystem respiration; Frs, soil respiration; Frsh, heterotrophic respiration; Fraa and Frab, above and below ground autotrophic respirations) and their respective carbon isotopic signatures (δr, δrs, δrsh, δraa, and δrab) in a wheat–maize rotation in the North China Plain. The annual patterns in Fr, Frs, Fraa, and Frab showed a bimodal curve in response to plant development, nitrogen fertilization, irrigation and precipitation events. Frs, Frsh, Fraa and Frab accounted for 43.4, 13.5, 56.6 and 29.9 % of Fr in the wheat season and 34.0, 15.2, 66.0 and 18.8 % of Fr in the maize season, respectively. The annual values of Fr, Frs, Frsh, Fraa, and Frab in the maize season were 2.18, 1.71, 2.45, 2.54, and 1.37 times those in the wheat season, respectively. In comparison, the annual values of δr, δrs, δrsh, δraa, and δrab in the wheat season were 5.84, 10.4, 9.84, 9.63, and 11.6 % more depleted than those in the maize season, respectively. The δraa and δrab means in the wheat (C3) season significantly depleted than those in the maize (C4) season due to the different photosynthetic carbon metabolisms in the two systems. Hysteretic response (2-3 hours) where soil temperature leads soil respiration was found, suggesting a causal role of temperature in the relationship. Higher soil temperature and water filled pore space (≥ 50 %) depleted δ13CO2 signatures. Overall, this study revealed the carbon balance of nocturnal respiratory components and their respective δ13CO2 signatures in a wheat-maize rotation.

Deciphering microbial mechanisms underlying soil organic carbon storage in a wheat-maize rotation system

A link between microbial life history strategies and soil organic carbon storage in agroecosystems is presumed, but largely unexplored at the gene level. We aimed to elucidate whether and how differential organic material amendments (manure versus peat-vermiculite) affect, relative to sole chemical fertilizer application, the link between microbial life history strategies and soil organic carbon storage in a wheat-maize rotation field experiment. To achieve this goal, we combined bacterial 16S rRNA gene and fungal ITS amplicon sequencing, metagenomics and the assembly of genomes. Fertilizer treatments had a significantly greater effect on microbial community composition than aggregate size, with soil available phosphorus and potassium being the most important community-shaping factors. Limitation in labile carbon was linked to a K-selected oligotrophic life history strategy (Gemmatimonadetes, Acidobacteria) under sole chemical fertilizer application; defined by a significant enrichment of genes involved in resource acquisition, polymer hydrolysis, and competition. By contrast, excess of labile carbon promoted an r-selected copiotrophic life history strategy (Cytophagales, Bacillales, Mortierellomycota) under manure treatment; defined by a significant enrichment of genes involved in cellular growth. A distinct life history strategy was not observed under peat-vermiculite treatment, but rather a mix of both K-selected (Acidobacteria) and r-selected (Actinobacteria, Mortierellomycota) microorganisms. Compared to sole chemical fertilizer application, soil organic carbon storage efficiency was significantly increased by 26.5% and 50.0% under manure and peat-vermiculite treatments, respectively. Taken together, our results highlight the importance of organic material amendments, but in particular a one-time peat-vermiculite application, to promote soil organic carbon storage as a potential management strategy for sustainable agriculture.

Effects of tillage and fertility on soil nitrogen balance and greenhouse gas emissions of wheat-maize rotation system in Central Henan Province, China.

