Peanut-based Rotation Stabilized Diazotrophic Communities and Increased Subsequent Wheat Yield.

The introduction of legumes into rotations can improve nitrogen use efficiency and crop yield; however, its microbial mechanism involved remains unclear. This study aimed to explore the temporal impact of peanut introduction on microorganisms related to nitrogen metabolism in rotation systems. In this study, the dynamics of diazotrophic communities in two crop seasons and wheat yields of two rotation systems: winter wheat - summer maize (WM) and spring peanut → winter wheat - summer maize (PWM) in the North China Plain were investigated. Our results showed that peanut introduction increased wheat yield and biomass by 11.6% (p < 0.05) and 8.9%, respectively. Lower Chao1 and Shannon indexes of the diazotrophic communities were detected in soils that sampling in June compared with those sampling in September, although no difference was found between WM and PWM. Principal co-ordinates analysis (PCoA) showed that rotation system significantly changed the diazotrophic community structures (PERMANOVA; p < 0.05). Compared with WM, the genera of Azotobacter, Skermanella, Azohydromonas, Rhodomicrobium, Azospirillum, Unclassified_f_Opitutaceae, and Unclassified_f_Rhodospirillaceae were significantly enriched (p < 0.05) in PWM. Furthermore, rotation system and sampling time significantly influenced soil properties, which significantly correlated with the top 15 genera in relative abundance. Partial least squares path modeling (PLS-PM) analysis further showed that the diazotrophic community diversity (alpha- and beta-diversity) and soil properties (pH, SOC and TN) significantly affected wheat yield. In conclusion, legume inclusion has the potential to stabilize diazotrophic community structure at the temporal scales and increase subsequent crop yield.

Plant growth stages covered the legacy effect of rotation systems on microbial community structure and function in wheat rhizosphere.

Legume-based crop rotation is conducive to improve soil multifunctionality, but how the legacy effect of previous legumes influenced the rhizosphere  microbial community of the following crops along with growth stages remains unclear. Here, the wheat rhizosphere microbial community was assessed at the regreening and filling stages with four previous legumes (mungbean, adzuki bean, soybean, and peanut), as well as cereal maize as a control. The composition and structure of both bacterial and fungal communities varied dramatically between two growth stages. The differences in fungal community structure among rotation systems were observed at both the regreening and filling stages, while the difference in bacterial community structure among rotation systems was observed only at the filling stage. The complexity and centrality of the microbial network decreased along with crop growth stages. The species associations were strengthened in legume-based rotation systems than in cereal-based rotation system at the filling stage. The abundance of KEGG orthologs (KOs) associated with carbon, nitrogen, phosphorus, and sulfur metabolism of bacterial community decreased from the regreening stage to the filling stage. However, there was no difference in the abundance of KOs among rotation systems. Together, our results showed that plant growth stages had a stronger impact than the legacy effect of rotation systems in shaping the wheat rhizosphere microbial community, and the differences among rotation systems were more obvious at the late growth stage. Such compositional, structural, and functional changes may provide predictable consequences of crop growth and soil nutrient cycling.

Replacing chemical fertilizer with manure reduces N2O emissions in winter wheat - summer maize cropping system under limited irrigation.

Nitrous oxide (N2O) emissions from agroecosystems are a major contributor to global warming and stratospheric ozone depletion. However, knowledge concerning the hotspots and hot moments of soil N2O emissions with manure application and irrigation, as well as the underlying mechanisms remain incomplete. Here, a 3-year field experiment was conducted with the combination of fertilization (no fertilizer, F0; 100% chemical fertilizer N, Fc; 50% chemical N + 50% manure N, Fc + m; and 100% manure N, Fm) and irrigation (with irrigation, W1; and without irrigation, W0; at wheat jointing stage) for winter wheat - summer maize cropping system in the North China Plain. Results showed that irrigation did not affect annual N2O emissions of the wheat-maize system. Manure application (Fc + m and Fm) reduced annual N2O emissions by 25-51% compared with Fc, which mainly occurred during 2 weeks after fertilization combined with irrigation (or heavy rainfall). In particular, Fc + m reduced the cumulative N2O emissions during 2 weeks after winter wheat sowing and summer maize top dressing by 0.28 and 0.11 kg ha-1, respectively, compared with Fc. Meanwhile, Fm maintained the grain N yield and Fc + m increased grain N yield by 8% compared with Fc under W1. Overall, Fm maintained the annual grain N yield and lower N2O emissions compared to Fc under W0, and Fc + m increased the annual grain N yield and maintained N2O emissions compared with Fc under W1, respectively. Our results provide scientific support for using manure to minimize N2O emissions while maintaining crop N yield under optimal irrigation to support the green transition in agricultural production.

Silver lining to a climate crisis in multiple prospects for alleviating crop waterlogging under future climates.

Extreme weather events threaten food security, yet global assessments of impacts caused by crop waterlogging are rare. Here we first develop a paradigm that distils common stress patterns across environments, genotypes and climate horizons. Second, we embed improved process-based understanding into a farming systems model to discern changes in global crop waterlogging under future climates. Third, we develop avenues for adapting cropping systems to waterlogging contextualised by environment. We find that yield penalties caused by waterlogging increase from 3-11% historically to 10-20% by 2080, with penalties reflecting a trade-off between the duration of waterlogging and the timing of waterlogging relative to crop stage. We document greater potential for waterlogging-tolerant genotypes in environments with longer temperate growing seasons (e.g., UK, France, Russia, China), compared with environments with higher annualised ratios of evapotranspiration to precipitation (e.g., Australia). Under future climates, altering sowing time and adoption of waterlogging-tolerant genotypes reduces yield penalties by 18%, while earlier sowing of winter genotypes alleviates waterlogging by 8%. We highlight the serendipitous outcome wherein waterlogging stress patterns under present conditions are likely to be similar to those in the future, suggesting that adaptations for future climates could be designed using stress patterns realised today.

