Crops vary in their sensitivity to deficiencies of various nutrients. Even within the same species the differences between cultivars or varieties can be large. The chart below provides a general classification of major crop responsiveness to additions of zinc.
Zinc is an essential micronutrient for humans, animals and plants. Zinc, as well as all of the micronutrients, are required in small amounts per acre in comparison to the macronutrients nitrogen, phosphorus and potassium. The fact that only a small amount of zinc is required does not mean that zinc is not of critical importance to the development, quality and yield of plants. The nutrients or elements that are required or necessary for plants to complete their life cycle are called essential nutrients. In the total absence of an essential nutrient plants don't even complete their life cycle and yield can be nil. The fact that nature provides some, most, or all of a crop's essential micronutrient needs should not reduce our appreciation for the essentiality of these nutrients for high yields and quality.
An excellent current publication on Zinc agronomics, written by Dr. Brian J. Alloway entitled "Zinc in Soils and Crop Nutrition", can be downloaded from the internet for free. An internet search for ( 2008_IAZ_IFA_ZincInSoils.pdf) will find this publication on numerous site.
Zinc Soil Testing
Soil testing is an excellent agronomic tool to determine the amount of fertilizer required to produce the maximum economic yield of a crop and to do so in an environmentally responsible manner. But like all other tools, soils testing must be done correctly for the soil test result numbers to be usefully. One of the first considerations is which zinc soil procedure does the lab you send your soil samples to use. The North America Proficiency Testing program runs analysis for 4 different zinc soil testing procedures. If you use one lab and get your recommendations from that lab this is not an important issue. But if you look for recommendations on the internet and don't know which testing procedure was used to develop those recommendations nor which procedure was used to test your soil, you could get yourself into trouble. The chart (Click on this link to see the chart) below shows the four zinc soil test procedures used by NAPT and results from 2 different soils tested in the 2nd quarter of 2011. Note that for the same soil the numbers for the different procedures are significantly different.