Influence of temperature on nutrient concentration and tetany potential of hardinggrass and tall fescue

Grass tetany (Hypomagnesemia) potential of TAM Wintergreen Hardinggrass and 16 tall fescue lines and varieties was estimated by determining the K, Ca and Mg concentrations in the herbage and the ratio of K/(Ca + Mg) (milliequivalent basis). Data were obtained at four dates during a two‐year period to determine the environmental conditions under which selections should be made to achieve the greatest progress in decreasing the tetany potential of tall fescue and to determine if either of the grasses have high tetany potential in the North Texas area. Hardinggrass had a greater potential to produce grass tetany than tall fescue when grown on the Northern Blackland Prairie of Texas. There were significant differences in K, Ca and Mg concentrations and K/(Ca + Mg) ratio among dates and tall fescue lines. The average temperature for the 30 days before harvest was related to the mineral content and to the K/(Ca + Mg) ratio in all varieties. The K(Ca + Mg) ratio was highest at approximately 18°C but the Mg content fell below the 0.18% required for lactating beef cows when the average temperature for the 30 days before harvest was 22.4°C. Progress could be made in breeding for low grass tetany proneness but selections should be made over a wide range of temperatures considering both the Mg content and ratio of K/(Ca + Mg).     

Chlorophyll meter predicts nitrogen status of tall fescue

The nitrogen (N) status of a crop can be used to predict yield and supplemental N fertilizer requirements, and rapid techniques for evaluating the N status of crops are needed. A study was conducted to determine the feasibility of using a hand held chlorophyll meter (SPAD 502, Minolta Co. Ltd., Japan) to monitor N status of tall fescue (Festuca arundinacea Schreb.). Four diverse tall fescue genotypes were grown at three locations in Alabama and fertilized at four N‐rates from 0 to 336 kg ha^‐1. A similar experiment was conducted in the greenhouse using soil from the same field sites. Chlorophyll meter readings (SPAD) were taken, and extractable chlorophyll content, tissue N concentration and dry matter yield were determined at harvest. SPAD, extractable chlorophyll content, tissue N concentration, and dry matter yield increased quadratically (0.67 < R² < 0.99) with increasing N fertilization in both experiments. All genotypes responded similarly to applied N, with some differences in magnitude. Relationships between SPAD meter readings and extractable chlorophyll and tissue N concentrations were linear with r² > 0.95. An additional independent variable, the square root of the inverse of SPAD, lowered the residual mean square by 11 and 16%, respectively, for tissue‐N and chlorophyll concentrations, but did not increase the R². This would be preferred for predictive purposes. Tissue N concentrations at higher N‐rates were sufficient for maximum yield which occurred at 290 and 248 kg N ha^‐1 for greenhouse and field, respectively, but were lower than previously reported sufficiency values. The chlorophyll meter is an easy and efficient method of detecting tall fescue N status.     

Optimizing nutrient availability and potential carbon sequestration in an agroecosystem

The uniformity, low cost and ease of application associated with inorganic fertilizers have diminished the use of organic nutrient sources. Concern for food safety, the environment and the need to dispose of animal and municipal wastes have focused attention on organic sources of N such as animal-derived amendments, green manures, and crop rotations. Managing organic N sources to provide sufficient N for crop growth requires knowledge of C and N decomposition over several years, particularly where manure and compost are applied. We report a comparison of compost and chemical fertilizer, use of a corn-corn-soybean-wheat rotation compared to continuous corn and the use of cover crops. Nitrogen (150 d) and C incubations (317 d) were conducted to determine the effect of cropping system and nutrient management on: N mineralization potential (NMP), the mineralizable organic N pool (N_o), the mean residence time (MRT) of No, C mineralization (C_min), and soil organic carbon (SOC) pool sizes and fluxes. Compost applications over 6 y increased the resistant pool of C by 30% and the slow pool of C by 10%. The compost treatment contained 14% greater soil organic C than the fertilizer management. Nitrogen was limiting on all compost treatments with the exception of first year corn following wheat fallow and clover cover crop. The clover cover crop and wheat-fallow increased inorganic N in both nutrient managements. We recommend that growers adjust their N fertilizer recommendation to reflect the quantity and timing of N mineralized from organic N sources and the N immobilization that can be associated with compost or other residue applications. Proper management of nutrients from compost, cover crops and rotations can maintain soil fertility and increase C sequestration.     

Stability of soil organic carbon and potential carbon sequestration at eroding and deposition sites

Purpose

This study aims to explore the dynamics of the factors influencing soil organic carbon (SOC) sequestration and stability at erosion and deposition sites.

