Deli Chen

Nitrogen losses from fertilizers applied to maize, wheat and rice in the North China Plain

Ammonia volatilization, denitrification loss and total nitrogen (N) loss (unaccounted-for N) have been investigated from N fertilizer applied to a calcareous sandy loam fluvo-aquic soil at Fengqiu in the North China Plain. Ammonia volatilization was measured by the micrometeorological mass balance method, denitrification by the acetylene inhibition – soil core incubation technique, and total N loss by 15N-balance technique. Ammonia loss was an important pathway of N loss from N fertilizer applied to rice (30–39% of the applied N) and maize (11–48%), but less so for wheat (1–20%). The amounts of unaccounted-for fertilizer N were in the order of rice > maize > wheat. Deep placement greatly reduced ammonia volatilization and total N loss. Temperature, wind speed, and solar radiation (particular for rice), and source of N fertilizer also affect extent and pattern of ammonia loss. Denitrification (its major gas products are N2 and N2O) usually was not a significant pathway of N loss from N fertilizer applied to maize and wheat. The amount of N2O emission (N2O is an intermediate product from both nitrification and denitrification) was comparable to denitrification loss for maize and wheat, and it was not significant in the economy of fertilizer N in agronomical terms, but it is of great concern for the environment.

Prospects of improving efficiency of fertiliser nitrogen in Australian agriculture: a review of enhanced efficiency fertilisers

Fertiliser nitrogen use in Australia has increased from 35 Gg N in 1961 to 972 Gg N in 2002, and most of the nitrogen is used for growing cereals. However, the nitrogen is not used efficiently, and wheat plants, for example, assimilated only 41% of the nitrogen applied. This review confirms that the efficiency of fertiliser nitrogen can be improved through management practices which increase the crops ability to compete with loss processes. However, the results of the review suggest that management practices alone will not prevent all losses (e.g. by denitrification), and it may be necessary to use enhanced efficiency fertilisers, such as controlled release products, and urease and nitrification inhibitors, to obtain a marked improvement in efficiency. Some of these products (e.g. nitrification inhibitors) when used in Australian agriculture have increased yield or reduced nitrogen loss in irrigated wheat, maize and cotton, and flooded rice, but most of the information concerning the use of enhanced efficiency fertilisers to reduce nitrogen loss to the environment has come from other countries. The potential role of enhanced efficiency fertilisers to increase yield in the various agricultural industries and prevent contamination of the environment in Australia is discussed.

Microbial regulation of terrestrial nitrous oxide formation: understanding the biological pathways for prediction of emission rates

The continuous increase of the greenhouse gas nitrous oxide (N2O) in the atmosphere due to increasing anthropogenic nitrogen input in agriculture has become a global concern. In recent years, identification of the microbial assemblages responsible for soil N2O production has substantially advanced with the development of molecular technologies and the discoveries of novel functional guilds and new types of metabolism. However, few practical tools are available to effectively reduce in situ soil N2O flux. Combating the negative impacts of increasing N2O fluxes poses considerable challenges and will be ineffective without successfully incorporating microbially regulated N2O processes into ecosystem modeling and mitigation strategies. Here, we synthesize the latest knowledge of (i) the key microbial pathways regulating N2O production and consumption processes in terrestrial ecosystems and the critical environmental factors influencing their occurrence, and (ii) the relative contributions of major biological pathways to soil N2O emissions by analyzing available natural isotopic signatures of N2O and by using stable isotope enrichment and inhibition techniques. We argue that it is urgently necessary to incorporate microbial traits into biogeochemical ecosystem modeling in order to increase the estimation reliability of N2O emissions. We further propose a molecular methodology oriented framework from gene to ecosystem scales for more robust prediction and mitigation of future N2O emissions.

Dissimilatory nitrate reduction to ammonium and responsible microorganisms in two Chinese and Australian paddy soils

Dissimilatory nitrate reduction to ammonium (DNRA) and the responsible microflora were studied in two typical Chinese and Australian paddy soils. The DNRA accounted for 14.9% of total reduction of 15N-labeled nitrate added to the soil from Griffith (NSW, Australia) under anaerobic incubation without any exogenous carbon source addition, but only 5% for the soil from Yangzhou (China). Addition of reducing agents (sodium thioglycollate and l-cysteine) resulted in lower redox potentials and enhanced the DNRA process, with the majority of the product of reduction being ammonium. However, redox potential alone could not explain the difference of DNRA potentials between the two soils. Additions of glucose also resulted in substantial increases in DNRA, especially for Griffith soil, with the majority of the product being organic-N. The significantly higher DNRA in Griffith soil compared to Yangzhou soil is consistent with the higher DNRA microorganism population isolated from Griffith soil than that in Yangzhou soil, which is also consistent with higher fraction of labile carbon in Griffith soil than that in Yangzhou soil. In contrast, the denitrifiers population in the Griffith soil was about 10-fold smaller than that in the Yangzhou soil. The results demonstrate that the soil indigenous labile carbon was the key factor influencing the partitioning of nitrate reduction between denitrification and DNRA. Most DNRA bacteria and denitrifiers isolated were spore-forming bacteria.

