This test was first proposed in the mid-1940s and has been extensively evaluated since that time. The idea behind this test is that the concentration of nitrogen in corn leaves near the primary ear should be a good indicator of the amount of N supplied to the developing grain. However, a wide range of critical N levels have been reported in the literature. Although this method can be used to determine deficiencies throughout the season, it is most useful if the farmer could identify a developing deficiency early enough in the season to correct the problem. A disadvantage of this test may be that if more N is needed, the crop may be too tall to apply it mechanically unless fertigation is possible or high-clearance equipment is available.
Many factors can control the number of green leaves on a corn plant.
Sum the total number of green leaves below the ear on each plant and then calculate the average number of green leaves for the area by counting leaves on about 20 to 25 plants per area. Compare the average number of green leaves between the two areas. The advantages of using this procedure are that it gives and instantaneous reading of N status, it is easy, and it is cheap. However, this test can only be used to quantify N deficiencies and it will usually be too late to correct any deficiencies that are found. The chlorophyll meter can allow farmers to fine-tune N management by detecting developing deficiencies early enough that they can be corrected before they reduce grain yields.