Materials and methods

Thermal properties and dissolved aromatic carbon concentration along with Al, Fe concentration and soil specific surface area (SSA) were studied to 1 meter depth at two contrasting sites.

Results and discussion

Fe, Al concentrations and SSA size increased with depth and were negatively correlated with SOC concentration at the erosion site (P?<?0.05), while at the deposition site, these values decreased with increasing depth and were positively correlated with SOC concentration (P?<?0.05). TG mass loss showed that SOC components in the two contrasting sites were similar, but the soils in deposition site contained a larger proportion of labile organic carbon and smaller quantities of stable organic carbon compared to the erosion site. SOC stability increased with soil depth at the erosion site. However, it was slightly variable in the depositional zone. Changes in SUVA₂₅₄ spectroscopy values indicated that aromatic moieties of DOC at the erosion site were more concentrated in the superficial soil layer (0–20 cm), but at the deposition site they changed little with depth and the SUVA₂₅₄ values less than those at the erosion site.

Conclusions

Though large amounts of SOC accumulated in the deposition site, SOC may be vulnerable to severe losses if environmental conditions become more favorable for mineralization in the future due to accretion of more labile carbon. Deep soil layers at the erosion site (>30 cm deep) had a large carbon sink potential.

     

Modeling long-term soil carbon dynamics and sequestration potential in semi-arid agro-ecosystems

Long-term soil carbon (C) dynamics in agro-ecosystems is controlled by interactions of climate, soil and agronomic management. A modeling approach is a useful tool to understand the interactions, especially over long climatic sequences. In this paper, we examine the performance of the Agricultural Production Systems sIMulator (APSIM) to predict the long-term soil C dynamics under various agricultural practices at four semi-arid sites across the wheat-belt of eastern Australia. We further assessed the underlying factors that regulate soil C dynamics in the top 30 cm of soil through scenario analysis using the validated model. The results show that APSIM is able to predict aboveground biomass production and soil C dynamics at the study sites. Scenario analyses indicate that nitrogen (N) fertilization combined with residue retention (SR) has the potential to significantly slow or reverse the loss of C from agricultural soils. Optimal N fertilization (N_opt) and 100% SR, increased soil C by 13%, 46% and 45% at Warra, Wagga Wagga and Tarelee, respectively. Continuous lucerne pasture was the most efficient strategy to accumulate soil C, resulting in increases of 49%, 57% and 50% at Warra, Wagga Wagga and Tarlee, respectively. In contrast, soil C decreases regardless of agricultural practices as a result of cultivation of natural soils at the Brigalow site. Soil C input, proportional to the amount of retained residue, is a significant predictor of soil C change. At each site, water and nitrogen availability and their interaction, explain more than 59% of the variation in soil C. Across the four sites, mean air temperature has significant (P < 0.05) effects on soil C change. There was greater soil C loss at sites with higher temperature. Our simulations suggest that detailed information on agricultural practices, land use history and local environmental conditions must be explicitly specified to be able to make plausible predictions of the soil C balance in agro-ecosystems at different agro-ecological scales.     

Variability in carbon sequestration potential in no-till soil landscapes of southern Ontario

Soil organic carbon (SOC) in Canadian agricultural soils plays an important role in the global cycle of C, and management can influence its fate. Although the scientific literature suggests that practicing no-till (NT) can sequester C, this is not always the case. Furthermore, there are many other factors including climate, management history, soil type and soil landscape processes that may affect the dynamics of SOC under NT. We measured the changes in SOC under NT in southern Ontario, at varying positions in the landscape in Gleyic and Orthic Luvisols at the end of a 15-year-period. Soil cores taken to depths beyond the solum, were segmented with depth, and total SOC was determined for each segment on an equivalent mass basis. When the entire soil column was considered, there was a loss of SOC in more profiles than there were gains. Furthermore, the erosion/deposition history at each landscape position appeared to influence the dynamics of SOC. In depression areas where A_p horizons were greater than 27 cm thick due to a history of soil deposition from upslope and local hydrology, there was a loss of total SOC after 15 years of NT. While where the A_p thickness was less than 27 cm, there were 18 profiles with SOC gains and 15 with net losses. Multiple linear regression analysis revealed that the change in SOC after 15 years was negatively related to the initial total SOC content and positively related to mass of clay. The results of this study suggest that landscape position and erosion/deposition history play a significant role in the ability of NT soils to sequester SOC. Interpretations of long-term SOC monitoring studies must take into account the location of samples within fields if useful information is to be gained on C dynamics in agricultural soils.     

