不同覆盖位置下草地坡面水流路径长度变化特征

为深入探索植被覆盖及其格局的减水减沙的水动力学过程及其机理,该研究利用室内放水冲刷试验,分析了不同植被盖度及其覆盖位置在不同冲刷流量下水流路径长度的变化,以及水流路径长度与植被覆盖度、水动力学参数和产流产沙量之间的关系,探讨坡面水流路径长度作为表征植被格局参数的可行性。结果表明:1)植被覆盖度可有效影响水动力参数的变化,并且随着植被覆盖度的增加,流速和单位水流功率呈线性减小趋势(P0.01);而糙率系数、阻力系数和径流剪切力则呈指数增加趋势(P0.01)。坡面水流受阻可能性增加,动能减弱,进而导致产流产沙量不断减少,并且冲刷流量越大,减小幅度越大。2)在不同冲刷流量下,水流路径长度与植被覆盖度、水动力参数和产流产沙量之间均存在显著的相关关系(P0.01)。同时随着水流路径长度的增加,一方面,流速和单位水流功率呈对数式上升,坡面水流动能增强;另一方面糙率系数、阻力系数和径流剪切力分别呈对数式和指数式减小,坡面阻滞能力下降,水流侵蚀力增强。最终导致坡面侵蚀状况发生变化,产流产沙量呈对数式增加。因此,水流路径长度可作为反映植被减水减沙的动力学过程和预测坡面产水产沙的参数之一。该研究为深化理解植被格局与水文连通性的作用关系,建立合适的植被格局表征和植被减蚀效应评价提供依据,以期增强地区生态环境的质量和稳定性,为现代化农业发展,特别是保障农业生产环境做出贡献。     

Nitrogen fertilizer requirements of cereals following grass

Abstract. The effect of increasing rates of nitrogen (N) fertilizer on the yield response of 3 or 4 consecutive winter cereal crops after ploughing out grass was investigated at six field sites on commercial farms in England and Wales. Amounts of N required for an economically optimum yield (>3 kg of grain for each kg of fertilizer N applied) ranged from 0 to 265 kg ha⁻¹ and were dependent on soil N supply, but not on crop yield. Optimum N rates were large (mean 197 kg N ha⁻¹) at three sites: two sites where cereals followed 2-year grass leys receiving low N inputs (<200 kg N ha⁻¹), and at one site where a cut and grazed 4-year ley had received c . 315 kg N ha⁻¹ of fertilizer N annually. At the other three sites where 4 and 5-year grass leys had received large regular amounts of organic manures (20–30 t or m³ ha⁻¹) plus fertilizer N ( c . 300 kg ha⁻¹ each year), optimum N rates were low (mean 93 kg N ha⁻¹) and consistently over-estimated by the farmer by an average of 107 kg N ha⁻¹. Optimum N rates generally increased in successive years after ploughing as the N supply from the soil declined. Determination of soil C:N ratio and mineral N (NO₃N+NH₄N) to 90 cm depth in autumn were helpful in assessing fertilizer N need. The results suggest there is scope to improve current fertilizer recommendations for cereals after grass by removing crop yield as a determinant and including an assessment of soil mineralizable N during the growing season.     

Transfer of legume nitrogen to associated grass

In improved hill-peat a rapid increase in rhizosphere soil bacteria occurs following clover defoliation. The increase in bacterial-cell N is equivalent to 19% of the N released from the clover roots in the first 5 days after cutting. Subsequent ammonification of the immobilized N is dependent on the resistance of the microbial fraction to further degradation. In three fertilized hill soils examined, [¹⁵N]labelled bacterial N was mineralized quite rapidly, some 20% of the bacterial N being taken up by grass over 17 days. Under glasshouse conditions the rate of mineralization is different in the three soils examined, the peat providing a more favourable environment than brown earth for bacterial N transfer.     

Reclamation of colliery spoil: the effect of amendments and grass species on grass yield and soil development

Results are presented of a field trial in which various methods for the reclamation of coarse colliery waste were tested. The site was divided into three blocks and each block received a different level of deep cultivation; however, these treatments appeared to have no long-term significant effect on grass yield. Within each cultivation block a number of treatments were superimposed. These included: amendments of soil and organic materials, deep placement of P fertilizer, and the use of different grass seed mixtures. Grass yield was measured annually for 6 years. At the end of that period soil samples were taken for analysis and tests were conducted in the field to measure the effects of treatments on the developing soil conditions. There was a general decline in grass yields during the course of the experiment. However, the rate of decline varied with the different treatments, being lower on amended spoil (i.e. treated with soil or organic materials) and on treatments sown with a seeds mixture containing S143 cocksfoot (Dactylis glomerata). Differences in the soil conditions resulting from the use of amendments were detected; in particular, the soil-amended plots had higher pH and exchangeable Ca and greater penetrability.     

