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.     

The N transformation mechanisms for rapid nitrate accumulation in soils under intensive vegetable cultivation

Purpose  

Rapid soil degradation occurring under intensive vegetable cultivation, an increasingly common agricultural strategy in China, is characterized by soil acidification, salinity, and NO₃⁻ accumulation. However, to date, the reasons for rapid NO₃⁻ accumulation in soils at the nitrogen (N) levels have not been completely understood. In this study, we explored the underlying mechanisms for rapid NO₃⁻ accumulation in soils used for intensive vegetable cultivation and implications of altered gross N transformation rates on soil properties and sustainable cultivation.     

福建菜田氮磷积累状况及其淋失潜力研究

本文通过采集460个福建菜田代表性耕层土样,采用土壤测试和土柱渗漏水模拟试验的方法研究菜田土壤硝态氮和Olsen P含量状况和淋失临界指标及其淋失潜力。结果表明,耕层土壤硝态氮含量为47.455.5 mg/kg,Olsen-P含量则为61.743.2 mg/kg, 其中瓜果类蔬菜种植地土壤硝态氮和Olsen-P含量明显高于叶菜类和根茎类蔬菜种植地。 应用双速率转折点建模法,得到氮、 磷淋失临界指标X0分别为土壤硝态氮76.3 mg/kg和Olsen-P 42.8 mg/kg。 淋失临界值相当于或略高于满足蔬菜营养的农学指标。当土壤硝态氮或Olsen-P含量低于X0时,随着其含量增加,渗漏水硝态氮或总磷浓度以线性方式缓慢增加,反之,则以非线性形式急剧增大。土壤硝态氮和Olsen-P含量高于其X0的土样数分别占17.9%和81.3%, 表明这些样点具有较高的氮、 磷淋失潜力,是氮、 磷污染控制的关键地块。 瓜果类菜田土壤硝态氮和Olsen-P含量高于其X0的土样数分别占到32.3%和96.3%,淋失潜力明显高于叶菜类和根茎类菜田,是氮、 磷污染控制的优先区域。     

Strategies for high nitrogen production and fertilizer value of plant-based fertilizers

Background

Organic vegetable production has a demand for alternative fertilizers to replace fertilizers from sources that are not organic, that is, typically animal-based ones from conventional farming.

Aims

The aim of this study was to develop production strategies of plant-based fertilizers to maximize cumulative nitrogen (N) production (equal to N yield by green manure crops), while maintaining a low carbon-to-nitrogen (C:N) ratio, and to test the fertilizer value in organic vegetable production.

Methods

The plant-based fertilizers consisted of the perennial green manure crops—alfalfa, white clover, red clover, and a mixture of red clover and ryegrass—and the annual green-manure crops—broad bean, lupine, and pea. The crops were cut several times at different developmental stages. The harvested crops were used fresh or pelleted as fertilizers for field-grown white cabbage and leek. The fertilizer value was tested with respect to biomass, N offtake, N recovery, and soil mineral N (N_min). Poultry manure and an unfertilized treatment were used as controls.

Results

The cumulative N production of the perennial green manure crops ranged from 300 to 640 kg N ha^–1 year^–1 when cut two to five times. The highest productions occurred at early and intermediate developmental stages, when cut three to four times. Annual green manure crops produced 110–320 kg N ha^–1 year^–1, since repeated cutting was restricted. The C:N ratio of the green manure crops was 8.5–20.5, and increased with developmental stage. The fertilizer value of green manure, as measured in white cabbage and leek, was comparable to animal-based manure on the condition that the C:N ratio was low (<18). N recovery was 20%–49% for green manure and 29%–42% for poultry manure. A positive correlation was detected between soil N_min and vegetable N offtake shortly after incorporating the green manure crops, indicating synchrony between N release and crop demand.

Conclusions

Plant-based fertilizers represent highly productive and efficient fertilizers that can substitute conventional animal-based fertilizers in organic vegetable production.     

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.     

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.     

Mineral‐nitrogen and phosphorus leaching from vegetable gardens in Niamey,Niger

Urban and periurban agriculture (UPA) contributes significantly to meeting increasing food demand of rapidly growing urban populations in West African cities. The often intensive high‐input vegetable production within UPA results in large positive nutrient balances, being presumably linked to strong nutrient leaching which needs quantification. This study aimed at estimating leaching losses of mineral N and P in three representative urban gardens of Niamey, Niger, using ion‐exchange‐resin cartridges installed below the crop rooting zone at 0.6 m soil depth. In 2007, a year with below‐average annual rainfall (425 mm as compared to 542 mm), mean leaching of mineral N amounted to 5.9 and 7.3 kg N ha^–1 for two gardens with > 80% sand fraction and only 2.2 kg N ha^–1 for a garden with 40% silt and clay. Apparent annual P leaching was 0.7 kg P ha^–1 in all three gardens. Additional multiannual studies are necessary to assess the effect of inter‐ and intraannual variation in precipitation on nutrient leaching in intensive UPA vegetable production of semiarid West Africa.     

