Remediation of a long-term copper-contaminated soil using a polyacrylate polymer

Abstract. We investigated whether a polyacrylate polymer could be used to remediate a soil which had been contaminated with copper for many years. Perennial ryegrass was grown in a loamy sand containing 230 mg ammonium-acetate-EDTA extractable Cu kg⁻¹ and amended with 0, 0.1 and 0.2% of polymer. Growth of perennial ryegrass was stimulated in the polymer-amended soil, especially in the soil with 0.1% of polymer. After plant growth for 177 days, the amount of water extractable copper present in the unamended soil was 17 times that of the original soil. In the soil amended with 0.1% of polymer the level of copper after plant growth was only 0.11 times the amount present in the unamended soil. When the soil was incubated with polymer in the absence of plants, the level of water extractable copper was not reduced. The polymer seems to compete with plants for copper, and to prevent the increase of copper in soil solution brought about by root exudates.     

Polyacrylate polymers as immobilizing agents to aid phytostabilization of two mine soils

We evaluated the effect of polyacrylate polymers as immobilizing agents to aid phytostabilization of two mine soils. One soil had a very low pH (3.7) and a large Pb content, while the other was less acidic but had a greater content of Cu and Zn. Growth of perennial ryegrass ( Lolium perenne L. cv. Victorian) was stimulated in polymer-amended soils. After ryegrass had been growing for 35 days, the amounts of water-extractable Cu, Zn and Pb (one soil only) present in the polymer-amended soils were smaller than those from soil without polymer. The number of culturable heterotrophic bacteria and the activities of dehydrogenase and β-glucosidase increased following polymer application. In contrast, the urease activity was impaired by polymer application, presumably because of the presence of ammonium as a counter ion. In another experiment, the acidic soil was limed to pH 6.5 before growth of perennial ryegrass took place. Liming the soil greatly enhanced plant growth, but by the third cut, differences between treatments became apparent, with plants from polymer-amended limed soil accumulating a greater biomass compared with limed soil without polymer. After ryegrass had been growing for 119 days (five cuts), the amount of water-extractable Pb and the urease activity in the polymer-amended soil were smaller than those from limed soil without polymer. The numbers of culturable heterotrophic bacteria and the activities of dehydrogenase, β-glucosidase and acid phosphatase increased following polymer application. The results are consistent with phytostabilization being achieved by the application of polyacrylate polymers, improving soil chemical and biological properties. In very acidic soils, the use of both a liming material and polymer together appears to give a considerable advantage.     

Amendment of an Acid Mine Soil with Compost and Polyacrylate Polymers Enhances Enzymatic Activities but may Change the Distribution of Plant Species

Many soils derived from pyrite mines spoils are acidic, poor in organic matter and plant nutrients, contaminated with trace elements, and support only sparse vegetation. The establishment of a plant cover is essential to decrease erosion and the contamination of water bodies with acid drainage containing large concentrations of trace elements. We tested the application of compost and polyacrylate polymers to promote the growth of indigenous plant species present in the mine area. Soil treatments consisted of unamended soil (control), soil with mineral fertilizers only, soil with fertilizer plus compost, soil with fertilizer plus polyacrylate polymers, and soil with fertilizer plus both amendments. Half of the soil was grown with Briza maxima L. (greater quaking grass), Chaetopogon fasciculatus (Link) Hayek (chaetopogon), and Spergularia purpurea (Persoon) G. Don fil. (purple sandspurry), while the remainder was left bare. In the absence of plants, the greatest improvements in soil conditions were obtained by the application of both amendments, which was associated with the greatest values of protease, acid phosphatase, and β-glucosidase, whereas the activity of cellulase and microbial respiration were similar in soil amended with compost or polymer. Dehydrogenase activity was greatest in soil with compost (with or without polymer), whereas urease activity was impaired by both amendments. In the presence of plants, the application of both amendments led to the greatest activities of protease, urease, β-glucosidase, cellulase, and microbial respiration, but acid phosphatase was mainly enhanced by polymer and dehydrogenase was increased by compost. Plant growth was stimulated in all treatments compared with unamended soil, but the greatest value for total accumulated biomass was obtained in fertilized soil receiving both amendments. However, species responded differently to treatment: while the growth of B. maxima was greatest in soil with compost and polymer, the growth of C. fasciculatus responded better to soil with compost, and S. purpurea grew better in polymer-amended soil. The amendments tested improved the quality of a mine soil and stimulated plant growth. However, botanical composition likely changes over time with amendments, and this needs to be considered when a large scale application of amendments is projected.     