Catalytic characteristics of peroxidase from wheat grass

The crude enzyme extract of wheat grass was heated at 60 degrees C for 30 min, followed by ammonium sulfate fractionation and isoelectric chromatofocusing on Polybuffer exchanger (PBE 94) for purification. The purified peroxidase was then characterized for its catalytic characteristics. It was found that AgNO3 at a concentration of 0.25 mM and MnSO4 and EDTA at concentrations of 5 mM significantly inhibited the activity of wheat grass peroxidase. However, KCl, NaCl, CuCl2, CaCl2, ZnCl2, and MgCl2 at concentrations of 5.0 mM and HgCl2 at a concentration of 0.25 mM enhanced enzyme activity. Chemical modification significantly influenced the activity of wheat grass peroxidase. Particularly, N-bromosuccinimide (5 mM) inhibited 16% of the enzyme activity, whereas N-acetylimidazole (2.5 mM), diethyl pyrocarbonate (2.5 mM), and phenylmethanesulfonyl fluoride (2.5 mM) enhanced by 18-29% of the enzyme activity. Such results implied that tryptophan, histidine, tyrosine, and serine residues are related to enzyme activity. The pH optima for wheat grass peroxidase to catalyze the oxidation of o-phenylenediamine (OPD), catechol, pyrogallol, and guaiacol were 5.0, 4.5, 6.5, and 5.0, respectively. The apparent Km values for OPD, catechol, pyrogallol, and guaiacol were 2.9, 18.2, 2.5, and 3.8 mM, respectively. Under optimal reaction conditions, wheat grass peroxidase catalyzed the oxidation of OPD (an aromatic amine substrate) 3-11 times more rapidly than guaiacol, catechol, and pyrogallol (phenolic substrates containing one to three hydroxy groups in the benzene ring).     

Estimating 10-cm soil temperatures under grass

In order to comply with the increasing demand from the agricultural industry for more accurate short-range weather information, in this paper a statistical method for forecasting 10-cm soil temperatures under grass is presented. Regression equations are derived that predict 0600 GMT, 1200 GMT as well as daily mean 10-cm soil temperatures. Predictors are sine and cosine of the day of the year, the minimum air temperature of the previous night and the maximum air temperature of the previous day. A similar equation is derived for an experimental potato field. The equations are tested on independent material. Finally, soil temperatures calculated for De Bilt are compared with simultaneous measurements at two remote locations; the forecasting potential is evaluated.     

The influence of grass density on effectiveness of contour grass strips for control of soil erosion on low angle slopes

Abstract. The effectiveness of contour grass strips in erosion control was investigated in a field experiment involving two grass treatments ( Festuca ovina and Poa pratensis ) and a bare soil control on an erodible sandy loam soil on a 5° slope using simulated rainstorms of 40 mm h^–1 for 45 minutes duration. The grass strips resulted in significantly ( P < 0.05) lower runoff and soil loss than the bare soil but there was no significant difference in the performance of the two grasses, despite their differences in density, height and leaf size. The effect of the lower density of the Poa pratensis was offset by its larger stem diameter so that the surface area facing the flow was similar for both grasses. Instead of acting as a filter with sedimentation occurring within the barrier, the grass strips operated by ponding water upslope of the barriers. Deposition then occurred in the ponded area above the barrier.     

