Observations on patterns of granular fertiliser deposition beside hedges and its likely effects on the botanical composition of field margins

Patterns of granular fertiliser deposition differed markedly between a pneumatic boom applicator and a spinning disk machine, both of which were tractor-mounted. The pneumatic applicator gave relatively even distribution across the boom width. A spinning disk gave more variable deposition and significant amounts were spread further than the expected 12 m overlapping pattern. When operating with a deflector plate on the spinning disk, significant amounts of fertiliser were also spread further than the expected 6 m. However, when operating next to a hedge, there was evidence of fertiliser concentration at the base of the hedge and prevention of granules passing through to adjacent habitat. A peak concentration of up to 150 kg ha^-1 of fertiliser was deposited at the hedge/field edge interface. In a tray experiment on seedling competition and establishment, there was no evidence of nitrogen fertiliser effects, at rates found in the field, on early plant establishment or species diversity. However, in a competition experiment with established plants of four grass species grown in pots, the nitrophilous species Bromus sterilis was able to increase growth at increasing nitrogen level, at the expense of slow-growing Brachypodium sylvaticum and Anthoxanthum odoratum. Whilst hedges may buffer fertiliser contamination of habitats adjacent to agricultural fields, deposition of concentrated nitrogen fertiliser beside the hedge is likely to encourage the growth of nitrophilous plant species. In the short term, this may not affect botanical composition or diversity, but to reduce the likely long-term adverse effects of fertiliser misplacement, we recommend that farmers are encouraged to use pneumatic fertiliser applicators and to introduce vegetation buffer strips at field edges.     

Improving grasslands: the influence of soil moisture and nitrogen fertilization on the establishment of seedlings

1. In order to investigate the factors influencing the establishment of seedlings in permanent grassland, the influence of soil moisture and nitrogen fertilization on competition between established plants of Lolium perenne and seedlings of Phleum pratense or Trifolium pratense was studied in two experiments under greenhouse conditions using the 'split-box'-technique.
2. There was no difference in the production of plant dry matter of P. pratense or T. pratense between 30% volumetric soil water content (−0·005 MPa) and 22% (−0·04 MPa), but 15% soil moisture (−0·33 MPa) reduced plant growth. L. perenne yields were linearly reduced by reduced soil moisture content.
3. Shoot competition from L. perenne reduced the plant dry matter yield of P. pratense and T. pratense more than did root competition in these experiments. When shoot competition was present, differences between moisture contents were not detected, indicating that light was probably the limiting resource under such conditions. No significant interaction between root competition and soil moisture was observed for plant weight.
4. Root competition was not prevented even though sufficient water and nitrogen were supplied. This indicated either that some other growth factor was limiting or the plants competed for resources at the root hair level even though sufficient resources were supplied at the pot or field scale. Therefore, in the situation of direct drilling of species during grassland renovation, it may be difficult to alleviate competition by adequate provision of water and nitrogen.     

Influence of pasture management (nitrogen and lime addition and insecticide treatment) on soil organisms and pasture root system dynamics in the field

At an upland field site in Scotland on an established Festuca-Agrostis pasture, the effects of soil amendment on root dynamics, using nitrogen and lime and the regular application of insecticide, were studied over a period of 1 year. The most common insect root herbivore at the site was Tipula paludosa, and the application of insecticide (chlorpyrifos) reduced numbers of all insect larvae of all species. Root biomass, root appearance, root disappearance and root density were all reduced by insecticide. This reduced rooting could reflect reduced root replacement, due to the reduction in root herbivory in insecticide-treated plots or could be a direct affect of insecticide application on the roots. Root appearance, root disappearance and C and N input to the soil were increased by treatment with nitrogen and lime, while root survival time was reduced. The nitrogen and lime treatment also increased bacterial numbers in the soil and enhanced their potential C utilization. An altered rooting density and longevity was brought about by the two soil treatments, which could have both direct and indirect effects on the soil biota.     