Nitrates in soil after long‐term management for dryland grain sorghum and winter wheat

Abstract

The leaching of phosphorus (P), nitrogen (N), and radionuclides (²³²Th, ²²⁶Ra, ²²⁸Ra, and ⁴⁰K) from Joel sands amended with red mud/gypsum (RMG) at 9 rates (0, 2, 4, 8, 16, 32, 64, 128, and 256 t/ha) was measured using columns. Intense leaching conditions (34 mm/day for 12 days) and a high rate of applied P (320 kg/ha as superphosphate) and N (680 kg/ha as ammonium nitrate) were used to simulate extremes of irrigated vegetable production on the Swan Coastal Plain. Addition of the highest rate of RMG (256 t/ha) reduced leaching of fertiliser P and ammonium‐nitrogen (NH₄‐N) by 85% and 50%, respectively, compared with 0 t/ha after 12 days. At 641 RMG/ha P leaching was reduced 50% compared with 0 t/ha. Nitrate‐nitrogen (NO₃‐N) leaching was not affected by addition of RMG.

Reduced leaching of NH₄‐N was attributed to an increase in cation exchange capacity of the soil with the addition of RMG. Bicarbonate‐extractable P in the soil increased with rate of RMG to >50 μg P/g soil at 256 t/ha. This indicates that soil testing of residual P could be used to reduce P inputs to vegetable crops after soils were amended with RMG. This would further reduce the impact of vegetable production on the water systems of the Swan Coastal Plain and extend the period of effectiveness of RMG amended soils. The increase in ²³²Th specific activity in Joel sand amended with RMG was well below statutory limits even at the highest rate. Neither ⁴⁰K nor ²²⁶Ra were detectable in RMG amended sands up to 2561 RMG/ha. There was no evidence of leaching of ²²⁶Ra or ²²⁸Ra at any rate of RMG. These results suggest that the use of RMG amendment on commercial horticultural properties on the Swan Coastal Plain could be feasible.     

Effects of two contrasting agricultural land‐use practices on nitrogen leaching in a sandy soil of Middle Germany

The objective of this study is to evaluate different agricultural land‐use practices in terms of N leaching and to give recommendations for a sustainable agriculture on sandy soils in Middle Germany. Soil mineral N (N_min) and leachate N were quantified at a sandy soil in N Saxony during 3 years. Two treatments were applied: intensive (I)—using inorganic and organic fertilizer and pesticides, and organic (O)—exclusively using organic fertilizer, legume‐based crop rotation, and no pesticides. Split application of mineral fertilizers did not result in substantial N losses at treatment I. Legumes induced a considerable increase of soil mineral N and particularly of leachate mineral N (N_{min_perc}) at treatment O. High N_{min_perc} concentrations (up to 78 mg N L^–1) were observed during as well as after the cultivation of legumes. These high N_{min_perc} concentrations are the reason why clearly higher N_{min_perc} losses were determined at treatment O (62 kg N ha^–1 y^–1) compared to treatment I (23 kg N ha^–1 y^–1). At both treatments, the quantity of N losses was strongly affected by the precipitation rates. Concentrations and losses of dissolved organic N (DON_perc) were assessed as above average at both treatments. The results suggest that the DON_perc concentration is influenced by precipitation, soil coverage, and organic fertilizers. Higher values were determined in the percolation water of treatment O. The average annual DON_perc losses amounted to 15 kg N ha^–1 at I and to 32 kg N ha^–1 at O. The average monthly percentage of DON_perc losses on the loss of the dissolved total N of percolation water (DTN_perc) ranged between <1% and 55% at O and between 2% and 56% at I. For the whole measuring period of 29 months, the relative amounts of DON_perc of DTN_perc (21% at O and 25% at I) were more or less the same for both treatments. The results show that DON_perc can contribute significantly to the total N loss, confirming the importance to consider this N fraction in N‐leaching studies. It was concluded that at sandy sites, a split application of mineral fertilizers, as applied at treatment I, seems to be more expedient for limiting the N leaching losses than legume‐based crop rotations.     