Toxic effect of cadmium and nickel on soil enzymes and the influence of adding sewage sludge

Sewage sludge is increasingly used as an organic amendment to soil, especially to soil containing little organic matter. However, little is known about the utility of this organic amendment in the reclamation of soil polluted with heavy metals. We studied the effects of adding sewage sludge on enzymatic activities of a semi-arid soil contaminated with Cd or Ni in the laboratory. The activities of urease, phosphatase, β-glucosidase and protease-BAA were measured in soil containing concentrations of Cd or Ni in the range 0–8000 mg kg⁻¹ soil, and their inhibition was compared with those of the enzymatic activities in the same soil amended with sewage sludge and containing similar concentrations of the heavy metals. The inhibition was tested for three different incubation times to determine changes in the effect of the heavy metals on hydrolase activity with the time elapsed after contamination. Ecological dose (ED) values of Cd and Ni were calculated from three mathematical models which described the inhibition of the enzymatic activities with increasing concentrations of heavy metal in the soil. For urease and phosphatase activities, the ED values for Cd and Ni increased after application of sewage sludge to soil, indicating a decrease in Cd and Ni toxicity. The other two enzymes (β-glucosidase and protease-BAA) were less sensitive to Cd or Ni contamination, and it was more difficult to determine whether addition of sewage sludge had affected the inhibition of these enzymes by the heavy metals.     

Influence of smoke exposure on soil enzyme activities and nitrification

Summary Soil was exposed to red phosphorous/butyl rubber (RP/BR) aerosols at various relative humidities in a recirculating environmental wind tunnel. Soil microbial and enzymatic activities were measured immediately after exposure and periodically thereafter for 56 days. The nitrification potential was significantly reduced in soil amended with ammonium sulfate and exposed to RP/BR smoke, and could be related to a decline in soil pH. The rate of nitrate formation in unamended soil with time was also reduced, but by 57 days postexposure, concentrations were similat to those of unexposed controls in all but the thinnest soil lense. Soil dehydrogenase and phosphatase enzyme activities were sensitive to RP/BR smoke and in some treatments no activity was detected. The measured activities did not recover within the 56-day postexposure period and in some cases declined. Soil lense thickness was the greatest factor controlling the degree of RP/BR effects, indicating that injury to soil microbial and enzymatic activities may be surficial. Deposition of smoke particles increased with increasing relative humidity, which had a significant impact on the activities measured.     

Remediation of a Sandy Soil Contaminated with Cadmium,Nickel, and Zinc using an Insoluble Polyacrylate Polymer

Abstract

This study was carried out to investigate whether an insoluble polyacrylate polymer could be used to remediate a sandy soil contaminated with cadmium (Cd) (30 and 60 mg Cd kg^?1 of soil), nickel (Ni) (50 and 100 mg Ni kg^?1 of soil), zinc (Zn) (250 and 400 mg Zn kg^?1 of soil), or the three elements together (30 mg Cd, 50 mg Ni, and 250 mg Zn kg^?1 of soil). Growth of perennial ryegrass was stimulated in the polymer‐amended soil contaminated with the greatest amounts of Ni or Zn, and when the three metals were present, compared with the unamended soil with the same levels of contamination. Shoots of plants cultivated in the amended soil had concentrations of the metals that were 24–67% of those in plants from the unamended contaminated soil. After ryegrass had been growing for 87 days, the amounts of water‐extractable metals present in the amended soil varied from 8 to 53% of those in the unamended soil. The results are consistent with soil remediation being achieved through removal of the metals from soil solution.     

Remediation of a mine soil with insoluble polyacrylate polymers enhances soil quality and plant growth

We investigated the effects of different application rates of insoluble hydrophilic polyacrylate polymers on plant growth and soil quality from a Pb‐contaminated mine soil. The polymer increased the water‐holding capacity of the soil from about 250 g/kg in unamended soil to almost 1000 g/kg in soil with 0.6% polymer. However, the capacity of the polymer to retain water decreased progressively, presumably as the polymer sorbed Pb. Growth of orchardgrass (Dactylis glomerata L. cv. Amba) was stimulated in the polymer‐amended soil. The greatest accumulated biomass over four cuts was obtained in soil amended with 0.4% of polymer. After orchardgrass had been growing for 101 days, the amounts of CaCl₂‐extractable Pb present in the polymer‐amended soil were 15–66% of those in the unamended soil, depending on polymer application rate. The number of bacteria culturable on agar enriched with ‘Nutrient’ and yeast extract, and the activities of dehydrogenase, phosphatase, β‐glucosidase, protease and cellulase increased following polymer application. In contrast, urease activity was impaired by polymer application, presumably due to the presence of ammonium as a counter ion. Principal component analysis was used to compare the effects of the different rates of polymer application. Overall, the application of 0.2 or 0.4% polymer resulted in closer values for the indicators of soil quality used than the treatment with 0.6% polymer.     

长期施肥土壤中酶活性的剖面分布及其动力学特征研究

对连续25年的长期培肥试验地中土壤剖面酶活性的分布及土壤酶的催化反应特性进行了研究,结果发现,土壤脲酶、碱性磷酸酶和蔗糖酶活性在土壤剖面中的分布从表层到深层,酶活性依次减小;而多酚氧化酶呈波浪型分布。土壤中脲酶、碱性磷酸酶、蔗糖酶活性与相应土层的有机质含量呈极显著正相关;多酚氧化酶无此相关性。土壤脲酶和碱性磷酸酶活性均随时间的延长而逐渐趋于一个稳定值,且各个时段酶活性均为施肥处理高于不施肥处理,说明施肥能显著提高土壤酶活性。土壤脲酶和碱性磷酸酶酶促反应初速度(V0)均随温度和底物浓度的增加而增加,至一定温度和底物浓度时,V0不再增加;不同培肥措施下V0为:厩肥秸秆化肥对照。     

Relationship between vegetation diversity and soil functional diversity in native mixed-oak forests

Most studies on the interactions between aboveground vegetation and belowground soil diversity have been carried out in microcosms or manipulated field plots. In the current study, we investigated the relationship between forest vegetation diversity and soil functional diversity (calculated from the activity of soil enzymes) in naturally developed plant communities of native mixed-oak forests without imposing any disturbances to already existing plant–soil relationships. In order to do so, five different vegetation types, i.e., herbaceous plants, climbing plants, trees, shrubs, and ferns, were considered. Correlations between plant diversity, soil physicochemical properties, and soil enzyme activities were determined. Soil physicochemical parameters appeared strongly correlated with both enzyme activities (e.g., pH was positively correlated with amidase and arylsulphatase, and negatively with acid phosphatase; OM content was positively correlated with β-glucosidase, acid and alkaline phosphatase and urease, and negatively with amidase; total N was positively correlated with β-glucosidase, and acid and alkaline phosphatase, and negatively with amidase) and soil functional diversity. For ferns, strong correlations between enzyme activities and plant diversity indexes were found (i.e., dehydrogenase was positively correlated with species richness and Shannon's diversity; acid and alkaline phosphatase were negatively correlated with Shannon's diversity; acid phosphatase was also negatively correlated with species richness). Most interestingly, herbaceous plants and ferns showed a strong positive correlation between Shannon's plant diversity and soil functional diversity. Furthermore, herbaceous plants showed a strong positive correlation between species richness and soil functional diversity. Although these correlations between plant diversity and soil functional diversity might possibly be due to the fact that higher values of plant richness and diversity result in a greater habitat heterogeneity in the soil, current knowledge on the topic is mixed and very incomplete and, then, one must be extremely cautious when interpreting such correlations.     

土壤酶活性对土壤中土霉素的动态响应

采用室内培养试验研究了土霉素（OTC）对土壤过氧化氢酶、磷酸酶、脲酶、蔗糖酶和脱氢酶活性的影响。结果表明,在整个培养期间,土霉素对土壤过氧化氢酶和土壤磷酸酶活性具有明显的抑制作用;对土壤蔗糖酶和脱氢酶活性在培养前期具有轻微的抑制作用,但培养后期（培养第112 d）具有较强的抑制作用;而对土壤脲酶活性的影响则相反,在培养第1 d,OTC 100 mg/kg处理对脲酶具有显著的刺激作用,以后土霉素对脲酶活性影响不明显。土壤过氧化氢酶和磷酸酶对土霉素污染响应比土壤脲酶、蔗糖酶和脱氢酶更敏感,因而可以表征土壤受土霉素的污染程度。     

Fractions of Cu, Cd, and enzyme activities in a contaminated soil as affected by applications of micro- and nanohydroxyapatite

Purpose

With the rapid development of nanotechnology, hydroxyapatite-based nanoparticles have been applied in wastewater and soil remediation. However, limited studies have been conducted on the remediation of heavy metal-contaminated soils by microhydroxyapatite (MHA) and nanohydroxyapatite (NHA). Thus, we investigated the effects of MHA and NHA on soil pH values and fractions of copper (Cu) and cadmium (Cd). The changes of soil enzymes with application of MHA and NHA were also evaluated.

Materials and methods

Pots contained 200 g of the soil with MHA and NHA ranging from 1 % to 5 % incubated for 60 days under greenhouse condition, and maintained at 60 % of soil water holding capacity by adding deionized water. Soil pH, catalase, urease, and acid phosphatase were analyzed at incubation times of 7, 14, 30, and 60 days by chemical assays. The fractions of Cu and Cd were analyzed after 60 days by a sequential extraction procedure.

Results and discussion

Application of MHA and NHA significantly increased soil pH values. Especially, we found for the first time that soil pH values with 3 % (pH?>?7.90) and 5 % (pH?>?8.83) application rates of MHA were larger than that of MHA itself (pH?=?7.71). MHA was more effective than NHA in immobilizing Cu and Cd by significantly decreasing exchangeable fractions of Cu and Cd and transforming them from active to inactive fractions. Soil catalase and urease significantly increased, but acid phosphatase apparently decreased with increasing application rates of MHA. However, three enzymes activities changed slightly for NHA treatments.

Conclusions

MHA was more effective than NHA in immobilizing Cu and Cd. MHA had a more positive effect on soil catalase and urease activities than NHA. Furthermore, Pearson’s correlation coefficients showed that soil pH value was a key factor to influence the bioavailability of Cu and Cd and the activity of soil enzymes. The results of this study provided an efficient method for the remediation of heavy metal-contaminated soils.     

聚丙烯酸盐对长期重金属污染的矿区土壤的修复研究（Ⅱ）——对土壤微生物数量和土壤酶活性的影响

采用盆栽试验方法研究了聚丙烯酸盐对SDomingos金矿区重金属污染土壤的修复作用。在《聚丙烯酸盐对长期重金属污染土壤的修复研究（I）》^[30]（以下简称研究I）中聚丙烯酸盐的应用显著提高了土壤持水能力和土壤的pH,同时土壤中水溶性重金属的含量也比对照显著降低,从而使果园草Orchardgrass（Dactylis glomerata L．cv．Amba）的生物量得到显著增加。为更全面地说明聚丙烯酸盐在该重金属污染土壤修复上的作用,进一步探讨了聚丙烯酸盐对重金属污染土壤微生物属性的影响。结果表明,土壤细菌数量随聚丙烯酸盐水平的增加而增加,不同处理之间差异显著（P≤0．05）;与对照相比,聚丙烯酸盐处理的真菌数量显著增加（P≤0．05）,但随着聚丙烯酸盐水平的增加而显著降低（P≤0．05）,这可能是由于0．4％和0．6％的聚丙烯酸盐处理土壤pH显著提高所导致的。因此使用微生物数量评价土壤质量时,细菌比真菌表现更突出。使用聚丙烯酸盐修复的土壤脱氢酶、磷酸酶、蔗糖酶、蛋白酶和纤维素酶的活性均比对照显著增加（P≤0．05）,而脲酶活性的下降则可能是由于聚丙烯酸盐带来大量的铵态氮产生的抑制作用所致。综合研究I中的结果,聚丙烯酸盐不仅可以改善重金属污染土壤的理化性状而且对于土壤微生物属性也有显著的改善作用。从果园草生物量来看,0．4％聚丙烯酸盐的用量对该污染土壤的修复具有实践应用价值。     

Influence of long-term residue management on soil enzyme activities in relation to soil chemical properties of a wheat-fallow system

Summary Soil enzyme activities (acid and alkaline phosphatase, arylsulfatase, -glucosidase, urease and amidase) were determined (0- to 20-cm depth) after 55 years of crop-residue and N-fertilization treatment in a winter wheat (Triticum aestivum L.)-fallow system on semiarid soils of the Pacific Northwest. All residues were incorporated and the treatments were: straw (N₀), straw with fall burn (N₀FB), straw with spring burn (N₀SB), straw plus 45 kg N ha^–1 (N₄₅), straw plus 90 kg N ha^–1 (N₉₀), straw burned in spring plus 45 kg N ha^–1 (N₄₅SB), straw burned in spring plus 90 kg N ha^–1 (N₉₀SB), straw plus 2.24 T ha^–1 pea-vine residue and straw plus 22.4 T ha^–1 of straw-manure. Enzyme activities were significantly (P<0.001) affected by residue management. The highest activities were observed in the manure treated soil, ranging from 36% (acid phosphatase) to 190% increase in activity over the control (N₀). The lowest activities occurred in the N₀FB (acid phosphatase, arylsulfatase and -glucosidase) and N₉₀ treated soils (alkaline phosphatase, amidase and urease). Straw-burning had a significant effect only on acid phosphatase activity, which decreased in spring burn treated soil when inorganic N was applied. Urease and amidase activity decreased with long-term addition of inorganic N whereas the pea vine and the manure additions increased urease and amidase activity. There was a highly significant effect from the residue treatments on soil pH. Arylsulfatase, urease, amidase and alkaline phosphatase activities were positively correlated and acid phosphatase activity was negatively correlated with soil pH. Enzyme activities were strongly correlated with soil organic C and total N content. Except for acid phosphatase, there was no significant relationship between enzyme activity and grain yield.Journal Paper No. 8072 of the Agricultural Experimental Station, Oregon State University, Corvallis, OR 97331, USA     

Effects of conventional tillage on biochemical properties of soils

Modification of soil environment by different farming practices can significantly affect crop growth. Tillage causes soil disturbance, altering the vertical distribution of soil organic matter and plant nutrient supplies in the soil surface, and it may affect the enzyme activity and microbial biomass which are responsible for transformation and cycling of organic matter and plant nutrients. In this study, the influence of three conventional tillage systems (shallow plowing, deep plowing and scarification) at different depths on the distribution and activity of enzymes, microbial biomass and nucleic acids in a cropped soil was investigated. Analysis of variance for depth and tillage showed the influence of the different tillage practices on the activity of some enzymes and on the nucleic acids. Glucosidase, galactosidase, nitrate reductase and dehydrogenase activity were significantly affected by the three tillage modalities. Activity in the upper layer (0–20 cm) was higher in the plots tilled by shallow plowing and scarification than in those tilled by deep plowing. Positive relationships were observed between the soil enzymes themselves, with the exception of urease and pyrophosphatase activity. Moreover, significant correlations were found between DNA and β-galactosidase, and between RNA and β-glucosidase, β-galactosidase, alkaline phosphatase and phosphodiesterase. α-Glucosidase, β-galactosidase, alkaline phosphatase and phosphodiesterase were highly correlated with biomass C determined by the fumigation-extraction method. Received: 27 June 1996     

长期定位施肥对小麦玉米间作土壤酶活性的影响

为探讨长期施肥条件下土壤酶活性的动态变化以及土壤酶活性之间的相关性,对灌漠土小麦/玉米间作不同肥料长期定位试验地第26年耕层土壤过氧化氢酶、蔗糖酶、碱性磷酸酶和脲酶酶活性进行了测定与分析。结果表明,长期定位施肥下,间作小麦/玉米生育期内土壤过氧化氢酶、蔗糖酶和碱性磷酸酶总体均呈先升高后下降的变化趋势,在小麦拔节期至灌浆...     

超积累植物东南景天根际土壤酶活性研究

通过野外调查和盆栽试验研究了超积累植物东南景天根际土壤酶活性变化及其与重金属有效态的关系。研究结果表明,在矿山土壤、重度污染土壤和轻度污染土壤上,种植超积累生态型东南景天后,根际土壤有效态Zn分别比非根际减少了14.3%,7.9%和47.4%,有效态Cd分别比非根际减少25.1%,21.9%和20%。在铅锌矿区,东南景天生长地段土壤蔗糖酶、酸性磷酸酶、脱氢酶活性高于其它植物生长地段。在矿山土壤和重度污染土壤中,超积累生态型东南景天根际土壤酶活性明显高于非根际土壤,同时也高于非超积累生态型根际土壤。Pb、Zn、Cd、Cu4种重金属对东南景天根际土壤脲酶、蔗糖酶、脱氢酶活性均有抑制作用,而Pb对磷酸酶有一定的刺激作用。东南景天根际土壤脱氢酶、酸性磷酸酶活性与重金属有效态含量呈极显著相关。     

The effect of soil texture and soil drainage on emissions of nitric oxide and nitrous oxide

