Soil nitrogen fluctuations in citrus plots fertilized with sulfur-coated urea and ammonium nitro sulfate

Summary The release of nitrogen from a slow release fertilizer (sulfur-coated urea, SCU) in an orange orchard was studied during three annual cycles and at three soil depths. The release of N from SCU was compared with that from a standard fertilizer (ammonium nitrate sulfate, ANS). The amounts of available soil nitrogen were compared at different periods of the year and for the whole year. The SCU granules maintained higher levels of available nitrogen in the soil during critical periods. Soil N levels were similar between treatments consisting of 1500 g of N from ANS and 750 g of N from SCU.     

Availability and utilization of fertilizer nitrogen by rice under alternate flooding

Summary A greenhouse pot experiment with three N sources—¹⁵N-depleted ammonium sulfate, urea and sulfur-coated urea (SCU), three N levels—0, 50 and 200 ppm, and three irrigation treatments was conducted with rice in an Alamo clay soil. The irrigation treatments consisted of continuous flooding, alternating flooded-saturated and alternating flooded-drained conditions. The kinetics of NH ₄ ⁺ and NH ₄ ⁺ +NO ₃ ⁻ (available N) in soil was investigated under rice culture. Alternating flooded-drained conditions maintained a significantly lower level of available N in the soil than the other irrigation treatments. Among the N sources evaluated, urea and A/S had similar effects but SCU maintained significantly lower levels of available N in the soil during the growth of rice. Appreciable quantities of NO ₃ ⁻ accumulated during the draining periods of alternating flooded-drained treatments were apparently lost from the soil system upon reflooding.     

缓控释肥料在不同介质中的养分释放特性及其肥效

采用水浸法和土壤培养法测定了4种缓控释肥料（CRF1、CRF2、SCU、IBDU）的养分释放特性,并通过盆栽试验评价了缓控释肥料养分释放特性与油菜需肥规律的吻合性.结果表明：CRF1和CRF2在水中的释放曲线为“S”型,SCU为“破裂式释放”,IBDU的释放曲线呈倒“L”型;4种缓控释肥料在水浸法和土壤培养法中的养分释放特性均可用二项式方程进行拟合,说明两种方法存在一定的相关性.CRF1、CRF2两处理的油菜养分吸收量和生物量显著高于其他处理,以CRF2处理为最高,并且CRF1、CRF2的养分释放特性更接近油菜的需肥规律.     

15N标记水稻控释氮肥对提高氮素利用效率的研究

本文应用^15N示踪技术研究了水稻对空控释氮肥和尿素氮吸收利用效率的影响以及氮的去向,结果表明：施肥后11天内,水稻控释氮肥和尿素的NH3挥发损失分别占施入氮量的0.69%和1.81%,NH3的挥发损失在施肥后第5天时达到最大值,此后逐渐降低。水稻控释氮肥和尿素氮的淋溶损失分别占施入氮量的0.95%和1.02%,水稻控释氮肥氮的淋溶损失在水稻整个生长期间均比较平缓,施肥后40天时略有上升,此后又缓慢降低。用氮素平衡帐中的亏缺量和缺量扣除氨的损失量后计为硝化-反硝化损失量的结果表明,水稻控制氮肥氮的硝化-反硝化损失量占施氮量的3.46%,而尿素氮在硝化-反硝化损失量却高达37.75%,肥料氮在土壤中的残留主要集中在0～35cm的土层中,达91.4%-91.5%,残留在35cm以下土层中的氮甚微,水稻控制氮肥残留在土壤中的氮量略高于尿素处理。水稻控释氮肥利用率高达73.8%,比尿素高出34.9%,水稻控释氮肥氮利用率高的原因是因氮从颗粒中缓慢释放、受淋溶、氨挥发、尤其受硝化-反硝化途径损失的氮较少。在施等氮量的条件下,施用水稻控制氮肥的稻谷产量比尿素的增产25.5%,达到p=0.05的显著水平。     