Impact of cultivation on soil organic carbon and carbon sequestration potential in semiarid regions of China

Dynamic changes in soil organic carbon (SOC) have become a popular topic in global research on organic carbon as part of the increasing attention being paid to food security and reducing greenhouse gas emissions. In this paper, the semiarid regions of China were selected as a research focus, and SOC data from 1980 to 2015 were analysed using IBM SPSS Statistics 20.0 software. SOC in farmland varied according to cultivated land type, mulching material type and planting method in the studied regions. The SOC content is 10.3–10.8 g kg⁻¹ in supplementally irrigated land and flat dry land, 7.1–8.7 g kg⁻¹ in terraced dry land and river beach land, and 6.2–6.4 g kg⁻¹ in sloping dry land. The SOC content increased to 16.1–17.4 g kg⁻¹ when crop stalks were used as mulch. The increase was only 11.5–13.5 g kg⁻¹ in soils mulched with film or sandstone. The SOC value in wheat, maize and potatoes sown on single or double ridges was 2.4%–3.2%, 35.7%–36.4% and 4.4%–4.8%, respectively, which are higher than the values for wheat, maize and potatoes sown using the flat planting method. The SOC sequestering potential also varied according to the previously noted factors and was improved from 224.1% to 383.8% depending on cultivated land type, from 96.5% to 182.3% depending on mulching material type and from 96.1% to 191.3% depending on planting method. The SOC sequestering potential can be improved by 453.2%–757.4% with the integration of the optimal cultivated land type, mulching material type and planting method. Thus, there is substantial soil carbon sequestration potential in China's semiarid regions.     

Growth and magnesium uptake of tall fescue clones with varying root diameters

Abstract

A cool season perennial grass with a root system capable of penetrating hardpans and which can accumulate adequate Mg to prevent deficiencies in forage is needed in the Coastal Plain region. A greenhouse experiment was conducted to determine the effects of magnesium (Mg) concentration in nutrient solution and root diameter on Mg uptake and growth of tall fescue (Festuca arundinacea Schreb.). Propagules of two fescue clones with large root diameter (LDR >1 mm), two clones with small root diameter (SDR <0.8 mm), and a single clone from ‘Kentucky 31’ (Ky‐31) were transferred into 12‐liter tanks containing Mg concentrations of 3, 21, 42, 125, 250, and 500 μM as MgSO₄ and grown for 39 or 70 days. Leaf Mg concentration was increased linearly with Mg solution concentration in LDR clones for a 39‐day growth period (Harvest 1), but increased according to a cubic equation in the SDR clones and the Ky‐31. Predicted leaf Mg concentration as a function of solution Mg followed a cubic equation for a 70‐day growth period (Harvest 2) in all clones. Predicted root Mg concentration was linearly related to Mg solution concentration for the LDR clones and the Ky‐31, but followed a cubic equation for the SDR clones for the first growth period. For the second growth period, the root Mg concentration of the SDR clones and the Ky‐31 was increased linearly, while the LDR clones followed a quadratic equation. Magnesium uptake followed a cubic equation with Mg solution concentration for both growth periods on all tall fescue clones. This nonlinear variation of Mg uptake and plant Mg concentration with respect to solution Mg concentration strongly suggests that a dual uptake mechanism might have been present in tall fescue clones. Root volume was greater in the SDR than LDR clones or Ky‐31 for both growth periods. The Ky‐31 had the greatest leaf and root dry weight for both growth periods, while the LDR clones had the lowest.     

The effects of stubble burning and tillage on soil carbon sequestration and crop productivity in southeastern Australia

Abstract. In Australia, stubble burning and tillage are two of the major processes responsible for the decline of soil organic carbon concentration in cropped soils, and the resulting soil degradation. However, the relative importance of these two practices in influencing the soil organic carbon concentration and the long-term impact on soil quality and productivity are not clear. The effects of stubble burning as practised by farmers in southeastern Australia were evaluated in two field trials, one of 19 years duration, the other of 5 years. Conventional tillage (three tillage passes) led to greater loss of soil organic carbon than stubble burning. Loss of total soil organic carbon attributed to stubble burning in the 0–10 cm layer was estimated to be 1.75 t C ha⁻¹ over the period of the 19-year trial, equivalent to 29% of that lost due to tillage. In the 5-year trial, no change in soil organic carbon due to stubble burning was detectable. Changes in soil quality associated with stubble burning detected in the longer trial included a reduction in macro-aggregate stability, and increases in pH and exchangeable K⁺. Only the latter two were detected in the shorter trial. A higher mean wheat yield (average 0.15 t ha⁻¹) following stubble burning was observed in the 19-year trial but not in the 5-year trial. Research to monitor the longer term effects of stubble burning is needed, and to identify conditions where loss of soil organic carbon is minimized.     

