Extraction of three light-textured, New York soils by a modified soxhlet procedure before and after intensive cropping indicated that the procedure removed all forms of soil boron available to plants. The purpose of the present study was to determine how generally this conclusion can be applied and what portion of these forms of boron is available to plants. Samples of 16 soils differing widely in content of available boron were intensively cropped in a greenhouse experiment. Boron removed from the soil by cropping was studied in relation to associated changes in boron removed by two water extraction procedures. The first procedure was the well known 5-minute boiling period technique; the second a 6-hour modified soxhlet extraction. Soxhlet-extractable boron appeared to include all forms of soil boron available to plants and the extractable boron was available. The soxhlet-extractable boron also replenished water-soluble boron to a marked extent as this form was removed by cropping.
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