摘要:

We present a simple model for predicting the water-retention characteristics of sandy soils from routinely available textural and structural soil properties.Using the basic concept of shape similarity between the retention curveh(&thetas;) and the cumulative particle-size distribution functionF(d), we derive an analytical expression forh(&thetas;), following the well-known Brooks and Corey equation and taking into account air entrapment and hysteresis. Except for the water content at natural saturation, which is used as an independent input parameter, the operation parameters of the model are obtained directly fromF(d) and dry bulk density.The results obtained for 10 sandy soils available from laboratory and field experiments show an excellent agreement between predicted and experimentalh(&thetas;) curves. The errors introduced by the prediction model are of the same order of magnitude as the experimental errors ofh(&thetas;).In this paper we consider only sandy soils without organic materia. In a subsequent paper we will extend the analysis to more general soils.

ISSN:0038-075X    

出版商:OVID    

年代:1986

数据来源: OVID

摘要:

We conducted a greenhouse experiment, at Haryana Agricultural University, to learn the effects of N and Zn levels on concentration and uptake of P, K, Fe, Mn, and Cu in pearl millet (Pennisetum americanum). Applying 200 ppm N produced an antagonistic relationship on the concentration of P and K in leaves, stems, and roots and also on Fe and Cu concentrations in stems. We observed 42.6, 25.9, and 59.3% reductions in P concentrations in leaves, stems, and roots; also concentrations of Fe and Cu in stems decreased by 19.7 and 42.3%. Nitrogen increased the concentrations of Fe in leaves and roots, Cu in leaves, and Mn in leaves and stems. The effect of Zn on the concentrations of P and K in all plant parts was antagonistic. Zinc had a synergistic effect on the concentrations of Fe and Mn in leaves, stems, and roots up to 10 ppm Zn, and an antagonistic effect at 20 ppm Zn. However, the concentration of Cu and Zn had no effect on Cu contents of stems and roots. N × Zn interactions on the concentrations of P, K, and Fe in roots, Cu in leaves, and the uptake of P, K, Fe, Mn, and Cu in different plant parts of pearl millet were found to be significant.

ISSN:0038-075X    

出版商:OVID    

年代:1986

数据来源: OVID

摘要:

We investigated the effects of anaerobic decomposition of organic matter on the amorphous Fe contents and P transformations in four soils used for a flooded rice-upland crop rotation. The soils were amended with 0, 0.5, and 1.0% organic matter as cellulose and kept flooded for 85 d. The anaerobic decomposition of organic matter significantly increased the amorphous Fe content and produced significant transformations in inorganic P fractions. The Al-P decreased and Fe-P and RS-P fractions increased, due to the anaerobic decomposition of organic matter. We concluded that the anaerobic decomposition of organic matter increased the transformation of crystalline iron into amorphous iron. This led to an increase in Fe-P and severe occlusion of P, resulting in the increase in RS-P fraction upon soil drainage.

ISSN:0038-075X    

出版商:OVID    

年代:1986

数据来源: OVID

摘要:

A respirometer system was developed to study the dynamics of partial anaerobiosis and denitrification in unsaturated soil. The system enables one to measure simultaneously the distribution of water, oxygen, nitrate, nitrite, ammonium, and pH as a function of space and time in an unsaturated, artificially made, homogeneous, cylindrical aggregate and the changes in atmospheric composition as a function of time in the chamber the contains the aggregate. Except for water transport, these processes are caused by microbial activity, because roots are not present in the aggregate.The respirometer system was especially designed to generate coherent data sets to evaluate a simulation model that calculates the development of denitrification products as a function of environmental conditions. Nondestructive measurements during an experiment involve gamma-ray attenuation, gas chromatography, and polarography. Destructive measurements are executed the end of an experiment in the form of chemical analyses of soil.The reported experiment shows that hysteresis in the soil water characteristic strongly affects the water distribution in the aggregate. As a result, the oxygen supply to the interior of the aggregate is decreased to such an extent that anaerobiosis is maintained there after the oxygen is consumed. The respiratory quotient and the release of denitrification products are underestimated in the partially wet soil because of the high solubilities of carbon dioxide and nitrous oxide in soil moisture. Large amounts of nitrite have been found. Therefore, assessment of denitrification through the measurement of nitrate alone will overestimate nitrogen losses, while the measurement of nitrous oxide and molecular nitrogen alone will given an under-estimation. The consumption rate of oxygen and the production rates of carbon dioxide, nitrous oxide, and molecular nitrogen compare wel with field data. This is the result of the pretreatment of the soil, which aimed at avoiding the flush of microbial activity upon wetting. The results support the thesis that denitrification will occur in soil when at a certain place and time oxygen is absent and bacteria capable of denitrification, water, nitrate, and decomposable organic compounds are present.The respirometer system yields valuable data to evaluate the simulation model. However, full account of the interrelationships among the generated data can be achieved only by the same simulation model, because the measured variables reflect the integrated effect of biological activity and transport processes.The objective of this paper is to describe the respirometer system and its measuring devices and to report some of the measurements.

ISSN:0038-075X    

出版商:OVID    

年代:1986

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1986

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1986

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1986

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1986

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1986

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1986

数据来源: OVID