草鱼肉块渗透脱水规律研究

为了研究草鱼渗透脱水的一般规律,考察了温度(5～30℃),时间(2～24 h),NaCl浓度(5%～15%),麦芽糊精浓度(0.6～1.2 g/g)以及黄原胶添加量(0～0.004 g/g)等对草鱼渗透脱水过程中鱼块失水量、糖吸收量和盐吸收量的影响。并从理论上详细解释了整个传质过程。试验结果表明：随着时间和温度的增加,失水量、糖吸收量和盐吸收量都增大。NaCl浓度增加,失水量、盐吸收量增大,糖吸收量无显著变化。麦芽糊精浓度增加,盐吸收量显著降低,糖吸收量和失水量一定程度上增大。黄原胶的添加,增大了溶液黏度,三者都减小。     

Landscape benching from tillage erosion between grass hedges

Grass hedges are narrow (1–2 m wide) parallel strips of stiff, erect, grass planted near to or on the contour of fields but crossing swale areas at angles convenient for farming. They serve as guides for contour cultivation, retard and disperse surface runoff, cause deposition of eroded sediment, and reduce ephemeral gully development. After three years of tilled fallow between mixed-species hedges, the average grade of 18 m wide tilled strips between 1.5 m wide hedges was reduced from 0.068 to 0.052 as a result of surface lowering below hedges and on the shoulders of swale areas combined with increases in elevation above hedges. Annual surveys show progressive lowering of high spots and filling of low spots as contours lines more closely aligned with hedges. Survey data indicated annual erosion rates of nearly 250 t ha⁻¹ year⁻¹. Both RUSLE and WEPP over-predicted erosion rates, partly because backwater and slope modification affects were not considered. A tillage translocation model predicted enough soil movement to account for 30–60% of the observed changes. A combination of tillage translocation and water erosion/deposition provides the best explanation for the observed aggradation/degradation patterns.     

Electron probe microanalysis of silicon in grass leaves

Abstract

Silicon is a major constituent of grasses, therefore, research was initiated to evaluate the use of the paraffin technique for electron probe microanalysis of Si in grass leaf tissue. Mature healthy leaves of a tropical grass, Wilmington bahiagrass (Paspalum notatum Flügge), and a cool season grass, tall fescuegrass (Festuca arundinacea Schred), were selected for study. Paradermal sections (10 μ) of paraffin impregnated leaf tissue were placed on sheet carbon that had been attached with Haupt's adhesive to 2.5 cm glass discs. The grass sections were fixed to the sheet carbon with Haupt's adhesive and the paraffin removed with xylene prior to microanalysis. Silicon was found to be highly concentrated in the epidermis of fescuegrass and bahiagrass. Short cells, many containing opal bodies, had the highest contents of Si of the epidermal cells. Large quantities of Si was also present in guard cells but long cells contained relatively small amounts.     

Atrazine and phenanthrene degradation in grass rhizosphere soil

Organic contaminants often disappear more quickly from planted than from non-planted soils. Five grass species (Sudan grass, ryegrass, tall fescue, crested wheatgrass and switch grass) were grown in soils without (Phase I) or with (Phase II) prior atrazine (ATR) and phenanthrene (PHE) amendment to study the degradation of these compounds by rhizosphere microorganisms. In suspensions of soil without prior chemical exposure, no significant loss of ATR was observed after 16 days incubation. The most probable number (MPN) of ATR-degrading bacteria in the soils was below detection. Phenanthrene degradation was observed in suspensions inoculated with all soils, but the rates of degradation were not significantly different among them. The number of PHE-degrading bacteria was similar in planted and non-planted soils (10⁵ cells g⁻¹ soil) except the number in tall fescue soil was significantly higher than in non-planted soil. In the Phase II study, both compounds were mineralized whether or not soils had been conditioned with ATR or PHE. Prior amendment with either ATR or PHE significantly reduced the acclimation period preceding the onset of mineralization. However, enumeration procedures detected ATR-degrading bacteria only in ATR-amended soils. Prior exposure to PHE did not alter the number of PHE-degrading bacteria significantly.     