富营养化河水灌溉对稻田土壤氮磷养分贡献的影响——以太湖地区黄泥土为例

以太湖地区主要稻田土壤类型黄泥土为对象,利用当地富营养化河水对回填土柱和植稻原状土渗漏池进行模拟稻田灌溉试验,系统研究了灌溉水对稻田土壤氮磷营养的贡献.在回填土柱灌溉试验中,在试验初期,不同形态的氮素均有较高的淋失量,以后逐渐降低,表明初期淋失的氮素主要来自土壤,而不是灌溉河水.在整个水稻生长季,均观测到有可溶性有机氮淋失,表明富营养化河水灌溉条件下可溶性有机氮是稻田土壤主要的氮素淋失形态.在本试验中,磷素的淋失动态与氮素的淋失动态截然相反,淹水后很长一段时间内均没有土壤磷素淋失,但在淹水灌溉后期有大量的土壤磷素淋失损失,这可能是淹水后期土壤对磷的吸持已达到饱和状态,不能继续固持土壤中多余的磷所致.与回填土柱模拟灌溉淋洗试验相比,在当前供肥条件下,原状土渗漏池试验氮磷淋失量远低于回填土柱试验,而灌溉水对土壤氮磷养分的贡献远高于回填土柱.通过富营养化河水灌溉带入当季稻田的N量达到每公顷56.3 kg,其中有55.8 kg N可被土壤吸持和作物吸收,表明太湖地区稻田土壤对氮磷养分来说是一个环境友好的生态系统.在利用当地富营养化河水进行稻田土壤灌溉时可适量减少肥料施用量、优化氮磷肥料管理.     

Intrarenal haemodynamics in postobstructive diuresis in the dog

Intrarenal haemodynamics were investigated in the dog prior to and after relief of 24 hr bilateral ureteral ligation (BUL), by the radioactive microsphere technique. Prior to release of 24 hr BUL there was an about 50% reduction in total blood flow (RBR), with a nearly proprotional decrease in the perfusion of the four cortical layers. Following release of the obstruction, total renal and outer cortical (zones 1 and 2) blood flow remained diminished, while perfusion of the inner (juxtamedullary) layers (zones 3 and 4) increased as compared to its prerelease values and equalled controls. Glomerular filtration rate (GFR) amounted to about 27% of controls in the postrelease phase. A marked increase in absolute and fractional sodium water excretion was observed after release of 24 hr BUL, as contrasted to normal controls and dogs after 24 hr unilateral ureteral ligation (UUL). This state, designated as postopstructive diuresis, might be explained by redistribution of intrarenal blood flow towards the juxtamedullary zones, and by a powerful natriuretic substance accumulated during complete obstruction.     

Nitrogen incorporation and remobilization in different shoot components of field-grown winter oilseed rape (Brassica napus L.) as affected by rate of nitrogen application and irrigation

The seasonal course of nitrogen uptake, incorporation and remobilization in different shoot components of winter oilseed rape (Brassica napus L.) was studied under field conditions including three rates of ¹⁵N labelled nitrogen application (0, 100 or 200 kg N ha^-1) and two irrigation treatments (rainfed or watered at a deficit of 20 mm). The total amount of irrigation water applied was 260 mm, split over 13 occasions in a 7-week-period ranging from 1 week before onset of flowering until 4 weeks after flowering.Nitrogen application and irrigation increased plant growth and nitrogen accumulation. Irrespective of N and irrigation treatment more than 50% of total shoot N was present in the stem when flowering started. At the end of flowering, pod walls were the main N store containing about 30–40% of shoot N. The quantities of N remobilized from stems and pod walls amounted in all treatments to about 70% of the N present in these organs at mid-flowering. At harvest, stem and pod walls each contained about 10% of total shoot N, the remaining 80% being incorporated into seeds. The main component contributing to the response of seed N accumulation to nitrogen application and irrigation was pods in axillary racemes. Up to 20 kg N ha^-1, corresponding to about 10% of final shoot N content, was lost from the plants by leaf drop.Irrigation increased the recovery at harvest of applied N from 30% to about 50%, while the level of N application did not affect the N recovery. ¹⁵N labelled (fertilizer derived) nitrogen constituted a greater proportion of the N content in old leaves than in young leaves and increased with age in the former, but not in the latter. Relative to soil N, fertilizer derived N also contributed more to the N content of vegetative than to that of reproductive shoot components. Small net changes in shoot N content after flowering reflected a balance between N import and export, leading to continuous dilution of ¹⁵N labelled N with unlabelled N.     

