摘要:

The effect of alternating waterlogged and drying conditions on nitrogen (N) availability and sorption was studied in three soils of contrasting texture. Air‐dry samples of each soil were treated with three levels of nitrate (0, 30, and 300 mg kg‐1; N0, N30, and N300), waterlogged for 21 days, allowed to dry at room temperature for 21 days, and rewaterlogged for an additional 21 days. Ammonium (NH4) sorption isotherms were determined using the standard batch technique for air‐dry, waterlogged (with and without ponded water), and waterlogged/dried conditions. Waterlogging reduced the Eh and increased the pH of all soils. The magnitude of change in Eh and pH was related to soil organic carbon levels and nitrate (NO3) concentration as this chemical became the principal electron acceptor following depletion of dissolved O2. Ammonium concentrations generally increased over the waterlogged periods due to mineralization of organic nitrogen and its subsequent accumulation under O2‐deficient conditions. Where NH4concentrations decreased, losses were attributed to nitrification and denitrification reactions in aerobic and anaerobic soil zones. Denitrification was assumed to have caused the loss in NO3over the waterlogged period. Reoxidation caused only small changes in NH4and NO3. Rewaterlogging increased NH4concentrations, whereas further losses in NO3were observed in N300 only. Waterlogging reduced NH4sorption in the krasnozem A horizon soil, and increased sorption in the wetland soil. Waterlogging did not significantly affect NH4sorption in the remaining soils. Ammonium sorption was greatest in soils which had been waterlogged then dried. The extent of sorption depended on CEC and the relative affinity of NH4for the sorption sites. This study has provided further evidence that inclusion of alternating waterlogged and drying conditions in the management of constructed wetlands could represent an effective method of maximizing N removal from wastewaters. Furthermore, results suggest that maximum removal of N would be achieved by optimizing contact time between the wastewater and wetland soil materials, and avoiding overland flow as much as possible.

ISSN:0010-3624    

DOI:10.1080/00103629909370180

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Tartaric acid is a low‐molecular weight organic acid commonly present in the soil solutions of humic horizons. Tartrate anion forms relatively stable complexes with heavy metals, which may affect heavy metal mobility in the root zone and uptake by plants. However, no methods are available for determining its content in soils and there are no data on behavior of tartrate anion in soil media. This study was conducted to develop a technique to determine tartrate anion content in soils and to evaluate its retention by the silty clay Typic Haplustoll. The results indicated that tartrate anion interaction with soil consists of a fast stage of adsorption and calcium tartrate precipitation (about 2 hours), followed by a microbial degradation after a lag‐period of 30–40 hours. Tartrate anion retention reached a maximum at a pH from 4.2 to 4.5. Retained tartrate anion was effectively extracted from the soil by successive treatments with water and 0.1M HCl, and quantitatively determined by ion chromatography. The relation between added (Ga) and recovered (Gr) tartrate anion amounts in the range from 2.6 to 40 mmol kg‐1was expressed by the equation Gr=0.991*(Ga‐1.1), where Grand Gaare in mmol kg‐1soil. The standard deviation of the recovered amount of tartrate anion was 1.5 mmol kg‐1soil. The retention isotherms can be fitted by the Freundlich equation.

ISSN:0010-3624    

DOI:10.1080/00103629909370181

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Understanding seasonal soil mineral nitrogen (N) dynamics under various cover cropping systems will aid in making supplemental fertilizer N recommendations for corn (Zea maysL.) using soil nitrate testing. A split‐plot field study was conducted to track early season soil mineral N under corn grown after cover crops and to determine the usefulness of the pre‐sidedress soil nitrate test (PSNT) in cover crop‐corn systems. The cover crop treatments rye (Secale cerealeL.), hairy vetch (Vicia villosaRoth), rye+hairy vetch, and fallow were established as main plots to provide a range of soil N availability for a subsequent corn crop. The split plot treatment was sidedress fertilizer N rate, which consisted of six rates ranging from 0–250 kg N ha‐1in 50 kg increments. Soil was sampled throughout the growing season and corn was sampled at Hanway's corn growth stage 5 in the 0 kg N ha‐1check plots to assess periodic soil N availability. Soil N concentrations peaked between Hanway's corn growth stage 1 and 3 and were concentrated in the top 15 cm of the soil. Vetch and fallow treatments provided higher amounts of available N as indicated by soil and corn N concentrations and corn yields. Recommended PSNT sampling times resulted in critical soil [NO3‐N] values that are similar to those used for PSNT fertilization; however, sampling to a depth of 15 cm may be adequate when a considerable portion of plant available N is supplied by cover crops. Addition of NH4‐N to NO3‐N testing did not improve the predictive capability of the soil test for supplemental corn N needs. The time of sampling may be delayed as much as two weeks without a loss of prediction accuracy.

ISSN:0010-3624    

DOI:10.1080/00103629909370182

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The effect of different methods of plant residue management on soil properties and maize yield were studied in a field experiment conducted on a Typic Kandihumult in Bambui, Northwest Province of Cameroon. Ankara (a local practice of slow burning partially buried dry plant residues) was compared with surface burning and burying plant residues under the ridges without burning. The comparison was made under no fertilizer and with fertilizer application. Intensive heat generation under the ankara resulted in aggregation of soil colloids into larger particles. The clay‐sized fraction fell by 48% while the silt‐sized fraction rose by 30%. The ankara released large amounts of phosphorus (P) and potassium (K), and trapped adequate nitrogen (N) to sustain a maize yield six times that where residues were buried under the ridges without burning and no fertilizer application, and three times that of surface burning plant residues. The residual effects of the ankara on a second maize crop were not significant unless fertilizer NPK was applied. Poor residual effects of the ankara may be due to enhancement of leaching losses of N, K, and magnesium (Mg) from the root zone as a result of changes in the textural characteristics of the soil. Surface burning plant residues did not produce any adverse effects on soil particle size distribution.

ISSN:0010-3624    

DOI:10.1080/00103629909370183

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

This study investigated changes in soil test results associated with sampling depths in fields managed with conventional tillage, no‐till for less than 3 years, no‐till for 3 to 6 years, and no‐till for more than 6 years. Soil samples from depths of 0–5, 0–10, 0–20, and 10–20 cm were collected from 59 fields with different tillage histories from several geologic regions, and analyzed by the North Carolina Department of Agriculture soil test laboratory. Some nutrient stratification was noted in all tillage categories. Soil test phosphorus (P), potassium (K), and zinc (Zn) concentrations were significantly higher in the 0–10 cm depth than in the 10–20 cm depth. Stratification probably results from the prevalence of tillage with disks, chisel plows or subsoilers, which do not mix the soil thoroughly. With the adoption of no‐till methods, stratification becomes even more pronounced. Our data suggest that stratification in pH, calcium (Ca), manganese (Mn), and sulfur (S) is more likely for fields in the early stages of no‐till (less than 6 years) than in longer‐term no‐till. In fields managed with no‐till for less than 3 years or for 3 to 6 years, pH and Ca, Mn, and copper (Cu) concentrations were higher and the S concentration was lower in the surface 0–10 cm layer than in the underlying 10–20 cm soil layer. These differences were not significant for fields managed with no‐till for more than 6 years or with conventional tillage. In fields with low P or K levels, higher nutrient concentrations near the surface result in lower fertilizer rate recommendations with shallower sampling depths. The overall pH effect across geologic regions was very small, generally 0.1 to 0.2 pH unit, so lime recommendation did not vary significantly with sampling depth in most cases. For monitoring changes in plant nutrient and heavy metal concentrations over time, sampling no‐till fields requires even more attention to depth than for conventionally tilled fields.

ISSN:0010-3624    

DOI:10.1080/00103629909370184

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The approximate composition of premature chibber fruit (Cucumis melovar. Agrestis) was analyzed. This fruit contained 9.31% carbohydrate, 0.48% protein, 0.29% lipid, 0.93% ash, and 88.99% moisture. Sufficient amounts of sodium (307.61 mg), potassium (218.88 mg), cobalt (1.025 mg), and iron (0.279 mg) were present in the total ash of the chibber fruit. Water soluble vitamins were (mg per 100 g of fruit) ascorbic acid (60), niacin (16.33), thiamine (12.60), and folic acid (10). Mannose, galactose, maltose, glucose, alanine, aspartic acid, phosphoserine, serine, glutamic acid, threonine, glycine, valine, leucine, histidine, lysine, cystine, isoleucine, tyrosine, phenylalanine, glutamine, and asparagine were found to be present in the aqueous extract of premature chibber fruit. These results suggest that chibber fruit contains sufficient amounts of all essential nutrients which could become a good source of human food. The object of this study was to determine the nutrient values of premature chibber fruit which is commonly used as fruit and vegetable in rural areas because such work has not been carried out earlier.

