Nutrient Inputs Research Articles

Menvironmental impacts of crop production systems in subtropical plateau regions: case study of Yunnan, China

Excessive fertilisation, improper nutrient management, and specific climatic factors are the main reasons for the high environmental risks associated with agricultural production in subtropical plateau regions. However, quantitative data of environmental impacts and emission reduction potential remain unclear. The development potential of such systems is likely to be significant. In that context, we conducted a case study in Yunnan Province, China, to quantify the environmental impact of crop production from 2002 to 2021. A life cycle assessment method was employed to identify the factors driving environmental impacts, and potential mitigation strategies were proposed. The yield and total nutrient input of grain crops in Yunnan Province increased over the 20-year period, and the environmental footprint of crop production in Yunnan Province was higher than that in other regions. The average annual mean greenhouse gas (GHG) emissions, soil acidification potential (AP), and water eutrophication potential (EP) of crop production from 2002 to 2021 were 837 kg CO2-eq·Mg−1, 15.7 kg SO2-eq·Mg−1, and 2.71 kg PO4-eq Mg−1, respectively. Environmental emissions from crops mainly originate from the application of agricultural inputs (including fertilisers (N, P, and K), pesticides, seed, diesel fuels, and plastic film) during the crop life cycle. There was a significant correlation between surplus nitrogen and environmental impacts. Scenario testing showed that optimised nutrient management practices could increase crop yield and reduce environmental costs. GHG emissions, AP, and EP from the production of rice, wheat, and maize are expected to decrease by 43.0–59.5%, 51.5–64.5%, and 57.4–71.5%, respectively (scenario 4, S4). Based on these findings, we propose that com-prehensive agricultural management measures can reduce the negative impacts of crop production on the environment in subtropical plateau areas and help achieve sustainable agricultural development.

A Comparative Evaluation of Biostimulants on Growth and Yield of Finger Millet (Eleusine coracana L. Gaertn.) in the Red Lateritic Region of West Bengal, India

Finger millet (Eleusine coracana L. Gaertn.), an ancient crop cultivated in India since 2300 BC, is highly valued in traditional production systems for its role in alleviating malnutrition, with a rich nutritional profile comprising 9.2% protein, 1.29% fat, 76.32% carbohydrates, and the highest calcium (344 mg%) and potassium (408 mg%) content among all cereals and millets. The present experiment entitled on “A Comparative Evaluation of Various Biostimulants on Finger Millet (Eleusine coracana L. Gaertn.) Growth and Yield in the Red Lateritic Region of West Bengal” was conducted during kharif season of 2022 at Farmers’ field, Chandrakona, Paschim Medinipur, West Bengal. The experiment was laid out in Randomized Block Design replicated thrice consisting of 6 treatments [T1: RDF (Recommended Dose of Fertlizes) + Seaweed Extracts at 0.2%, T2: RDF + Moringa Extracts at 2%, T3: RDF + Protein Hydrolysates & Amino acids at 0.2%) T4: RDF + Fulvic acid substances at 0.2%, T5: RDF + Panchagavya at 3%, T6: RDF (N: P: K- 30:15:15 kg ha-1)]. The objective of this study is to find out the effect of foliar nutrition on growth and yield attribute of Finger millets. The grain and straw yield of finger millet as influenced by different treatments are found to be significant. Foliar spray of nutrition has resulted variable yield differences among the treatments. The highest grain yield 26.19 q.ha-1 and straw yield 34.70 q.ha-1 were recorded by RDF + Protein Hydrolysates & Amino acids at 0.2% followed by T1 with the values of 25.12 q.ha-1 and 31.56 q.ha-1 respectively. From the above investigation it was evident that the foliar application of various biostimulants on finger millets had a positive impact on growth and yield, especially in nutrient-stressed soils. In this context, the present study aims to assess the feasibility and performance of finger millet cultivation with minimal nutrient input and the application of biostimulants in various combinations.

