摘要:

Optical emission spectroscopy provides a rapid and precise method for determining nitrogen (N) as the15N/14N ratios of15N‐enriched plant and/or soil samples. The objective of this study was to test whether15N/14N ratios of15N‐enriched soil samples could be determined using direct combustion of KCl extracts without distillation and titration procedures. Twenty soil samples with ranges of mineral N concentration (10 to 43 μg g‐1of dry soil) and15N atom % enrichment (a.e.) (0.37 to 1.10%) were tested. Our data indicate that soluble organic N in the KCl extract contained lower and more variable15N% a.e. levels than those of the mineral N (NO3‐and NH4+) fractions. Thus, direct combustion of KCl extract is not a reliable method for determining15N% a.e. in the soil mineral N pool.

ISSN:0010-3624    

DOI:10.1080/00103629809370132

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The development of a method using a chelating resin to assess heavy metal mobility in soil and the first results obtained from a pot experiment with sewage sludge additions were studied. The resin was Chelex 100 with the calcium (Ca)‐form of the resin proving to be best suited for the extraction. The efficiency of recovery of the heavy metals from an aqueous solution ranged from 81.2% for cadmium (Cd) to 102% for copper (Cu) within 24 hours. For heavy metal extractions from a soil sample, a 96 hour extraction period was found to be optimum. The extracted heavy metal portion was comparable with the results obtained with an ammonium acetate (NH4AOc) extraction. Total heavy metal contents in the substrate of the pot experiment did not show a significant influence due to the sewage sludge treatments, although considerable amounts of heavy metals were added by the sewage sludge. This effect can be both due to the incomplete recovery of heavy metals by anaqua regiaextraction and leaching losses of these elements from the pots. Rape(Raphanus sativusL.) plants did not have any heavy metal contents which might indicate a high availability in soil, with the Cd and Cr contents in the rape biomass being partly lower in the sewage sludge‐treated pots than in the control plants; however, zinc (Zn) uptake slightly increased with increasing sewage sludge treatments. The Chelex 100 extraction procedure was correlated with Cd plant uptake, while the NH4AOc extraction procedure was better related to the Zn uptake by rape plants.

ISSN:0010-3624    

DOI:10.1080/00103629809370133

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The effects of annual ryegrass(Lolium multiflorumL.), red clover(Trifolium pratenseL.), and oilseed radish(Raphanus sativusL.) established in separate barley(Hordeum vulgareL.) and winter wheat(Triticum aestivumL.) plots which had received 0.5, 1.0, and 2.0 times the recommended nitrogen (N) rates (in Ontario) on soil structural stability and subsequent corn(Zea maysL.) growth and yield were investigated in field studies at Ayr and Woodstock, Ontario. Soil aggregate stability and corn growth and development were affected more by cover crops than applied N. Generally, aggregate stability was higher following cover crops than where no cover crops were used. Aggregate stability before spring tillage tended to be higher after oilseed radish than ryegrass and clover, a phenomenon which might be due to short‐term enrichment of soil stabilizing materials resulting from the over‐winter kill of oilseed radish and early decomposition. However, after spring chisel low, soil stability was higher after ryegrass and clover than oilseed radish. No significant interaction between N and cover crops on aggregate stability was observed. Corn following ryegrass was shorter and had fewer leaves at 3 and 6 weeks after planting and accumulated less dry biomass at silking compared to corn after red clover, oilseed radish and no cover check. Similarly corn grain yield was significantly lower when corn followed ryegrass than the other cover crop treatments. Corn was tallest and yielded highest after red clover. A net immobilization and late release of available N with ryegrass and a net mineralization of available N with red clover explains the growth and yield patterns of corn.

ISSN:0010-3624    

DOI:10.1080/00103629809370134

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A soil sampling exercise was conducted throughout 60% of the smallholder farm sector of Malawi, a small country located at the base of the Great Rift Valley. Soil samples (1,130) were geo‐referenced and analyzed for pH, texture, soil organic carbon (C), phosphorus (P), zinc (Zn), potassium (K), and calcium (Ca) status. Descriptive statistics of soil characteristics were used to evaluate soil fertility for two agricultural districts in Northern Malawi, two agricultural districts in Central Malawi, and one agricultural district in Southern Malawi. Generally soils were loamy sands and moderately acid, with “low”; to “sufficient”; nutrient levels. Over three‐quarters of soils sampled had organic C levels which were greater than 0.8%. This indicated that organic C status was adequate in the main to maintain soil structure, although much reduced from the non‐cultivated state. The organic C data supported observations of widespread nitrogen (N) deficiency in Malawi. High spatial variability of P and Zn values was noted. However, over 60% of soils had a P status above the critical value of 15 mg kg‐1which was sufficient for smallholder maize production levels. This finding supported efforts to alter the current country‐wide fertilizer recommendation of 45 kg ha‐1phosphate. New findings reported here were location specific edaphic problems: i) widespread moderate soil acidity in Central Malawi, ii) natural regions in Central and Southern Malawi which were low in P and Zn, and iii) natural regions in Southern Malawi were very low in organic C. Research requirements were identified. Suggested priorities for technology development were those appropriate to smallholder farmers, such as combined use of small amounts of inorganic and organic fertilizers to address very nutrient deficient soils.

ISSN:0010-3624    

DOI:10.1080/00103629809370135

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Knowledge of relationships between variation in early plant growth and soil nutrient supply is needed for effective site‐specific management of no‐till fields. This study assessed relationships between soil test phosphorus (STP) and potassium (STK) with early plant growth and P or K content of young corn(Zea maysL.) and soybean[Glycine max(L.) Merr.] plants in eight no‐till fields. Composite soil (0–15 cm depth) and plant (V5‐V6 growth stages) samples were collected from 400‐m2areas at the center of 0.14‐ha cells of a 16‐cell square grid and from 2‐m2areas spaced 3 m along each of two 150‐m intersecting transects. Correlation, regression, multivariate factor analyses were used to study the relationships between the variables. Variability was higher for samples collected from the transects. Plant dry weight (DW), P uptake (PU), and K uptake (KU) usually were correlated with STP and STK but the correlations varied markedly among fields. Relationships between soil and plant variables could not always be explained by known nutrient sufficiency levels for grain production. Plant P concentration (PC) was not always correlated with STP and sometimes it increased linearly with STP, but other times increased curvilinearly until a maximum was reached. Plant K concentration (KC) usually was correlated with STK, however, and increased linearly with increasing STK even in fields with above‐optimum STK. The results suggest greater susceptibility of early growth to STP than to STK and greater plant capacity to accumulate K compared with P over a wide range of soil nutrient supplies. Variation in STK likely is a major direct cause of variation in KC over a wide range of conditions but variation in STP is not likely a major direct cause of variation in PC when high STP predominates.

ISSN:0010-3624    

DOI:10.1080/00103629809370136

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The compartmentation of ions in salinity‐stressed 6‐week‐old alfalfa seedlings was investigated in two cultivars, Batini (moderately salinity tolerant) and Hunter River (salinity sensitive). Both cultivars were grown under field conditions during the cool season (20–25°C) and the warm season (35–46°C). Two saline solutions (6.4 and 12.2 dS m‐1) were prepared by dissolving the required quantity of NaCl in half‐strength Hoagland solution. Tap water (0.8 dS m‐1) served as control. Plants were irrigated twice a week with saline solutions, commencing 3 weeks after seedling emergence. The seedlings were separated into leaf (including petiole), stem, and root after 6 weeks of growth and analysed for phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sodium (Na), chloride (Cl), and micronutrients [copper (Cu), boron (B), zinc (Zn), manganese (Mn), and iron (Fe)]. The concentration of P and K in the plant tissue increased with increase in temperature, while Ca and Mg concentrations were depressed. Increase in salinity, in general, resulted in decreased accumulation of all ions, including micronutrients. Hunter River maintained the same pattern of ion compartmentation (root<stem<leaf) for Na and Cl, whereas in Batini a different pattern was obtained for Na (stem<leaf<root). Since the compartmentation pattern of ions in Batini is different for Na and not Cl, it appears that compartmentation of Na may be an important factor in salt tolerance.

ISSN:0010-3624    

DOI:10.1080/00103629809370137

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A pot experiment was conducted to estimate the levels of iron (Fe) needed to correct Fe‐deficiency chlorosis in groundnut grown in an alkaline soil and to study Fe x nitrogen (N) interactions in soil and plant and their associated effects on growth and yield. Four levels of Fe (0, 2.5, 10, and 25 mg Fe kg‐1soil as Fe‐EDDHA) and two levels of N(0 and 100 mg N kg‐1soil as NH4NO3) were applied factorially in a completely randomized block design. Higher rates of 10 and 25 mg Fe kg‐1caused a significant reduction in leaf area and aerial biomass accumulation irrespective of N treatment. The Fe x N interaction was significant for all of these parameters. Specific leaf area increased at higher levels of Fe application. Higher Fe levels induced symptoms suggestive of manganese (Mn) deficiency. This diagnosis was supported by decreasing concentration of Mn in leaf blades with increasing Fe levels. By contrast concentrations of most other elements in leaf blades increased with increasing levels of Fe application, suggestive of plant growth but not uptake of other elements being reduced by Mn deficiency.

