Nitrogen Soil Test...interesting

The Scoop on Soil Testing for Nitrogen
Nitrogen can be added to soil in many forms. It can be applied as nitrates, 
ammonium, urea, etc. Soon after the nitrogen is added and if there is some 
moisture present, the indiginous bacteria called nitrosomonas and nitrobacter 
convert all forms of nitrogen to the nitrate form. The nitrate form of 
nitrogen is an ion with a negative charge (NO3-). The clays in South Carolina 
soils also have a negative charge and since similar charges repel, the 
nitrates are not attracted to the clays like the posit ively charged calcium, 
magnesium and potassium ions. Nitrates are also very soluble in water. As a 
result, the nitrate ions are very mobile in the soil and move through quite 
readily as water percolates down into the soil. If a soil is sandy, nitrates 
move through the soil even faster due to the large pore space and faster 
percolation of water. These factors are the reason for environmental and 
health concerns regarding nitrate movement into groundwater.

Because of nitrogen's rapid conversion to the nitrate form and its subsequent 
movement through the soil, it makes the soil test for nitrogen quite 
difficult to interpret. By the time you receive soil test results for nitrate 
nitrogen, it may have alre ady moved through the soil if some rain had fallen 
between sample collection and reporting of lab results. Some soil tests for 
nitrogen are done for certain crops but it is still in an experimental stage 
and not widely used or accepted in our region. Re searchers will collect soil 
samples at several depth intervals to monitor the nitrate movement during a 
crop's growing season.

Because of the mobility of nitrogen in the soil, most states in the Eastern 
region of the U.S. just make a blanket recommendation for each crop with the 
assumption that most of the residual nitrogen from the previous crop has 
moved past the root zone f or the new crop. You will notice that for many 
crops, nitrogen is recommended as a split application. If all of the nitrogen 
was added at the beginning of a growing season, much of it would move past 
the root zone before the crop matures. Splitting app lications allows the 
nitrogen to be applied more in accordance to the crop's needs at different 
stages of growth and thus reduce leaching.

---------------------------------------------------------------------
Pumpkin-growing FAQ: http://www.mallorn.com/lists/pumpkins/search.cgi
Other Mailing lists | Author Index | Date Index | Subject Index | Thread Index