EFFECTS OF POULTRY LITTER ON SOIL PHYSICO-CHEMICAL PROPERTIES FOR CROP PRODUCTION IN KAURU LOCAL GOVERNMENT AREA, KADUNA STATE, NIGERIA

Poultry litter is an important source of soil nutrients that supports beneficial soil bacteria by serving as a substrate, however, its excessive have adverse effects that lead to soil pollution, contamination and acidification of soil and groundwater. This study analyzed the effects of poultry litter on soil physico-chemical properties for crop production in Kauru Local Government Area, Kaduna State, Nigeria. Data on soil properties at the control and poultry littered sites were collected by sampling four farmlands in Barwa, Ungwan Noma, Kurmin-Shado and Dan-Daura and analyzed in the laboratory. Results were subjected to ANOVA and Correlation analyses tools. The findings revealed significant changes in soil physico-chemical properties due to excessive poultry litter application. Compared to the control site, treated soil showed increased pH (6.26 to 6.89), decreased organic carbon (4.29 to 3.63), increased organic matter (5.92 to 6.99), increased total nitrogen (0.49 to 0.58), altered particle size distribution (clay, silt, sand), reduced aggregate, stability (0.818 to 0.715) and increased CO2 (64.8 to 65.88%). Also, Correlation analysis revealed a significant relationship between poultry litter application and soil physico-chemical properties (Sig. value >0.05), indicating that poultry manure significantly alters soil parameters. The study concludes that while some of the soil properties identified were within safe limits, application of poultry manure altered other properties of the soil. Thus, the study recommends that farmers should use poultry litter in conjunction with other fertilizers and soil amendments to balance nutrient inputs.

Seasonal nitrogen sources and its transformation processes revealed by dual-nitrate isotopes in Xiamen Bay, China

The eutrophication load in coastal waters is gradually increasing due to excessive nitrate (NO3−) input caused by intense human activities. The tracing of NO3− sources as well as their biogeochemistry is crucial for the development of effective measures to alleviate the eutrophication load. In this study, seasonal seawater samples from Xiamen Bay were investigated to explore the sources and fates of NO3− using dual nitrate isotopes. The results indicated that the NO3− is less affected by biological processes and mainly influenced by the terrestrial sewage discharges (48%) during rainy seasons. Contrarily, as runoff input decreases and external seawater intrusion increases, the assimilation of phytoplankton dominates the process of nitrate removal during dry seasons. This study suggests that the increase in the input of terrestrial sewage nutrients is responsible for the increase in eutrophication in Xiamen Bay, providing a basis for controlling water eutrophication and regional environmental governance.

Comparative analysis of population parameters of the vendace <i>Coregonus albula</i> (Salmonidae, Coregoninae) in lake Samozero in different habitat conditions

The results of long-term studies of the dynamics of population parameters of the vendace Coregonus albula in Lake Syamozero in periods with different habitat conditions are presented. The vendace is the most abundant fish species in the lake and was the main object of commercial fishing for 39 years (1932-1970) (60% of the total catch). From 1971 until 2000, the input of nutrients into the lake increased significantly due to high human economic activity in the catchment area. This led to a change in the hydrochemical and hydrobiological regimes of the lake. As a result, favorable conditions were created for vendace feeding. The biomass of zooplankton which is the main component of its diet, increased fivefold from 1950 to 2000 (from 0.4 to 2.1 g/m3). However, the conditions of reproduction of vendace significantly worsened due to siltation of spawning grounds, which led to the mortality of eggs during a long period of its embryogenesis (6-7 months). The decrease in the vendace abundance in 1971-2000 was also caused by the accidental penetration of a new species, the European smelt Osmerus eperlanus into the lake. For a long time (about 15 years) vendace was not found either in catches or in the diet of predatory fish species of the lake. In recent years, as a result of a decrease in the impact of human activity on the lake and the disappearance of the smelt in 2015 due to its infection with the parasite, the vendace population has begun to recover.

Effect of intra-row spacing, gibberellic acid concentration and N:P<sub>2</sub>O<sub>5</sub>:K<sub>2</sub>O ratio on growth and yield of potato variety Royal

The potato variety Royal is suitable to make French fries due to its frying qualities. However, the tubers lack the long-oval shape which is preferred in processing of French fries. Despite the lower nitrogen (N) requirement of variety Royal, farmers apply same recommendation ignoring the varietyspecific needs. Thus, two experiments were conducted to (a) evaluate the possibility of changing tuber shape by manipulating intra-row spacing and gibberellic acid (GA3) application and to (b) identify the best N:P2O5:K2O ratio to optimize growth and yield. The first experiment was conducted with 45 cm inter-row spacing, as a two-factor factorial RCBD. Factors one and two were intra-row spacing (15, 20, 25, 30, and 35 cm) and foliar-applied GA3 concentration (0, 150, 200, and 250 ppm), respectively. In the second experiment, recommended N:P2O5:K2O ratio, 8.0:3.5:8.5, (Department of Agriculture, Sri Lanka) with organic manure (control) and the same without organic manure were compared with three other N:P2O5:K2O ratios. Each treatment had 4 replicates, with 12 plants per replicate in both experiments. Data were analysed with Two-Way ANOVA in the first experiment and One-Way ANOVA in the second, using Minitab 17. Tukey’s mean comparison test was used to compare the mean values of both experiments. Intra-row spacing and GA3 interaction did not significantly (P>0.05) affect the tuber yield and shape. By increasing IRS, yield per plant increased, but yield per unit land area (YPL) decreased. The effect of GA3 on tuber yield was not significant (P>0.05). GA3 at 200 ppm recorded the highest number of long-oval tubers (62% increment). N:P2O5:K2O ratio had no significant (P>0.05) effect on growth, yield, and quality. Therefore, a fertilizer ratio with low nutrient input will be more sustainable and cost-effective for potato variety Royal with lower nutrient needs. Closer intrarow spacing (15 cm) with 200 ppm GA3 can be recommended for higher YPL with higher number of long-oval tubers.

Long-term organic matter inputs enhance soil health and reduce soil-borne pathogen pressure in maize-bean rotations in Kenya

In smallholder farming systems across East Africa, soil-borne pathogens lead to significant crop losses, with their impact shaped by various factors such as management practices and soil properties. We conducted our research within an existing long-term (45-year) trial that manipulated synthetic fertilizers (N and P applied vs. no application), manure application (10 Mg ha⁻¹ yr⁻¹ farmyard manure vs. no application), and maize stover management (retained vs. removed) in a full-factorial design within a maize–bean rotation. This study aimed to assess the impact of continuous organic nutrient inputs (farmyard manure and maize stover) and synthetic fertilizers on soil-borne pathogens (Fusarium, Pythium, root knot and lesion nematodes) and their relationships with key soil health parameters (organic matter fractions, aggregate stability, available P, soil pH, bulk density). Our results indicated that the addition of manure led to increases of 37 % in particulate organic matter, 114 % in permanganate oxidizable C, 74 % in aggregate stability, and 24 % in pH, compared to plots that did not receive manure. Similarly, maize residue retention enhanced particulate organic matter by 47 %, permanganate oxidizable C by 11 %, mean weight diameter by 28 %, and pH by 5 %. Manure significantly reduced root knot nematodes by 68 %, Pythium colonies by 39 %, and lesion nematodes by 28 %, but increased Fusarium by 205 %. In contrast, the impacts of synthetic fertilizers on soil health were less pronounced, with significant effects observed only for permanganate oxidizable C (5 % increase), available P (67 % increase), and Pythium (41 % reduction). Additionally, relationships between soil-borne pathogens and soil health variables indicated significant negative associations between particulate organic matter, permanganate oxidizable C, and pH with the abundance of plant parasitic nematodes and Pythium, but a positive association with Fusarium. Pythium and lesion nematodes were positively associated with bulk density. Our findings suggest that both manure and plant residue retention hold great promise for supporting long-term soil health and fertility, which can, in turn, reduce the impact of soil-borne pathogens on crop yields. This is a major challenge for low-income farmers in Kenya who practice continuous cultivation.