Gaseous nitrogen loss from temperate perennial grass and clover dairy pastures in south-eastern Australia

The use of nitrogen (N) fertiliser on dairy pastures in south-eastern Australia has increased exponentially over the past 15 years. Concerns have been raised about the economic and environmental impact of N loss through volatilisation and denitrification. Emissions of NH3, N2, and N2O were measured for 3 years in the 4 different seasons from a grazed grass/clover pasture, with or without 200 kg N fertiliser/ha, applied as ammonium nitrate and urea. Nitrogen-fertilised treatments lost significantly more N than the control treatments in all cases. More NH3 was lost from urea-fertilised treatments than from either the control or ammonium nitrate treatments, whereas ammonium nitrate treatments lost significantly more N through denitrification than the control or urea treatments in all seasons, except for summer. More NH3 was lost in summer than in the other seasons, whereas denitrification and N2O losses were highest in winter and lowest in summer. The total annual NH3 loss from the control, ammonium nitrate, and urea treatments averaged 17, 32, and 57 kg N/ha.year, respectively. Annual denitrification losses were estimated at around 6, 15, and 13 kg N/ha.year for the control, ammonium nitrate, and urea treatments, respectively. Total gaseous N losses were estimated to be 23, 47, and 70 kg N/ha.year from the control, ammonium nitrate, and urea treatments respectively. Although the use of ammonium nitrate fertiliser would significantly reduce NH3 volatilisation losses in summer, this fertiliser costs 45% more per unit N than urea, so there is no economic justification for recommending its use over urea for the other seasons. However, the use of urea during the cooler, wetter months may result in significantly less denitrification loss. The results are discussed in terms of potential management strategies to improve fertiliser efficiency and reduce adverse effects on the environment.

Nitrogen mineralisation, immobilisation and loss, and their role in determining differences in net nitrogen production during waterlogged and aerobic incubation of soils

Abstract Twenty air-dried soil samples were incubated for 14 days at 30°C to determine net N production ( np ) under aerobic and waterlogged conditions. The results showed that np was not always higher under waterlogged than under aerobic conditions, which differed from some previous reports. Five analytical equations were compared and used to estimate gross rates of N mineralisation, immobilisation and loss. It was elucidated that the equations based on changes in the AT and AL pools gave estimates of gross mineralization and consumption rates, with the values obtained with the equation of Shen et al. (Shen, S.M., Pruden, G., Jenkinson, D.S., 1984. Mineralization and immobilization of nitrogen in fumigated soil and the measurement of microbial biomass nitrogen. Soil Biology & Biochemistry 16, 437–444) ≥the equation of Kirkham and Bartholomew (Kirkham, D., Bartholomew, W.V., 1954. Equations for following nutrient transformations in soil, utilizing tracer data. Soil Science Society of America Proceedings 18, 33–34) >the equation of Tiedje et al. (Tiedje, J.M., Sorensen, J., Chang, Y.-Y.L., 1981. Assimilatory and dissimilatory nitrate reduction: Perspectives and methodology for simultaneous measurement of several nitrogen cycle processes. Ecological Bulletin 33, 331–342) . The equations based on AT, AL and OL pools estimated gross immobilisation rates, of which the equation of Shen et al. (1984) gave higher values than the equation of Guiraud et al. (Guiraud, G., Marol, C., Thibaud, M.C., 1989. Mineralization of nitrogen in the presence of a nitrification inhibitor. Soil Biology & Biochemistry 21, 29–34) . The difference between gross consumption and immobilisation rates represented the rate of N loss from the exchangeable NH 4 + , NO 3 − and organic N pools. Gross N mineralization was not always higher under aerobic than under waterlogged conditions during the 14 days incubation of air-dried soils. Immobilisation was greater under aerobic conditions than under waterlogged conditions. Significant amounts of N were lost from some soils during the 2 weeks of incubation. Soils that lost N during aerobic incubation also lost substantial amounts of NH 4 + –N under waterlogged conditions. However, soils that lost NH 4 + –N during waterlogged incubation did not necessarily lose N when incubated aerobically. Mechanisms causing the difference in net N production between waterlogged and aerobic conditions are soil-dependent. Although the rate of gross mineralisation predominantly determines the amount of mineral N that may accumulate in soils, immobilisation and loss have the potential to significantly affect the quantity of mineral N accumulation.