Incidence and viability of Acremonium endophytes in tall fescue accessions from North Spain

The tall fescue (Festuca arundinacea Schreb.) seed collection of the Centro de Investigaciones Agrarias de Mabegondo was surveyed to determine Acremonium infection rates. One hundred seeds from each of 19 accessions were microscopically examined for endophyte. Seventeen accessions (90%) contained endophyte with a range of 7 to 100%. Leaf sheaths of seedlings from the infected accessions were examined to determine the percentage of infection with viable endophyte. Only seven (41%) of the seventeen infected accessions collected and stored in 1995 at 4°C and 45–50% relative humidity contained viable endophyte with a range of 70 to 100%. While existing germplasm collections of Festuca arundinacea can provide only a small basis of Acremonium germplasm for study, newly collected Festuca arundinacea accessions will offer a greater diversity of Acremonium genotypes.     

Response of tall fescue to composted sewage sludge used as a soil amendment

A pot experiment was conducted in the greenhouse to investigate the effects of composted sewage sludge as a soil amendment on growth and mineral composition of ‘Mustang’ tall fescue (Festuca arundinacea Schreb.). Three desert soils (loamy sand, sandy loam, clay) were amended with two different composted sewage sludges (city and county) at rates of 0, 7.5, 15, 30 and 60% by volume. Tall fescue was grown in the amended soils for four months. Growth rates, measured as harvested clippings, increased with sludge loading rate and also with clay content of the soil. Higher growth rates were maintained with the city as compared to the county sludge, although for both sources, growth declined for most treatments after nine weeks. Turf color ratings and percent N in the tissue increased with sludge loading rate and were highly correlated. Tissue analysis indicated a varied response between soil types.     

Seasonal variations in nutrient and carbohydrate levels of tall fescue cultivars in Japan

Quality (color and density) of tall fescue (Festuca arundinacea Schreb.) as a turfgrass is reduced during both the winter and summer in Japan. Seasonal variations in nutrient and carbohydrate levels of six cultivars of tall fescue were measured to determine if these changes are related to the reduction in the turf quality. There were significant differences among the cultivars in nutrient and carbohydrate levels. The nutrient and carbohydrate levels of tall fescue cultivars changed seasonally. Levels of calcium (Ca) and zinc (Zn) were below the sufficiency, but the concentrations of other nutrients were sufficient during the summer suggesting that the reduction in the quality of tall fescue cultivars during the summer in Japan may not be related to the lack of these nutrients in the plant tissues. The nitrogen (N), Ca, magnesium (Mg), phosphorus (P), Zn, iron (Fe), and copper (Cu) levels in the plant tissues were below the adequate range in the spring which could be attributed to high growth rate since no deficiency symptom was observed. With exception of Ca content, plants contained sufficient or more than sufficient nutrients in their tissues during the fall. Though concentrations of other nutrients were sufficient in the plant tissues in the winter, levels of N, Ca, Mg, P, molybdenum (Mo), Zn, and Cu were lower than plant's requirement which could be due to low temperature since availability of the nutrients reduces under low temperature. There were no deficiency symptoms of these nutrients, but lack of N in the plant tissue could be the cause of the reduction in the color of the tall fescue cultivare in winter. Levels of glucose, fructose, sucrose, fructan, and starch in the summer were higher or equal to those carbohydrate levels in the spring or fall suggesting that decline in tall fescue quality in Japan during the summer may not be related to carbohydrates shortages. Though starch levels were lower in the winter than other seasons, other carbohydrate levels were equal or higher than the levels in the spring and the total carbohydrate content was much higher in the winter than other seasons, suggesting that reduction in tall fescue quality in Japan during the winter may not be related to carbohydrates shortages.     