水氮配合对绿洲沙地农田玉米产量、土壤硝态氮和氮平衡的影响

在黑河中游边缘绿洲沙地农田研究了不同的水氮配合对玉米产量、土壤硝态氮在剖面中的累积和氮平衡的影响.结果表明,施氮处理较不施氮处理产量增加48.22%～108.6%,施氮量超过225 kg hm-2,玉米产量不再显著增加.受土壤结构影响土壤硝态氮在土壤中呈"W"型分布,即土壤硝态氮含量在0～20 cm、140～160 cm和260～300 cm土层均出现峰值,并随施氮量增加,峰值增高.在常规高灌溉量处理硝态氮含量峰值最高值出现在260～300 cm土层,节水25%灌溉处理硝态氮含量峰值最高值出现在土壤表层0～20 cm土层.在常规高灌溉量处理0～300 cm土层中200～300土层硝态氮累积量所占比例最高,介于27.56%～51.86%之间;节水25%灌溉处理在0～300 cm土层中100～200土层硝态氮累积量所占比例最高,介于32.94%～38.07%之间;表明低灌溉处理下土壤硝态氮在土壤浅层累积较多,而高灌溉处理使更多的硝态氮淋溶至土壤深层.与2006年相比,2007年不施氮处理0～200 cm土层土壤硝态氮含量和积累量均明显减少;而施氮处理变化很小,在低灌溉处理甚至表现出硝态氮含量和积累量增加,表明施氮是土壤硝态氮累积的主要来源,而灌溉则使硝态氮向土壤深层淋溶.0～200 cm 土层土壤硝态氮累积量平均介于27.66～116.68 kg hm-2、氮素表观损失量平均介于77.35～260.96 kg hm-2,和施氮量均呈线性相关,即随施氮量增加,土壤硝态氮累积量和氮素表观损失量均增加,相关系数R2介于0.79～0.99之间,相关均显著.随施氮量增加,玉米总吸氮量和氮收获指数增加,氮的农学利用率降低,而灌溉的影响较小.施氮量超过225 kg hm-2时,地上部植株氮肥吸收利用率和籽粒氮肥吸收利用率开始有降低趋势.所以,在沙地农田,节水10%～25%的灌溉水平和225 kg hm-2的施氮水平可以在避免水肥过量投入的基础上减少土壤有机氮淋溶对地下水造成的污染威胁.     

Antisense GAP-43 Inhibits the Evoked Release of Dopamine from PC12 Cells

Abstract: To investigate the role of the neuronal growth-associated protein GAP-43 (neuromodulin, B-50, F1, P-57) in neurotransmitter release, we transfected PC12 cells with a recombinant expression vector coding for antisense human GAP-43 cRNA. Two stable transfectants, designated AS1 and AS2, were selected that had integrated the recombinant sequence and expressed antisense GAP-43 RNA. Immunoblot analysis of proteins from AS1 and AS2 cells indicated that the level of GAP-43 in these cell lines was reduced. In the presence of extracellular calcium, a depolarizing concentration of K⁺ (56 m M ) evoked dopamine release from control cells, but not from AS1 and AS2 cells. Similarly, the calcium ionophore A23187 evoked dopamine release from control cells, but was ineffective in stimulating dopamine release from AS1 and AS2 cells. The antisense transfectants, as well as the control cells, contained appreciable quantities of dopamine and secretory granules with a normal appearance. Because the expression of antisense GAP-43 RNA in PC12 cells leads to a decrease in GAP-43 expression and to the loss of evoked dopamine release, these results provide evidence of a role for GAP-43 in calcium-dependent neurotransmitter release.     

