Agricultural Fertilizer Application Research Articles

Climate neutral in agricultural production system: a regional case from China.

The concept of climate neutral has been introduced in the agricultural production system to re-examine the connotation of agricultural carbon footprint (CF). According to the integrated accounting framework of the agricultural CF we built, then selected a case from China, and carried out the climate economic effect quantitative analysis of the agricultural production system. The results indicated that CO2 emissions accounted the largest percentage of total carbon emissions by 52.05%, which was driven strongly by the application of agricultural fertilizers and consumption of diesel oil and CH4 emissions (ME) from cattle fed intestinal fermentation, and the driving force behind carbon sequestration was derived from the woody cash crops of carbon sequestration by vegetation and the input of residual carbon from straw returning to field and root stubble in the soil carbon pool. The carbon sink finally realized in the agricultural production system and the agricultural CF index reflected the surplus of 1.801 Mt C in the study area. In addition, we used the indicators of carbon density, carbon intensity, and carbon efficiency to judge the trade-offs of cost-benefit between the agroecosystem and economic system, so as to put forward some potential mitigation strategies for the study area. The mitigative effect of agricultural production system on climate neutral need to be further estimated in a more rigorous manner while controlling for more uncertainties in the future.

Hydrochemical appraisal of groundwater quality and pollution source analysis of oil field area: a case study in Daqing City, China.

Serious groundwater pollution not only affects the development of enterprises but also threatens the life and health of residents. To explore the utilization potential of shallow groundwater and the status of water quality pollution in Daqing city, factor analysis and Kriging spatial interpolation methods were applied to analyze the spatial distribution characteristics of pollution sources. The results showed that the HCO3-Ca + Mg type water with a maximum salinity of 1.5g/L was the main chemical type of shallow groundwater in this area. Based on the Fe pollution index, the shallow underground water quality in the northeast of Daqing city can be used for drinking. Due to higher salinity, the locations of the availability of groundwater for irrigation only were in the west. Multivariate statistical analysis was carried out using a factor analysis method, and eight main impact factors were extracted in the study. The pollution sources of human activity impact factors were mainly found to be the direct discharge of organic matter from industrial wastewater in petrochemical enterprises and domestic sewage and the inappropriate or excessive application of agricultural fertilizers. The primary geological environment factors were mainly affected by the hydrogeological and runoff conditions in the study area. Pollution factors were mainly distributed in the northeast of the study area where the pollution was a serious problem, while those in the south-central area were fewer and the pollution was light. This study provides a scientific decision basis for the application of groundwater and the management of groundwater resources in this area.

Ecological Security Evaluation Algorithm for Resource-Exhausted Cities Based on the PSR Model

Today, resource depletion threatens a number of resource-based cities in China. The ecological security problem caused by the long-term exploitation of natural resources is a key issue to be solved in the development of resource-exhausted cities. Using 23 indicators, this study evaluated the ecological security status and development trends of 21 resource-exhausted cities in China from 2011 to 2017. The results showed that from 2011 to 2015, the overall ecological security of this type of city was low, with over 60% of the cities at an unsafe level. However, ecological security improved rapidly after 2016, and by 2017, all of the cities had reached the critical safety level. The top 10 indicators of ecological security included industrial sulfur dioxide emissions, water supply, agricultural fertilizer application, and forest coverage. These 10 indicators’ cumulative contribution to ecological security was 48.3%; among them, reducing industrial sulfur dioxide emissions contributed the most at 5.7%. These findings can help governments better understand the ecological security status of resource-exhausted cities, and it can provide a reference for the allocation of funds and other resources to improve the ecological safety of these cities.

