Gardening with Gary

Gardening Advice from an Expert

Nitrogen

Q. I had a soil sample analyzed. I was surprised when it came back that it was lacking remarks concerning nitrogen. The explanation I received when I called about the report was less than, shall we say, explanatory. Something about nitrogen passing quickly through the soil. The impression was left that it was not part of the normal test. Could you shed further light?

A. I am trying a basic approach here and feel this should help you:

As long as nitrogen is supplied in adequate amounts, it makes little difference to the plant if they are organic, inorganic, natural or synthetic. Inorganic fertilizer, however, is immediately available to plants, whereas organic fertilizer must be converted by microorganisms in the soil to an inorganic form before it can be used by the plants.

You will find three numbers with hyphens separating them. The numbers indicate, in order, the percentage of nitrogen (N), phosphorus (P), potassium or potash (K) - the letters in parentheses are the chemical symbols for the elements.

Nitrogen is needed for the green, leafy, vegetative growth of plants. When lacking, the plant will show deficiency symptoms as an overall pale yellow color of the leaves, and plants which are dwarfed or stunted. Nitrogen is mobile in the plant; that is, it moves from the older growth to the newer growth, where it is most needed. Therefore deficiency signs will appear first in older leaves.

Nitrogen moves easily through the soil in the soil water. For this reason, it is said to be very "mobile." It is easily "leached" or washed downward by rain or irrigation water. If it is washed below the root zone of the plants, it will not be available for plant use. Therefore, it is the fertilizer element most often lacking and most often needing replacement. Because of complex bacterial interaction, nitrogen is usually not "available" for plant use until the soil has warmed up in the spring and the soil temperature has reached 60F. This is why plants may appear yellow and stunted in early spring when the soil is still cold, even if nitrogen fertilizer has been applied. As soon as the soil warms up, they will appear green and vigorous.

Too much nitrogen or a nitrogen imbalance can delay flowering, fruiting and seed set. The resultant growth is soft and succulent and may be more vulnerable to fungal and bacterial infection. As well, nitrogen can desiccate or "burn" the roots of plants if placed too close to seeds, seedlings or newly planted plants.

Assistance from: Sara Williams, U. of Saskatchewan