Energy saving, emission reduction, and efficiency improvement are important directions for agricultural development in Central Henan Province, the main grain production area in the Huang-huai-hai Plain. Based on the tillage and fertilization positioning experiment in 2010, we investigated the effects of three tillage methods (deep tillage, shallow tillage, and no-tillage) and two fertilization methods (nitrogen fertilizer and nitrogen fertilizer+organic fertilizer) on soil nitrogen balance and greenhouse gas emissions from 2018 to 2019. The results showed that soil nitrogen accumulation increased with organic fertilizer addition. During wheat and maize maturation, soil total nitrogen accumulation in the 0-60 cm layer was the highest under the treatment of shallow tillage+organic fertilizer, being 8058.53 and 8299 kg N·hm-2, respectively, being 3.2%-27.4% and 4.3%-7.2% higher than other treatments. The treatment with organic fertilizer addition resulted in nitrogen surplus. The shallow tillage+organic fertilizer treatment led to the highest nitrogen surplus (13.57 kg N·hm-2), which was 9.52 and 0.18 kg N·hm-2 higher than deep tillage+organic fertilizer and no tillage+organic fertilizer treatments. Nitrate leaching was the main way of nitrogen losses, accounting for 73.4%-76.9% of the total losses. The amount of nitrate leaching was the highest in deep tillage+organic fertilizer treatment (48.37 kg N·hm-2), being 18.9%-35.1% higher than other treatments. Results of greenhouse gases emission during 2018-2019 showed that global warming potential was the highest under the treatment of deep tillage+organic fertilizer, which was 33070 kg N·hm-2, being 6.6%-26.8% higher than other treatments. The treatment of organic fertilizer addition increased the emission of N2O and CO2 and reduced the absorption of CH4. The annual grain yield was highest under the treatment of deep tillage+organic fertilizer, which was 5.0%-17.1% higher than other treatments. The crop harvest index was the highest under the treatment of shallow tillage+organic fertilizer. The recommended cropping mode in Central Henan Pro-vince is shallow tillage+organic fertilizer, which could ensure crop yields, maintain soil nitrogen balance, and reduce greenhouse gas emissions.

Fifteen-year Variations of Water Use Efficiency over a Wheat-Maize Rotation Cropland in the North China Plain

Based on fifteen-year observations, we explored the interannual variations of five water use efficiency (WUE) indicators (i.e., standard ecosystem WUE (EWUE), plant-canopy WUE (PWUE), inherent WUE (IWUE), underlying WUE (uWUE) and stomatal slope (G1)) over a typical winter wheat-summer maize rotation cropland in the North China Plain. The results showed that none of WUE indicators had a significant interannual trend. PWUE showed the lowest interannual variability and could be regarded as stationary for these two crops. G1 was stationary for wheat which was under an essentially constant soil water condition, whereas exhibited a strong fluctuation for maize experiencing more variable soil water content (SWC) than wheat. IWUE and uWUE were non-stationary for both crops. SWC and leaf area index (LAI) dominated EWUE for maize and wheat, respectively. PWUE was dominated by the shortwave solar radiation (Rg) in maize seasons and not significantly affected by any meteorological or biophysical factors in wheat seasons. For IWUE and uWUE, air temperature (Ta) and LAI were the most important drivers in maize and wheat seasons, respectively. Atmospheric CO2 concentration (Ca) and vapor pressure deficit (VPD) were not revealed as important controllers. These findings reflected that the meteorological and biophysical regulatory mechanisms of WUE indicators at the ecosystem level were quite different from that at the leaf level. But G1 was an exception due to that for both maize and wheat, G1 was only significantly affected by SWC. Moreover, we found that none of the remote sensing (RS)-based global products performed satisfactorily on capturing interannual variations of EWUE for both crops. These results cautioned that using these global RS-based products to explore the interannual variations of EWUE for the cropland ecosystem may lead to substantial bias.

Combined Urea Humate and Wood Vinegar Treatment Enhances Wheat–Maize Rotation System Yields and Nitrogen Utilization Efficiency Through Improving the Quality of Saline–Alkali Soils

We aimed to investigate the effect of combining urea humate and wood vinegar on the improvement of saline soils and the yield of wheat and maize. The following seven treatments were designed and conducted for 2 years, a no nitrogen fertilizer (CK) treatment, and a further six treatments consisting of a combination of three rates of urea humate (H0: no urea humate; H1: 50% urea humate; H2: 100% urea humate) and two rates of wood vinegar as a foliar fertilizer (W0: no wood vinegar; W1: 90 L ha−1 wood vinegar). The results indicated that the wood vinegar treatment increased wheat yields by 12.4–44.3% and maize yields by 6.8–13.7% and that 100% urea humate application increased wheat yields by 8.1–38.0% and maize yields by 3.5–9.7%. Furthermore, nitrogen use efficiency was significantly improved with the combined application of humic acid urea and wood vinegar. Compared with the no urea humate treatment (H0), at the end of the 2-year field trial, microbial biomass carbon and nitrogen increased by 9.8–24.9% and 18.1–29.2%, respectively, urease activity decreased by 16.6–25.0%, and mineral nitrogen (NH4+-N and NO3--N) content increased in the 0–40 cm soil layer. Collectively, our findings thus indicate that the combined application of urea humate and wood vinegar can increase the yields and nitrogen fertilizer utilization of rotation wheat and maize, although the extent of these increases differed according to the amount of urea humate input.

Arbuscular mycorrhizal fungal communities of topsoil and subsoil of an annual maize-wheat rotation after 15-years of differential mineral and organic fertilization

Arbuscular mycorrhizal fungi (AMF) could improve crop yield by nutrient uptake from soil. However, how AMF of topsoil and subsoil respond to long-term differential application of mineral and organic fertilizers and how they are influenced in presence of different crops and growth stages have never been assessed together. Next generation sequencing was applied to profile soil AMF communities in both topsoil and subsoil from a typical arable soil (Eutric Regosol) in the Sichuan Base, southwest China. Soils were collected at anthesis and harvest of winter wheat and maize after 15-years of differential fertilization of an annual maize-wheat rotation (same inputs of nitrogen, N; but different in carbon, C; phosphorus, P; and potassium, K): (i) no-fertilization control (CT), (ii) 100% mineral NPK fertilizer (NPK), (iii) 60% mineral N and 100% mineral PK plus 40% N as crop residues (NPKCR); and (iv) 60% mineral N and 100% mineral PK plus 40% N as pig (organic) manure (NPKOM). Compared to CT, AMF diversity significantly decreased in topsoil, but increased in subsoil for both wheat and maize under NPK, NPKCR and NPKOM. The AMF community composition differed between NPK and CT in both topsoil and subsoil of maize and wheat. Both distance-based redundancy analysis (db-RDA) and structural equation modeling (SEM) suggested that AMF communities in topsoil and subsoil of maize and wheat responded in differences in soil available P, soil organic carbon, fertilization and climate (temperature and/or rainfall). Fertilization and available N, not AMF community, had significantly positive effects on wheat and maize aboveground dry matter and grain yield. Results from the present study shed light on how AMF communities in topsoil and subsoil respond to different soil fertility management over the long-term. Insights of this study are valuable in managing an important part of biological soil fertility.

Response of soil bacterial communities, antibiotic residuals, and crop yields to organic fertilizer substitution in North China under wheat–maize rotation

Manure application can benefit soil quality and sustainable food productivity, but overapplication can spread high levels of antibiotics and antibiotic resistance genes. A two-year field experiment was conducted to evaluate the comprehensive impacts of organic fertilizer substitution in North China under a wheat–maize rotation. Four treatments were conducted: control (ZF), mineral fertilizer (MF), 50% nitrogen (N) mineral fertilizer substituted with organic fertilizer (MOF), and organic fertilizer (OF). Sulfonamide content, abundance of sulfonamide resistance (sul) genes, soil bacterial community, crop yield, and grain mineral elements were analyzed. Results showed that the MOF and OF treatments increased grain nutrients (phosphorus, potassium), and enriched sulfonamide residue and sul genes in soil. Additionally, the relative abundances of sul1 and sul2 in MOF and OF soils planted with maize were higher than in those planted with wheat. Compared to MF, the OF treatment decreased soil pH and crop yields but increased soil total nitrogen, phosphorus contents, and the abundance of Firmicutes. However, the MOF treatment significantly increased soil bacterial diversity and maintained yields of both wheat and maize. Increases in potential sul genes source bacteria (Planifilum), antibiotics, and soil nutrients accelerated the spread of sul genes in soil. Partial least squares path modeling analysis indicated that the soil bacterial diversity had a strong positive effect on maize yield. These results indicate that substitution of 50% N mineral fertilizer with organic fertilizer has the potential to benefit the stability and sustainability of the soil ecosystem, helping to meet the food demand in North China. However, the risk of antibiotics should be reduced through technical advances.