土壤有效氮及其相关因素对植物细根的影响

细根(直径≤2mm)作为植物吸收水分和养分的主要器官之一,在陆地生态系统养分循环和能量流动中起重要作用。开展土壤有效氮变化对植物细根影响研究对于了解全球气候变化条件下的陆地生态系统养分循环具有重要意义。本文就相关研究进行了综述:1)土壤有效氮变化对植物细根生长、发育、寿命及呼吸的直接影响;2)土壤质地、温度、大气CO2浓度和氮沉积等相关因素对植物细根的影响。由于研究方法及物种间差异等的影响,研究结果不尽相同。今后,应在不同空间尺度上深入研究土壤有效氮对植物细根的影响,而植物细根-土壤-微生物三者间相互关系变化对土壤氮变化的潜在响应将可能成为今后研究的热点问题之一。     

Effects of tree competition on corn and soybean photosynthesis, growth, and yield in a temperate tree-based agroforestry intercropping system in southern Ontario, Canada

In 1987, the University of Guelph established a large tree-based intercropping system on 30 ha of prime agricultural land in southern Ontario, Canada. The purpose was to investigate various aspects of intercropping trees with prime agricultural crops. In this study, objectives were to investigate tree competitive effects (i.e., shading and competition for soil moisture) on under-story crop net assimilation (NA), growth, and yield. The effects of tree competition on corn (C4 plant) and soybean (C3 plant) photosynthesis and productivity in the intercropped system were studied during the 1997 and 1998 growing seasons. Corn and soybeans were intercropped with hybrid poplar (clone-DN-177) and silver maple (Acer sacharrinum) at a within-row spacing of 6 m and between-row spacing of 12.5 or 15 m. Trees were absent from control rows. Tree rows were oriented approximately north and south. Twelve crop locations were sampled around each tree. These were at 2 and 6 m east and west of the tree, located along a primary axis running through the tree trunk and perpendicular to the tree row, and at 2 m north and south of each location along the primary axis. Net assimilation and plant water deficit measurements were made three times daily (morning, noon, afternoon) on sampling days in July. Generally, tree competition significantly reduced photosynthetic radiation (PAR), net assimilation (NA), and growth and yield of individual soybean or corn plants growing nearer (2 m) to tree rows in both years and soil moisture in 1998. NA was highly correlated with growth and yield of both crops. These correlations were higher for corn than soybeans in both years, with corn, rather than soybeans being more adversely impacted by tree shading. In 1997, poplar, rather than maple, had the greatest competitive effect on NA. In 1997, the lowest plant water deficits, for soybeans and for corn, were observed for the maple treatment. Nonetheless, in both years, daily plant water deficits were non-significantly and poorly correlated with NA and growth and yield of both crops. However, soil moisture (5 and 15 cm depth) was significantly correlated with soybeans yield in 1998. Possible remediation strategies are discussed to reduce tree competitive interactions on agricultural crops.     

Modelling and measuring the effect of nitrogen catch crops on the nitrogen supply for succeeding crops

Nitrogen catch crops are grown to absorb nitrogen from the rooting zone during autumn and winter. The uptake of N (N_upt) from the soil inorganic N pool (N_min) to a pool of catch crop nitrogen, will protect the nitrogen against leaching. After incorporation, a fraction (m) of the catch crop nitrogen is mineralized and becomes available again. However, not all available nitrogen present in the soil in the autumn is lost by leaching during winter. A fraction (r) of the nitrogen absorbed by the catch crop would, without a catch crop, have been retained within the rooting zone. The first year nitrogen beneficial effect (N_eff) of a catch crop may then be expressed b N _eff = m*N _upt - r* N _upt The soil-plant simulation model DAISY was evaluated for its ability to simulate the effects of catch crops on spring N_min and N_eff. Based on incubation studies, parameter values were assigned to a number of catch crop materials, and these parameter values were then used to simulate spring Nmin. The model was able to predict much of the vairiation in the measured spring Nmin (r² = 0.48***) and there was good agreement between the measured and the simulated effect of winter precipitation on spring N_min and Neff.Scenarios including variable soil and climate conditions, and variable root depth of the succeeding crop were simulated. It is illustrated that the effect of catch crops on nitrogen availability for the succeeding crop depends strongly on the rooting depth of the succeeding crop. If the succeeding crop is deep rooted and the leaching intensity is low, there is a high risk that a catch crop will have a negative effect on nitrogen availability. The simulations showed that the strategy for the growing of catch crops should be adapted to the actual situation, especially to the expected leaching intensity and to the rooting depth of the succeeding crop.     

