Monitoring crop N status during the growing season accomplishes little unless it is possible to correct an N deficiency before it reduces yields. Fertigation is generally limited to moving sprinkler systems due to the uniformity of application possible with center pivots or lateral move systems, although much progress is reported in the development of surge-flow fertigation systems. One benefit of fertigation is that the applied N is rapidly taken up by the crop to correct the N deficiency. In a non-irrigationd system, N application to dry topsoil may not be utilized until the next rain occurs, which may be too late for the plants to fully recover and produce optimal grain yields. Although the technique is quite new, we feel chlorophyll meters can be utilized on a large number of acres in Nebraska, and promises to improve fertilizer N efficiency and decrease risks associated with reduced fertilizer applications.
Many factors affect chlorophyll meter readings.
Variety or hybrid differences can greatly affect the meter reading as some corn and sorghum hybrids are darker green than others. Stage of growth can affect leaf greenness as can recent environmental conditions such as temperature, moisture stress and sunlight. Plant diseases, nutrient deficiencies and nearly any other kind of plant stress can affect the ability of the plant to produce chlorophyll, thus affecting leaf greenness. Because the chlorophyll meter is affected by so many things, we are not able to say that a given meter reading indicates sufficient N. Meter readings mean very little by themselves and must be calibrated for each field, soil, hybrid and environment in order to make use of the readings. The best way to calibrate the meter is to maintain several adequately fertilized reference strips in each field.