Enhanced warming and bacterial biomass production as key factors for coastal hypoxia in the southwestern Baltic Sea

Coastal ecosystems are affected by a multitude of anthropogenic stressors. As the Baltic Sea ecosystems rank among the most altered marine ecosystems worldwide, they represent ideal model regions to study ecosystem responses to anthropogenic pressures. Our statistical analysis of data including dissolved organic carbon and nitrogen, as well as bacterial abundance and -biomass production from the time-series station Boknis Eck in the southwestern Baltic Sea reveals that bacterial biomass production intensifies towards summer following the phytoplankton spring bloom. Moreover, warming, especially very high temperatures in summer, enhances stratification and bacterial biomass production despite long-term reduction in nutrient input. A strong decrease in oxygen in the bottom layer is possibly linked to this. We detect an increasing trend in bacterial biomass production along with intensifying warming and stratification, and more frequently occurring hypoxia despite ongoing restoration efforts. If this trend continues, the coastal Baltic Sea ecosystem is likely to be altered even further. Coastal ecosystems play pivotal roles in mitigating impacts of climate change but if destroyed, they may amplify climate change further calling for stronger ecosystem management strategies.

Management implications following the reconstruction of the small and shallow Lake Mustijärv (Estonia)

Lake Mustijärv was reconstructed by sediment removal following an almost complete siltation. Here we evaluate challenges and opportunities for the management of the lake. We focused on the stream discharging to the lake (i.e., external loading), sediment retention in accumulation basins (i.e., internal processes) as well as the ecosystem-level response to stressors based on biological variables (phyto- and zooplankton, macrophytes, fishes and zoobenthos). Urban and agricultural inputs elevated ammonium and total phosphorus concentrations in the lake, challenging lake reconstruction efforts. Sediment transport highly increased the risk of faster filling of the lake, associated with upstream streambed excavation. Sediments trapped at the accumulation basins release nutrients that enhance eutrophication. We, however, observed a rapid recovery in fish, macrophytes, and zoobenthos, despite the significant disturbances. Lake Mustijärv is in eutrophic condition, reflected by phytoplankton (Pseudanabaena, Closteriopsis dominance) and zooplankton (Keratella, Polyarthra dominance) composition. To improve lake water quality will require controlling external nutrient inputs, underlining the importance of better coordinated activities between the local (lake restoration) and regional (catchment use) scales.

Human settlement and destructive activities disrupt the positive contribution of dust to plant biomass growth over the past 2000 years

The dual pressures of global warming and increased anthropogenic activities pose significant threats to terrestrial vegetation ecosystems. To better understand the impacts of climate change and human activities on terrestrial vegetation ecosystems, we reconstructed the changes in vegetation and plant biomass over the past 4500 years using n-alkane records from sediments of two alpine lakes in northwestern China: Xiannv Lake and Tianchi Lake. Our results indicate that changes in the spatial variability of plant biomass are not related to temperature and precipitation. Furthermore, CO2 fertilization and nutrient inputs from dust contributed to the observed changes in plant biomass. We also compared the history of human activities in the Tianshan Mountains, the eastern Silk Road, and the Hunsandak Sandy Land, and find that the demand for plant resources—whether for human settlement, military construction, or warfare—may have caused a sudden decline in terrestrial vegetation, thereby disrupting the positive effects of dust on plant biomass growth.

Fruit traits of different variants of Zanthoxylum planispinum var. dingtanensis in the karst plateau valley area of Guizhou Province, Southwest China.

