摘要:

SUMMARYUses of soil for a wide variety of purposes are largely governed by interactions between soils and climatic conditions. The soil‐water state at any given moment depends on the hydraulic properties of the soil horizons, the weather and soil drainage. Emphasis in this presentation is on the manner in which the soil‐water state is being characterized in the context of land evaluation. Land evaluation is concerned with the assessment of land performance when used for specified purposes (FAO, 1976). Current and future developments in land evaluation are discussed, emphasizing the particular input of soil survey when using computer simulation models for the soil‐water regime. The soil‐water regime plays a key role in land evaluation, as it governs the soil‐water state at any given time during

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1986.tb00001.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARYUrea application to soil raises the pH and ammonium concentration, thus providing ideal conditions for ammonia volatilization. A mechanistic model is presented, which combines the process of ammonia volatilization with the simultaneous transformation and movement of urea and its products in soil, for predicting the concentration profiles of urea, ammoniacal‐nitrogen and soil pH, and ammonia losses, following application of urea.The model consists of continuity equations describing the diffusion and reaction of urea, ammoniacal‐nitrogen and soil base; it takes into account the volatilization of ammonia and the concurrent acidification of the soil surface; and considers a variablePCo2profile due to soil respiration and urea hydrolysis. The derivation of the continuity equations and their boundary conditions, calculations of ammonia volatilization, and appropriate methods for numerical solutions are descri

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1986.tb00002.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARYExperimental methods for the measurement of the transfer coefficient for ammonia volatilization from the soil surface to the atmosphere, the gaseous diffusion impedance factor in soil, and other parameters required by the predictive model are described. Following surface application of urea to soil columns, the measured concentration profiles of urea, ammoniacal‐nitrogen and soil pH, and the losses of ammonia by volatilization, were compared with the model predictions. The very good agreement between the measured and the predicted results suggested that all important processes have been accounted for in the mode

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1986.tb00003.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARYA sensitivity analysis of the model described in Part I showed that the proportion of N lost as ammonia from surface applied urea is very sensitive to the initial pH of the soil, its pH buffer capacity, the rate of urea application, and the soil urease activity. Under the conditions tested, the diffusion of bicarbonate ion to the soil surface, to neutralize the acid generated when NH4+is volatilized as NH3, appeared to be the main process controlling the rate of ammonia volatilization.The amount of ammonia volatilized was not very sensitive to the value of the transfer coefficient between the soil surface and the atmosphere, nor to the soil moisture status if this was around field capacity. Adsorption of ammoniacal‐nitrogen was less important than the soil pH buffer capacity in influencing the ammonia volatilization.Further applications and extensions of the model are discusse

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1986.tb00004.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARYThe physicochemical and microbiological changes occurring in a fine sandy loam soil following the application of ammonium chloride were followed experimentally and with a simulation model. Two levels of ammonium addition were used corresponding to application rates of 37 and 143 kg ha−1. The measured concentration profiles of ammonium nitrate and pH, which developed in soil columns as a result of the diffusion and simultaneous nitrification of the added NH4+, were measured at different incubation times. The measured profiles suggested that nitrification was inhibited at the site of application of the ammonium salt. This inhibition was attributed to an effect of increased osmotic pressure or chloride ion in the soil. A simulation model was developed to account for the inhibition by examining and testing two hypotheses about the response of nitrifiers to a fluctuating osmotic pressure. These were the irreversible inhibition model, which assumed that exposure to high osmotic pressures irreversibly inactivated a portion of the nitrifier population, and the reversible inhibition model, which assumed that the nitrifiers would recover after exposure to high osmotic pressures. The model included terms for the adsorption equilibria of NH4+and soil acidity with the soil solid phase, and the influence of other ions on the rate of diffusion of each diffusing ion. The inputs to the model were based on parameters obtained independently of the diffusion experiments. Good agreement was found between experimental and predicted concentration profiles for both models although the reversible inhibition model gave the better simulation of the dat

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1986.tb00005.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARYThe simultaneous nitrification and diffusion of NH4+, applied as ammonium sulphate to laboratory columns, was followed experimentally and with a simulation model. Ammonium was applied as a fertilizer band at levels equivalent to 69 kg N ha−1to a 1 cm depth. The concentration profiles of NH4+, NO3−, SO2−4and pH were measured in two columns for incubation times of 214 and 286 h. The simulation model provided for the precipitation and ion pair formation of CaSO4, the adsorption equilibria of NH4+and soil acid with the soil solid phase, and nitrifier growth and activity. In general, good agreement was found between the experimental and simulated concentration profiles. The effect of CaSO4precipitation on the diffusion of N was investigated using model simulations of the diffusion of NH4+in the absence of nitrification. The simulations suggested that the reactions of SO2−4in the soil could markedly affect the spread of NH4+from a band of (N

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1986.tb00006.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARYConcentrations of nitrous oxide (N2O) and oxygen were monitored over a 2‐yr period in an imperfectly drained grassland soil receiving applications of N as cattle slurry or Ca(NO3)2. In both years N2O concentrations in the different treatments were in the order nitrate>slurry>control. Gaseous diffusion coefficients were determined in soil cores by a krypton‐85 tracer method and used to calculate approximate N2O fluxes from the soil. Only 1–5 kg N ha−1was lost as N2O after a single application of>1200 kg N ha−1as slurry compared with 3–11 kg N ha−1lost after 100 kg was added as NO3−. Total gaseous losses (N2O+N2) could be expected to be highe

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1986.tb00007.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARYLosses of N by denitrification from an imperfectly drained grassland soil were measured by the acetylene‐inhibition technique over a 1‐yr period, during which applications of up to 200 kg ha−1of N as cattle slurry or calcium nitrate were made. The quantities of N lost from nitrate‐treated soil were much greater than from slurry‐treated areas, and ranged up to 21% of the N applied. The losses occurred predominantly over brief periods following fertilizer application in the spring. Ratios of N released as N2to that released as N2O increased as denitrification rates increased. The highest ratio recorded, 24, may have been a conservative estimate because inhibition of N2O reduction may not have been complete on all occasions. Increased respiration was observed in the soil profile as a result of adding C2H2. This effect should be taken into account in interpreting experiments using the C2H2‐inhibitio

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1986.tb00008.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARYThe kinetics of phosphate sorption and release from soils are often described by a simplified form of the Elovich equation. However, examination of data obtained with three soils from Greece as well as of published data, based on a modified version of the Elovich equation, showed that the assumptions underlying derivation of the simplified form are not valid in all cases. This modified version is free from anya prioriassumptions, describes the kinetics of phosphate reactions with soils in a realistic manner and points out to the existence of more than one stage in the process.

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1986.tb00009.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARYThe paper examines some of the physical and chemical properties of a deep red friable clay profile (Nitosol) developed in the Kenya highlands over trachyte. This soil is widely planted to coffee. The profile is remarkable for the depth and uniformity of the B horizon and for its stable microaggregation. Despite a clay content of 50–60% throughout the deep solum, the soil feels and handles like a loam.Work with radioactive phosphorus on samples from the profile and from nearby experimental plots under coffee showed that the activity, and the amounts, of surface phosphate fractions decreased in the order Fe‐P, Al‐P and Ca‐P, but the order of decrease of specific surface activity was Al‐P, Fe‐P, Ca‐P. The relative availabilities of these forms

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1986.tb00010.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY