Oven dry soil

Soil water content may be reported in a number of different ways but is most commonly reported as the amount of water in grams per gram or kilogram of oven dry soil (see equations in Figure 5.13). It may also be reported... 

A more recent study of the effect of drying on various species of phosphate in soil showed that drying had little effect on some species while having a pronounced effect on others [13]. In nature, soil is never heated to the temperatures used in oven drying, and thus the results of analysis of oven-dried soils are not considered representative of the soils natural conditions. 

Figure 7.10. Uptake of hydroscopic water by oven dry soil.

Soil is hygroscopic. The water content of air dry soil will increase and decrease as the relative humidity of the air it is exposed to changes. The uptake of water by oven dry soil is shown in Figure 7.10. Thus, determination of water content just before analysis is critical. 

Normally, mass measurements are not made on hot objects. Waiting for an oven-dried soil sample to cool in air will have what effect on its mass ... 

Calculation. Read from the standard graph the number of pg boron equivalent to the absorbance of the sample, and the absorbance of the blank. Multiply the difference by 2 to give the mg of boron in the air-dry soil sample. To express in terms of oven-dry soil, see Method 5.2, Calculation (2). 

Calculation. Ash-free fulvic acid y mg 100 ml is read from the chart. This solution resulted from 10 g air-dry soil in 250 ml solution. Therefore 250 ml solution contains yx 250/100 mg fulvic acid from 10 g air-dry soil, which converts to 25y mg fulvic acid 100 g or 0.025y% air-dry soil. This must be multiplied by any dilution factor before reading the optical density, also converted to percent oven-dry soil (see Method 5.2, Calculation (2)). 

The weight of ash-free humic acid was derived from 10 g air-dry soil, therefore should be multiplied by 10 to convert to percent air-dry soil and further converted to percentage oven-dry soil. The fulvic and humic acid content may be expressed as a percentage of total soil organic matter, which is quantified as soil organic carbon (SOC). SOC is conveniently determined from the loss on ignition, where the correlation is ... 

Calculation. There were 20 ml soil in 50 ml of extractant, therefore sample concentration values from the standard graph should be multiplied by 2.5, the results being expressed as mg b nitrate-N calcium sulphate extractable in air-dry soil. Include any extra dilution factors, and, if required, convert to oven-dry soil using the appropriate factor, as in Method 5.2, Calculation (2). 

Calculation. Subtract the blank from the soil titre, multiply the difference by 700 and divide by y, to get the mg kg ammonium-N, potassium chloride extractable, in air-dry soil. Express results for oven-dry soil as in Method 5.2, Calculation (2). 

Express results for oven-dry soil as in Method 5.2, Calculation (2). 

After this time, the clips on the tubing are opened, and the water that drains from each funnel for thirty minutes is collected in a measuring cylinder held beneath the funnel stem. The final volume of water drained is recorded. Alternatively, the soils may be weighed into filter funnels containing filter papers and then water added as already described. Then, the surplus water is drained off, and the soils, still in the filter papers, and blanks may be weighed and oven-dried for 24 hours at 25°C, reweighed, and the water retained calculated by difference. Results are usually expressed as percent of WHC (ml H20 retained 100 g-1 oven dry soil). 

Gravimetric soil water content (%) (Mass of water/mass of oven dry soil) x 100... 

Soil bulk density (g cm ) Mass of oven dry soil/volume of soil core... 

The amount of extracted radioactivity per gram of oven-dry soil declined as a function of incubation time (Fig. 3). Since radio-HPLC proved that virtually that virtually all the extracted radioactivity was due to unchanged test substance (Fig. 4), the extent of depletion of extracted radioactivity was used to calculate the parent substance halfJife. The application of first-order kinetics equations [11]... 

Empty the pycnometer and fill into it lOg oven-dried soil. 

Then fill the cylinder in such a way that the same compactness as in field condition is maintained. This may be done by measuring the volume of the cylinder and the amount of oven dry soil which is filled in this volume to bring the soil to the required bulk density level. 

Let an oven dry soil having mass im ), specific heat (s ) and initial temperature (9 ) be dropped all of a sudden into water contained in a calorimeter with mass, specific heat and initial temperature as m, and 02 respectively. If and Sg are the mass and specific heat of the calorimeter and if the resulting temperature of soil-water mixture at equilibrium is 9 then according to the principle of calorimetry (Heat gained = Heat lost) with all limitating it follows that... 

Total water = water added + (Wt. air dry soil - Wt. oven dry soil)... 

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