Crop development has more influence on shaping rhizobacteria of wheat than tillage practice and crop rotation pattern in an arid agroecosystem

Root-associated bacteria are studied under a single agricultural measure, but the responses of rhizosphere bacterial communities toward agricultural management, in an arid agroecosystem, are unclear. Here, we evaluated the effects of tillage practice, crop rotation pattern, and crop development on rhizobacteria in a field experiment in the dryland region of northern China. Three tillage [chisel plow tillage (conservation), zero tillage (conservation), and plow tillage (conventional)] practices and two crop rotation (maize–wheat rotation and soybean–wheat rotation) patterns were been combined to assess changes in rhizosphere bacterial communities during wheat development. Our results showed that conservation tillage practices had considerable effects on soil physicochemical properties compared with conventional tillage, thus changing the rhizosphere microenvironment. Spearman's correlation analysis also indicated that soil physicochemical properties were closely related to the relationships among the rhizosphere bacterial communities and taxa. Furthermore, the composition and α-diversity of the rhizosphere bacterial communities were substantially affected by the crop growth stage and tillage practices; however, the legacy effect of the previous crop had different effects on the rhizosphere bacterial communities owing to the short period of implementing crop rotation. The phylogenetic diversity and taxonomic composition of rhizosphere bacterial communities were mainly explained by the crop growth stage and tillage practice, respectively. Additionally, conservation tillage practices and soybean–wheat rotation pattern both delayed rhizobacteria successions. Co-occurrence networks also showed that the differential modules among the rhizosphere bacterial communities decreased with wheat development, whereas the soybean–wheat rotation pattern increased their degree of co-occurrence. The differences in taxonomic compositions and phylogenetic diversities of the rhizosphere bacterial communities may affect their potential functions and alter crop growth and development.

Does continuous straw returning keep China farmland soil organic carbon continued increase? A meta-analysis

The straw returning technique is one of the important measures for soil carbon sequestration and soil organic carbon (SOC) promotion in the world. However, the patterns of straw utilization in China with various methods among regions, the effect and variability of straw returning on SOC in different areas of China remain uncertain. We conducted a meta-analysis of 446 sets of data from 95 studies in China field to explore how the environmental factors and field management affect SOC after straw returning. The results showed that straw returning to the field significantly increase SOC content by an average of 13.97% (n = 446). The SOC increased effects are more obvious under areas with mean annual precipitation (MAP) > 500 mm, temperature (MAT) > 10 °C, loam or sandy soil, or the initial SOC content <10 g kg−1. The effect of straw returning on SOC also depends on planting systems, ranging from 5.43% of rice continuous cropping to 17.05% of the maize-wheat ration. In the rotation system, the SOC increasing effect under paddy-wheat rotation (15.79% in rice and 14.87% in wheat season) was more significant than under wheat-maize rotation (17.05% in wheat and 11.81% in maize season). The proper duration of straw returning is 6–9 years, while it will decrease SOC by 17.06%–20.05% more than 10 years. Moreover, the effects of straw returning under the conditions with deep tillage, the amount of straw more than 9000 kg ha−1, or combined pure N with 180–240 kg N ha−1 were better than other methods.