Revitalization of an alpine protective forest by fertilization

In a highly damaged, 120–150 year old Norway spruce (Picea abies L. Karst.) stand, still used for grazing, with a protective function against avalanches and rockfall, a fertilization experiment for revitalization was carried out. A slow release fertilizer containing macro-and micronutrients was applied over three years, from 1986 to 1988. Four years after the last treatment, the proportion of trees with a needle loss of >25% decreased from initially 60–80% to 24% in the treated plots, while in the control plots it remained unchanged. A significant increase of radial increment (+100%), shoot growth (+40%), needle length (+20%) and starch content in the fine roots (+40%) was established as well. The supply with P which had been low initially was significantly increased. No changes could be observed in fine root biomass or mycorrhization. In the soil, an alpine rendzina on dolomite, a significant reservoir of P and tendentially of K was still detectable three years after the last treatment. Cellulose decomposition was slightly enhanced in the uppermost soil layer of the treated plots but no changes in the C/N ratio or in pH were found.     

Effects of fertigation scheme on N uptake and N use efficiency in cotton

While fertigation can increase fertilizer use efficiency, there is an uncertainly as to whether the fertilizer should be introduced at the beginning of the irrigation or at the end, or introduced during irrigation. Our objective was to determine the effect of different fertigation schemes on nitrogen (N) uptake and N use efficiency (NUE) in cotton plants. A pot experiment was conducted under greenhouse conditions in year 2004 and 2005. According to the application timing of nitrogen (N) fertilizer solution and water (W) involved in an irrigation cycle, four nitrogen fertigation schemes [nitrogen applied at the beginning of the irrigation cycle (N–W), nitrogen applied at the end of the irrigation cycle (W–N), nitrogen applied in the middle of the irrigation cycle (W–N–W) and nitrogen applied throughout the irrigation cycle (N&W)] were employed in a completely randomized design with four replications. Cotton was grown in plastic containers with a volume of 84 l, which were filled with a clay loam soil and fertilized with 6.4 g of N per pot as unlabeled and ¹⁵N-labeled urea for 2004 and 2005, respectively. Plant total dry matter (DM) and N content in N–W was significantly higher than in N&W in both seasons, but these were not consistent for W–N and W–N–W treatments. In year 2005, a significantly higher nitrogen derived from fertilizer (NDFF) for the whole plant was found in W–N and N–W than that in W–N–W and N&W. Fertigation scheme had a consistent effect on total NUE: N–W had the highest NUE for the whole plant, but this was not significantly different from W–N. Treatments W–N and W–N–W had similar total NUE, and N&W had the lowest total NUE. After harvesting, the total residual fertilizer N in the soil was highest in W–N, lowest in N–W, but this was not significantly different from N&W and W–N–W treatments. Total residual NO₃–N in the soil in N&W and W–N treatments was 20.7 and 21.2% higher than that in N–W, respectively. The total ¹⁵N recovery was not statistically significant between the four fertigation schemes. In this study, the fertigation scheme N–W (nitrogen applied at the beginning of an irrigation cycle) increased DM accumulation, N uptake and NUE of cotton. This study indicates that Nitrogen application at the beginning of an irrigation cycle has an advantage on N uptake and NUE of cotton. Therefore, NUE could be enhanced by optimizing fertilization schemes with drip irrigation.     

持续施用缓/控释尿素条件下水田土壤NH3挥发与N2O排放特征

以持续9年施用不同缓／控释尿素的水田棕壤为试验对象,以普通大颗粒尿素为对照,研究了持续施用不同缓／控释尿素条件下水田土壤NH₃挥发与N₂O排放特征.结果表明: 与普通大颗粒尿素(U)相比,除1% 3,4－二甲基吡唑磷酸盐(DMPP)+U处理 NH₃挥发增加了25.8%外,其他缓／控释尿素肥料处理对NH₃有明显的减排效果.树脂包膜尿素(PCU)对NH₃减排效果最明显,为73.4%,硫包膜尿素(SCU)为72.2%,0.5% N-丁基硫代磷酰三胺(NBPT)+1% DMPP+U为71.9%,1% 氢醌(HQ)+3% 双氰胺(DCD)+U为46.9%,0.5% NBPT+U为43.2%,1% HQ+U为40.2%,3% DCD+U为25.5%, 1% DMPP均与施用普通大颗粒尿素差异显著;所有缓／控释尿素处理与对照相比均可显著减少N₂O排放.1% DMPP+U对N₂O减排效果最明显,为74.9%,PCU为62.1%,1% HQ+3% DCD+U为54.7%,0.5% NBPT+1% DMPP+U为42.2%,3% DCD+U为35.9%,1% HQ+U为28.9%,0.5% NBPT+U为17.7%,SCU为14.5%,均与施用普通大颗粒尿素差异显著.比较0.5% NBPT+1% DMPP+U、SCU、PCU对NH₃和N₂O减排的综合效果,3种肥料作用相近,且均明显优于其他处理,但包膜材料的成本较抑制剂高数倍.因此,同时添加脲酶和硝化抑制剂的缓释尿素是减少水田氮素损失及环境污染的首选氮肥.     

川西南常绿阔叶林凋落物分解及养分释放对模拟氮沉降的响应

通过原位进行了对照(CK)、低氮(LN,50kgN.hm-2.a-1)、中氮(MN,100kgN.hm-2.a-1)和高氮(HN,150kgN.hm-2.a-1)处理,研究了川西南天然常绿阔叶林凋落物分解及养分释放对模拟N沉降的响应.结果表明:凋落物分解95%需要4.72～6.33年,分解率最高的为CK,最低的为HN.经过365d,各处理的分解率均低于CK,仅HN与CK间差异显著(P<0.05);C残留率均高于CK;N和K残留率均显著高于CK(P<0.05);P残留率均高于CK,仅LN与CK间差异显著(P<0.05).各处理凋落物的C/N升高3.9%～23.7%.凋落物分解过程中N元素的迁移模式为富集-释放,C、P和K元素则表现为直接释放.N沉降对凋落物中养分元素的释放及木质素和纤维素的降解均具有抑制作用.随着处理时间的延长,N沉降对川西南常绿阔叶林凋落物分解的影响从正效应转向负效应,且负效应随沉降浓度的增加而加强.     

Nitrogen balance of effluent irrigated silage cropping systems in southern Australia

The nitrogen (N) balance in a double-cropped, effluent spray irrigation system was examined for several years in southern Australia. The amounts of N added by irrigation, removed in the crop, and lost by ammonia (NH3) volatilisation, denitrification, and leaching were measured. Results from the project provide pig producers with the knowledge necessary to evaluate the efficiency of such systems for managing N, and enable sustainable effluent reuse practices to be developed. Oats were grown through the winter (May to November) without irrigation, and irrigated maize was grown during the summer/autumn (December to April). Approximately 18 mm of effluent was applied every 3 days. The effluent was alkaline (pH 8.3) and the average ammoniacal-N (NH4+ + NH3) concentration was 430 mg N/l (range: 320 to 679 mg N/l). Mineral N in the 0- to 1.7-m layer tended to increase during the irrigation season and decrease during the winter/spring. About 2000 kg N/ha was found in the profile to a depth of 2 m in October 2000. N removed in the aboveground biomass (oats + maize) was 590 and 570 kg N/ha/year, equivalent to 25% of the applied N. Average NH3 volatilisation during the daytime (6:00 to 19:00) was 2.74 kg N/ha, while volatilisation at night (19:00 to 6:00) was 0.4 kg N/ha, giving a total of 3.1 kg N/ha/day. This represents approximately 12% of the N loading, assuming that these rates apply throughout the season. The balance of the N accumulated in the soil profile during the irrigation season, as 15N-labelled N studies confirmed. The high recovery of the 15N-labelled N, and the comparable distribution of 15N and Br in the soil profile, implied that there was little loss of N by denitrification, even though the soil was wet enough for leaching of both tracers.     

