Nitrification,acidification, and nitrogen leaching from subtropical cropland soils as affected by rice straw-based biochar: laboratory incubation and column leaching studies

Purpose

Few studies have examined the effects of biochar on nitrification of ammonium-based fertilizer in acidic arable soils, which contributes to NO₃ ^? leaching and soil acidification.

Materials and methods

We conducted a 42-day aerobic incubation and a 119-day weekly leaching experiment to investigate nitrification, N leaching, and soil acidification in two subtropical soils to which 300 mg N kg^?1 ammonium sulfate or urea and 1 or 5 wt% rice straw biochar were applied.

Results and discussion

During aerobic incubation, NO₃ ^? accumulation was enhanced by applying biochar in increasing amounts from 1 to 5 wt%. As a result, pH decreased in the two soils from the original levels. Under leaching conditions, biochar did not increase NO₃ ^?, but 5 wt% biochar addition did reduce N leaching compared to that in soils treated with only N. Consistently, lower amounts of added N were recovered from the incubation (KCl-extractable N) and leaching (leaching plus KCl-extractable N) experiments following 5 wt% biochar application compared to soils treated with only N.

Conclusions

Incorporating biochar into acidic arable soils accelerates nitrification and thus weakens the liming effects of biochar. The enhanced nitrification does not necessarily increase NO₃ ^? leaching. Rather, biochar reduces overall N leaching due to both improved N adsorption and increased unaccounted-for N (immobilization and possible gaseous losses). Further studies are necessary to assess the effects of biochar (when used as an addition to soil) on N.     

Nitrogen leaching and phosphorus accumulation in a perennial pasture after composted goat manure was topdressed and incorporated in the Three Gorges region

Purpose  

Improper utilization of composted manure might increase risk of nutrients leaching and phosphorus (P) accumulation, hence causing eutrophication and threatening the ecological safety of river. In the current study, composted manure from a goat feedlot was applied to a perennial pasture in the Three Gorges region to evaluate its effects on pasture yield, NO₃–N leaching, and phosphorus accumulation in soil.     

A lysimeter study of nitrate leaching and optimum nitrogen application rates for intensively irrigated vegetable production systems in Central China

Background, aim, and scope  

Nitrate leaching from intensive vegetable production is an important contributor of nitrate contamination of water resources. The aim of this study was to quantify NO₃ ⁻ leaching losses under intensive vegetable production as affected by different rates of N fertilizer and to determine the optimum N application rates both for vegetable production and for meeting the drinking water standard.     

Effective mitigation of nitrate leaching and nitrous oxide emissions in intensive vegetable production systems using a nitrification inhibitor,dicyandiamide

Purpose  

Vegetable production is one of the most intensive agricultural systems with high rates of nitrogen (N) fertilizer use and irrigation, conditions conducive for nitrate (NO₃⁻) leaching, and nitrous oxide (N₂O) emissions. The objective of this study was to determine the effectiveness of a nitrification inhibitor, dicyandiamide (DCD), in decreasing NO₃⁻ leaching and N₂O emissions in vegetable production systems.     

Carbon mineralization and retention of livestock manure composts with different substrate qualities in three soils

Purpose  

Since substrate quality can influence the C mineralization pattern of compost in soils, proper selection of compost is important in increasing soil organic carbon (SOC) levels. This study investigated the effect of substrate quality of livestock manure composts on compost C mineralization and retention in soils.     

Suppression of NH<Subscript>3</Subscript> and N<Subscript>2</Subscript>O emissions by massive urea intercalation in montmorillonite

Purpose  

A large amount of nitrogen (N) fertilizers has been broadcasted over soil surface for reliable crop production. Unfortunately, the broadcasted N vulnerable to volatilization and leaching can lead to serious environmental problems. As a new approach to mitigate N loss of broadcasted fertilizers, massive intercalation of urea into montmorillonite (MMT) was recently proposed to innovatively enhance the urea use efficiency. This study focuses on demonstrating the behaviors of the urea intercalated into MMT in soils.     

Plant availability and leaching of 15N-labelled mineral fertilizer residues retained in agricultural soil for 25 years: A lysimeter study

Background

A high use-efficiency of fertilizer N remains essential to sustain high crop productivity with low environmental impact. However, little is known on the long-term lability of mineral fertilizer N.

Aims

To quantify crop uptake and leaching of ¹⁵N-labelled mineral fertilizer that has been retained in an agricultural soil for 25–30 years in crops with variable growing season.

Methods

A field plot received ¹⁵N-labelled mineral fertilizers over a period of 5 years and was then kept under arable cropping for 12 years. After relocation to 16 lysimeters, the topsoil grew set-aside grassland for the next 13 years. Then crop uptakes and leaching losses of ¹⁵N remaining in soil was tested over a 2-year period by either converting set-aside grass to production grassland, or by replacing it with spring barley (+/− autumn cover crop) or vegetation-free fallow. All treatments received unlabelled mineral N fertilizers.

Results

Crop uptake and leaching of ¹⁵N were generally highest in the first test year after termination of the set-aside. The leaching of residual ¹⁵N in soil declined in the order: vegetation-free soil (4.7%), spring barley (1.9%), spring barley + cover crop (0.7%) and production grassland (0.2%). Corresponding losses for the second leaching period were 2.7%, 0.9%, 0.4% and 0.06%. There was a fixed relationship between leaching losses of ¹⁵N and total N.

Conclusions

After residing in soil for 25–30 years, the lability of labelled mineral N fertilizer residues appeared slightly higher than the lability of bulk soil N. Autumn vegetation was crucial for reducing leaching losses.     

Soil and Compost Type Affect Phosphorus Leaching from Inceptisol,Ultisol, and Andisol in a Column Experiment

A column leaching experiment using three soils (Inceptisol, Ultisol, and Andisol) and seven livestock manure composts that had different characteristics was conducted for 19 weeks to investigate the interactive effects of composts and soils on the phosphorus (P) leaching potential of compost-amended soils and to identify the principal variables that affect P leaching. Cumulative total P leaching (TP_cum) tended to increase with increasing total and available P concentration in the soils. Among various compost properties, total P concentration was positively correlated with TP_cum from the compost-amended soils, except for the Andisol, which has a high P-sorption capacity. There was no significant relationship between TP_cum and water-extractable P concentration of the composts, suggesting that total P rather than inorganic P concentration of composts may be successfully used in predicting P leaching potential from compost-amended soils except for soils that have a high P-sorption capacity, as in Andisol.     

Effects of nitrogen fertilizer application rates on nitrate nitrogen distribution in saline soil in the Hai River Basin,China

Background and Objectives  

Soil nitrate nitrogen (NO₃ ⁻-N) accumulation is related closely to NO₃ ⁻ leaching, which is an important issue in groundwater pollution, especially in intensive agricultural areas with saline soils where volumes of water are used in irrigation to avoid salt accumulation in the root zone. However, in the saline environment in Hai River Basin, China, the importance of detailed research into NO₃ ⁻-N distribution in the root zone has not been adequately recognized. Considering the impacts of eco-environmental system N and crop production, the present study aimed at contributing to an understanding of the effects of N application rate on soil NO₃ ⁻-N distribution, NO₃ ⁻-N residue, N loss, and maize (Zea mays L.) yield in this region.     

Leaching of Nitrate,Ammonium, and Phosphate From Compost Amended Soil Columns

Compost amendment to agricultural soils has been reported to reduce disease incidence, conserve soil moisture, control weeds, or improve soil fertility. Application rate and placement of compost largely depends on the proposed beneficial effects and the rate may vary from 25 to 250 Mg ha^?1 (N content up to 4 percent). Application of high rates of compost with high N or P levels may result in excessive leaching of nitrate, ammonium, and phosphate into the groundwater. Leaching could be a serious concern on the east coast of Florida with its inherent high annual rainfall, sandy soils and shallow water table. In this study, five composts (sugarcane filtercake, biosolids, and mixtures of municipal solid wastes and biosolids) were applied on the surface of an Oldsmar sand soil (in 7.5 cm diameter leaching columns) at 100 Mg ha^?1 rate and leached with deionized water (300 ml day^?1, for five days; equivalent to 34 cm rainfall). The concentrations of NO₃-N, NH₄-N, and PO₄-P in leachate reached as high as 246, 29, and 7 mg L^?1, respectively. The amount of N and P leached accounted for 3.3-15.8 percent of total N and 0.2-2.8 percent of total P in the compost. The leaching peaks of NO₃-N occurred following the application of only 300-400 ml water (equivalent to 6.8-9.1 cm rainfall).     

Field-applying an inexpensive, 13C-depleted,labile carbon source to study in situ fate and short-term effects on soils

Background

Labile carbon (C_labile) limits soil microbial growth and is critical for soil functions like nitrogen (N) immobilization. Most experiments evaluating C_labile additions use laboratory incubations. We need to field-apply C_labile to fully understand its fate and effects on soils, especially at depth, but high cost and logistical difficulties hinder this approach.