Soybean Crops Penalize Subsequent Wheat Yield During Drought in the North China Plain.

Contemporary wisdom suggests that inclusion of legumes into crop rotations benefit subsequent cereal crop yields. To investigate whether this maxim was generically scalable, we contrast summer soybean-winter wheat (SW) with summer maize-winter wheat (MW) rotation systems in an extensive field campaign in the North China Plain (NCP). We identify heretofore unseen interactions between crop rotation, synthetic N fertilizer application, and stored soil water. In the year with typical rainfall, inclusion of soybean within rotation had no effect on wheat ear number and yield, while N fertilization penalized wheat yields by 6-8%, mainly due to lower dry matter accumulation after anthesis. In contrast, in dry years prior crops of soybean reduced the rate and number of effective ears in wheat by 5-27 and 14-17%, respectively, leading to 7-23% reduction in wheat yield. Although N fertilization increased the stem number before anthesis in dry years, there was no corresponding increase in ear number and yield of wheat in such years, indicating compensating reduction in yield components. We also showed that N fertilization increased wheat yield in MW rather than SW as the former better facilitated higher dry matter accumulation after flowering in dry years. Taken together, our results suggest that soybean inclusion reduced soil available water for subsequent wheat growth, causing yield penalty of subsequent wheat under drought conditions. We call for more research into factors influencing crop soil water, including initial state, crop water requirement, and seasonal climate forecasts, when considering legumes into rotation systems. Graphical AbstractResponse of wheat population and yield to soybean inclusion under limited-irrigation.

Do cropping system and fertilization rate change water-stable aggregates associated carbon and nitrogen storage?

Soil aggregates not only store carbon (C) and nitrogen (N) but hold a critical role in determining the nutrients supply, crop productivity, and climate change mitigation. However, the impact of cropping system and N fertilization on aggregate-associated C and N in both topsoil and subsoil remains unclear. Here, we assessed the effect of cropping systems (wheat-soybean vs. wheat-maize cropping systems) and N fertilization rates (0 N; medium N, 120 kg N ha-1; high N, 240 kg N ha-1) on soil water-stable aggregates distribution, as well as aggregate-associated C and N based on a field study in North China Plain. Our study suggests that the variations of soil organic carbon (SOC) and total nitrogen (TN) stocks were more affected by N fertilization than short-term cropping systems. In the wheat-soybean system, medium N increased the SOC stock by 19.18% and 15.73% as compared to high N in the topsoil and subsoil, respectively. Additionally, medium N resulted in 6.59-18.11% higher TN stock in the topsoil for both wheat-soybean and wheat-maize cropping systems as compared to 0 N and high N. Notably, the water-stable macroaggregates (> 0.25 mm) in the topsoil occupied more than 70% of the soil, which increased under medium N in the wheat-soybean cropping system. In conclusion, medium N fertilization combined with a legume-based cropping could be used to improve SOC stock, promote soil aggregation, and enhance aggregate-associated C.

Methane emissions responding to Azolla inoculation combined with midseason aeration and N fertilization in a double-rice cropping system.

Methane (CH4) is an important greenhouse gas (GHG), and paddy fields are major sources of CH4 emissions. This pot experiment was conducted to investigate the integrated effects of Azolla inoculation combined with water management and N fertilization on CH4 emissions in a double-rice cropping system of Southern China. Results indicated that midseason aeration reduced total CH4 emissions by 46.9%, 38.6%, and 42.4%, followed by N fertilization with 32.5%, 17.0%, and 29.5% and Azolla inoculation with 32.5%, 17.0%, and 29.5%, on average, during the early, late, and annual rice growing seasons, respectively. The CH4 flux peaks and total CH4 emissions observed in the late rice growing season were significantly higher than those in the early rice growing season. Additionally, CH4 fluxes correlated negatively to soil redox potential (Eh) and dissolved oxygen (DO) concentration. Azolla inoculation and N fertilization greatly increased the rice grain yields, whereas midseason aeration had distinct effects on grain yields in both rice seasons. The highest annual rice grain yields of approximately 110 g pot-1 were obtained in the Azolla inoculation and N fertilization treatments. In terms of yield-scaled CH4 emission, Azolla inoculation combined with midseason aeration and N fertilization generated the lowest yield-scaled CH4 emissions both in the early and in the late rice growing seasons, as well as during the annual rice cycle. In contrast, the highest yield-scaled CH4 emission was obtained in the treatment employed continuous flooding, without Azolla and no N application. Our results demonstrated that Azolla inoculation, midseason aeration, and N fertilization practices mitigated total CH4 emissions by 18.5-42.4% during the annual rice cycle. We recommend that the combination of Azolla inoculation, midseason aeration, and appropriate N fertilization can achieve lower CH4 emissions and yield-scaled CH4 emissions in the double-rice growing system.