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.     

Effects of 3,4-dimethylpyrazole phosphate (DMPP) on the abundance of ammonia oxidizers and denitrifiers in two different intensive vegetable cultivation soils

Purpose

Nitrification and denitrification in the N cycle are affected by various ammonia oxidizers and denitrifying microbes in intensive vegetable cultivation soils, but our current understanding of the effect these microbes have on N₂O emissions is limited. The nitrification inhibitor, 3,4-dimethylpyrazole phosphate (DMPP), acts by slowing nitrification and is used to improve fertilizer use efficiency and reduce N losses from agricultural systems; however, its effects on nitrifier and denitrifier activities in intensive vegetable cultivation soils are unknown.

Materials and methods

In this study, we measured the impacts of DMPP on N₂O emissions, ammonia oxidizers, and denitrifying microbes in two intensive vegetable cultivation soils: one that had been cultivated for a short term (1 year) and one that had been cultivated over a longer term (29 years). The quantitative PCR technique was used in this study. Three treatments, including control (no fertilizer), urea alone, and urea with DMPP, were included for each soil. The application rates of urea and DMPP were 1800 kg ha^?1 and 0.5% of the urea-N application rate.

Results and discussion

The application of N significantly increased N₂O emissions in both soils. The abundance of ammonia-oxidizing bacteria (AOB) increased significantly with high rate of N fertilizer application in both soils. Conversely, there was no change in the growth rate of ammonia-oxidizing archaea (AOA) in response to the applied urea despite the presence of larger numbers of AOA in these soils. This suggests AOB may play a greater role than AOA in the nitrification process, and N₂O emission in intensive vegetable cultivation soils. The application of DMPP significantly reduced soil NO₃^?-N content and N₂O emission, and delayed ammonia oxidation. It greatly reduced AOB abundance, but not AOA abundance. Moreover, the presence of DMPP was correlated with a significant decrease in the abundance of nitrite reductase (nirS and nirK) genes.

Conclusions

Long-term intensive vegetable cultivation with heavy N fertilization altered AOB and nirS abundance. In vegetable cultivation soils with high N levels, DMPP can be effective in mitigating N₂O emissions by directly inhibiting both ammonia oxidizing and denitrifying microbes.

     

Utilization of waste office paper to reduce nitrate leaching into the Northern Guam aquifer

 Rapid nitrate leaching losses due to current agricultural N management practices under the humid tropical environmental conditions of the Pacific island of Guam may contaminate fresh and salt water resources. Potential environmental contamination of the Northern Guam aquifer, which is overlain by shallow limestone-derived soils, is a major public concern because the aquifer is the sole underground source of fresh water for the island. The objectives of this study were to examine the use of waste office paper as a possible management alternative for reducing nitrate leaching due to N fertilizer applications in northern Guam while also providing sufficient N for crop growth. In a laboratory study, increasing rates of waste paper application reduced NO₃ ^–-N leaching up to approximately 200 days after incorporation of N fertilizer and paper treatments. Subsequent mineralization of immobilized N from paper applications was also observed, although cumulative NO₃ ^–-N leaching at the highest rate of paper addition was lower than the control after 394 days of incubation. The effect of waste paper on N availability and NO₃ ^–-N leaching after application of N fertilizer at rates up to 500 kg N ha^–1 was also evaluated in two field experiments planted with sweet corn (Zea mays var. rugosa Bonaf.) during consecutive dry and wet periods. Leaching losses of NO₃ ^–-N were higher during the wet cropping season, leading to lower crop yields and crop N uptake. Combining paper with N fertilizer reduced NO₃ ^–-N leaching losses but also decreased crop ear yields up to N fertilizer application rates of 250 kg N ha^–1 during the dry cropping season and up to rates of 100 kg N ha^–1 during the wet period. Although combining waste paper with N fertilizer reduced NO₃ ^–-N leaching losses, no improvements in fertilizer N recovery were observed during the field experiments. This lack of crop response may be due to the importance of early season N availability for the short-season horticultural crops grown on Guam. We suggest that the application of waste paper may be a useful management practice to reduce NO₃ ^–-N leaching losses when high soil NO₃ ^–-N levels remain after cropping due either to crop failure or to over-application of N fertilizer. Received: 11 May 1999     

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.     

