We’re adding more drainage tile this year to a field with some serious wet spots. I know every time I mention tile drainage there will be criticism due to the linkage between nitrate runoff and tile effluent. I have tried to keep up with research on whether tile is a big contributor or not, but the efforts to monitor this problem have not received much attention, and each report I read seems to be less than relevant to our farm. Or so my brain desperately wants me to think.
Tile systems like this one have made enormous positive differences in our yields, soil tilth, timeliness, compaction, and even fertilizer use, so I am very aware of the bias my mind has on information that seems implicate tile as a serious problem for nitrate pollution. Oddly, most agree tile reduces phosphate pollution by making soils more absorbent and thus reducing surface runoff. Phosphorus is lost when soil is lost. This matches with our observed results as well – we simply have fewer washes and gullies even with increased rainfall.
My idea is this problem needs some empirical data specific to our farm. To that end I have invested in my own water nitrate test kit. My plan is to regularly sample tile outlets over the next few years and see what I get. I’ll probably add extra samples after nitrogen applications, heavy rains, and other unusual conditions to see if I can spot a trend. I am aware this is pretty crude data, although the accuracy is supposedly enough to spot nitrate levels that make my farm part of the problem. And even if the absolute numbers have a wide error band, maybe we can spot seasonal and long-term trends.
We have had our wells tested on several occasions, and they vary from 24 to 65 feet deep. None have even shown a nitrate level above 4 ppm. The EPA limit is 10 ppm. I was confident our 24” of topsoil, and heavy clay below that would prevent most nitrogen leaching. However, my new nitrate photometer and carefully followed instructions changed this happy narrative. My initial reading was 9.6 mg/L, which is the same as ppm. Just below the safety limit for drinking.
Stay tuned. To quote the ancient cartoon strip character Pogo misquoting Oliver Hazard Perry, “We have met the enemy and he is us”. I’ll try to post updated graphs and sample information, but this issue suddenly became a little more real for me.