Many studies have shown that seed traits, which are among the most important plant traits, can be inherited stably, a finding which is of great value for the improvement of seed germination, seed propagation, seedling establishment, plant breeding, and ecological restoration. The differences in phenotype and nutritional traits and their interactions in Zanthoxylum planispinum var. dingtanensis were ascertained, and the nutrient input rule and the strategy of resource balancing were analyzed in order to provide a scientific basis for the screening of improved variants of the test plant. The nutrient distribution with in the tissues of Z. planispinum var. dingtanensis fruit was that the pericarp had adequate concentrations of N and P concentrations and the seed was also sufficient in P, but low in N concentration. Inorganic nutrients were particularly invested in the pericarp, while organic nutrients are more likely to be stored in the seed. In the economic spectrum of seed traits, the large leaf Zanthoxylum variant represented the low-investment economic type, the tufted leaf Zanthoxylum variant represented the high-investment luxury type, and the safflower Zanthoxylum and acutifoliate leaf Zanthoxylum variants represented transitional types. Inorganic nutrients were more invested in the pericarp to produce secondary metabolites, while organic nutrients are more likely to be stored in the seed to ensure seed germination and seedling establishment in order to achieve inheritance. The variants of Z. planispinum var. dingtanensis differ in terms of resource allocation and balance, which could be further exploited through combining characters in breeding programs.

Natural and Organic Input-Based Integrated Nutrient-Management Practices Enhance the Productivity and Soil Quality Index of Rice–Mustard–Green Gram Cropping System

The effects of integrated nutrient-management (INM) practices on soil quality are essential for sustaining agro-ecosystem productivity. The soil quality index (SQI) serves as a tool to assess the physical, chemical, and biological potential of soils as influenced by various edaphic and agronomic practices. A multiyear (2018–2021) field experiment was performed at the University Organic Research Farm, Narendrapur, West Bengal, India, to investigate the influence of integrated and sole applications of different conventional fertilizers, organic (e.g., vermicompost), and natural farming inputs (e.g., Dhrava Jeevamrit and Ghana Jeevamrit) on SQIs and crop productivity of rice–mustard–green gram-based cropping systems. A total of 12 parameters were selected for the assessment of SQI, amongst which only four, namely pH, organic carbon %, total actinomycetes, and bulk density, were retained for the minimum data set based on principal component analysis (PCA). In this study, the maximum SQI value (0.901) of the experimental soil was recorded in the INM practice of 25% organic and 25% inorganic nutrient inputs, and the rest with natural farming inputs, which augments the SQI by 24% compared to the 100% inorganic nutrient treatment. Amongst the different soil parameters, the highest contribution was from the pH (35.18%), followed by organic carbon % (26.77%), total actinomycetes (10.95%), and bulk density (6.98%). The yields in different cropping systems varied year-wise across treatments. Notably, the highest yield in rainy rice was estimated in the 100% organic treatment, followed by INM practices in the subsequent years, and finally, the combination of organic and natural inputs in the final year. In the case of mustard, the combination of organic and natural inputs resulted in the highest productivity in the initial and last years of study, while the 100% organic treatment resulted in higher productivity in subsequent years. Green gram showed a dynamic shift in yield between the 100% organic and integrated treatments over the years. Further, a strong correlation was also established between the soil physico-chemical parameters and the SQI. Overall, this study concludes that the natural and organic input-based INM practice enhances the soil quality and crop productivity of the rice–mustard–green gram cropping system under the coastal saline zone.

