Nitrous oxide emissions from grassland and spring barley, following N fertiliser application with and without nitrification inhibitors

The aims of this study were to assess the effectiveness of the nitrification inhibitors dicyandiamide (DCD) and nitrapyrin on reducing emissions of nitrous oxide (N₂O) following application of NH₄ ⁺ or NH₄ ⁺-forming fertilisers to grassland and spring barley. DCD was applied to grassland with N fertiliser applications in April and August in 1992 and 1993, inhibiting N₂O emissions by varying amounts depending on the fertiliser form and the time of application. Over periods of up to 2 months following each application of DCD, emissions of N₂O were reduced by 58–78% when applied with urea (U) and 41–65% when applied with ammonium sulphate (AS). Annual emissions (April to March) of N₂O were reduced by up to 58% and 56% in 1992–1993 and 1993–1994, respectively. Applying DCD to ammonium nitrate (AN) fertilised grassland did not reduce emissions after the April 1993 fertilisation, but emissions following the August application were reduced. Nitrapyrin was only applied once, with the April fertiliser applications in 1992, reducing N₂O emissions over the following 12 months by up to 40% when applied with U. When N fertiliser was applied in June without DCD, the DCD applied in April was still partly effective; N₂O emissions were reduced 50%, 60% and 80% as effectively as the emissions following the April applications, for AS in 1993, U in 1992 and 1993, respectively. In 1992 the persistence of an inhibitory effect was greater for nitrapyrin than for DCD, increasing after the June fertiliser application as overall emissions from U increased. There was no apparent reduction in effectiveness following repeated applications of DCD over the 2 years. N₂O emissions from spring barley, measured only in 1993, were lower than from grassland. DCD reduced emissions from applied U by 40% but there was no reduction with AN. The results demonstrate considerable scope for reducing emissions by applying nitrification inhibitors with NH₄ ⁺ or NH₄ ⁺-forming fertilisers; this is especially so for crops such as intensively managed grass where there are several applications of fertiliser nitrogen per season, as the effect of inhibitors applied in April persists until after a second fertiliser application in June. Received: 30 August 1996     

Effect of cattle slurry in grassland on microbial biomass and on activities of various enzymes

We examined the long-term effects of cattle slurry, applied at high rates, on microbial biomass, respiration, the microbial quotient (qCO₂) and various soil enzyme activities. In March, June, July, and October 1991, slurry-amended grassland soils (0–10 cm) contained significantly higher levels of microbial biomass, N mineralization and enzyme activities involved in N, P, and C cycling. With microbial biomass as the relative value, the results revealed that the slurry treatment influenced enzyme production by the microbial biomass. High levels of urease activity were the result not only of a larger microbial biomass, but also of higher levels of enzmye production by this microbial biomass. The ratio of alkaline phosphatase and xylanase to microbial biomass was nearly constant in the different treatments. The metabolic quotient (qCO₂) declined with increased levels of slurry application. Therefore it appears that microorganisms in slurry-amended soils require less C and energy if there is no competition for nutrients. The results of this study suggest that urease activity, nitrification, and respiration (metabolic quotient) can be used as indicators of environmental stress, produced by heavy applications of cattle slurry.     

Nitrous oxide emissions from two dairy pasture soils as affected by different rates of a fine particle suspension nitrification inhibitor, dicyandiamide

In grazed pasture systems, a major source of N₂O is nitrogen (N) returned to the soil in animal urine. We report in this paper the effectiveness of a nitrification inhibitor, dicyandiamide (DCD), applied in a fine particle suspension (FPS) to reduce N₂O emissions from dairy cow urine patches in two different soils. The soils are Lismore stony silt loam (Udic Haplustept loamy skeletal) and Templeton fine sandy loam (Udic Haplustepts). The pasture on both soils was a mixture of perennial ryegrass (Lolium perenne) and white clover (Trifolium repens). Total N₂O emissions in the Lismore soil were 23.1–31.0 kg N₂O-N ha⁻¹ following the May (autumn) and August (late winter) urine applications, respectively, without DCD. These were reduced to 6.2–8.4 kg N₂O-N ha⁻¹ by the application of DCD FPS, equivalent to reductions of 65–73%. All three rates of DCD applied (7.5, 10 and 15 kg ha⁻¹) were effective in reducing N₂O emissions. In the Templeton soil, total N₂O emissions were reduced from 37.4 kg N₂O-N ha⁻¹ without DCD to 14.6–16.3 kg N₂O-N ha⁻¹ when DCD was applied either immediately or 10 days after the urine application. These reductions are similar to those in an earlier study where DCD was applied as a solution. Therefore, treating grazed pasture soils with an FPS of DCD is an effective technology to mitigate N₂O emissions from cow urine patch areas in grazed pasture soils.     