Colonization of torrefied grass fibers by plant-beneficial microorganisms

This study aimed to assess the colonization of thermally treated (i.e. torrefied) grass fibers (TGFs), a new prospective ingredient of potting soil. Eleven bacterial strains and one fungus, Coniochaeta ligniaria F/TGF15, all isolated from TGF or its extract after inoculation with a soil microbial community, were tested for their ability to colonize TGF. Surprisingly, none of these bacteria were able to directly colonize TGF either as single inoculants or as a consortium. Furthermore, bacterial persistence or growth in TGF was not improved by the addition of nutrients or a surfactant. Only extensive washing of the substrate, presumably removing bacteriostatic or bactericidal compounds, allowed bacterial growth on the fibers. Strikingly, the fungal strain consistently colonized TGF up to high densities (up to 10¹⁰ CFU per g dry TGF). Given the unique capacity of this fungus to degrade toxic compounds including phenols, TGF was colonized with it for different periods of time, after which a consortium of seven selected bacterial isolates was added. Co-presence of the fungus, or 3 and 24 h pre-colonization with it, was insufficient to create a habitable environment for the bacterial consortium. However, fungal pre-colonization of minimally 3 days allowed the bacterial consortium to colonize the TGF at numbers up to 10⁹ to 10¹⁰ CFU per g dry substrate. The resultant bacterial community consisted of at least four strains, i.e. Pseudomonas putida 15/TGE5, Serratia plymuthica 23/TGE5, Pseudomonas corrugata 31/TGE5, and Methylobacterium radiotolerans 56/TGF10, as shown by PCR of colonies on plates and PCR–DGGE profiling. Two persisters, S. plymuthica 23/TGE5 and P. corrugata 31/TGE5, were highly antagonistic towards several phytopathogenic fungi. Thus, a microbial community with plant-beneficial potential was established on TGF, provided that the fungus C. ligniaria F/TGF15 first creates habitable space in the matrix.     

Soil engineering ants increase grass root arbuscular mycorrhizal colonization

The role of edaphic factors in driving the relationship between plant community structure and ecosystem processes is a key issue of the current debate on functional implications of biodiversity. In this study, we draw a direct link between aboveground/belowground relationships, vegetation structure, and aboveground management. We used ground nesting ants and arbuscular mycorrhizal fungi (AMF) as an example for quantifying the role of biotic interactions in soil. Although both groups are known to have a major impact on grasslands, the interactive effect of these taxa on vegetation structure and its sensitivity to grassland management is poorly understood. We show that the ant Lasius flavus increases the root arbuscular mycorrhizal colonization (AMC) of grasses by modifying biotic and abiotic soil properties. As a possible consequence, the shoot length of grass growing on ant mounds was shorter and shoot N and P concentrations were higher than in grass growing off of the mounds. In addition, management affected ant nest architecture and soil and, in turn, AMC. These results emphasize the need to consider the interactions between plants, soil microorganisms, soil fauna, and aboveground management to increase the understanding of the drivers of biodiversity and ecosystem functioning in grasslands both aboveground and belowground.     

Soil nitrogen mineralization not affected by grass species traits

Species N use traits was evaluated as a mechanism whereby Bromus inermis (Bromus), an established invasive, might alter soil N supply in a Northern mixed-grass prairie. We compared soils under stands of Bromus with those from three representative native grasses of different litter C/N: Andropogon gerardii (Andropogon), Nassella viridula (Nassella) and Pascopyrum smithii (Pascopyrum); in ascending order of litter quality. Net mineralization (per g soil N) measured in year-long laboratory incubations showed no differences in comparisons of Bromus with two of the three native grasses: Andropogon and Nassella. Higher mineralization in Pascopyrum stands relative to Bromus was consistent with its higher litter quality. However, an unusually high occurrence of an N-fixing legume in Pascopyrum stands, potentially favoring high mineralization rates, confounded any conclusions regarding the effects of plant N use on N mineralization. Instead of an initial flush of net mineralization, as would be expected in laboratory incubation, we observed an initial lag phase. This lag in net N mineralization coincided with high microbial activity (respiration) that suggests strong N limitation of the microbial biomass. Further support for the importance of immobilization initially came from modeling mineralization dynamics, which was explained better when we accounted for microbial growth in our model. The absence of strong differences in net mineralization beneath these grasses suggests that differences in plant N use alone were unlikely to influence soil N mineralization through substrate quality, particularly under strong N control of the microbial biomass.     

Response of grass leys to applications of calcified seaweed

Abstract

Calcified seaweed has long been used as a soil conditioner in northern Europe, but supposed beneficial responses have not been experimentally substantiated. Field and glasshouse studies examined treatment responses on the characteristics of sandy silt loam Hapludalf soils and on the growth and elemental composition of Loliumperenne. Agricultural lime was a treatment in both experiments, being chemically similar to calcified seaweed. Calcified seaweed was applied at 2 t ha^‐1 and produced small increases in soil pH and extractable calcium (Ca). Significant increases in Lolium perenne growth were found in field studies after both calcified seaweed and lime applications. Smaller, but consistent, increases in growth were found in glasshouse pot studies. However, only one harvest showed a significant dry weight yield increase after calcified seaweed application compared with the untreated control. In pot studies, increases in soil extractable Ca were associated with increases in shoot elemental Ca. Decreases in shoot zinc (Zn) and manganese (Mn) concentrations were found after both calcified seaweed and lime applications. Total shoot element accumulation of Zn and Mn after calcified seaweed application were similar to those produced by the control, suggesting that decreases in shoot Zn and Mn concentrations resulted from dilution after increased shoot growth. However, total Zn and Mn accumulation decreased after lime application compared to the control and calcified seaweed treatments, probably resulting from fixation of available soil Zn and Mn through greater increases in soil pH.     