ISSN:0010-3624    

DOI:10.1080/00103629909370185

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Coir (coconut mesocarp pith) is the fibrous material that constitutes the thick mesocarp (middle layer) of the coconut fruit (Cocos nuciferaL.). It has ion‐exchange and gas adsorption properties that can be utilized to adsorb the important plant nutrient N in its NH4+and/or NH3form, protecting it from losses such as during composting of N‐rich wastes. The NH4+adsorption process and the pH buffering capacity of the coir were studied to quantify its effectiveness as an NH4+adsorbent. The one‐ and two‐surface Langmuir, van Bemmelen‐Freundlich, Temkin, and first‐order models were fitted to the NH4+sorption data at an equilibrium pH range of 4.6 to 5.1. Each model was found to describe the NH4+sorption data with comparable success (r2≥0.88), with the Langmuir and Temkin being superior (r2≥0.99). Although the equilibrium pH did not change much after adding buffers of pH 4 to 7 to the coir, there was a consistent increase in the amounts of NH4+‐N sorbed with increasing pH, as estimated using the two‐surface Langmuir model. The estimated amounts of NH4+‐N sorbed were 516 mmol kg‐1at pH 4.6, 521 mmol kg‐1at pH 4.63, 571 mmol kg‐1at pH 4.88, and 573 mmol kg‐1at pH 5.1. The coir showed a good buffering ability at pH range 3.7 to 10.4. The coir buffer strength, defined as the amount of OH” required to increase pH by one unit, was 11.3 cmol kg‐1for the pH range 3.7 to 8.4, and 22.1 cmol kg‐1for the pH range 8.4 to 10.4. The high CEC, surface area, and buffer strength of the coir indicated its high ability to retain cations and buffer against pH change.

ISSN:0010-3624    

DOI:10.1080/00103629909370186

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The effect of soil inoculation with urea,Nostoc muscorum,andTolypothrix tenuison rice seedlings, nutrient contents, and structure of postharvest soil was studied.Tolypothrix tenuisandT. tenuis+ urea produced the highest increase in oxidizable C (54.60% both) which resulted 7.63% higher than urea.Tolypothrix tenuisalso produced the highest increase in soluble C (241.14%). Regarding nitrogen (N) soil content all treatments produced a positive difference. No treatment exerted any effect on soil available phosphorus (P). The percentage of aggregates >50 (m increased with all treatments from 6 to 12%, exceptN. muscorum. Tolypothrix tenuisproduce the highest effect, with 50% more of these aggregates than urea. Seedling dry weight and shoot length were higher than control for all treatments. Shoots were longest withN. muscorum+ urea being this treatment more effective than each Cyanobacteria alone. There was no effect on the number of leaves. Except forN. muscorum,all treatments increased the seedling N content. Postharvest soil showed a better quality when inoculated withT. tenuisorT. tenuis+ urea compared to urea. Cyanobacterial fertilizers are a promising alternative to avoid soil pollution caused by agrochemicals and recover the nutrient content and structure lost after harvest as they bring to soil combined N (some of them are N fixers), exopolysaccharide that improve soil structure and bioactive substances that enhance seedlings growth.

ISSN:0010-3624    

DOI:10.1080/00103629909370187

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

A mathematical model is needed to relate the dynamics of soil phosphorus (P) chemistry in a batch reactor to the soil/solution ratio and to initial P in the reactor. The Langmuir‐Hinshelwood model appears to describe this system quite well. According to this model reversible adsorption of P from solution to the colloidal surface (Langmuir component) is followed by an irreversible reaction of the surface species (Hinshelwood component). The system is an example of heterogeneous catalysis. Adsorption follows 2nd order kinetics related to solution P concentration and concentration of available surface sites for adsorption. Desorption and reaction are assumed to follow 1st order kinetics. The system is described by three simultaneous equations, two of which are 1st order nonlinear ordinary differential equations. Numerical integration is by the Euler finite difference method. Data from the literature are used to calibrate the model and to demonstrate its characteristics for a sandy soil. Rapid drop in solution P concentration is followed by a gradual decline. The first step in calibration is to assume quasi‐equilibrium in the early phase (analogous to that in enzyme kinetics), which leads to values for the total concentration of adsorption sites, So, and the Langmuir coefficient, potassium (K). The second step then estimates the adsorption coefficient, ka, and the reaction coefficient, kr. Full simulation of the transient process over time requires great care in size of time step, t, to maintain stability and accuracy in the procedure. Analysis shows a linear correlation between total surface sites, So, and soil/solution ratio, M, as expected.

ISSN:0010-3624    

DOI:10.1080/00103629909370188

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

This study was conducted to find out the effect of season, cultivars, zone of leaf sampling, and direction of shoot on the foliar macro‐nutrient content of guava (Psidium guajavaL.) trees grown in the foot‐hills of Nagaland, India. Foliar nitrogen (N) and potassium (K) contents decreased gradually in the beginning of the season and remained constant at harvest time by initially showing no effect, but increased in August to reach maximum from September through December, whereas no significant effect was noticed on foliar P content. With some exceptions, the Mg content exhibited a trend similar to that of calcium (Ca). The leaves of cv. Allahabad Safeda contained markedly higher amounts of K, whereas Ca and magnesium (Mg) concentrations were found to be higher in cv. Lucknow‐49. Direction of shoots and zone of leaf sampling had no perceptible influences on the foliar macro‐nutrient levels.

ISSN:0010-3624    

DOI:10.1080/00103629909370189

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor