Soil testing can provide us with helpful indications of the nutrient status of fields, but most soil samples consist of just the topsoil. What’s happening below the topsoil can be critical to both successful farming and environmental stewardship. Many cash crops are inefficient at using all the fertilizer applied, regardless of the form (compost, urea, etc.). Much of what is applied may leach below the rooting zone of most cash crops.
The right cover crops can capture nutrients that have escaped the roots of your cash crops, keeping nutrients on the farm and out of waterways.
We had a field day in Clarksville, Maryland on November 14 at which participants augered down to 80 cm (~2.5 ft) in plots without a cover crop (some weeds were present) and with a radish cover crop. They then measured nitrate-N in the soil layers using a portable meter.
The results were mind-blowing! To verify that these results weren’t anomalous, I made another trip out, augered down to 125 cm (~4 ft) and measured the nitrate-N in the lab. The results from Clarksville as well as other sites in Maryland and a farm field in Maine are presented below. Click on the images for more information.
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- After augering down to 80 cm, we measured nitrate-N in the soil using a portable meter.
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- Over 165 kg per hectare (150 lb per acre) nitrate-N in this silt loam soil had leached down to below 50 cm where there was no cover crop…
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- In a sandy soil in Maine that had no recent history of compost or manure, there was approximately 40 kg per hectare (36 lb per acre) of nitrate-N that had leached below 50 cm where there was no cover crop…
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- Forage radish nutrient capture
Of course, the next logical question is: when does all that N that radish (or other cover crops) captures become available to the following crop? That will be another post.