Forage grass response to harvest interval and reclaimed water

Accumulation of dry matter and plant nutrients by perennial grass over the growing season is dependent upon harvest interval and availability of water and applied nutrients. Mathematical models are frequently incorporated in the analysis, design, and operation of systems for land application of reclaimed water (municipal or agricultural). The objective of the present work was to measure response of warm‐season Coastal bermudagrass [Cynodon dactylon (L.)] to irrigation with reclaimed municipal wastewater and to evaluate parameters for a simplified model. Grass was harvested at intervals of 2, 4, and 6 wk. Measurements included yields (dry matter and digestible organic matter) and plant nutrient uptake (N, P, and K). The probability model described time trends rather well. The linear model parameter A showed linear dependence on harvest interval At over the range studied, in agreement with results from the literature. Maximum values for a harvest interval of 6 wk were 16.5 Mg ha^‐1 (dry matter), 8.0 Mg ha^‐1 (digestible organic matter), 350 kg N ha^‐1,57 kg P ha^‐1, and 272 kg K ha^‐1.     

Variation in the supracritical nitrogen concentration of kikuyu grass

Abstract

The N concentration was monitored in grazed pastures of kikuyu (Pennisetum clandestinum) where regular applications of nitrogen fertilizer removed any nitrogen deficiency for growth. The heavy fertilizer applications maintained supracritical N concentrations of 3.7–5.3% in the last fully‐formed laminae. The concentration increased with increasing temperature or growth rate, but not with changing soil water content.

Supracritical N concentrations will buffer the onset of a N deficiency, and the difference between the actual and critical N concentrations provides a quantitative measure of reserve N. Estimates of reserve N in a heavily fertilized pasture with a top yield of 2,000 kg DM/ha, ranged from zero to 32 kg N/ha. This is sufficient to supply N to an additional 0–914 kg DM/ha without diluting the average N concentration below the critical level.     

Relationships between single tree canopy and grass net radiations

It is reported a simple approach to transform daily values of grass net (all-wave) radiation (R_n, MJ m⁻² day⁻¹), as measured over standard grass surface at meteorological stations, into whole tree canopy net radiation (A, MJ tree⁻¹ day⁻¹). The revolving Whirligig device [McNaughton, K.G., Green, S.R., Black, T.A., Tynam, B.R., Edwards, W.R.N., 1992. Direct measurement of net radiation and photosynthetically active radiation absorbed by a single tree. Agric. For. Meteorol. 62, 87–107] describing a sphere about the tree measured A in five trees of different species (walnut, dwarf apple, normal apple, olives and citrus), with leaf area L_A varying from 8.65 to 40 m². For each tree, A and R_n were linearly related (A = bR_n), as previously reported elsewhere, but it was found that the slope of such regression was also a linear function of L_A or, b = 0.303 (±0.032) L_A. Consequently, the hypothesis that total daily tree canopy net radiation per unit leaf area is linearly related to grass net radiation could not be rejected after 86 days of measurements in five locations, and the empirical relationship is A = 0.303 (±0.032) R_nL_A (R² = 0.9306).     

Alfalfa/grass response to nitrogen and phosphorus applications

Abstract

Alfalfa/grass (Medicago sativa/Dactylis glomerata, Bromus) yield and quality responses to nitrogen (N) and phosphorus (P) fertilizer applications are well documented. The magnitude of the P response and in turn N, may however, be limited by the relative immobility of P in the soil. A two‐year field study was conducted to determine the response of an established alfalfa/grass stand to combinations of a one‐time broadcast application of N, P, and sulfur (S) rates with fall or spring applications of P. Nitrogen and P applications increased forage production, nutrient concentration and nutrient content, particularly in the first production year. No S response was observed. Fall P applications were superior to spring applications only in the first year of production. If annual broadcast applications of P are made to existing alfalfa/grass stands in Intermountain areas, fall applications are recommended.