Aims

Here, we evaluated the impact of adding an in situ pulse of an inexpensive and ¹³C-depleted source of C_labile—crude glycerol carbon (C_glyc), a by-product from biodiesel production—to agricultural soils under typical crop rotations in Iowa, USA.

Methods

We broadcast-applied C_glyc at three rates (0, 216, and 866 kg C ha⁻¹) in autumn after soybean harvest, tracked its fate, and measured its impact on soil C and N dynamics to four depths (0–5, 5–15, 15–30, and 30–45 cm). Nineteen days later, we measured C_glyc in microbial biomass carbon (MBC), salt-extractable organic C, and potentially mineralizable C pools. We paired these measurements with nitrate N (NO₃⁻–N) and potential net N mineralization to examine short-term effects on N cycling.

Results

C_glyc was found to at least 45-cm depth with the majority in MBC (18%–23% of total C_glyc added). The δ¹³C values of the other measured C pools were too variable to accurately track the C_labile fate. NO₃⁻–N was decreased by 13%–57% with the 216 and 866 kg C ha⁻¹ rates, respectively, and was strongly related to greater microbial uptake of C_glyc (i.e., immobilization via microbial biomass). Crude glycerol application had minor effects on soil pH—the greatest rate decreased pH 0.18 units compared to the control.

Conclusions

Overall, glycerol is an inexpensive and effective way to measure in situ, C_labile dynamics with soil depth—analogous to how mobile, dissolved organic C might behave in soils—and can be applied to rapidly immobilize NO₃⁻–N.     

Biochar-application rate and method affect nutrient availability and retention in a coarse-textured,temperate agricultural Cambisol in a microcosm experiment

Background

Agricultural soils often require organic amendments, which improve crop yield and ecosystem services. Biochar has been proven to increase nutrient availability and retention in fine-textured, tropical soils.

Aims

Here we determine how coarse-textured, temperate soils react to different biochar-application rates in different tillage systems.

Methods

We conducted a 6-month laboratory incubation experiment in microcosms filled with a coarse-textured, temperate agricultural soil to determine the effects of biochar-application rate (none, low, or high, i.e., 0, 20, or 40 t dw ha⁻¹, respectively) and application method (mixed into the soil or applied to the soil surface) on microbial activity and biomass, and nutrient availability and leaching.

Results

Microbial activity and biomass and contents of carbon, nitrogen, and phosphorus in leachates were higher in biochar-addition treatments (by 134%, 37%, 372%, 28%, and 801%, respectively) than in the no-addition treatment. The effect was stronger with the low than with the high biochar-application rate. Biochar applied by both methods acted as a slow-release fertilizer, but this effect was stronger when biochar was mixed into the soil. Although available nutrient contents in the soil remained high, nutrient leaching decreased with incubation time. This effect was especially evident when biochar was mixed into the soil.

Conclusions

Biochar is an effective organic amendment in coarse-textured soils providing available nutrients. On the other hand, nutrient-retention mechanisms develop slowly after biochar application and may be greater when biochar is mixed into the soil than applied on the soil surface.     

Effect of soil sealing on the microbial biomass,N transformation and related enzyme activities at various depths of soils in urban area of Beijing,China

Purpose  

Sealing of soils prevents the exchange of gas, water and nutrient between soil and other environmental compartments, and affects urban N flux, thereby resulting in certain negative impacts on soil functioning and urban environment. However, little information is available on the biogeochemical cycling and biological activities after sealing of soils in urban areas. The aim of this study was to assess the effects of soil sealing on N transformation and associated microbial properties.     

Agrochemical characterization,net N mineralization,and potential N leaching of composted olive‐mill pomace currently produced in southern Spain

