tailieunhanh - Soil and Environmental Analysis: Physical Methods - Chapter 8

Mật độ số lượng lớn ẩm của đất, r, khối lượng của nó, bao gồm bất kỳ nước hiện nay, mỗi lượng đơn vị trong lĩnh vực này; khô số lượng lớn, mật độ của nó rs, là khối lượng cho mỗi đơn vị khối lượng của đất lĩnh vực sau khi sấy lò. Các tham số này liên quan đến nội dung đất nước trọng lực, W, như sau: rs 100 r 100 W (1) W là khối lượng của nước được thể hiện như là một tỷ lệ phần trăm của khối lượng đất khô. Các phương pháp có. | 8 Bulk Density Donald J. Campbell and J. Kenneth Henshall Scottish Agricultural College Edinburgh Scotland I. INTRODUCTION The wet bulk density of a soil p is its mass including any water present per unit volume in the field its dry bulk density ps is the mass per unit volume of field soil after oven-drying. These parameters are related to the soil gravimetric water content W as follows ps 100 i p i Ps 100 WJ 1 where W is the mass of water expressed as a percentage of the mass of dry soil. The methods available for the measurement of soil bulk density fall into two groups. In the first group are the long-established direct methods which involve measurement of the sample mass and volume. The mass Ms of the oven-dried sample is obtained by weighing and the total volume V of the soil including air and water is obtained by measurement or indirect estimation. The dry bulk density p s is then given by n Ms p s V 2 Such methods have been used by both agricultural soil scientists Freitag 1971 and civil engineers DSIR 1964 and many of them reduce essentially to the problem of the accurate determination of the sample volume. As these methods have not always proved entirely effective a second group of methods has evolved in which the attenuation or scattering of nuclear radiation by soil is used to give an indirect measurement of bulk density. Radiation methods are capable of Copyright 2000 Marcel Dekker Inc. measuring more accurately and precisely than direct methods but they too have limitations of their own. Thus there is no single measurement method suitable for all circumstances. Sometimes a very crude but quick measurement is all that is required to characterize soil conditions but in other circumstances it may well be appropriate to use a slower method involving expensive equipment in order for example to detect detailed differences between experimental treatments. II. RADIATION METHODS A. Theory Radiation methods involve measuring either the attenuation or the .