Interactions between elevated CO2 concentration, nitrogen and water: effects on growth and water use of six perennial plant species

Two experiments are described in which plants of six species were grown for one full season in greenhouse compartments with 350 or 560 μ mol mol^–1 CO₂. In the first experiment two levels of nitrogen supply were applied to study the interaction between CO₂ and nitrogen. In the second experiment two levels of water supply were added to the experimental set-up to investigate the three-way interaction between CO₂, nitrogen and water. Biomass and biomass distribution were determined at harvests, while water use and soil moisture were monitored throughout the experiments. In both experiments a positive effect of CO₂ on growth was found at high nitrogen concentrations but not at low nitrogen concentrations. However, plants used much less water in the presence of low nitrogen concentrations. Drought stress increased the relative effect of elevated CO₂ on growth. Available soil moisture was used more slowly at high CO₂ during drought or at high nitrogen concentrations, while at low nitrogen concentrations decreased water use resulted in an increase in soil moisture. The response to the treatments was similar in all the species used. Although potentially faster growing species appeared to respond better to high CO₂ when supplied with a high level of nitrogen, inherently slow-growing species were more successful at low nitrogen concentrations.     

Effects of Dominant Plant Species on Soils during Succession in Nutrient-poor Ecosystems

During the initial phases of succession on nutrient-poor, mineral substrates dead plant material accumulates rapidly in the soil. This accumulation of soil organic matter can result in a more than 10-fold increase in nitrogen mineralization within a few decades. These changes in soil features have important consequences for plant growth and the competition between plant species. During succession in heathlands an increase in nutrient mineralization leads to species with low maximum growth rates and low biomass loss rates being replaced by species with high potential growth rates and high biomass losses. The plant properties responsible for reduced biomass loss rates appear to result in the litter produced being poorly decomposable, whereas the litter from plants with high potential growth rates decomposes more easily. Model simulations suggest that such combinations of plant features greatly influence the increase in mineralization and the change in plant species composition during ecosystem development. Studies in the field and garden plot experiments confirmed this hypothesis.     

模拟氮沉降对温带阔叶红松林地土壤氮素净矿化的影响

以长白山阔叶红松混交林为研究对象,于2006—2008年原位模拟不同形态氮((NH4)2SO4、NH4Cl和KNO3)沉降水平(22.5和45kgN·hm-2·a-1),利用树脂芯法技术(resin-core incubation technique)测定了表层(有机层0～7cm)和土层(0～15cm)土壤氮素净矿化、净氨化和净硝化通量的季节和年际变化规律。同时,结合前人报道的有关林地碳、氮过程及其环境变化影响的结果,力求有效预估森林生态系统中氮素年矿化通量对大气氮沉降量和水热条件等因子变化的响应。结果表明,长白山阔叶红松林地土壤氮素年净矿化通量为1.2～19.8kgN·hm-2·a-1,2008年不同深度的土壤氮素年净矿化通量均显著高于2006和2007年(P<0.05)。随着模拟氮沉降量增加,土壤氮素净矿化通量也随之增加,尤其外源NH4+-N输入对净矿化通量的促进作用更为明显(P<0.05),但随着施肥年限的延长,这种促进作用逐渐减弱。与林地0～15cm土壤相比,氮沉降增加对0～7cm有机层氮素净氨化和净矿化通量的促进作用更为明显,尤其NH4Cl处理的促进作用更大。结合前人报道的野外原位观测结果,土壤氮素年净矿化通量随氮素沉降量的增加而增大,氮沉降量对不同区域森林土壤氮素净矿化通量的贡献率约为52%;氮沉降量(x1)和pH值(x2)可以解释区域森林土壤氮素年净矿化通量(y)变化的70%(y=0.54x1-18.38x2-109.55,R2=0.70,P<0.0001)。前人研究结果仅提供区域年均温度,未考虑积温的影响,这可能是造成年净矿化通量与温度无关的原因。今后的研究工作应该加强区域森林土壤积温观测,进而更加准确地预估森林土壤氮素的年净矿化通量。     

Effects of a catch crop on leaching of nitrogen from a sandy soil: Simulations and measurements