In S Spain, the Andalusian olive oil industry generates annually 2.5–3.0 million tons of olive mill pomace, a by‐product which is comprised of the residues from the two‐phase oil‐extraction process. The agricultural policies of the EU have led to widespread interest in recycling these agricultural by‐products. Olive mill pomace might be evaluated as an organic fertilizer after composting, however, before wider use of composted olive mill pomace is advocated, characterization of the final product is needed. In this study, the physico‐chemical characteristics, net N mineralization, and the potential for N leaching of 7 out of the 11 olive‐mill‐pomace composts currently produced in the Andalusian olive mills were investigated. Compost of olive mill pomace differed in the proportions of raw materials co‐composted with the olive mill pomace, such as olive leaf material, manure, and straw. In all the composts tested, organic matter, total C and K were high with 60.5%, 30.7%, and 1.7% on average, respectively, whereas total P was low (0.4%) and with intermediate levels of N (1.5%). Compost pH (8.03), electrical conductivity (2.85 dS m^–1), and germination index (65% on average) were adequate for agricultural use. Furthermore, principal component analyses revealed a clear relationship between the quality of the composts and the proportion of manure mixed with the raw materials. Net N mineralization was negative on average (–20 μg IN g^–1) after 1 y, but positive after 2 y of incubation with up to 94% of available N from the total N added and the short‐term potential N leaching after compost application was negligible (less than 3.9% of added N) and much lower than the other N fertilizer with up to 80% added N leached. Overall, results of this study clearly show that these currently produced composts of olive mill pomace are suitable as soil improvers for agricultural purposes, but may not contribute significantly as a N fertilizer for up to 2 y after application.     

Alternatives to regular urea for abating N losses in lettuce production under sub-tropical climate

Alternative fertilization practices are needed for reducing gaseous and leaching N losses at high urea application rates. The objective of this study was to compare gaseous N emissions (N₂O and NH₃) and NO₃ ^? concentrations in the soil solution during two successive lettuce cropping seasons under contrasting fertilization practices. Treatments were fertilization with regular urea (U), urea treated with urease [N-(n-butyl) thiophosphoric triamide (NBPT)] and nitrification [dicyandiamide (DCD)] inhibitors (UIs), non-acidified pig slurry compost (PSC), acidified pig slurry compost (APSC), and an unfertilized control (C). Acidification of pig slurry during composting had no impact on soil cumulative N₂O emissions during the cropping seasons. The use of composts resulted in emission factors (EFs) (PSC, 0.09% of applied N; APSC, 0.16%) an order of magnitude smaller than with regular urea (1.63%). Similarly, adding NBPT and DCD to urea reduced the N₂O EF from 1.63 to 0.37% of applied N and fertilizer-induced NH₃ emissions from 30.2 to 3.4% of applied N. Composts and UI resulted in yield-scaled N₂O emissions that were 33 to 49% lower than the unfertilized control and 64 to 73% lower than the regular urea estimates, indicating a greater efficiency of supplied N with composts and UI. Nitrate concentration of the soil solution (at 0.1 and 0.3 m) in PSC, APSC, and UI plots was similar to the control and up to 17 times lower than with regular urea, indicating reduced risks for leaching losses. We conclude that, as compared to regular urea, the use of composted pig slurry, with and without acidification, and the addition of NBPT and DCD inhibitors to urea are good practices to reduce environmental N losses from lettuce production under sub-tropical climate.     

Analysis and behavior of soluble organic nitrogen in forest soils

Background, aim, and scope  

A large proportion of soil nitrogen (N; >80%) is present in organic form. Current research on plant N uptake in terrestrial ecosystems has focused mainly on inorganic N such as ammonium (NH₄ ⁺) and nitrate (NO₃ ⁻), while soluble organic N (SON) has received little attention. In recent years, the increasing evidence showing the direct uptake of various amino acids by plants and the predominance of the organic form in N loss by leaching in many forest ecosystems has drawn attention to critically re-examine the nature and the ecological role of soil SON in terrestrial N cycling. However, little is known about the sources and dynamics, chemical nature, and ecological functions of soil SON in forest ecosystems. This paper reviews recent advances in the areas of research on current techniques for characterizing soil SON and the size, nature, and dynamics of soil SON pools in forest ecosystems.     

Mobilisation of AS and trace metals in saline,acidic Sopolic Technosols: the role of the rhizosphere and flooding conditions

Purpose  

The aim of this work was to study the risk of As and metal pollution in saline wetlands affected by slightly acidic mine wastes, in the presence or absence of a plant rhizosphere, under different flooding regimes. Some guidelines for management will be proposed in order to minimise the risk of metal leaching in metal-polluted salt marshes.     