Microbial community PLFA and PHB responses to ecosystem restoration in tallgrass prairie soils

Native North American prairie grasslands are renowned for the richness of their soils, having excellent soil structure and very high organic content and microbial biomass. In this study, surface soils from three prairie restorations of varying ages and plant community compositions were compared with a nearby undisturbed native prairie remnant and a cropped agricultural field in terms of soil physical, chemical and microbial properties. Soil moisture, organic matter, total carbon, total nitrogen, total sulfur, C:N, water-holding capacity and microbial biomass (total PLFA) were significantly greater (p<0.05) in the virgin prairie remnant as well as the two long-term (21 and 24 year) prairie restorations, compared with the agricultural field and the restoration that was begun more recently (7 years prior to sampling). Soil bulk density was significantly greater (p<0.05) in the agricultural and recently restored sites. In most cases, the soil quality indicators and microbial community structures in the restoration sites were intermediate between those of the virgin prairie and the agricultural sites. Levels of poly-β-hydroxybutyrate (PHB) and PLFA indicators of nutritional stress were significantly greater (p<0.05) in the agricultural and recent restoration sites than in the long-term restorations or the native prairie. Samples could be assigned to the correct site by discriminant analysis of the PLFA data, with the exception that the two long-term restoration sites overlapped. Redundancy analysis showed that prairie age (p<0.005) was the most important environmental factor in determining the PLFA microbial community composition, with C:N (p<0.015) also being significant. These findings demonstrate that prairie restorations can lead to improved quality of surface soils. We predict that the conversion of farmland into prairie will shift the soil quality, microbial community biomass and microbial community composition in the direction of native prairies, but with the restoration methods tested it may take many decades to approach the levels found in a virgin prairie throughout the soil profile.     

Soil moisture controls on temperature sensitivity of soil organic carbon decomposition for a mesic grassland

We examined relationships between soil moisture and the temperature sensitivity of decomposition of labile soil organic carbon at a central North American grassland. For soils collected from shallow, xeric uplands, temperature sensitivity was greatest at intermediate soil moisture. For soils collected from the deeper, mesic lowlands, temperature sensitivity increased with increasing soil moisture. For example, lowland soils incubated at 75% WHC exhibited an apparent activation energy (E_a) that was 15 kJ mol⁻¹ greater than soils incubated at 30% WHC, the equivalent of a Q₁₀ of 2.8 vs. 2.3. Although further research is still needed to understand why moisture-temperature sensitivity relationships would differ between topographic positions, the magnitude of the soil moisture effect is large enough to alter soil C budgets and should be considered explicitly when predicting ecosystem responses to global change scenarios.     

Fungal, bacterial and plant dsDNA contributions to soil total DNA extracted from silty soils under different farming practices: Relationships with chloroform-labile carbon

Twelve differently-managed silty soils from North-Western France were chosen to compare two common methods of quantifying soil microbial biomass: Chloroform fumigation and extraction-labile carbon (CL_C) and microbial double stranded DNA (dsDNA). We also determined the contributions of each of the fungal, bacterial, and plant kingdoms to the total community dsDNA using real-time Polymerase Chain Reaction with kingdom-specific ribosomal primer sets. Regardless of the method, the highest microbial biomasses were associated with long-term untilled plots. Site (locations) specificities could also be detected, especially in conventionally cultivated lands. Regardless of site, a strong linear relationship could be drawn between CL_C and dsDNA in tilled lands (r = 0.91, n = 15, P = 0.01) and in grasslands (r = 0.78, n = 21, P = 0.01). Moreover, we propose a logarithmic model describing all of our silty soils, irrespective of management. In order to explain the non-linearity (log) of this relationship, we tested the hypothesis of a weak plant dsDNA contribution in total dsDNA in comparison with the well-documented root cell contribution to CL_C quantifications. Plant dsDNA never exceeded 2.6% of total dsDNA content for all of the soils studied. Among groups examined, the bacterial dsDNA contribution to the community dsDNA pool was the most site- and/or pedoclimatic-dependent. Fungi constituted a major component of total microbial biomass in grassland or in land with permanent plant cover where their proportion reached almost 50% of total dsDNA. More precisely, fungal dsDNA concentration was highly related to tillage. Our study demonstrated the expediency of the total microbial dsDNA quantification in agricultural silty soils rather than the time-consuming quantification of CL_C. Quantifying the relative contribution of bacterial or fungal biomass in total dsDNA by real-time PCR allows to access to a new level of knowledge of the soil microbial biomass and to reveal the balances between those two kingdoms according to soils or farming practices.     