A validated method for gas chromatographic analysis of gamma-aminobutyric acid in tall fescue herbage

Gamma-aminobutyric acid (GABA) is an inhibitory neurotransmitter in animals that is also found in plants and has been associated with plant responses to stress. A simple and relatively rapid method of GABA separation and quantification was developed from a commercially available kit for serum amino acids (Phenomenex EZ:faast) and validated for tall fescue (Festuca arundinacea). Extraction in ethanol/water (80:20, v/v) at ambient temperature yielded detectable amounts of GABA. Clean separation from other amino acids in 28 min was achieved by gas chromatography (GC) with flame ionization detection (FID), using a 30 m, 5% phenyl/95% dimethylpolysiloxane column. The identity of the putative GABA peak was confirmed by GC with mass spectrometric (MS) detection. The relatively small effects of the sample matrix on GABA measurement were verified by demonstrating slope parallelism of GABA curves prepared in the presence and absence of fescue extracts. Limits of quantification and detection were 2.00 and 1.00 nmol/100 microL, respectively. Method recoveries at two different spike levels were 96.4 and 94.2%, with coefficients of variation of 7.3 and 7.2%, respectively.     

Effects of soil acidity and phosphorus on the yield and chemical composition of tall fescue

Abstract

Tall fescue (Festuca arundinacea) is assuming increasing importance as a pasture species in South Africa. Many of the soils on which fescue is grown are inherently high in exchangeable Al and are characterized by high P‐immobilization capacities. The responses of fescue to dolomitic lime and P were examined in a factorial field trial on a red clay (Kandiustalfic Eustrustox) having a pH(KCl) and acid saturation [100(Al+H)/(Al+H+Ca+Mg+K)] in the unlimed state of 4.1 and 48%, respectively. A significant, though very limited, dry‐matter yield response to lime was evident (yields in the absence of lime were approximately 80% of the yields obtained at high lime levels). This pattern in the response to lime remained consistent over the three seasons of experimentation, despite soil acidity levels being substantially increased through the periodic use of ammonium sulphate as the N source in the trial. A significant response to P was evident at the first harvest after establishment; thereafter, P treatments had no effect on yield. The lime and P response data obtained in this investigation indicate that tall fescue is much more tolerant of soil acidity and has substantially lower soil P requirements than other important crop and pasture species in this country, such as maize (Zea mays) and Italian ryegrass (Lolium multiflorum). Lime significantly increased herbage Mg levels yet, in general, did not influence Ca levels in the herbage. Concentrations of Mg in the herbage exceeded Ca concentrations at all lime rates. Luxury uptake of K resulted in the K/(Ca+Mg) equivalents ratio in the herbage frequently exceeding the tetany hazard threshold of 2.2.     

不同耕作措施下江苏省稻田土壤固碳潜力的模拟研究

以江苏省稻田为对象,整合DNDC和1:100万土壤数据库,以土壤图斑为基本模拟单元,定量估算少耕、免耕和综合措施（少耕 + 30% 秸秆还田）下江苏省稻田土壤的固碳潜力（0 ~ 30 cm）。模拟结果表明：相对于传统耕作,采用少耕、免耕和少耕 + 30% 秸秆还田均可明显地增加稻田SOC的积累,其在2009—2050年间的固碳潜力分别为24.5、47.7和43.8 Tg。免耕和少耕 + 30% 秸秆还田条件下稻田固碳速率大约是少耕的2倍。结合实际情况,少耕 + 30% 秸秆还田将是最可行的固碳措施之一。     

The phosphorus source determines the arbuscular mycorrhizal potential and the native mycorrhizal colonization of tall fescue and wheatgrass

The study assesses the effect of two phosphate (P) sources (soluble superphosphate (SP) and rock phosphate (RP)) on the arbuscular mycorrhizal potential (AMP), the root arbuscular mycorrhizal colonization (AMC) and the growth of tall fescue and wheatgrass of a grassland soil from Argentina. Mycorrhizal potential was assessed with soil samples collected from 2 years for tall fescue and wheatgrass swards before and after field plots were fertilized with 0 and 60 kg P ha⁻¹ as SP or RP. Mycorrhizal potential both at unfertilized and at RP fertilized plots was high (12–14 AM propagules g⁻¹), however fertilization with SP caused a decrease in AMP (0.70–0.95 AM propagules g⁻¹). A range of soil P between 4 and 46 mg P kg⁻¹ and a range of root AMC between 6% and 50% were obtained after fertilization with four rates of SP and RP (0, 15, 30, and 60 kg P ha⁻¹) in plots where tall fescue and wheatgrass were grown during 2 years. Soil P and root mass were higher in the top 10-cm depth than in the 20-cm of the soil profile, but AMC did not change with depth. Shoot dry matter (SDM) production of both grasses did not differ after fertilization with SP or RP, particularly at second year. The AMP positively correlated with the indigenous AMC, and they were not different between tall fescue or wheatgrass. Lineal-plateau relationships between soil P, relative SDM and AMC were established. Highest relative SDM was attained at 6.5 mg P kg⁻¹ in plots fertilized with RP, and at 15.2 mg P kg⁻¹ with SP. Variability in colonization was well accounted by the soil P (at 0–10 cm depth) fertilized with SP (r² = 0.48, P 0.01), but any relationship was found with RP. The AMC decreased with increasing available soil P from plots with SP until 18.3 mg kg⁻¹ (a decrease of 2.2% per mg P kg), after that AMC was stabilized at about 6.9%. Our study clearly showed that fertilization with SP or RP produced similar available soil P content and grasses SDM production. Mycorrhiza root colonization and propagules decreased after fertilization with SP, but fertilization with RP did not decrease mycorrhizal propagules nor colonization. It can be concluded that RP fertilization instead SP could allow obtaining acceptable tall fescue and wheatgrass yield enhancing mycorrhizal potential of soils and indigenous colonization of plants and thus maximizing the use of fertilizer.     