Plant and soil responses to sediment deposition and nutrient‐enrichment in healthy, deteriorating, and newly created coastal marshes of the Mississippi River Delta

Coastal marshes vulnerable to sea‐level rise may benefit from sediment amendments to increase elevation. However, nutrient‐loading to estuaries may counter elevation gain through reduced root production and/or increased decomposition. Here, we test if belowground plant productivity, root decomposition, and marsh accretion response to nutrient‐loading differs with sediment addition in three marsh types: a healthy intermediate salinity marsh, a deteriorating brackish marsh, and a created marsh in Barataria Basin, Louisiana, United States. In this region, wetland loss is rapid, and a major restoration project is underway to introduce Mississippi River water, sediment, and nutrients to offset marsh loss. Porewater nutrient concentrations, vegetation structure, belowground productivity and decomposition, and accretion rates were measured over 450 days. Experimental nitrate additions yielded high porewater ammonium‐N concentrations in the Deteriorating marsh but had a smaller effect in Healthy and Created marshes. Belowground productivity in the Deteriorating marsh was neutral to negatively affected by nutrient and sediment treatments, whereas positive effects occurred in Healthy and Created marshes. Despite elevation increase from sediment treatments, and substantial effects of nutrient treatments on porewater nutrient concentrations, belowground decomposition and surface accretion rates were not affected by treatments. Sediment deposition increased species richness in the Healthy marsh and added sediment and added nutrients with sediment increased plant height in the Created and Deteriorating marshes, respectively. Over the timescale measured, experimental sedimentation and pulsed nutrient input had few consistent effects on belowground ingrowth, decomposition, or surface accretion. Our findings highlight that response to nutrient pulses are complex and depend on baseline marsh conditions.

Simulated nitrogen deposition and precipitation events alter microbial carbon cycling during early stages of litter decomposition

Abstract Plant litter decomposition is a major nutrient input to terrestrial ecosystems that is primarily driven by microorganisms. Litter quality is considered a key drive of decomposition; however, human-induced global disturbance like nitrogen deposition and increasing extreme precipitation events will shift nutrient availability during litter decomposition. Little is known about how shifting nutrient availability will impact dissolved organic matter concentrations and microbially driven carbon cycling that are critical to soil organic matter formation. This study investigated the effect of simulated nitrogen deposition and repeated precipitation events on microbially-driven carbon flow during short-term litter decomposition using a ‘common garden’ experiment with microcosms containing sand and blue grama grass litter inoculated with different microbial communities. Overall, nitrogen deposition decoupled respiration and dissolved organic carbon (DOC) by increasing respiration and not affecting DOC concentrations. Moreover, nitrogen deposition had no effect on microbial carbon use efficiency (CUE). Repeated simulated precipitation events significantly increased DOC concentrations, decreased microbial CUE, increased the microbial metabolic quotient (qCO2), and altered microbial composition and diversity. These findings highlight the complex interactions and responses of surface litter decomposers to shifting nutrient availability and contradicts previous findings that nitrogen deposition will increase soil carbon sequestration from a larger supply of DOC and reduced respiration.

Experimental investigation of surface buoyant jet interactions with grid obstructions: implications for aquaculture

Freshwater inputs originating from terrestrial streams and gullies that discharge into quiescent, semi-enclosed coastal regions (such as estuaries, tidal inlets or lagoons), typically provide point sources of nutrients (e.g. nitrates, phosphates) and/or contaminants (e.g. pesticides, pathogens) that may have a deleterious impact on water quality. Many of these sheltered coastal regions also increasingly support aquaculture operations (e.g. finfish, shellfish, or seaweed farms), which can therefore be directly impacted by nutrient and contaminant inputs. Dynamically, these terrestrial freshwater inflows behave as surface buoyant jets or plumes within the coastal saline or brackish receiving waters, due to the salinity-induced density gradients. As such, the presence of infrastructure associated with aquaculture operations in sheltered coastal waters can provide obstruction to the propagation characteristics and residence times for these surface freshwater flows. Consequently, an improved physical understanding of the flow-structure interaction is clearly crucial to assessing the potential contamination risk of aquaculture products. The aim of the current study is therefore to explore, through scaled laboratory experiments within a channel-basin facility, the impact of physical obstruction induced by a vertical grid structure on the flow evolution of a 2D – 3D expanding, surface buoyant jet. Two grid obstructions with different solidity ratios are tested, along with surface gravity currents of different density excesses and freshwater inflows to infer the influence of different parametric conditions on the propagation, blockage and mixing characteristics of the surface current in the vicinity of the grid obstruction. Measurements of the velocity structure and thickness of the expanding surface plume are obtained by ultrasonic velocity profilers, while the density excess in the evolving plume is measured by micro-conductivity probes. Dye visualization results also show that, in the presence of the grid obstruction, the generation of shear-induced billows at the lower interface of the expanding surface current is largely blocked and a local deepening of the fresh-salt water interface in the immediate vicinity of the grid obstruction is observed. In this sense, the obstruction imposed by aquaculture infrastructure in coastal domains can have a considerable influence of the local turbulent mixing and vertical transfer of substances (e.g. nutrients and contaminants), but is likely to have relatively minimal impact in the final dispersion of the surface plume.