Global soil‐derived ammonia emissions from agricultural nitrogen fertilizer application: A refinement based on regional and crop‐specific emission factors

Ammonia (NH3 ) emissions from fertilized soils to the atmosphere and the subsequent deposition to land surface exert adverse effects on biogeochemical nitrogen (N) cycling. The region- and crop-specific emission factors (EFs) of N fertilizer for NH3 are poorly developed and therefore the global estimate of soil NH3 emissions from agricultural N fertilizer application is constrained. Here we quantified the region- and crop-specific NH3 EFs of N fertilizer by compiling data from 324 worldwide manipulative studies and focused to map the global soil NH3 emissions from agricultural N fertilizer application. Globally, the NH3 EFs averaged 12.56% and 14.12% for synthetic N fertilizer and manure, respectively. Regionally, south-eastern Asia had the highest NH3 EFs of synthetic N fertilizer (19.48%) and Europe had the lowest (6%), which might have been associated with the regional discrepancy in the form and rate of N fertilizer use and management practices in agricultural production. Global agricultural NH3 emissions from the use of synthetic N fertilizer and manure in 2014 were estimated to be 12.32 and 3.79TgN/year, respectively. China (4.20TgN/year) followed by India (2.37TgN/year) and America (1.05TgN/year) together contributed to over 60% of the total global agricultural NH3 emissions from the use of synthetic N fertilizer. For crop-specific emissions, the NH3 EFs averaged 11.13%-13.95% for the three main staple crops (i.e., maize, wheat, and rice), together accounting for 72% of synthetic N fertilizer-induced NH3 emissions from croplands in the world and 70% in China. The region- and crop-specific NH3 EFs of N fertilizer established in this study offer references to update the default EF in the IPCC Tier 1 guideline. This work also provides an insight into the spatial variation of soil-derived NH3 emissions from the use of synthetic N fertilizer in agriculture at the global and regional scales.

Chemical Characteristics of Groundwater and Material Sources Analysis in Shiqi River Basin

To investigate the chemical characteristics of groundwater and material sources in a typical karst hill (valley) depression, 41 groundwater samples were systematically collected in the Shiqi River basin. The statistical analysis of the conventional ion content in the groundwater shows that pH of the groundwater in the study area is between 6.06-8.07, the total solid solubility is between 18.21 mg ·L-1 and 336.28 mg ·L-1, and the charges of anions and cations in the water body are balanced. Ca2+, Mg2+, and HCO3- are the main ions in groundwater, with concentrations of 2.61-108.7 mg ·L-1, 0.54-27.61 mg ·L-1, and 8.1-370.74 mg ·L-1, respectively. The groundwater characteristics in the study area are consistent with the high calcium and weak alkalinity characteristics of karst water. By using the Gibbs diagram, piper diagram, end-member analysis, and ion proportional coefficient, hydrochemical characteristics and material sources of groundwater were further analyzed. The results show that Ca2+ and Mg2+ are mainly controlled by the weathering of limestone and dolomite in which carbonic acid is involved. Na+ mainly comes from the dissolution of silicate rocks. At the same time, Ca2+ and Na+ undergo cationic exchange adsorption in the groundwater flow process. K+, Cl-, and NO3- are mainly affected by agricultural fertilizer application and domestic wastewater discharge. The hydrogen and oxygen isotope analysis of groundwater shows that atmospheric precipitation is the main recharge source of groundwater in this region, which impacts the chemical characteristics and material sources of local groundwater. The results of this study show that the geological background of groundwater is the main factor that affects its hydrochemical characteristics and material sources in areas with relatively little anthropogenic activity.

Effect of balanced nutrient fertilizer: A case study in Pinggu District, Beijing, China

Agriculture has played an indispensable role in the economic and social development of China. However, the inappropriate application of fertilizers in agriculture has brought about environmental pollution. Therefore, under the requirements of green development, the inevitable choice has been reducing the application amount while increasing the utilization rate of fertilizers. To solve the problems resulting from fertilizers, this research designed and made Balanced Nutrient Fertilizer based on the nutrient balance method. To test Balanced Nutrient Fertilizer, continuous planting experiments on three crops (peas, corns, and peaches) were carried out in Pinggu District, Beijing. Furthermore, a substance flow analysis (SFA) was conducted to obtain a deeper understanding of the Balanced Nutrient Fertilizer. Through a series of tests, the application of Balanced Nutrient Fertilizer was shown to increase the crop yield by 3%. The product quality was also improved. In addition, the amount of nutrients applied was significantly reduced in the experimental group (specifically, 35%–88% for nitrogen, 69%–93% for phosphorus, and 8%–82% for potassium). The results of the SFA revealed that applying the Balanced Nutrient Fertilizer could meet the required amount of nutrients for the best crop growth, greatly decrease the negative influence of chemical fertilizers on the soil and reduce agricultural non-point source pollution.