Preferential sequestration of microbial carbon in subsoils of a glacial-landscape toposequence, Dane County, WI, USA

Microorganisms participate in soil carbon storage by contributing biomass in the form of refractory microbial cell components. However, despite the important contribution of microbial biomass residues to the stable carbon pool, little is known about how the contribution of these residues to soil carbon storage varies as a function of depth. In this study, we evaluated microbial residue biomarkers (amino sugars) in varied pedogenic horizons from six soil profiles of two geographic sites on a glacial-landscape toposequence in Dane County, WI. We found that the amino sugars appeared to preferentially accumulate in subsoil. Specifically, although total amounts of amino sugars decreased downward through the profile as even as total organic carbon did, the rate of decrease was significantly lower, suggesting that these compounds are more refractory than general soil organic carbon. The proportion of amino sugars to soil organic carbon increased along the depth gradient (from top to bottom), with the exception of Bg horizons associated with high water tables. We also observed that microbial residue patterns measured by amino sugar ratio (e.g., glucosamine to muramic acid) showed different dynamic tendencies in the two different geographic sites, suggesting that residue carbon contribution by fungi and bacteria is likely site-specific and complex. In summary, regardless of the redox microenvironment created by groundwater dynamics in a given soil, our study supports the hypothesis that microbial residues are refractory and that they contribute to terrestrial carbon sequestration.     

Growth and magnesium uptake of tall fescue lines at high and low potassium levels 1

Five tall fescue (Festuca arundinacea Schreb.) clonal lines with diverse root and xylem diameters were grown in nutrient solutions with magnesium (Mg) concentrations of 42, 125 and 250 μM and potassium K concentrations of 133 and 333 μM. Leaf Mg concentrations increased with increasing Mg rates at both low and high K concentrations. The tall fescue line with the largest root and xylem diameters had low leaf Mg concentrations, indicating a possible increased Mg tetany potential when consumed by cattle. The response of the K/(Mg+Ca) ratio in the plant, an indicator of tetany potential, to varying solution Mg at low and high K was determined for each of the five lines. No Mg effects or interactions were significant. Line, K, and line x K effects were all significant for the K/(Mg+Ca) ratios. The line with the largest root and xylem diameters had the highest tetany potential (highest cation ratio). Higher solution K gave higher K/(Mg+Ca) ratios.     

氮磷钾肥对高羊茅生长及抗寒性的影响

利用盆栽试验研究了氮磷钾肥对冷季型草坪草高羊茅生长、叶绿素含量及抗寒性的影响。结果表明,NPK配合施用能有效促进草坪草生长、叶绿素合成及提高抗寒性。NPK处理的叶片数、叶长及株高分别是不施氮处理的1.23、1.73和1.68倍,是不施磷处理的1.96、2.25和2.04倍。播种后100.d,NPK处理SPAD值分别比PK和NK处理高出2.53和3.14倍;越冬期NPK处理的脯氨酸(Pro)、丙二醛(MDA)和电解质渗透率(EL)分别是PK处理的313.6%、36.4%和13.4%,是NK处理的104.2%、14.0%和11.6%。试验结果还表明,磷肥对草坪草生长影响最大,氮肥次之,氮磷肥缺乏均降低草坪草抗寒性;钾肥施用与否对草坪草生长及抗寒性影响不大。说明氮磷钾肥合理施用能有效改善越冬期草坪质量。