Nutrients, isolation and lack of grazing limit plant diversity in restored wetlands

Abstract Agricultural intensification has led to the loss of most natural wetlands from human‐dominated landscapes but, in recent decades, wetland restoration has gained traction worldwide. Restoration of suitable habitat conditions is hampered by nutrient residues from decades of high‐input farming, by continued input of nutrients from surrounding farmland and by incomplete restoration of natural hydrology. We assessed the effect of wetland restoration and disturbance (grazing) on vascular plant and bryophyte diversity in restored wetlands in Denmark at plot and landscape scales. Compared to near‐natural wetlands, we found a lower species richness and community uniqueness in restored wetlands, but we also found that grazing had a positive effect on vascular plant richness in restored wetlands. The size of the local species pool, presence of near‐natural habitat prior to restoration and near‐natural restored hydrology all had positive effects on plant diversity, whereas high soil iron and nitrogen had negative effects. Synthesis and applications: Restoration of plant diversity in wetlands is challenging, but our results point to potential remedies: plan restoration areas near colonisation sources of the target biota, restore hydrology to near‐natural conditions, discontinue nutrient loads from surrounding arable land and restore near‐natural grazing regimes. Bryophytes may be particularly useful as indicators for successful restoration of wetlands.

Optimizing residue return with soil moisture and nutrient stoichiometry reduced greenhouse gas fluxes in Alfisols

Optimum soil moisture and high crop residue return (RR) can increase the active pool of soil organic carbon and nitrogen, thus modulating the magnitude of greenhouse gas (GHG) fluxes. To determine the effect of soil moisture on the threshold level of RR for the wheat production system, we analyzed the relationship between GHG fluxes and RR at four levels, namely 0, 5, 10, and 15 Mg ha−1 (R0, R5, R10, and R15) under two soil moisture content (80% FC and 100% FC) and three levels of nutrient management (NS0: no nutrient; NS1, NS2= 3x NS1). Nutrient input (N and P) in NS1 balanced the residue C/nutrient stoichiometry to achieve 30% stabilization of the residue C input in RR (R5). All RR treatments (cf. R0) were found to significantly reduce N2O emission in moderate soil moisture content (80% FC) by 22–56% across nutrient management due to enhanced soil C mineralization, microbial biomass carbon, and N immobilization. However, averaged across nutrient management, a linear increase in N2O emission was observed with increasing RR under 100% FC soil moisture. A significant decrease in CH4 emission by ca. 46% in most RR treatments was observed in 100% FC compared with the R0. The N2O emission was negatively correlated (p = <0.001) with nutrient stoichiometry. Partial least square (PLS) regression indicated that GHG emissions were more responsive (values > 0.8) to management variables (RR rate, nitrogen (N) input rate, soil moisture, and nutrient stoichiometry of C: N) and post-incubation soil properties (SMBC and NO3-N) in Alfisols. This study demonstrated that the mechanisms responsible for RR effects on soil N2O, CH4 fluxes, and carbon mineralization depend on soil moisture and nutrient management, shifting the nutrient stoichiometry of residue C: N: P.