Effects of Composted Pulp and Paper Industry Wastewater Treatment Residuals on Soil Properties And Cereal Yield

The aim of this study was to investigate effects of pulp and paper industry wastewater treatment sludge composts on soil and cereal crops. Five forest industry wastewater sludge composts were tested in a field study which was conducted in a silty clay soil in southern Finland with barley in 1998, with oats in 1999 and with barley in 2000. Two composts contained only pulp mill biosludge and bark in a ratio of 1:4 and 1:2, respectively. Two other composts were mixtures of biosludge and primary sludge with the addition of bark in a ratio of 1:2 and 3:4, respectively. These two wastewater sludges originated from a pulp mill and from a recycled paper mill. The fifth compost consisted of biosludge and primary sludge from a board mill. Two application rates of each compost were studied: the low rate was based on an annual P fertilization rate recommended for barley, 50-200 m³/ha; and the high rate was a double or triple the low rate depending on the mineral N concentration of the compost, 150-600 m³/ha. Based on the Finnish fertilizer recommendations, nutrient demands of the test plants were annually fulfilled by mineral fertilizers depending on the treatment. Total contents of N, P, K and Ca in composts were 8.8-17.5, 0.7-3.9, 1.5-6.5, and 4-25 g/kg dry matter, respectively. Especially at high doses, composts had beneficial effects on soil bulk density, porosity, C and N contents and C:N ratio. Despite the high total N rates applied with the composts, the mineralization following crop harvest did not significantly increase soil nitrate late autumn or following spring as compared to the soils that received mineral fertilization. There was no significant difference in the grain yields between plots that received mineral fertilization and compost treatments supplemented with mineral fertilizers. However, there was a decreased fertilization effect of some composts on straw yields during the first experimental year, indicating immobilization of mineral N. Heavy metals added in soil with the composts did not significantly increase their concentrations in the grain crops. All the composts had relatively low nutrient contents and low fertilizing value, but beneficial effects on soil properties and were regarded as soil conditioners. Soil improving and fertilizing effects of the composts varied annually depending on the weather conditions during the growing season. Heavy metal concentrations of the composts studied were far below the limit values set for the soil conditioners in the Finnish government regulations.     

Effect of 7-year application of a nitrification inhibitor, dicyandiamide (DCD), on soil microbial biomass, protease and deaminase activities, and the abundance of bacteria and archaea in pasture soils

Purpose

The nitrification inhibitor dicyandiamide (DCD) has been shown to be highly effective in reducing nitrate (NO₃ ^?) leaching and nitrous oxide (N₂O) emissions when used to treat grazed pasture soils. However, there have been few studies on the possible effects of long-term DCD use on other soil enzyme activities or the abundance of the general soil microbial communities. The objective of this study was to determine possible effects of long-term DCD use on key soil enzyme activities involved in the nitrogen (N) cycle and the abundance of bacteria and archaea in grazed pasture soils.

Materials and methods

Three field sites used for this study had been treated with DCD for 7 years in field plot experiments. The three pasture soils from three different regions across New Zealand were Pukemutu silt loam in Southland in the southern South Island, Horotiu silt loam in the Waikato in the central North Island and Templeton silt loam in Canterbury in the central South Island. Control and DCD-treated plots were sampled to analyse soil pH, microbial biomass C and N, protease and deaminase activity, and the abundance of bacteria and archaea.

Results and discussion

The three soils varied significantly in the microbial biomass C (858 to 542 μg C g^?1 soil) and biomass N (63 to 28 μg N g^?1), protease (361 to 694 μg tyrosine g^?1 soil h^?1) and deaminase (4.3 to 5.6 μg NH₄ ⁺ g^?1 soil h^?1) activity, and bacteria (bacterial 16S rRNA gene copy number: 1.64?×?10⁹ to 2.77?×?10⁹ g^?1 soil) and archaea (archaeal 16S rRNA gene copy number: 2.67?×?10⁷ to 3.01?×?10⁸ g^?1 soil) abundance. However, 7 years of DCD use did not significantly affect these microbial population abundance and enzymatic activities. Soil pH values were also not significantly affected by the long-term DCD use.

Conclusions

These results support the hypothesis that DCD is a specific enzyme inhibitor for ammonia oxidation and does not affect other non-target microbial and enzyme activities. The DCD nitrification inhibitor technology, therefore, appears to be an effective mitigation technology for nitrate leaching and nitrous oxide emissions in grazed pasture soils with no adverse impacts on the abundance of bacteria and archaea and key enzyme activities.     

Influence of two-phase olive mill waste application to soil on terbuthylazine behaviour and persistence under controlled and field conditions

Purpose  

Terbuthylazine is one of the most common herbicides used to control weeds in olive groves. Application of two-phase olive mill waste (OW) to soils may play a fundamental role in the management of leaching losses of pesticides, especially in Mediterranean areas where soils are characterized by low organic matter levels. We evaluated the impact of OW amendments on the sorption–desorption, degradation, leaching, and persistence of the herbicide terbuthylazine in a representative olive grove soil from Portugal.