Proper levels of nitrogen (N) in the soil are critical for ideal plant growth. Too little nitrogen, and the plant will become stunted and never bear fruit or vegetables. Too much nitrogen, and the plant will be all green leaves with little to no fruit or vegetables. Testing for nitrogen is best conducted by taking soil samples from the growing area. Your local agricultural extension service offers a testing service for little cost. In those results, the laboratory will have specific fertilizer recommendations for the plants you wish to grow.
Dig several soil samples from the field or growing area you'll be testing, using a shovel. Typically a small handful of soil must be taken from various areas around the field. A good rule of thumb is to take five soil samples for every acre tested. A small garden that has a large diversity of plants may need as many as 10 samples for every 1,000 square feet of growing space. Consult the extension service for soil collection methods.
Place all soil samples from that area in the plastic bucket. Mix the soil together using your hands. Crush any large clumps of soil into smaller pieces.
Arrange the plastic sheet under an overhead covering. Spread the soil over the plastic sheet so it can thoroughly dry out.
Mix the soil well during the drying period. Keep any form of moisture from the soil as this may affect the end testing result.
Identify the field or garden area on the side of the soil container. Add any extra notes or information concerning the area from which the soil was collected. The information may also contain the type of crop or plants to be grown in the garden or field. This information will aid the laboratory in determining special fertilization requirements.