Abstract. Agricultural soils are important sources of the tropospheric ozone precursor NO and the greenhouse gas N₂O. Emissions are controlled primarily by parameters that vary the soil mineral N supply, temperature and soil aeration. In this field experiment, the importance of soil physical properties on emissions of NO and N₂O are identified. Fluxes were measured from 13 soils which belonged to 11 different soil series, ranging from poorly drained silty clay loams to freely drained sandy loams. All soils were under the same soil management regime and crop type (winter barley) and in the same maritime climate zone. Despite this, emissions of NO and N₂O ranged over two orders of magnitude on all three measurement occasions, in spring before and after fertilizer application, and in autumn after harvest. NO emissions ranged from 0.3 to 215 μg NO-N m^–2 h^–1, with maximum emissions always from the most sandy, freely drained soil. Nitrous oxide emissions ranged from 0 to 193 μg N₂O-N m^–2 h^–1. Seasonal shifts in soil aeration caused maximum N₂O emissions to switch from freely drained sandy soils in spring to imperfectly drained soils with high clay contents in autumn. Although effects of soil type on emissions were not consistent, N₂O emission was best related to a combination of bulk density and clay content and the NO/N₂O ratio decreased logarithmically with increasing water filled pore space.     

Remediation of a sandy soil artificially contaminated with copper using a polyacrylate polymer

Abstract. We investigated whether a Na-K polyacrylate polymer could be used to remediate a sandy soil artificially contaminated with copper. An experiment, carried out in solution culture, showed that ionic copper was rapidly trapped within the polymer to a maximum content of c. 190mg Cu g ^-1 dry polymer, the proportion needed for chelation of each copper ion by four carboxylic groups present in the polymer chains. Cu-EDTA was not retained by the polymer. Growth of perennial rygrass in 10 kg pots was stimulated in the gel-amended soil, and even in the pots with the highest levels of copper, growth was much less impaired than in pots without polymer. Copper concentrations of the shoot.; were smaller in the plants cultivated in the amended soil. Water extractable copper was considerably reduced in the contaminated gel-amended soil and polymer particles removed from the soil were shown to contain high levels of copper.     

Improvements in soil quality and performance of mycorrhizal Cistus albidus L. seedlings resulting from addition of microbially treated sugar beet residue to a degraded semiarid Mediterranean soil

Abstract. A field experiment was undertaken to assess the effectiveness of a combined treatment, involving addition of Aspergillus niger -treated sugar beet (SB) residue in the presence of rock phosphate and mycorrhizal inoculation of seedlings with Pisolithus tinctorius . The aim was to improve the physical, chemical, biochemical and biological properties of a degraded semiarid Mediterranean soil. Short-term effects of such improvements on the establishment of Cistus albidus L. seedlings were evaluated. Eight months after planting, macronutrients (NPK), total carbohydrates, water-soluble C, water-soluble carbohydrates, microbial biomass C and enzyme activities (dehydrogenase, urease, protease, acid phosphatase and β-glucosidase) measured in the rhizosphere soil of C. albidus were increased greatly by addition of fermented SB residue. Soil structural stability improved only with the fermented SB addition (about 79% higher in the amended soils than in the non-amended soils). The mycorrhizal inoculation was the most effective treatment in improving the growth of C. albidus plants, but only slightly improved soil quality. Growth of inoculated plants was about 33% greater than plants grown in the amended soil and about 131% greater than control plants. The combined benefit of mycorrhizal inoculation of seedlings and addition of fermented SB residue to soil on plant growth was similar to that of the treatments applied individually.     

Denitrification in drained and undrained arable clay soil

Emissions of nitrous oxide (N₂O) and nitrogen gas (N₂) from denitrification were measured using the acetylene inhibition method on drained and undrained clay soil during November 1980-June 1981. Drainage limited denitrification to about 65% of losses from undrained soil. Emissions from the undrained soil were in the range 1 to 12 g N ha^–1 h^–1 while those from the drained soil ranged from 0.5 to 6 g N ha^–1 h^–1 giving estimated total losses (N₂O + N₂) of 14 and 9 kgN ha^–1.
Drainage also changed the fraction of nitrous oxide in the total denitrification product. During December, emissions from the drained soil (1.8±0.6 gN ha^–1 h^–1) were composed entirely of nitrous oxide, but losses from the undrained soil (2.7 ± 1.1 g N ha^–1 h^–1) were almost entirely in the form of nitrogen gas (the fraction of N₂O in the total loss was 0.02). In February denitrification declined in colder conditions and the emission of nitrous oxide from drained soil declined relative to nitrogen gas so that the fraction of N₂O was 0.03 on both drainage treatments. The delayed onset of N₂O reduction in the drained soil was related to oxygen and nitrate concentrations. Fertilizer applications in the spring gave rise to maximum rates of emission (5–12g N ha^–1 h^–1) with the balance shifting towards nitrous oxide production, so that the fraction of N₂O was 0.2–0.8 in April and May.