Hanna Instruments HI 3896 - Manual (Page 6)

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For example, fungi prefer acidic conditions whereas most bacteria, especially those put-
ting nutrients at the plants’ disposition, have a preference for moderately acidic or slightly
alkaline soils. In fact, in strongly acidic conditions, nitrogen fixing and the mineralization
of vegetable residual is reduced.
Plants absorb the nutrients dissolved in the soil water and the nutrient solubility depends
largely on the pH value. Hence, the availability of elements is different at different pH
levels (Fig. 4).
Each plant needs elements in different quantities and this is the reason why each plant
requires a particular range of pH to optimize its growth.
For example, iron, copper and manganese are not soluble in an alkaline environment. This
means that plants needing these elements should theoretically be in an acidic type of soil.
Nitrogen, phosphorus, potassium and sulfur, on the other hand, are readily available in a
pH range close to neutrality.
Fig. 4. Solubility of the
elements according to
varying pH values
Furthermore, abnormal pH values, increase the concentration of toxic elements for plants.
For example, in acid conditions, there can be an excess of aluminum ions in such quantities
that the plant can not tolerate. Negative effects on chemical and physical structure are
also present when pH values are too far from neutral conditions (break up of aggregates,
a less permeable and more compact soil).
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Garlic 100 80 30 60
Lettuce 200 60 35 100
Maize (grain) 120 160 65 80
Melon 350 180 65 260
Onion 350 150 60 160
Pea 50 190 55 170
Pepper 250 100 35 130
Potato 350 140 55 220
Rice (whole plant) 60 100 45 95
Soybean 40 300 70 35
Spinach 250 120 40 130
Strawberry 150 165 60 265
Sunflower 30 130 45 145
Sugar beet 600 170 75 250
Tobacco (leaves) 24 85 55 230
Tomato 500 150 60 290
Watermelon 600 110 45 190
Soft Wheat (whole plant) 60 170 25 100
Hard Wheat (whole plant) 45 130 20 80
Apple 350 90 33 130
Apricot 150 110 35 125
Cherry 75 50 20 75
Grapevine 150 70 35 115
Grapefruit 300 130 45 180
Lemon 200 45 20 70
Olive 50 50 20 65
Orange 250 70 25 100
Peach 200 130 30 130
Pear 250 70 15 80
Plum 180 100 20 90
CROP YIELD Nitrogen Phosphorus Potassium
(q/ha) N (kg/ha) P
2
O
5
(kg/ha) K
2
O (kg/ha)
Tab.6.
The relationship between dosages of fertilizer elements and their presence in the soil is
shown in Tab. 7. As above, the quantities reported are only indicative. Chemical
analysis can be used as a basis for the evaluation, however other factors connected with
the production also need to be considered.
CROP SOIL CONTENT ADVISED DOSES (kg/ha)
N P
2
O
5
K
2
O
Alfalfa very low 0 150 230
low 0 130 150
medium 0 100 120
medium-high 0 80 90
high 0 60 60
very high 0 40 40
Tab. 7. Relation between
dosages of fertilizer
elements and their presence
in the soil