Page 151 - Soil Degradation, Conservation and Remediation

140 5 Chemical Soil Degradation

estimate lime requirement from existing pH, desired pH, clay content, CEC,
3+
+
exchangeable Al and H , and percent base saturation.
There are a number of lime requirement determination methods for different
types of soils. Two methods are generally used: the SMP (Shoemaker–McLean–
Pratt) and Adams–Evans buffer methods. The SMP method was designed for use
with soils that have large lime requirements and significant reserves of exchangeable
Al (Shoemaker et al. 1961). The Adams–Evans buffer was designed for soils that
are coarse textured, with low cation exchange capacities and organic matter contents,
and thus low lime requirements (Adams and Evans 1962). The Mehlich lime buffer
was developed for use on Ultisols, Histosols, Alfisols, and Inceptisols (Mehlich
1976). To avoid hazardous chemicals, all three buffers have been modified. All three
modifications correlated well with the original buffer, and no changes in calibration
were necessary for any of the modified methods (Hoskins 2005; Huluka 2005; Sikora
2006). The original SMP buffer or its modification (Sikora buffer) is the most
commonly used method.

Lime Requirement Procedure (SMP Buffer Method)

SMP Buffer
1. Weigh 32.4 g of para-nitrophenol, 54.0 g of K 2 CrO 4 , and 955.8 g CaCl 2 ⋅2H 2 O
into an 18 L bottle. Add 9 L distilled water, shaking vigorously during addition.
2. Weigh 36.0 g of Ca(OAc) 2 into a large container and dissolve in 5 L of distilled water.
3. Combine the two solutions, shaking during mixing and every 15–20 min for 2–3 h.
4. Add 45 mL triethanolamine, shaking during addition and periodically thereafter
until completely dissolved.
5. Dilute to 18 L with distilled water, adjust to pH 7.50 using 15 % NaOH, and filter.
6. Store in a container with the air inlet protected by drierite and ascarite to prevent
contamination by water vapor and carbon dioxide. Avoid excessive agitation of
the solution after pH adjustment.

Procedure
1. Add 10 mL of SMP buffer to the soil–water slurry used for pH determination.
2. Place in a mechanical shaker, close tightly, shake at 250 excursions/min for 10 min,
and let it sit for 20 min.
3. Swirl, insert electrodes, and read the pH. Read to the nearest 0.01 pH unit.
4. Determine lime requirement from soil buffer pH and calibration data for local soils.

5.3.3.5 Applying Lime
Application of lime of proper quality and at appropriate rates on the surface of
soil and incorporation is usually recommended. Good results have been achieved
with deep placement of lime using modified farm-scale machinery as well, but it is