Every grower is trying to reach maximum corn yields and discover the total rate of nitrogen needed to help them reach their goal. In general, we figure of around 1lb of N per yield goal bushel is needed for corn. During a time of lower grain prices, the efficient use of inputs is more important than ever before. Can the particular timing and split application of nitrogen help us improve our water quality as well as our rate of return on our investment? These questions have led to both agricultural and regulatory interest in measuring nitrate (NO3-N) concentrations over time from the subsurface water being released from farms.
The amount of (NO3-N) that is leached through the soil and lost through the tile outlet's drainflow will depend on many factors such as crop and fertility management. However, the concentration of (NO3-N) will also depend on the time of year, our soil, and our ol’ friend Mother Nature (temperature and rainfall), which is totally out of our control. Most might automatically assume that most of the (NO3-N) is lost from corn acres; but in actuality, (NO3-N) concentration levels have been known to be higher from soybean acres because they have a lower carbon-to-nitrogen ratio (25:1) than corn (70:1), so nitrogen is recycled faster. This leads to the controversial issue of adding nitrogen to soybeans, a crop that can supply its own nitrogen. However, after years of drought, the unused N by corn, can also be released at higher levels.
Keep in mind, some of the most productive ground is considered “naturally poorly drained soils”, therefore; some loss of (NO3-N) is bound to occur. (NO3-N) is mobile, so it is carried by water from the root zone to adjacent surface water tile lines, where it can be lost. Typically, tile lines flow from November to June, but some research has shown that flow peaks within April to June. In order to engage farmers in the nutrient and water quality issues currently facing agriculture, the Illinois Nutrient Loss Reduction Strategy was developed by the IEPA, IDoA, C-BMP (Illinois Council on Best Management Practices), and others to help provide information on just how much (NO3-N) is being lost from their farming operation.
This program offers free, confidential water testing at many locations, such as Soil and Water Conservation Districts/USDA-Natural Resource Conservation Service offices in Illinois. Click here for dates. The (NO3) results, measured in ppm, from tile, surface runoff, nearby stream, or wetland samples are just a snapshot in time. If you continue to test multiple samples, from various locations, throughout several weeks, this might help you to get a clearer picture of nutrient loss from your farm. Remember, (NO3-N) concentration is only one part of the equation. The tile flow is just as important and can be calculated the day of your test. Timing how fast your bucket fills will get you an estimate of load (lbs. of N/day) and with drainage area, it is important to estimate the yield (lbs. of N per acre/day). Low (NO3-N) concentration with high flow can add up faster than high (NO3-N) concentration with low flow.
I took my 8 oz., water sample from a tile line on our family farm this week, and then kept it cool until I was able to get it tested at my local SWCD/USDA -NRCS by Sue Davis and Tony Hammond in Christian County, Illinois. My Dad was happy to hear that our results were 11.2ppm, which is within the normal range for “for row crop with N applied for optimum N rate or for soybeans.” In the last several years, my Dad and brother have started to make more timely and split applications of N, but could get their nitrate concentrations even lower by implementing cover crops within their farming operation.
|Sue Davis, Christian County Soil and Water Conservation District, testing a water sample for (NO3-N) concentration in ppm|
Over 20ppm indicates unusual circumstances or a potential to modify practices to reduce losses. For more information see Purdue’s Interpreting Nitrate Concentration in Tile Drainage Water.
Special thanks to Sue Davis, Christian County SWCD, Tony Hammond, USDA-NRCS, and Kris Reynolds, Montgomery County SWCD and Illinois Council on Best Management Practices, Cover Crops.