Application of biofertilizer containing Bacillus subtilis reduced the nitrogen loss in agricultural soil

Nitrogen losses caused by excess fertilizer application in agriculture are one of the main sources of non-point pollution. Biofertilizer has been considered as an effective alternative to synthetic nitrogen fertilizer, but the effectiveness and mechanism for controlling non-point pollution remains unclear. In this study, the effect of biofertilizer containing Bacillus subtilis on nitrogen loss in agricultural soil was investigated. Compared with the application of urea alone, the strategy of substituting 50% urea with biofertilizer reduced the nitrogen loss from farmland soil by 54%. Moreover, this strategy also increased nitrogen use efficiency by 11.2% and achieved a 5.0% increase in crop yield. Application of biofertilizer decreased the abundance of bacterial amoA gene and increased the abundance of narG, nirS, nirK, and nosZ genes in soil. This implied a decrease in nitrification and an increase in denitrification. Thus, it reduced the accumulation of NO3−-N in soil and greatly reduced nitrogen runoff and leaching loss. In addition, biofertilizer decreased the abundance of nitrogen-fixing gene nifH by up to 2 times. Application of biofertilizer also increased the abundance of Bacteroidetes and Chloroflexi, which play important roles in degradation of soil organic matter. In conclusion, the biofertilizer regulated the microbial nitrogen transformation process in soil and reduced nitrogen loss from agroecosystems.

Bacillus pumilus promotes the growth and nitrogen uptake of tomato plants under nitrogen fertilization

Some plant growth-promoting bacteria (PGPB) are capable of fixing atmospheric N2 and can be used to reduce nitrogen (N) fertilizer application in agriculture. Large amounts of N fertilizers are applied in tomato (Solanum lycopersicum L.). However, less attention has been given to the role of PGPB in the N nutrition of tomato. The present study was carried out under greenhouse conditions to investigate the principal mechanisms underlying PGPB-improved N nutrition in tomato. Tomato plants were grown in pots under –N (native soil N without N fertilization) or + N (supply 150 mg N kg–1 dry soil in the form of urea), with or without Bacillus pumilus (PGPB) inoculation. Nitrogen supply improved the growth of tomato, soil NH4+ concentration, and plant N uptake. Nitrogen increased the rhizobacterial population, bacterial nifH gene expression, and soil nitrogenase activity only with the inoculation of B. pumilus. B. pumilus inoculation improved the tomato growth, N uptake, soil NH4+ concentrations, rhizobacterial population levels, soil bacterial gene expression, and soil nitrogenase activity only under + N condition. These results suggest that the inoculation of B. pumilus improves the growth of tomato under the condition of additional fertilizer N supply due to an increase in N uptake by roots from B. pumilus-assisted fixed N in soil.

Impacts of the Sanmenxia Dam on the Interaction between Surface Water and Groundwater in the Lower Weihe River of Yellow River Watershed

Sanmenxia Dam, one of the most controversial water conservancy projects in China, has seriously impacted the lower Weihe River of the Yellow River Watershed since its operation. At the Huaxian Station, the dam operation controls the surface water level and leads to the variation of the surface water–groundwater interaction relationship. The river channel switched from a losing reach during the early stage (1959) to a gaining reach in 2010 eventually. The comparison of tracer (Cl−, δ18O and δ2H) characteristics of surface water in successive reaches with that of ambient groundwater shows that the general interaction condition is obviously affected by the dam operation and the impact area can be tracked back to Weinan City, around 65 km upstream of the estuary of the Weihe River. The anthropogenic inputs (i.e., agricultural fertilizer application, wastewater discharge, and rural industrial sewage) could be responsible for the deterioration of hydro-environment during the investigation periods of 2015 and 2016, as the population and fertilizer consumption escalated in the last 60 years. The use of contaminated river water for irrigation, along with the dissolved fertilizer inputs, can affect the groundwater quality, in particular resulting in the NO3− concentrations ranging from 139.4 to 374.1 mg/L. The unregulated industrial inputs in some rural areas may increase the Cl− contents in groundwater ranging from 298.4 to 472.9 mg/L. The findings are helpful for the improved comprehensive understanding of impacts of the Sanmenxia Dam on the interaction between surface water and groundwater, and for improving local water resources management.

