SOIL ACIDITY OR ALKALINITY

Articles In This Section:

· PLANT FOODS

· ANALYSIS OF PLANT ASH

· ORGANIC WASTE MATTER

· MAJOR PLANT FOOD ELEMENTS

· MINOR PLANT FOOD ELEMENTS - Part 1

· MINOR PLANT FOOD ELEMENTS - Part 2

· FOLIAGE FEEDING

· SOIL ACIDITY OR ALKALINITY

· HUMUS AND ANIMAL MANURES - Part 1

· HUMUS AND ANIMAL MANURES - Part 2

· VEGETABLE MANURES

· COMPOST

· LIQUID MANURES

Soil acidity or alkalinity greatly affects the behaviour and availability of most plant nutrients. When soil is rich in available calcium, it is alkaline. The main soil acids are the colloidal particles of the clay itself. Thus heavy soils are usually more acid than sands. Carbonic acid, tannic acid, citric acid, and other organic acids are less important.

Soils will become very acid if fed regularly with flowers of sulphur, ammonium sulphate, superphosphate, potassium sulphate, magnesium sulphate, or organic matter in large quantities. Tan-bark is the most acid of the many organic substances commonly used. The acidity can be decreased by using lime or dolomite. Any artificial increasing or decreasing of acidity of any plot of ground will not be permanent; it will slowly return to its original reaction.

Alkalinity reduces the availability of iron, potash, and manganese. Strong acidity reduces the availability of calcium, phosphorus, magnesium, and, to a lesser extent, nitrogen, because of an inhibiting effect on soil bacteria. The same soil will vary in degree of acidity from week to week, from level to level, and in areas separated by only a few yards. It is rarely constant anywhere.

Alkaline soil increases the incidence of crown gall in roses. Unduly acid soils are said by some growers to predispose rose plants to black spot, but opinions are by no means unanimous on this point.

Nutrients are not absorbed by either leaves or roots as elements, but as compounds, and, in solutions, no more concentrated than one or two parts to each thousand parts of water; root hairs are killed by stronger solutions.

Chemists have done wonderful service to horticulture and agriculture in recent times. They have given us our knowledge of the constituent elements and compounds of soils, plants, animal tissues, animal excreta, and many less common things; they have found reasons for crop failures by way of soil deficiencies and soil toxicities; they have told us what to use to remedy these defects; they have synthesized chemical (or inorganic) fertilizers of all kinds; they have devised compounds for use as sprays or dusts in combating disease; they have given us everything but synthetic sunlight, synthetic chlorophyll and a synthetic soil of good fertility.