Soil Amendments
Chemical Fertilizers
For the survival gardener, a knowledge of both organic and chemical methods is highly desirable. This article describes:Chemical Elements Essential to Plant Growth
Specifying the Content of Chemical Fertilizers
Chemical Elements Essential to Plant Growth
There are eighteen chemical elements that have been found essential to plant growth. Three of these, carbon, hydrogen, and oxygen, are supplied primarily by air and water. The others are absorbed through the plant roots. Each element is specified as a macro, secondary, or micro nutrient, depending on the quantity of each element that must be supplied for a particular crop:
- Macro nutrients - typically 10 lbs to 150 lbs/acre.
- Medium or Secondary nutrients - typically 3 lbs to 10 lbs/acre.
- Micro nutrients - typically 0.03 to 0.1 lbs/acre.
| Element | Nutrient Category | Chemical Sources For | Effects of Deficiency |
|---|---|---|---|
| Macro or Large Quantity |
|
Deficiency: Early sign is yellowing of older leaves. Tips of leaves may be
yellow-green color, referred to as a chlorosis condition.
Continued deficiency causes all growth to be stunted.
Note: Too much nitrogen results in lush foliage but suppressed fruit and seed development. |
|
| Macro or Large Quantity |
|
Deficiency: Signs include slow, stunted growth, and delayed maturity. Grain, fruit, or seeds are poorly developed. Leaves are dark green with tips dying. The leaves of some plants some a purplish coloration. | |
| Macro or Large Quantity |
|
Deficiency: Burning of tips of older leaves, weak stalks. Growth is slow, fruit is small, and seeds are shriveled. Resistance to certain diseases is diminished. | |
| Medium Quantity |
|
Deficiency: Terminal buds and growing tips of roots fail to develop. Stems are weakened and blossoms and buds are shed prematurely. Foliage has abnormally dark green appearance. | |
| Medium Quantity | Dolomite limestone, which also supplies calcium. | Deficiency: Leaves curl upward along leaf margins. Yellow-green color (chlorosis) of inter-vein areas of older leaves. Christmas-tree along the leaf mid-rib. | |
| Medium Quantity |
|
Deficiency: Greatly retarded plant growth. The overall condition resembles nitrogen deficiency, except that sulfur does not move from older to younger parts of the growing plant. In legumes (for example, peas) failure of nitrogen-fixing bacteria nodes to develop on roots. | |
Iron (Fe), Manganese (Mn), Copper (Cu) |
Micro or Trace Quantity | These elements are typically present in the soil and are not supplied separately. The availability of these elements, which depends a great deal on the acid/alkaline (pH) balance of the soil, is another matter. | Iron and Manganese are both necessary for chlorophyll formation. A deficiency of either results in inter-veinal chlorosis. |
Zinc (Zn) |
Micro or Trace Quantity | Zinc sulfate, which also supplies sulfur. | Necessary for chlorophyll formation. Deficiency symptoms include reduced fruit formation and interveinal chlorosis. |
| Micro or Trace Quantity | Copper sulfate, which also supplies sulfur. Copper ammonium phosphate, which also supplies nitrogen and phosphorus. | Deficiency symptoms include stunted growth and poor pigmentation.
Note: Excess cooper can interfere with the activity of iron, resulting in iron deficiency symptoms. |
|
| Micro or Trace Quantity | Borax, sodium pentaborate, and boric acid. | Deficiency symptoms include reduced flowering and pollination failure. | |
| Micro or Trace Quantity | Ammonium molybdate, which also supplies nitrogen, sodium molybdate, molybdium trioxide. | Required by plants for nitrogen utilization and by nitrogen fixing-bacteria for nitrogen fixation. Deficiency symptoms include those of nitrogen deficiency nd yellow spotting of citrus. | |
| Micro or Trace Quantity | Not added to fertilizers. | Required by nitrogen fixing-bacteria for nitrogen fixation. Deficiency symptoms include those of nitrogen deficiency nd yellow spotting of citrus. | |
| Micro or Trace Quantity | Universally present, so a fertilizer source is unnecessary. | Required for photosynthesis. |
Specifying the Content of Chemical Fertilizers
The chemical fertilizer industry is primarily concerned with supplying the macro nutrients, Nitrogen, Phosphorus, and Potassium. The content of chemical fertilizers is specified on the basis of the percentage of the three major elements, Nitrogen (N), Phosphorus (P), and Potassium (K) that the fertilizer contains. For example, a fertilizer specified as: 5-10-10 contains 5% N, 10% P, and 10% K.Note: In actuality, the system is more complicated than this. The amounts of Phosphorus and Potassium are not based on the percentages of these elements, but on the percentages of the compounds P2O5 and K2O, respectively. To further complicate matters, it is not the actual amounts of these compounds present in a particular fertilizer that is used - there may not be any! - but the "calculated" amount. In practice, when purchasing a fertilizer what matters is the relative amounts of the elements you are interested and in these complexities of chemistry can be ignored.
Soil Acidity and Alkalinity
The availability of nutrients to plants depends in part on the acid or alkaline properties of the soil. Acidity and Alkalinity are expressed in terms of the pH scale, from 1 to 14. A pH of 1 is highly acid, a pH of 7 is neutral, and a pH of 14 is highly alkaline. Most plants grow best in soil that is slightly acid, from pH 6 to pH 6.8.
Measuring Water pH
You can test the acid/alkaline balance of the water you use for your garden with litmus paper, which will indicate whether the water is acid (litmus paper turns red) or alkaline (litmus paper turns blue). More exact testing requires pH test paper, which changes colors over the entire acid-alkaline range, indicating the exact pH.
Adjusting Water pH
Water that is too alkaline can be corrected by adding vinegar (dilute acetic acid), a weak acid. Water that is too acid can be corrected by adding household ammonia (dilute ammonium hydroxide), a weak base (alkaline substance).
Note: The addition of ammonia also adds nitrogen to the soil.
Measuring Soil pH
Measuring soil pH requires a soil testing kit, which typically also test for nitrogen, phosphorus, and potassium. These kits may also include information on the preferred soil pH levels of various plants, together with the amounts of various additives that must be used to raise or lower the pH level.
Controlling Soil Acidity and Alkalinity
Even organic gardeners who use only organic matter as the source of nutrients for their crops may still need to make use of chemical additives to control the acid/alkaline balance in their soil.
The following table describes how soil acidity ("sourness") and alkalinity ("sweetness") can be controlled through some soil amendments.
| Desired Action | Material(s) to Use |
|---|---|
| Increase alkalinity, decrease acidity. | Calcium Carbonate (Chalk, Limestone) |
| Increase acidity, decrease alkalinity. | Sulfur dust, pine needles, peat moss |
Note: The natural tendency of most soils under natural conditions is to become increasingly acidic, reaching a level that many food plants cannot tolerate very well. In the garden, this tendency may be offset or even counteracted by other factors, such as specifically what plants are grown, whether they are left to decay after dying or are removed, and the pH level of the water used in the garden.