Distribution and Source Analysis of Nitrate in Surface Waters of China

The nitrate pollution of surface water has attracted worldwide attention, and it is not optimistic in China. To identify the distribution, sources, and transformation mechanisms of nitrate in China's surface waters, the nitrate data of 71 major rivers from 7 regions were systematically collected. The spatial distribution of nitrate concentrations in surface water was analyzed, and the main nitrate pollution sources were revealed based on nitrogen and oxygen isotopes of nitrate. The results show that approximately 7.83% of rivers in China exceeded the Chinese drinking water standard for nitrate (45 mg·L-1). The concentrations of nitrate in Mudanjiang, Haihe River, and the estuary of Yangtze River was even more than 90 mg·L-1, which indicates a serious pollution phenomenon. The isotopic compositions of surface water in China ranged from -23.5‰ to 26.99‰ for δ15N-NO3 and from -12.7‰ to 83.5‰ for δ18O-NO3. The main sources of nitrate are domestic sewage in Northeast, Central, and East China, while those are inorganic fertilizers and domestic sewage in Southwest and South China. The nitrate sources of surface water in Northwest and North China are complex, mainly from domestic sewage, inorganic fertilizer, and nitration of soil organic matter. Through correlation analysis, it is found that the nitrate concentrations of surface water have a positive relationship with population, wastewater discharge, agricultural nitrogen fertilizer application, and GDP per capita in China. It is urgent to solve the problem of pollution and prevent the further pollution of China's surface waters. The new "10-Point Water Plan" issued by the Chinese government solved the previous problems, but it will take decades to control and repair the polluted surface waters. In Northwest, North China, Southwest, and South China, not only the scale of sewage treatment plants in cities and counties should be increased but also the use of agricultural fertilizers should be controlled and managed by the government. Northeast, Central, and East China need to further control point source pollution and reduce the discharge of industrial wastewater and domestic sewage into rivers.

Effects of Composting Different Types of Organic Fertilizer on the Microbial Community Structure and Antibiotic Resistance Genes.

Organic fertilizer is a major carrier that stores and transmits antibiotic resistance genes (ARGs). In the environment, due to the application of organic fertilizers in agriculture, the increasing diversity and abundance of ARGs poses a potential threat to human health and environmental safety. In this paper, the microbial community structure and ARGs in different types of organic fertilizer treated with composting were examined. We found that the abundance and diversity of ARGs in earthworm cast organic fertilizer were the lowest and the highest in chicken manure organic fertilizer. Interestingly, the abundance and diversity of ARGs, especially beta-lactam resistance genes, sulfonamide resistance genes, and macrolide-lincosamide-streptogramin B (MLSB) resistance genes, in organic fertilizers were reduced significantly, while composting caused no significant change in mobile genetic elements (MGEs), where antibiotic deactivation and the use of efflux pumps were the two most dominant mechanisms. It was clear that removal of ARGs became more efficient with increasing reduction in the bacterial abundances and diversity of potential ARG hosts, and integron-mediated horizontal gene transfers (HGTs) played an important role in the proliferation of most ARG types. Therefore, the reduction in ARGs was mainly driven by changes in bacterial community composition caused by composting. Furthermore, rather than HGTs, the diversity and abundance of bacterial communities affected by compost physical and chemical properties were the main drivers shaping and altering the abundance and diversity of ARGs, which was indicated by a correlation analysis of these properties, antibiotic residues, microbial community structure, and ARGs. In general, high-temperature composting effectively removed antibiotic residues and ARGs from these organic fertilizers; however, it cannot prevent the proliferation of MGEs. The insights gained from these results may be of assistance in the safe and rational use of organic fertilizers by indicating the changes in microbial community structure and ARGs in different types of organic fertilizer treated with composting.

Lignocellulosic crop residue composting by cellulolytic nitrogen-fixing bacteria: A novel tool for environmental sustainability.