Response of a Stoichiometrically Imbalanced Ecosystem to Manipulation of Nutrient Supplies and Ratios

Cuatro Ciénegas Basin (CCB) is a desert ecosystem that hosts a large diversity of water bodies. Many surface waters in this basin have imbalanced nitrogen (N) to phosphorus (P) stoichiometry (total N:P > 100 by atoms), where P is likely to be a limiting nutrient. To investigate the effects of nutrient stoichiometry on planktonic and sediment ecosystem components and processes, we conducted a replicated in situ mesocosm experiment in Lagunita, a shallow pond located in the southwest region of the basin. Inorganic N and P were periodically added to mesocosms under three different N:P regimes (P only, N:P = 16 and N:P = 75) while the control mesocosms were left unamended. After three weeks of fertilization, more than two thirds of the applied P was immobilized into seston or sediment. The rapid uptake of P significantly decreased biomass C:P and N:P ratios, supporting the hypothesis that Lagunita is P-limited. Meanwhile, simultaneous N and P enrichment significantly enhanced planktonic growth, increasing total planktonic biomass by more than 2-fold compared to the unenriched control. With up to 76% of added N sequestered into the seston, it is suspected that the Lagunita microbial community also experienced strong N-limitation. However, when N and P were applied at N:P = 75, the microbes remained in a P-limitation state as in the untreated control. Two weeks after the last fertilizer application, seston C:P and N:P ratios returned to initial levels but chlorophyll a and seston C concentrations remained elevated. Additionally, no P release from the sediment was observed in the fertilized mesocosms. Overall, this study provides evidence that Lagunita is highly sensitive to nutrient perturbation because the biota is primarily P-limited and experiences a secondary N-limitation despite its high TN:TP ratio. This study serves as a strong basis to justify the need for protection of CCB ecosystems and other low-nutrient microbe-dominated systems from anthropogenic inputs of both N and P.     

Turfgrass (Cynodon dactylon L.) sod production on sandy soils: I. Effects of irrigation and fertiliser regimes on growth and quality

The effects on growth, quality and N uptake by turfgrass (Cynodon dactylon L.) during sod production of four fertiliser types applied at three application rates (100, 200 or 300 kg N ha⁻¹ per ‘crop’) under two irrigation treatments (70% and 140% daily replacement of pan evaporation) were investigated. The fertiliser types were: water-soluble (predominately NH₄NO₃), control-release, pelletised poultry manure, and pelletised biosolids; and the experiment was conducted on a sandy soil in a Mediterranean-type climate. Plots were established from rhizomes, with the turfgrass harvested as sod every 16–28 weeks depending upon the time of the year. Four crops were produced during the study. Applying water-soluble and control-release fertilisers doubled shoot growth and improved turfgrass greenness by up to 10% in comparison with plots receiving pelletised poultry manure and pelletised biosolids. Nitrogen uptake into the shoots after four crops (averaged across irrigation treatments and N rates) was 497 kg N ha⁻¹ for the water-soluble fertiliser, 402 kg N ha⁻¹ for the control-release, 188 kg N ha⁻¹ for the pelletised poultry manure and 237 kg N ha⁻¹ for the pelletised biosolids. Consequently, the agronomic nitrogen-use efficiency (NAE, kg DM kg⁻¹ N applied) of the inorganic fertilisers was approximately twice that of the organic fertilisers. Increasing irrigation from 70% to 140% replacement of pan evaporation was detrimental to turfgrass growth and N uptake for the first crop when supplied with the water-soluble fertiliser. Under the low irrigation treatment, inorganic N fertilisers applied at 200–300 kg N ha⁻¹ were adequate for production of turfgrass sod. Section Editor: P. J. Randall     

推迟拔节水对小麦氮素积累与分配和硝态氮运移的影响

摘要：2007—2008年度以高产冬小麦品种济麦22为材料,设置2个拔节水灌溉时期,为拔节期和拔节后10 d;3个目标相对含水量,灌水后0~140 cm土层土壤相对含水量分别达到65%、75%、80%,以W1、W2、W3表示拔节期灌水处理,DW1、DW2、DW3表示拔节后10 d灌水处理;开花期均灌水至0~140 cm土层土壤相对含水量为70%,研究推迟拔节水对小麦氮素积累与分配和硝态氮运移的影响。结果表明：（1）W2和DW2处理有利于提高0~60 cm土层土壤硝态氮含量,促进籽粒氮素积累;营养器官贮藏氮素向籽粒的转运量、籽粒产量和氮肥偏生产力分别高于W1和DW1,与W3和DW3处理无显著差异;开花后植株氮素积累量、籽粒蛋白质含量和水分利用效率分别高于W3和DW3,是拔节期和拔节后10 d灌水的最优处理。（2）W2和DW2处理比较,DW2成熟期100~140 cm土层硝态氮残留量低于W2,籽粒产量、籽粒蛋白质含量、氮素吸收效率、氮肥偏生产力和水分利用效率均显著高于W2,是本试验条件下的最佳灌水方案。2008—2009生长季试验各处理变化趋势同2007—2008年度。     