Monitoring bay-scale ecosystem changes in bivalve aquaculture embayments using flow cytometry.

Bay-scale empirical evaluations of how bivalve aquaculture alters plankton composition, and subsequently ecological functioning and higher trophic levels, are lacking. Temporal, inter- and within-bay variation in hydrodynamic, environmental, and aquaculture pressure complicate plankton monitoring design to detect bay-scale changes and inform aquaculture ecosystem interactions. Here, we used flow cytometry to investigate spatio-temporal variations in bacteria and phytoplankton (< 20 μm) composition in four bivalve aquaculture embayments. We observed higher abundances of bacteria and phytoplankton in shallow embayments that experienced greater freshwater and nutrient inputs. Depleted nutrient conditions may have led to the dominance of picophytoplankton cells, which showed strong within-bay variation as a function of riverine vs marine influence and nutrient availability. Although environmental forcings appeared to be a strong driver of spatio-temporal trends, results showed that bivalve aquaculture may reduce near-lease phytoplankton abundance and favor bacterial growth. We discuss confounding environmental factors that must be accounted for when interpreting aquaculture effects such as grazing, benthic-pelagic coupling processes, and microbial biogeochemical cycling. Conclusions provide guidance on sampling considerations using flow cytometry in aquaculture sites based on embayment geomorphology and hydrodynamics.

Soil available phosphorous and potassium stocks related to environmental properties, land uses and soils

Abstract Soil available phosphorus (SAP) and potassium (SAK) are indispensable for crops, and their stocks are important for food production needed for a growing global population. This study analysed 991 soil profiles across a large part of Romania covering forestland, grassland and cropland in almost all ecological regions. This study investigated SAP and SAK stocks for different soil depths and characterized their magnitude and variability within land uses under different environmental ecosystems, soil classes and soil types, for a better soil and land management under a temperate-continental climate. Cropland soils present the highest SAP and SAK stocks. Chernozems, Phaeozems and Vertosols possess the highest SAP and SAK stocks in Romania, representing the largest country's pool. Both SAP stocks and SAK stocks are significantly correlated with basic environmental properties, existing direct correlations between SAP, SAK, soil organic carbon (SOC) and total nitrogen (TN) stocks. For all land uses, SAP and SAK stocks correlated significantly and directly with each other, as well as with annual temperature, clay content, pH and sum of base cations, and inversely with altitude, slope and annual precipitation. The best predictive values using multiple regression models and basic environmental driving factors were found for forestland stocks of SAP and SAK, followed by grassland stocks, while the lowest prediction occurred for cropland stocks, probably due to the long-term additional nutrient input performed by farmers in cropland that changed the natural conditions otherwise present in grassland, and especially in forestland. Based on these results some management measures are discussed.

Past, Present, and Future of Forbs in Old-Growth Tropical and Subtropical Grasslands

Forbs are important contributors to species diversity and ecosystem functions in low-latitude grasslands, where they support diverse herbivore communities and millions of people. Native forb assemblages tolerate disturbances and physiological stressors (fire, herbivory, drought, and frost) that together have shaped their exceptional functional diversity. Yet, compared to trees and grasses, forbs have received much less attention in grassland studies until recently. Here, we review forb-centric literature to illustrate that land conversion and responsible management of fire and herbivory are crucial to maintaining forb diversity. Management practices promoting forb diversity offer (a) high-quality food items and medicinal resources that support rural livelihoods and animal diversity (from wild ungulates and livestock to fossorial rodents and insects), including their adaptive foraging patterns, and (b) carbon and nutrient inputs that regulate belowground processes. Improved understanding of the above- and belowground regeneration strategies of forbs is critical for restoration and conservation to secure their services in future old-growth tropical and subtropical grasslands.