Lignocellulosic crop residue (LCCR) composting is a cost-effective and sustainable approach for addressing environmental pollution associated with open biomass burning and application of chemical fertilizers in agriculture. The value-added bio-product of the composting process contributes to the improvement of the soil properties and plant growth in an environment-friendly way. However, the conventional process employed for composting LCCRs is slow and becomes an impediment for farmers who plant two or three crops a year. This concern has led to the development of different techniques for rapid composting of LCCRs. The use of cellulolytic nitrogen-fixing microorganisms for composting has emerged as a promising method for enhancing LCCR composting and quality of the compost. Therefore, this review addresses the recent progress on the potential use of cellulolytic nitrogen-fixing bacteria (CNFB) for LCCR composting and discusses various applications of nutrient-rich compost for sustainable agriculture to increase crop yields in a nature-friendly way. This knowledge of bacteria with both cellulose-degrading and nitrogen-fixing activities is significant with respect to rapid composting, soil fertility, plant growth and sustainable management of the lignocellulosic agricultural waste and it provides a means for the development of new technology for sustainability.

A nitrogen dynamic hydroponic culture on performance and quality of water spinach (Ipomoea aquatica)

In view of the unreasonable application of chemical fertilizers in agriculture and the groundwater pollution caused by nitrogen (N) leaching, a nitrogen dynamic hydroponic culture was used to simulate the dynamics variation of ammonium nitrogen (NH4-N) and nitrate nitrogen (NO3-N) in the leaching loss soil. Solutions with different ratio of NO3-N and NH4-N (100:0, 70:30, 50:50, 30:70 and 0:100) were prepared as well as the same solutions that not containing NO3-N .Water spinach was chosen to culture in the two solutions that differ from NO3-N every two (E2) or five days (E5) to observe the growth, quality and nutrient solution uptake. In terms of the growth, uptake of N source, N use efficiency and the chemical indicators, plants grown in the balanced solution all showed the best results. The nitrogen dynamic hydroponic culture showed some differences between E2 and E5 in some aspects. Under the same N source level, plants in E2 showed a better growth and higher NO3-N uptake than E5. On the other hand, the uptake of NH4-N seemed to be affected significantly by the interchanged frequency, which showed the same variations of glutamine synthetase activity. The activity of nitrate reductase and glutamine synthetase showed the coexist of NO3-N and NH4-N could play synergistic effect. It is not recommended to supplement NO3-N frequently in the case of N leaching loss, which has little impact on the growth and may lead to the hard taste and groundwater pollution.

Trace metal effects on gross primary productivity and its associative environmental risk assessment in a subtropical lake, China

The transport of trace metals in river–lake systems can potentially increase or decrease primary productivity in some basins and subsequently affect the carbon cycle of watersheds. In this study, we investigated a variety of trace metal concentrations and transport flux in the Poyang Lake basin during four seasons. Results show that the Gan River transports 78% of selenium (Se) and 42% of lead (Pb) into Poyang Lake each year, resulting in heavy metal pollution dominated by Pb and Se in 30%–75% of its water. Although toxic heavy metals, such as Pb, chromium (Cr), and copper (Cu), inhibit phytoplankton growth and decrease its gross primary productivity (GPP), excessive Se could effectually promote productivity. However, the negative effect of Pb on GPP is more significant than the positive effect of Se on GPP; hence, their interaction effectuates a decrease in total primary productivity. Additionally, under high nutrients level, the synergistic effect of heavy metals and nutrients will reduce GPP. Agricultural fertilizer is likely the source of both Pb, Cu, Se and N. Gan River contributes 35%–80% of the heavy metal inputs to Poyang Lake. It is therefore necessary to improve the ecological environment of phytoplankton and promote productivity in the Poyang Lake basin by reducing the application of agricultural chemical fertilizers to control pollution. Our results indicate that the role of certain, less studied trace elements (e.g., Pb, Cr, Cu, and Se) in regulating primary productivity of watershed ecosystems is more important than previously thought. This study also discusses potential impacting mechanisms associated with these metals on phytoplankton, whose biological functions need to be verified in future experiments.

