Field Day held at Central Maryland Research and Education Center Clarksville facility on November 14, 2013.

Soil auger in hand, Natalie Lounsbury regales the group of about 65 farmers and ag professionals before heading out to the cover crop plots. The soil auger was later used to obtain samples from as deep as 80 cm into the soil beneath ground with cover crop and with only fall weeds.

Ray Weil (in the soil pit) discusses the below ground story of the winter killed cover crops. The soil pit was dug so as to cut into stands of phacelia (on the left) forage radish in the middle and no-cover crop (weeds) on the right.

Half the participants examine plots of winter killed cover crops including spring oat, forage radish and phacelia (left front).

The business end of the compaction-fighting forage radish. While the fat fleshy root is impressive (even tasty!), it’s the long, thinner taproot that blazes permanent pathways through the plowpan into the subsoil. This taproot seen on November 14 was less than two months old. It resulted from seed that was sown September 01, but only emerged in mid-September after it received some moisture.

Using the soil they augered from under the cover crop plots, the participants then measured the concentration of nitrate nitrogen in each 20cm thick layer. Soil (12.5 grams or about 10 grams on a dry weight basis) was weighed on a small but precise battery powered balance and shaken with 20 mL of calcium chloride salt solution to extract the nitrate, and then filtered (row of beakers with filter paper cones).

Natalie helps two farmer participants to measure the nitrate concentration in the soil filtrate by placing a few drops on the ion-selective sensor in the small green and white Horiba nitrate meter. The results (see table) were quite amazing (average of two replicate auger samplings), even considering that these field had a long history of manure and compost application. In the soil (0-80 cm) under the weeds-only plots (no cover crop) the nitrate-N values added up to 384 kg N /ha (350 pounds nitrate-N/acre). Under the plots with forage radish cover crop the nitrate-N values added up to 27 kg N /ha (25 pounds nitrate-N/acre).

Trt / Depth (cm) / mgN/kg / kg N/ha
Forage Radish / 0-20 / 6.7 / 16
Forage Radish / 20-40 / 3.3 / 9
Forage Radish / 40-60 / 0.3 / 0.9
Forage Radish / 60-80 / 0.3 / 0.9
Total 0-80cm / 26.8
No Cover (weeds) / 0-20 / 33.3 / 80
No Cover (weeds) / 20-40 / 40.0 / 108
No Cover (weeds) / 40-60 / 38.7 / 104.4
No Cover (weeds) / 60-80 / 34.0 / 91.8
Total 0-80cm / 384.2

Zone planting of cover crops with spring oat growing in what will the tire tracks next spring and forage radish growing in what will be the planting beds. The idea is to produce a mulch in the tire tracks and a warm, drier, friable soil in the seedbed suitable for notill planting.

Ray Weil discusses the cover crop root growth exposed in a soil pit. The depth of penetration by the long, thin taproot did not appear related to the diameter of the fleshy part of the root.This cover crop contained well over 200 lbs N/acre in the plant tissue….nitrogen that had been brought up from deep in the soil profile and that will be deposited on and near the soil surface when the plant winterkill. Most of this captured N (along with substantial amounts of S, P, Ca, K and B) should be available to vegetable crops planted early in spring, rather than be on its way to the Bay.