Statewide
Across Texas crop consultants, producers, AgriLife staff, etc. are becoming more aware of the potential for accumulating nitrate-nitrogen (NO3-N) in the soil. This nitrogen has value for your sorghum and other crops. “Profile N” is nitrogen accumulating below standard soil sampling depths, most often 6”. This accumulation is due to over fertilization (or underutilization in years when production is sub-par) with N, and the majority of the time producers are not aware of the presence of this N in the soil. Historically this N is not accounted for in supplying crop nutrient requirements, but it should be.
The level of N accumulation can vary greatly due to fertilization practices, downward percolating moisture from rains which carries the soluble and mobile nitrate, soil type, etc. Sometimes substantial N is found even below 3’ in the soil, but only deep rooted crops can tap that N. Texas A&M AgriLife’s Soil, Water, and Forage Testing Lab offers a “Profile Soil Sample Information Form” (SP12) that pairs your standard 0-6” soil sample (analyzed for multiple nutrients including N, P, etc.; routine analysis, $10) with a second soil sample from 6” to as deep as 24”. This paired soil sample is analyzed for nitrate-N only, $4. The submitter marks the depth to a proper calculation of nutrient requirements can be made by the soil test lab.
Is profile nitrate-nitrogen down to 24” deep 100% available to grain sorghum?
Yes. Even slightly deeper N is largely available. The Profile Soil Sample form for N credits any 6-24” N to your crop requirement thus reducing fertilizer costs. Extension recommends that producers include at least some profile soil N sampling to establish whether there might be deeper N present.
The current Profile Soil Sample form is found at http://soiltesting.tamu.edu/files/profilesoil.pdf