Long-term monitoring of hydrochemical characteristics and nitrogen pollution in the groundwater of Yinchuan area, Yinchuan basin of northwest China

Research on the hydrochemical characteristics of groundwater can help to elucidate its evolution and distribution, as well as other hydrogeological conditions. The present study investigated the current status of groundwater hydrochemistry and nitrogen contamination in Yinchuan area, Yinchuan basin of northwest China. Piper and Gibbs diagrams were constructed and multivariate statistical methods were used to explore the groundwater hydrochemical characteristics and its controlling factors, as well as nitrogen contamination of groundwater and its sources. The results demonstrated that phreatic water was moderately salty with a large variation of TDS and major ion concentrations, while the confined water was mainly fresh water with TDS less than 1000 mg/L. Phreatic water was mainly HCO3·Cl–Na·Mg and HCO3·SO4–Na·Mg types, while the confined water was HCO3·Cl–Na·Ca and HCO3·SO4–Na·Ca types. The major ion chemistry of the confined water is governed by water–rock interactions, while evaporation plays a key role in phreatic water chemistry formation. Furthermore, the concentration of NO3− in phreatic water is significantly higher than that of confined water, and the opposite was observed for NH4+. The concentrations of NO3− and NH4+ exhibited an increasing tendency in groundwater in the last 26 years. The nitrogen sources in phreatic water involved human activities like nitrogen fertilizer application in agriculture, and industrial and domestic sewage. In confined aquifer, the higher NH4+ concentration is comprehensively affected by hydrogeological conditions, leakage of phreatic water and an anaerobic environment. Overall, the results of the present study are helpful for the groundwater protection in Yinchuan area, and will contribute to the effective management and reasonable development of groundwater resources in Yinchuan basin.

Sequential extraction analysis of U, Sr, V, Ni, Cr, B, and Mo in sediments from the Al-Batin Alluvial Fan, Southern Iraq

The distribution of U, Sr, V, Ni, Cr, B, and Mo in sediments of the Al-Batin Alluvial Fan in southern Iraq was investigated. A total of 18 sediment samples were collected in the study area and the clay and silt fraction was analyzed using a six-step sequential extraction method. Results of the sequential extraction were used to evaluate the potential origin and environmental impacts of the selected elements. Except for Sr, the highest average concentration of the investigated trace elements is mainly in the residual fraction with the following descending order: Cr > V > B > Ni > Mo > U. This suggests a geogenic origin of these trace elements. Sr occurs mainly in the acid soluble fraction due to its authigenic formation from the underlying carbonate beds. Anthropogenic pollution in the study area is restricted to agricultural activities and fertilizer application which adds B and Mo to the soil in some cases. The Sr elevation and fractionation within the sediments suggests a possibility of Sr accumulation in cultivated crops, and thus a potential risk to infants and children. High concentrations and fractionation pattern of U in three samples shows a considerable risk to the environment in certain areas.

GIBBERELLIN PRODUCING RHIZOBACTERIA Pseudomonas koreensis MU2 ENHANCE GROWTH OF LETTUCE (Lactuca sativa) AND CHINESE CABBAGE (Brassica rapa, chinensis)

Microbial biofertilizers are considered environmentally safe tool for the healthy production of a plant. Massive application of synthetic pesticides and fertilizers in agriculture has resulted detrimental effect on nature and human health. In the current study, we isolated several strains of rhizoshpheric bacteria through screening from the diversed agricultural soil of Daegu, South Korea. The growth promoting ability of the isolated strains was checked on gibberellin-deficient rice dwarf mutant Waito-C, lettuce var. cheongchima and chinese cabbage var. wangmat. The strain having the higher ability to promote the Waito-c growth was selected and further investigation was done. The selected isolate was identified as Pseudomonas koreensis MU2 through 16s rDNA gene sequence analysis. The cultural filtrate analysis revealed that the isolate could produce endogenous phytohormone gibberellic acid (GA1 and GA3) and organic acids, such as citric acid, malic acid, and tartaric acid. Pot experiment revealed that the inoculation of Pseudomonas koreensis MU2 significantly increased shoot length, root length, fresh biomass, and dry biomass of chinese cabbage and lettuce. These results suggest that the Pseudomonas koreensis MU2 might be the possible candidate for bio-fertilizer as a plant growth-promoting rhizobacteria in plant.