The effects of an undersown catch crop on the dynamics and leaching of nitrogen in cropping systems with spring cereals were investigated in southern Sweden. Field measurements of soil mineral nitrogen and nitrogen concentrations in drainage water were made for 4 years in a sandy soil. The experiment was performed on four tile-drained field plots sown with spring cereals. On two of the plots, Italian rye grass was undersown and ploughed down the following spring during three of the years. The other two plots were treated in a conventional way and served as controls. Soil nitrate levels were substantially reduced in the catch-crop treatment, but increased during the fourth year when no catch crop was grown. The differences between the treatments in soil nitrate were reflected in the nitrate concentrations measured in the drainage water. A mathematical model was used to simulate nitrogen dynamics in corresponding treatments. There was good agreement between measurements and simulations with regard to patterns of change in soil mineral nitrogen and nitrate concentrations in drainage water for each treatment. Simulated leaching of nitrate in the conventional treatment was 1.9–3.9 g N m^–2 y^–1 during the first three years while calculated leaching based on the measurements was 2.7–4.4 g N m^–2 y^–1. In the catch-crop treatment leaching of nitrate was reduced by 1.4–2.6 g m^–2 y^–1 according to the simulations and by 2.2–4.1 g m^–2 y^–1 according to calculations based on the measurements. Measurements showed that leaching of nitrogen compounds other than nitrate was hardly affected by the catch crop. In the simulations the ploughed-down catch crop resulted in temporary increases of the litter pool, a net increase of the humus pool and a reduced C-N ratio of the litter pool. Simulated net mineralization from the litter pool was substantially higher in the catch-crop treatment compared with the conventional treatment. In the fourth year, the yield of the main crop was 20–25% higher in the catch-crop treatment, and leaching was higher than in the conventional treatment.     

不同氮素水平下入侵种豚草与本地种黄花蒿、蒙古蒿的竞争关系

已有研究表明,土壤氮素增加可提高外来植物的入侵性,降低本地植物的竞争力.为揭示全球氮沉降对入侵种与本地种之间竞争关系的影响,我们于2010年5-8月在中国科学院北京森林生态系统定位研究站温室内,采用取代系列实验方法(standard replacement experiment),研究了3个氮素水平下入侵种豚草(Ambrosia artemisiifolia)与本地种黄花蒿(Artemisia annua)、蒙古蒿(Artemisia mongolica)的生长特征及种内、种间竞争关系的变化.实验采用双因素-随机区组设计,设置了低氮、中氮和高氮3个氮素水平,每一氮素水平分别设置豚草和黄花蒿、豚草和蒙古蒿组成的竞争实验,生长90 d后测量株高和生物量.结果表明:单栽情况下,随氮素水平的增加3个物种的株高均增加,而生物量均无显著变化;混栽情况下,3个物种株高和生物量随氮素水平的增加变化各异,豚草呈极显著增加趋势,而黄花蒿无明显变化,蒙古蒿则先增加后减少.豚草的快速生长使其在竞争中处于优势地位,对本地种黄花蒿和蒙古蒿产生明显的竞争效应.但不同氮素水平下,豚草对本地种的竞争力不同:低氮素水平下,豚草＜两个本地种;中氮素水平下,黄花蒿＜豚草＜蒙古蒿;高氮素水平下,豚草＞两个本地种.氮素添加显著提高了豚草的种间竞争力,改变了豚草与本地种之间的竞争关系,使竞争有利于入侵种.据此推测,在全球变化的背景下,氮沉降的增加将会促进外来种豚草的入侵,增加本地群落的可入侵性.     

A test of a potential short cut in the nitrogen cycle: The role of exudation of symbiotically fixed nitrogen from the roots of a N-fixing tree and the effects of increased atmospheric CO2 and temperature

N-fixing trees facilitate the growth of neighboring trees of other species. These neighboring species benefit from the simple presence of the N fixation symbiosis in their surroundings. Because of this phenomenon, it has been hypothesized that a change in atmospheric CO₂ concentration may alter the role of N-fixing trees in their environment. It is thought that the role of N-fixing trees in ecosystems of the future may be more important since they may help sustain growth increases due to increased CO₂ concentration in nitrogen limited forests. We examined: (1) whether symbiotically fixed N was exuded from roots, (2) whether a doubled atmospheric CO₂ concentration would result in increased organic N exudation from roots, and (3) whether increased temperature or N availability affected N exudation from roots. This study analyzed exudation of dissolved organic N from the roots of seedlings of the N-fixing tree Robinia pseudoacacia L. in a full factorial design with 2 CO₂ (35.0 and 70.0 Pa) × 2 temperature (26 or 30 °C during the day) × 2 N fertilizer (0 and 10.0 mM N concentration) levels. Trees with no other source of N except N fixation exuded about 1% to 2% of the fixed N through their roots as dissolved organic N. Increased atmospheric CO₂ concentrations did not, however, increase N exudation rates on a per gram belowground biomass basis. A 4 °C increase in temperature and N fertilization did, however, significantly increase N exudation rates. These results suggest that exudation of dissolved organic N from roots or nodules of N-fixing trees could be a significant, but minor, pathway of transferring N to neighboring plants in a much more rapid and direct way than cycling through death, decomposition and mineralization of plant residues. And, while exudation rates of dissolved organic N from roots were not significantly affected by atmospheric CO₂ concentration, the previously observed CO₂ fertilization effect on N-fixing trees suggests that N exudation from roots could play a significant but minor role in sustaining increases in forest growth, and thus C storage, in a CO₂ enriched atmosphere.     