Effect of N-nutrition and irrigation on fruit production of carob (Ceratonia siliqua)

A combined fertilization and irrigation experiment was initiated in order to see whether such treatment could improve the productivity of carob ( Ceratonia siliqua L. cv. Mulata) on Mediterranean marginal lands. Mature carob trees (20–30 years old) were submitted to 3 different irrigation levels (100%;, 50%; and 0%;) based on daily standard evaporation values, measured with a class A pan. For each water level either 21 or 63 kg N ha⁻¹ was applied as ammonium nitrate. The results reported here refer to a two-year experiment, and show that the productivity of the trees could be improved due to a positive interaction between water and N application. In addition, they suggest that also under the normal dry conditions of these Mediterranean systems nitrogen application is effective, even without irrigation.     

控释肥料对覆膜栽培稻田N2O排放的影响

采用静态箱-气相色谱法,研究了控释肥料对四川丘陵地区覆膜节水高产栽培稻田N₂O排放的影响.结果表明: 稻田施用尿素及控释肥料后水稻生长期N₂O排放总量分别为(38.2±4.4)和(21.5±5.2) mg N·m^-2;施用尿素处理N₂O排放系数为0.25%,施用控释肥料处理N₂O排放系数为0.14%,减少了43.6%(P<0.05),其中烤田前减少了49.6%(P<0.05);控释肥料可抑制施肥引起的N₂O排放峰值,降幅达52.6%;控释肥料对水稻不同生长季节土壤微生物生物量氮、NH₄⁺-N含量和水稻产量均无显著影响;N₂O排放与5 cm土壤温度、土壤Eh值无显著相关性.     

Turfgrass (Cynodon dactylon L.) sod production on sandy soils: II. Effects of irrigation and fertiliser regimes on N leaching

The effects of irrigation and fertiliser regimes on N leaching from the production of couch grass (Cynodon dactylon L.) sod, on a free-draining sandy soil, were evaluated in a 22-month field study. The experimental design used a randomised-block, split-plot design with three replicates. Main plots consisted of two irrigation treatments: 70 and 140% daily replacement of pan evaporation; four subplot fertiliser types (water-soluble (predominately NH₄NO₃), control-release, pelletised poultry manure and pelletised biosolids); and three N application rates (100, 200 and 300 kg N ha⁻¹ per crop). Nitrogen leaching was assessed by measuring the leachate volumes and concentrations of N species leached from soil lysimeters (250 mm in diameter by 950 mm in length) installed in 10 m² turfgrass plots. Nitrogen leaching ranged from 33 to 167 kg N ha⁻¹ over 22 months, depending upon the irrigation and fertiliser treatment. Irrigation treatment affected N leaching more than fertiliser treatment, and increasing the irrigation from 70 to 140% replacement of daily pan evaporation increased N leaching for all fertiliser types, and by up to four times. Forty six to 76% of losses occurred from the high irrigation treatments during the first 16 weeks after the turfgrass was planted as rhizomes. By contrast, N leaching did not appear to increase following harvest of sod. At the high irrigation treatment, N leaching was greater for the pelletised biosolids than the control-release; while at the low irrigation treatment, N leaching did not vary between fertiliser types. A significant proportion of the N leached was in the organic form. Therefore, we recommend total N and mineral N be measured when assessing N leaching from turfgrass. Nitrogen leaching from turfgrass production is low from all fertiliser types when the irrigation matches turfgrass water use and N is applied at a rate and frequency that approximates turfgrass requirements. Section Editor: P. J. Randall