ISSN:0010-3624    

DOI:10.1080/00103629809370138

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The distribution of zinc (Zn), copper (Cu), lead (Pb), and arsenic (As) in a soil of the Barada River bank in eastern Damascus, Syria, was studied. The results showed a normal distribution of these elements with some anomalies. The mineralogical and physical studies did not reveal any changes, indicating that elemental anomalies were man made.

ISSN:0010-3624    

DOI:10.1080/00103629809370139

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Laboratory and field experiments were conducted at the Regional Research Station of Kandi Area, Ballowal Saunkhri, Punjab, India, to determine the immediate influence of artificial topsoil removal (simulated erosion) on selected soil properties, maize(Zea mays)growth and yield, and restoration of crop productivity with nitrogen (N) fertilization. For the laboratory experiment, soil samples (0–15 cm) were obtained after removing 0, 6, 12, and 18 cm of a sandy loam topsoil from a cereal grain cropped field. In the field experiment, topsoil was removed at 0, 6, 12, and 18 cm in main plots, and six N treatments at rates of 0, 40, 80, 120, 160, and 200 kg N ha‐1were applied in subplots. Topsoil removal greatly decreased mineralized N, N mineralization potential and rate constant, and increased time for half mineralization of N. Bulk density and penetration resistance increased as a result of topsoil removal and infiltration capacity of the soil decreased. Total profile water was more at the time of harvest than at sowing in the plots where topsoil was removed, but the water expense efficiency decreased. Both grain and straw yield of maize decreased substantially as a result of adverse effect of topsoil removal on plant height, mass and depth of root, length and girth of cob, and thousand grain weight. Nitrogen application improved maize growth and yield, but the crop responded to higher doses of N on eroded plots than the uneroded plots, and yields on eroded plots did not match to those obtained on uneroded plots at any level of N application. In conclusion, artificial surface soil erosion deteriorated soil properties governing maize productivity. More N was required where topsoil had been eroded, but N application alone did not restore crop yield to that level obtained from uneroded soil. Therefore, there is a need to look for and quantify other factors also to improve soil productivity.

ISSN:0010-3624    

DOI:10.1080/00103629809370140

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

In an attempt to search for a cheaper source of phosphorus (P), both for direct application and industrial use, three P fertilizers were evaluated in incubation and greenhouse studies. Indigenous Sokoto rock phosphate (SRP) imported, Togo rock phosphate (TRP), and conventional single superphosphate (SSP) were applied on three soil types namely Oxisol, Ultisol, and Alfisol at rates ranging from 0–800 mg P kg‐1soil. Evaluation of the P sources was conducted for 12 weeks in incubation study, and five weeks in the greenhouse using maize as test crop. Evaluation of direct application of SSP and SRP on an oxic paleudult was carried out in the field for three years. The results of incubation studies revealed in general, that P availability increased as fertilizer rates increased. The P availability was, however, greater when SSP was applied on the Alfisol than on the Oxisol and Ultisol. The rock phosphates on the other hand were more efficient on acid soils than on soils neutral in pH. Optimum P availability from the fertilizers was observed to occur predominantly between four and eight weeks of incubation. In the greenhouse study, SSP gave the highest cumulative P uptake and optimum rate of application was 200 mg P kg‐1soil, while optimum rate for rock phosphate was 400 mg P kg‐1soil. The agronomic effectiveness (EA) of the rock phosphates was about 40% relative to SSP on the Alfisol. The EA, however, for TRP and SRP was 120% and 160%, respectively, on the Oxisol, while on the Ultisol, SRP was equally effective as SSP and TRP had 65% effectiveness. The results of the field trial indicated that the SRP had 54%, 83%, and 107% agronomic effectiveness of SSP, respectively, in the first, second, and third year of cropping. Optimum rate for SSP and SRP application was considered to be 50 and 75 kg P2O5ha‐1, respectively.

ISSN:0010-3624    

DOI:10.1080/00103629809370141

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor