From Seed to Seed:
Plant Science for K-8 Educators

 

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    Nutrients

Nutrients are the last big requirement for plants. Although we often say we are "feeding" our plants when we fertilize, that's not quite accurate. When we fertilize plants we are providing them with the nutrients they need so that they can manufacture their own food through the process of photosynthesis.

You can think of mineral nutrients in plants as similar to the vitamins and minerals that we get from supplements. Without the vitamins and minerals our bodies require, we wouldn't be able to carry out all of the various metabolic functions necessary for good health.

The nutrients that plants require in relatively large quantities are: carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur. These are called macronutrients. Plants also need a number of other nutrients in much smaller quantities. Plant micronutrients include iron, copper, zinc, manganese, molybdenum, and boron.

Plants obtain carbon, hydrogen, and oxygen from the atmosphere. And, as we mentioned before, some plants can fix atmospheric nitrogen. Plants must get all of the other necessary minerals from the soil or from soil additives-such as fertilizer, compost, or manure. Some soils are naturally deficient in certain minerals; others have had their reserves depleted through continuous farming. In either case, if you want to grow healthy plants in that soil, you will need to supply the missing minerals. Here are a few generalizations about diagnosing mineral deficiencies:

  • If the plant is chlorotic-that is, looks weak and has light green to yellow leaves-it may be suffering from nitrogen deficiency. Chlorosis can also be the result of iron deficiency.

  • Phosphorus deficiency results in small plants with small, purple-tinged leaves, and few fruits.

  • The yellowing or browning of leaf margins and weakened stems may be the result of potassium deficiency.


Some plants are classified as "heavy" feeders while others are considered "light" feeders. Corn is a heavy feeder because it requires large amounts of nitrogen. From year to year, gardeners will rotate where corn is grown in the garden to allow the soil to replenish its nitrogen supply. This rotation of crops is also beneficial in preventing diseases from ravaging the same food crop year after year.


 

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