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Step 1
Symptoms
Nitrogen deficiencies are fairly easy to identity because they affect the entire plant. Overall growth is poor and stunted; small leaves; pale, yellowing foliage; limited shoot growth; reduced flowering; and small, poor fruit. In the Brassicas (cabbage family) older leaves commonly develop a red, orange, or purple tint.
Signs of excess are rampant leaf growth; dark green, succulent leaves and stems; and little or no fruit. This is because the plant takes up the excess nitrogen and stores it in its leaves for future use. While this may be prudent of the plant, it does little to advance the main interest of the gardener, which is a nice harvest of vegetables. -
Step 2
Common Causes
Since plants take most of their nutrients from the soil, the most common causes are a deficiency of nitrogen in the soil, or soil conditions that make the nitrogen unavailable to the plants. If you add sufficient supplies of nitrogen sources at the beginning of the season, remember that nitrogen is removed from the soil by intensive cropping more than any other nutrient. Consequently,
if you succession plant or intercrop it is important to replace nitrogen between crops with organic matter or soil amendments. Big nitrogen feeders (such as tomatoes, spinach, cabbage, and lettuce) also appropriate most of the nitrogen around them, requiring the gardener to replenish it midseason.
It is possible, however, that your soil contains nitrogen but conditions simply will not allow the plants to obtain it. Cold or excessively wet soil renders nitrogen unavailable because the soil micro-organisms that break down organic matter to nutrient forms plants can use are made sluggish or inactive in such conditions. Another problem may be that an alkaline (high pH) soil is limiting the availability of nitrogen, or a too acidic soil is limiting the activities of the micro herd. Lastly, plants need adequate amounts of other macro nutrients, such as calcium and phosphorous, to uptake and process nitrogen, so a nutrient imbalance in the soil may be the culprit. Consider your soil conditions and maybe have the soil tested before you just start adding more nitrogen. -
Step 3
Sources and Remedies
The best source of nitrogen is organic matter or compost. This, however, is somewhat slow acting because the micro herd must break it down before your plants can use it. Other good sources of nitrogen are green manures, blood meal, alfalfa meal, and fish emulsion.
If your plants are in immediate need of a nitrogen fix, the best thing you can do is mix up a batch of fish emulsion and foliar feed them. Don’t go over board on this because, as explained, a nitrogen excess is almost as bad as a deficiency. For non-leafy crops, a weekly nitrogen feed should be enough when combined with a “top dressing” of blood meal or alfalfa meal placed around the plant’s root line. The foliar feed will give the plants an immediate boost and the slow release of the top dressing will provide slow and steady growth.
Long term, apply compost, manure, alfalfa meal, or cottonseed meal to your beds in the spring a week or two before planting. Do not add nitrogen to the soil in the fall if you intend to let the soil lie fallow. Nitrogen is easily leached out of the soil by rainfall so you will waste your efforts and your resources.
Comments
hradcliffe said
on 10/1/2009 Good article on how to recognize nitrogen deficiencies in your vegetables. I have soil that needs to be amended and always wonder what to use.