Leachability of Nitrate from Sandy Soil using Waste Amendments

Environmental issues associated with intensive use of nitrogenous fertilizers have generated an interest in alternative management systems. An experiment was conducted to mitigate nitrate leaching from sandy soil using different waste materials such as charcoal, manure, sawdust, wood ash, and control (no amendment). Urea was applied at the rate of 300 kg nitrogen (N) ha^?1. Nitrate was determined during six leaching events. During an incubation experiment, nitrate release was also determined in soil amended with charcoal at the rates of 0, 10, 20, and 40 t ha^?1. Urea was applied at the rates of 0, 100, 200, 400, and 1000 ppm N. Results indicated that urea application increased nitrate (NO₃) concentration in leachate. Soil amendments substantially reduced NO₃ in leachates irrespective of the type of material used. Waste amendments differed for NO₃ leaching as follows: charcoal < wood ash < sawdust < manure. Leaching of NO₃ enhanced up to the fourth leaching event and thereafter reduced significantly. Nitrate retention in soil varied among material in the order of manure > charcoal > wood ash > sawdust. Nitrate accumulation occurred in the lower layer (25–50 cm) of soil column after the leaching process. Application of charcoal retained greater NO₃ level as compared to control soil during an incubation. Enhanced urea applications also enhanced NO₃ release. This experiment suggests that waste material can be viably recycled to mitigate NO₃ concentration in water.     

中国北方主要农区农田氮磷淋溶特征与时空规律

中国北方黑土区、潮土区和褐土区是我国农业主产区,大水大肥问题尤为突出,氮磷淋溶是全国典型的地下水污染来源。然而,中国北方主要农区农田氮磷淋溶特征和时空规律尚不清楚。本文利用田间原位监测和文献荟萃分析方法,系统分析了中国北方主要农区285个监测点年的4种主要种植模式(春玉米、冬小麦-夏玉米、露地蔬菜、保护地蔬菜)农田氮磷淋溶特征与时空规律。研究结果表明,中国北方4个主要种植模式的平均氮和磷淋溶强度分别为:保护地蔬菜117.5 kg(N)·hm~(-2)和0.74 kg(P)·hm~(-2),露地蔬菜51.7kg(N)·hm~(-2)和0.10kg(P)·hm~(-2),冬小麦-夏玉米轮作49.9kg(N)·hm~(-2)和0.07kg(P)·hm~(-2),春玉米30.7kg(N)·hm~(-2)和0.09kg(N)·hm~(-2)。与粮田相比,蔬菜田的高水肥投入决定了其较高的氮磷淋溶量。受土壤质地以及区域间水肥管理差异的影响,同一种植模式下,总氮淋溶强度为黑土区褐土区潮土区。农田氮磷淋溶年际间变化主要受降雨强度的影响,总氮淋溶量与降雨强度呈正线性相关关系,尤其前一年无淋溶事件发生背景下,下一年的淋溶量会急剧增加。空间尺度上,潮土区和褐土区是氮素淋溶的主要风险区。值得注意的是一些蔬菜种植面积尤其是保护地蔬菜种植面积占比较大的省份表现出较高的氮磷淋溶风险。综上,北方主要农区农田氮磷淋溶风险以氮为主,磷的淋溶风险也不容忽视。潮土区和褐土区是氮素淋溶的主要风险区。区域尺度上,氮磷淋溶主要来自粮田,但菜田面积越大,氮磷淋溶风险越高。     

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.     

Effects of organic material amendment and water content on NO, N2O, and N2 emissions in a nitrate-rich vegetable soil

Amending vegetable soils with organic materials is increasingly recommended as an agroecosystems management option to improve soil quality. However, the amounts of NO, N₂O, and N₂ emissions from vegetable soils treated with organic materials and frequent irrigation are not known. In laboratory-based experiments, soil from a NO ₃ ^? -rich (340 mg N?kg^?1) vegetable field was incubated at 30°C for 30 days, with and without 10 % C₂H₂, at 50, 70, or 90 % water-holding capacity (WHC) and was amended at 1.19 g?C kg^?1 (equivalent to 2.5 t?C ha^?1) as Chinese milk vetch (CMV), ryegrass (RG), or wheat straw (WS); a soil not amended with organic material was used as a control (CK). At 50 % WHC, cumulative N₂ production (398–524 μg N?kg^?1) was significantly higher than N₂O (84.6–190 μg N?kg^?1) and NO (196–224 μg N?kg^?1) production, suggesting the occurrence of denitrification under unsaturated conditions. Organic materials and soil water content significantly influenced NO emissions, but the effect was relatively weak since the cumulative NO production ranged from 124 to 261 μg N?kg^?1. At 50–90 % WHC, the added organic materials did not affect the accumulated NO ₃ ^? in vegetable soil but enhanced N₂O emissions, and the effect was greater by increasing soil water content. At 90 % WHC, N₂O production reached 13,645–45,224 μg N?kg^?1 from soil and could be ranked as RG?>?CMV?>?WS?>?CK. These results suggest the importance of preventing excess water in soil while simultaneously taking into account the quality of organic materials applied to vegetable soils.     

Long-term tree growth rate,water use efficiency,and tree ring nitrogen isotope composition of <Emphasis Type="Italic">Pinus massoniana</Emphasis> L. in response to global climate change and local nitrogen deposition in Southern China

Purpose  

We aimed to investigate long-term tree growth rates, water use efficiencies (WUE), and tree ring nitrogen (N) isotope compositions (δ¹⁵N) of Masson pine (Pinus massoniana L.) in response to global climate change and local N deposition in Southern China.     

The potential of using 15N natural abundance in changing ammonium-N and nitrate-N pools for studying in situ soil N transformations

Purpose

This study examined the usefulness of ¹⁵N natural abundance (δ¹⁵N) with in situ core incubation to quantify the predominant N transformation processes in a natural suburban forest of subtropical Australia, which was subjected to prescribed burning.

Materials and methods

In situ core incubation for 3 days with 20 ml water, or 160.79 ml of 60 mg L^?1 NO₃^?-N surface application, and in situ core with 160.79 ml water but without incubation were set up in Toohey forest for sampling three times as before (once) and after (twice) a prescribed burning. The δ¹⁵N of NH₄⁺-N and NO₃^?-N in the top 5 cm soil before and after the incubation, and δ¹⁵N of NO₃^?-N in the 5–10 cm soil before incubation were compared with each other to examine the soil N mineralisation, nitrification, denitrification, and nitrate leaching processes.

Results and discussion

The significant decrease in δ¹⁵N of NH₄⁺-N after incubation under 20 ml water treatment was ascribed to soil N mineralisation, and the significant decrease in δ¹⁵N of NH₄⁺-N and significant increase in δ¹⁵N of NO₃^?-N after incubation with elevated water and nitrate inputs were associated with N mineralisation and nitrification, respectively, 2 months after the burning. The 160.79 ml water treatment also triggered nitrification in the baseline soil cores in both samplings after the burning. Water was crucial to stimulate soil N mineralisation and nitrification, but excessive water depleted labile N pools and reduced N mineralisation and nitrification. Burning effects were hard to separate from the seasonal impacts on soil N cycling processes.

Conclusions

The δ¹⁵N in soil mineral N pools was sensitive to indicate soil N mineralisation and nitrification processes. Soil water and labile N were determining factors for N transformations in the soil. It is suggested that δ¹⁵N combined with soil inorganic N concentrations and net N transformation rates could be used to identify primary N transformation processes. More frequent samplings would be needed to differentiate burning impacts from the seasonal impacts on soil N cycling processes.

     

Nitrogen leaching and herbage production on intensively managed grass and grass-clover pastures on sandy soil in Finland

The main aim of this study was to compare the N leaching from grass fertilized with 220 kg N ha⁻¹ and grass‐clover pastures receiving no fertilization during three grazing years and a renewal year, in a 4‐year ley rotation. The other aim was to compare the herbage and milk production of these pastures. The study was conducted on a lysimeter field; five lysimeters (size 10 × 10 m) were assigned to each treatment. Automated drinking water outlets for the cows were located on one of the lysimeters on each treatment. The amount of leachate was recorded and composite samples were analysed for total N, NO₃‐N, NH₄‐N and soluble organic N (SON). The number of grazing cows was adjusted according to the herbage mass production. The amount of milk was measured. The total input of N to the area was 290 and 215 kg N ha⁻¹ year⁻¹ for grass and grass‐clover treatments, respectively. The total N leaching during grazing years was 17 and 9 kg N ha⁻¹ from grass and grass‐clover treatments, respectively. Renewal of the sward increased N leaching in both treatments, up to 60 and 40 kg total N ha⁻¹ in grass and grass‐clover treatments, respectively. During the grazing years 96% of the leached N was in the form of NO₃‐N, but during the renewal year the proportion of NO₃‐N was lowered to 89% and the rest was in the form of SON. The total amount of N in the surface runoff was 3–5 kg ha⁻¹ year⁻¹. As high N fertilizer rates per application are a common practice in Finland, short‐term grass‐clover pastures can be considered environmentally beneficial when compared with intensively fertilized grass pastures in comparable circumstances.