Deep-rooted cover crops can mop up nutrients that cash crops didn’t use.
Certain nutrients, such as N and S, are common in forms that are especially prone to leaching. For N, this poses a substantial environmental threat when it reaches waterways, and losing N represents an economic loss for farms.
Because the Weil lab at the University of Maryland has worked on Brassica cover crops for over a decade, we may be a little Brassica-biased. Indeed, Brassicas are especially good at scavenging nutrients, but they are not the only cover crops that can serve this function.
In all honesty, very few researchers have looked at nutrient scavenging below 1 meter, but it in many soils and for many cover crops, 1 m may not be deep enough to determine nutrient leaching and “catch” crop potential!
Dean, J.E., and R.R. Weil. 2009. Brassica cover crops for N retention in the Mid-Atlantic coastal plain. J Environ Qual 38:520-528.
Utilising Differences in Rooting Depth to Design Vegetable Crop Rotations with High Nitrogen Use Efficiency (NUE) by Kristian Thorup-Kristensen