Real-time monitoring of nitrate in soils as a key for optimization of agricultural productivity and prevention of groundwater pollution

Abstract. Lack of real-time information on nutrient availability in cultivated soils inherently leads to excess application of fertilizers in agriculture. As a result, nitrate, which is a soluble, stable, and mobile component of fertilizers, leaches below the root zone through the unsaturated zone and eventually pollutes the groundwater and other related water resources. Rising nitrate concentration in aquifers is recognized as a worldwide environmental problem that contributes to water scarcity. The development of technologies for continuous in situ measurement of nitrate concentration in soils is essential for optimizing fertilizer application and preventing water resource pollution by nitrate. Here we present a conceptual approach for a monitoring system that enables in situ and continuous measurement of nitrate concentration in soil. The monitoring system is based on absorbance spectroscopy techniques for direct determination of nitrate concentration in soil porewater without pretreatment, such as filtration, dilution, or reagent supplementation. A new analytical procedure was developed to improve measurement accuracy while eliminating the typical measurement interference caused by soil dissolved organic carbon. The analytical procedure was tested at four field sites over 2 years and proved to be an effective tool for nitrate analysis when directly applied on untreated soil solution samples. A soil nitrate-monitoring apparatus, combining specially designed optical flow cells with soil porewater-sampling units, enabled, for the first time, real-time continuous measurement of nitrate concentration in soils. Real-time, high-resolution measurement of nitrate concentration in the soil has revealed the complex variations in soil nitrate concentrations in response to fertigation pattern. Such data are crucial for optimizing fertilizer application and reducing pollution potential of groundwater.

The influence of oxytetracycline on the degradation and enantioselectivity of the chiral pesticide beta-cypermethrin in soil

Pesticide residues most likely coexist with antibiotics due to the application of animal-based fertilizers in agriculture. In this study, the degradation and enantioselectivity of beta-cypermethrin in soil and chicken manure-amended soil were investigated. The effects of oxytetracycline on the soil microbial community were also estimated. The results showed that the half-life of beta-cypermethrin in the soil was 16.9 days and that the (+)-enantiomer was degraded preferentially in both pairs of enantiomers. The metabolites cis/trans-DCCA(3-(2′,2′-dichlorovinyl)-2,2-dimethylcyclopropane carboxylic acid) and 3-PBA (3-Phenoxybenzoic acid) were detected. The trans-DCCA concentrations ranged from 0.094 to 0.120 mg/kg, which were higher than the concentrations of cis-DCCA (0.091–0.120 mg/kg) and 3-PBA (0.022–0.061 mg/kg). In the presence of oxytetracycline, beta-cypermethrin degradation was inhibited slightly, while the enantioselectivity was not affected. Oxytetracycline increased the enrichment and persistence of the metabolites. Addition of chicken manure decreased the cis-DCCA residue levels in the soil and alleviated the effect of oxytetracycline; however, chicken manure increased the accumulation and persistence of 3-PBA. In addition, oxytetracycline perturbed the structure of the soil microbial community. The abundance of Proteobacteria increased, while the abundances of Firmicutes and Actinobacteria decreased. These changes might affect the biodegradation of beta-cypermethrin and its metabolites. Combined pollution with antibiotics should be considered for its potential impact on pesticide residues.

Soil potassium fractions under two contrasting land use systems of Assam

Potassium (K) plays an important role in growth, yield, quality, osmotic regulation, ionic balance and stress resistance of crops. Fertilizer application in Indian agriculture has remained largely skewed towards nitrogen (N) and phosphorus (P), while K remained neglected for over last five decades. On this background, the present study evaluates the soil K fractions under two contrasting land use systems, viz. rice-fallow and forest under three soil depths (0-15, 15-30 and 30-60 cm) and categorisation of soils based on exchangeable K (Exch-K) and non-exchangeable K (NEK) with the strategy for proper K management. Results indicated that the soils of rice-fallow land use system were present in a category which is low in both Exch-K and NEK and as a result it requires adequate K fertilization. Both Exch-K and NEK were higher in the forest soils as compared to rice-fallow soils in the three soil depths. The ratio of NEK/Exch-K was higher in the forest than rice-fallow land use system. The ratio was increased with increase in depth in the forest land use system which indicates that it has more potential to supply subsoil K in long term. This categorisation of soils into different groups provides a comprehensive assessment of K availability for different land use systems and better recommendation of K fertilizer for efficient K management.