Woody plant establishment during the early stages of volcanic succession on Mount Usu, northern Japan

The establishment patterns of woody plants were investigated on the volcano Usu, 9 years after the 1977–1978 eruptions. The former vegetation was covered by a 1–3 m thick volcanic deposit. Trees producing wind-dispersed seeds capable of long distance dispersal, such as Populus maximowiczii, Betula platyphylla var. japonica, Salix hultenii var. angustifolia, and Salix sachalinensis, were dominant. Most trees were only 2–4 years old in 1986, suggesting that chances for seedling establishment were restricted. The tree heights did not differ significantly among the species, while lengths of annual shoots differed due to herbivore preferences. Trees were established at higher densities on gravel-dominated pumice surfaces than on fine-textured surfaces. Tree density was not greatly affected by the nutrient content of deposits. From 1987 to 1990, tree height increments did not differ between the gravel and non-gravel areas. Ground surface texture is an important factor in determining seedling establishment in the early stages of volcanic succession, and nutrient status is unimportant.     

季节性雪被对高山生态系统土壤氮转化的影响

在高山生态系统中,季节性雪被对土壤氮含量及转化有着重大影响.降雪是氮沉降的一种重要形式,直接影响着土壤中的有效氮含量;降雪形成不同厚度和持续期的雪被后,造成环境因子(土壤温度和含水量)和生物因子(土壤微生物、高山植物和高山动物)的异质性,进而对土壤中氮素矿化和微生物固持过程产生复杂的影响.本文重点介绍了持续性雪被消融期冻融交替影响土壤氮素矿化和流失的机制,并针对高山地区未来季节性雪被可能发生的变化,综述了野外原位模拟实验的主要研究成果,最后提出了开展季节性雪被对土壤氮影响研究的一些建议.     

The effect of root temperature on the uptake of nitrogen and the relative size of the root system in Lolium perenne. I. Solutions containing both NH+4 and NO3−

Abstract Lolium perenne L. cv. S23 was grown in flowing culture solution, pH 5, in which the concentrations of NH₄⁺, NO₃^? and K⁺ were frequently monitored and adjusted to set values. In a pre-experimental period, plants were acclimatized to a regime in which roots were treated at 5°C with shoots at 25°C. The root temperature was then changed to one of the following, 3, 7, 9, 11, 13, 17 or 25°C, while air temperature remained at 25°C. When root temperature was increased from 5X, the relative growth rate of roots increased immediately while that of shoots changed much less for a period of approximately 9 d (phase 1). Thus, the root: shoot ratio increased, but eventually approached a new, temperature-dependent, steady value (phase 2). The fresh: freeze-dried weight ratio (i.e. water content) in shoots (and roots) increased during the first phase of morphological adjustment (phase 1). In both growth phases and at all temperatures, plants absorbed more NH₄⁺ than NO₄⁺, the tendency being extreme at temperatures below 9° where more than 85% of the N absorbed was NH₄⁺. Plants at different root temperatures, growing at markedly different rates, had very similar concentrations of total N in their tissues (cells) on a fresh weight basis, despite the fact that they derived their N with differing preference for NH₄⁺. Specific absorption rates for NH₄⁺, NO_x^?, K⁺ and H₂PO₄^? showed very marked dependence on root temperature in phase 1, but ceased to show this dependence once a steady state root: shoot ratio had been established in phase 2. The results indicate the importance of relative root size in determining ion fluxes at the root surface. At higher temperatures where the root system was relatively large, ‘demand’ per unit root was low, whereas at low temperatures roots were small relative to shoots and ‘demand’ was high enough to offset the inhibitory effects of low temperature on transport processes.