Soil Management Handbook - Ministry of Agriculture and Lands

efer to the following Factsheets: Soil Acidity and
Liming Facts, Liming Acid Soils in Central B.C. and
Soil Liming Recommendations available at the
Resource Management Branch, BCMAFF,
Abbotsford).
For best results, lime should be applied in the fall or a
few weeks prior to seeding, and thoroughly
incorporated into the plow layer on tilled fields. For
grape and tree fruits, lime can be applied at any time,
except within one month of fertilizer application.
Where possible, lime should be evenly broadcast and
incorporated with care between rows. Liming
programs should be considered carefully during the
establishment of perennial crops. Lime has a low
level of solubility, so lime applied and left on the soil
surface will only be slightly effective in raising soil
pH in the rooting zone.
Soil pH is a poor indicator of lime requirement.
Factors, such as organic matter levels, clay content
and age of soils, markedly affect the amount of lime
needed to adjust the pH level one unit. A lime
requirement test, performed by a reputable soil testing
laboratory, is recommended to ensure the correct rate
of lime application.
Surface application of lime on low pH areas under
trickle or drip irrigation may not alter the soil pH
below the soil surface. The use of lime in these
situations may have some affect on the soil nutrient
solution and reduce the negative impact of iron,
aluminum and manganese toxicity.
4.5.2.3 Acidification Resistance Index (ARI)
ARI is a soil test which measures the amount of acid
required to lower a soil to pH 5.0 from its present
level. From the ARI, recommendations on fertilizer
and lime use can be made to aid in controlling the pH
level of a soil. ARI takes into account both the
buffering capacity and pH of the soil.
Acidification often occurs in poorly buffered soils due
to irrigation and use of acidifying fertilizers such as
ammonium sulfate (21-0-0). Any producer
considering fertigation of orchards should have an
ARI test completed. The table below gives general
recommendations for 3 ARI ranges.
ARI Ranges
0 to 5 Very sensitive to acidification, lime to
pH 7 prior to planting tree fruits, use
calcium nitriate
6 to 25 Moderately sensitive to acidification,
lime to pH 7 prior to planting, use
calcium nitrate in combination with
other sources of nitrogen.
>26 Not sensitive, do not lime, use any
nitrogen fertilizer source.
4.5.2.4 Sulphur and Acidification
Sulphur
Sulphur may be required as an essential plant nutrient,
however, this section will refer to the use of sulphur
as a soil acidifier.
In some areas of the Okanagan and Similkameen
Valleys, soil pH is above 8.0. It may be desirable to
lower the pH to increase the availability of some plant
nutrients. Lowering soil pH involves the same
cultural practices and considerations as raising the pH
with liming, except that different products are
required. Adjusting a soil pH downward is more
difficult and often more costly than moving a soil pH
up. Care must be taken to ensure that the high pH
>8.0 is not the result of an alkali (sodium) or saline
condition which may require other soil management
such as gypsum addition or drainage.
Acidification
The principal agents used to lower soil pH are
elemental sulphur, sulphuric acid, aluminum sulphate
and iron sulphate (ferrous sulphate). Ammonium
sulphate, ammonium phosphate and other ammonium
containing fertilizers are also quite effective in
reducing soil pH, though they are primarily sources of
plant nutrients.
For large areas, elemental sulphur (or a mixture of it
and bentonite to improve its stability and safety when
handled in confined spaces) is probably the most
economic product. However, elemental sulphur has
to be oxidized by soil microorganisms. Sulphuric
76 Soil Management Handbook – Okanagan-Similkameen Valleys