Nitrogen losses from two grassland soils with different fungal biomass

Nitrogen losses from agricultural grasslands cause eutrophication of ground- and surface water and contribute to global warming and atmospheric pollution. It is widely assumed that soils with a higher fungal biomass have lower N losses, but this relationship has never been experimentally confirmed. With the increased interest in soil-based ecosystem services and sustainable management of soils, such a relationship would be relevant for agricultural management. Here we present a first attempt to test this relationship experimentally. We used intact soil columns from two plots from a field experiment that had consistent differences in fungal biomass (68 ± 8 vs. 111 ± 9 μg C g⁻¹) as a result of different fertilizer history (80 vs. 40 kg N ha⁻¹ y⁻¹ as farm yard manure), while other soil properties were very similar. We performed two greenhouse experiments: in the main experiment the columns received either mineral fertilizer N or no N (control). We measured N leaching, N₂O emission and denitrification from the columns during 4 weeks, after which we analyzed fungal and bacterial biomass and soil N pools. In the additional ¹⁵N experiment we traced added N in leachates, soil, plants and microbial biomass. We found that in the main experiment, N₂O emission and denitrification were lower in the high fungal biomass soil, irrespective of the addition of fertilizer N. Higher ¹⁵N recovery in the high fungal biomass soil also indicated lower N losses through dentrification. In the main experiment, N leaching after fertilizer addition showed a 3-fold increase compared to the control in low fungal biomass soil (11.9 ± 1.0 and 3.9 ± 1.0 kg N ha⁻¹, respectively), but did not increase in high fungal biomass soil (6.4 ± 0.9 after N addition vs. 4.5 ± 0.8 kg N ha⁻¹ in the control). Thus, in the high fungal biomass soil more N was immobilized. However, the ¹⁵N experiment did not confirm these results; N leaching was higher in high fungal biomass soil, even though this soil showed higher immobilization of ¹⁵N into microbial biomass. However, only 3% of total ¹⁵N was found in the microbial biomass 2 weeks after the mineral fertilization. Most of the recovered ¹⁵N was found in plants (approximately 25%) and soil organic matter (approximately 15%), and these amounts did not differ between the high and the low fungal biomass soil. Our main experiment confirmed the assumption of lower N losses in a soil with higher fungal biomass. The additional ¹⁵N experiment showed that higher fungal biomass is probably not the direct cause of higher N retention, but rather the result of low nitrogen availability. Both experiments confirmed that higher fungal biomass can be considered as an indicator of higher nitrogen retention in soils.     

Post-Soviet agricultural change predicts future declines after recent recovery in Eurasian steppe bird populations

The socioeconomic impacts of the break-up of the Soviet Union after 1991 have resulted in massive changes in agriculture on the Eurasian (Pontian) steppe, most of which is now confined to Kazakhstan. Recent trends in agriculture are well documented but their impacts on the characteristic bird community of this vast region, which contains over 10% of the world’s remaining grasslands, are poorly understood. We modelled bird population density in a representative region in central Kazakhstan along a land-use gradient ranging from pristine steppe to arable fields and heavily grazed pastures. Long-abandoned arable fields and ungrazed pristine steppe were the most important habitats for most species, and post-1991 abandonment of arable agriculture suggests that many species have enjoyed a period of significant population growth. Livestock concentration effects, leading to high grazing pressure in small areas, are also likely to have benefitted several species of high conservation concern. However, analysis of land-use statistics and socioeconomic surveys among land managers suggest that recent and predicted future trends in agriculture in the steppe zone, particularly the reclamation of abandoned cereal fields and reduced grazing pressure, may cause populations of most species, including a number of biome-restricted species, to decline in the near future. We discuss possible conservation solutions, including improvements in the protected area system and land-sparing options.     

Modelling trade offs between public and private conservation policies

To reduce global biodiversity loss, there is an urgent need to determine the most efficient allocation of conservation resources. Recently, there has been a growing trend for many governments to supplement public ownership and management of reserves with incentive programs for conservation on private land. At the same time, policies to promote conservation on private land are rarely evaluated in terms of their ecological consequences. This raises important questions, such as the extent to which private land conservation can improve conservation outcomes, and how it should be mixed with more traditional public land conservation. We address these questions, using a general framework for modelling environmental policies and a case study examining the conservation of endangered native grasslands to the west of Melbourne, Australia. Specifically, we examine three policies that involve: (i) spending all resources on creating public conservation areas; (ii) spending all resources on an ongoing incentive program where private landholders are paid to manage vegetation on their property with 5-year contracts; and (iii) splitting resources between these two approaches. The performance of each strategy is quantified with a vegetation condition change model that predicts future changes in grassland quality. Of the policies tested, no one policy was always best and policy performance depended on the objectives of those enacting the policy. This work demonstrates a general method for evaluating environmental policies and highlights the utility of a model which combines ecological and socioeconomic processes.     

高等学校草地保护学课程现状与教学改革实践——以沈阳农业大学为例

介绍了我固革业科学专业课程草地保护学的起源和发展,并对当前的发展现状进行分析,结合沈阳农业大学草业科学系草地保护学课程的建设、改革与发展情况,充分地说明只有通过与时俱进的课程内容和授课手段的研究与改革,才能促进革业科学高等教育的发展,培养符合国家及社会发展需要的复合型草业人才.