Soil factors affecting the sustainability and productivity of perennial and annual pastures in the high rainfall zone of south-eastern Australia.

A field study was carried out in the high rainfall zone (HRZ, >600 mm p.a.) of southern Australia from March 1994 to August 1997 to test the hypothesis that sown perennial grasses and liming could make the existing pastures more sustainable through better use of water and nitrogen. The site, on an acid duplex soil at Book Book near Wagga Wagga in southern New South Wales, was typical of much of the HRZ grazing country in southern New South Wales and north-east Victoria. The experiment consisted of 4 replicate paddocks (each 0.135 ha) of 4 treatments: annual pasture (mainly ryegrass Lolium rigidum, silver grass Vulpia spp., subterranean clover Trifolium subterraneum and broadleaf weeds) without lime, annual pasture with lime, perennial pasture (phalaris Phalaris aquatica, cocksfoot Dactylis glomerata and subterranean clover T. subterraneum) without lime, and perennial pasture with lime. Soil pH (0–10 cm) in the limed treatments was maintained at 5.5 (0.01 mol/L CaCl2), compared to 4.1 in the unlimed treatments. The pastures were rotationally grazed with Merino ewe or wether hoggets at a stocking rate which varied with the season, but was 10–25% higher on the limed pastures [14.8–17.3 dry sheep equivalent (dse)/ha] than the unlimed pastures. One replicate set of pasture treatments was intensively monitored for surface runoff, subsurface flow (at the top of the B horizon), water potential gradients and ammonium volatilisation. Other measurements of nitrogen inputs, transformations and losses were made on all paddocks. In a normal to wet year, surface runoff, subsurface flow and deep drainage (>180 cm depth) were about 40 mm less from the perennial than the annual pastures. The reduction in deep drainage under the perennials was about one-third to one-half (20–29 mm/year). The smaller loss of solution NO3– from the perennial pastures (up to 12 kg N/ha.year) suggested soil acidification under perennials was reduced by about 1 kmol H+/ha.year. Denitrification and volatilisation losses of N were small (1–12 kg N/ha.year). Nitrogen fixed by subterranean clover (above ground parts) ranged from 2–8 kg N/ha in the drought of 1994–95 to 128 kg N/ha in a normal year (1996). The soil-pasture nitrogen balance was positive for all treatments and averaged 76 kg N/ha.year over 2 years. The abundance of introduced and native earthworms increased from 85 to 250/m2 in the limed pastures between 1994 and 1997. Introduced species, such as Aporrectodea trapezoides, were especially responsive to lime. Animal production per hectare was 10–25% higher on pastures with lime. Critical gross margins per dse were lowest (

Use of nitrification inhibitors to increase fertilizer nitrogen recovery and lint yield in irrigated cotton

16/ha) for a long-lived perennial pasture (>15 years), and highest (

The potential for carbon sequestration in Australian agricultural soils is technically and economically limited

20/ha) for a short-lived perennial (5 years). Overall, there were substantial benefits in animal production, improved soil quality and water use from establishing perennial grass pastures with lime on these strongly acid soils.

Gaseous nitrogen losses from urea applied to maize on a calcareous fluvo-aquic soil in the North China Plain

This paper describes field experiments designed to evaluate the effectiveness of several nitrification inhibitors to prevent loss of fertilizer nitrogen (N) applied to cotton. The usefulness of nitrapyrin, acetylene (provided by wax-coated calcium carbide), phenylacetylene and 2-ethynylpyridine to prevent denitrification was evaluated by determining the recovery of N applied as15N labelled urea to a heavy clay soil in 1 m × 0.5 m microplots in north western N.S.W., Australia. In a second experiment, the effect of wax-coated calcium carbide on lint yield of cotton supplied with five N levels was determined on 12.5 m × 8 m plots at the same site.The15N balance study showed that in the absence of nitrification inhibitors only 57% of the applied N was recovered in the plants and soil at crop maturity. The recovery was increased (p < 0.05) to 70% by addition of phenylacetylene, to 74% by nitrapyrin, to 78% by coated calcium carbide and to 92% by 2-ethynylpyridine.In the larger scale field experiment, addition of the wax-coated calcium carbide significantly slowed the rate of NH4+ oxidation in the grey clay for approximately 8 weeks. Lint yield was increased (p < 0.05) by the addition of the inhibitor at all except the highest level of N addition. The inhibitor helped to conserve the indigenous N as well as the applied N.The research shows that the effectiveness of urea fertilizer for cotton grown on the heavy clay soils of N.S.W. can be markedly improved by using acetylenic compounds as nitrification inhibitors.