Snow is in the forecast for tomorrow in Maryland, and fields are neither drying out nor warming up quickly. Unlike a living cover or mulch that prevent the soil from drying in spring, low-residue winterkilled cover crops can facilitate faster soil warming and drying. “Low-residue winterkilled” is moderately descriptive, but a photo may do more to illustrate the concept.
It is easy to pick out the “no cover crop/weed” plots in spring. The living cover (weeds in this case, but a living cover crop would function the same) keeps the soil from drying in spring.
Note the difference in the amount of bare soil visible (below). Like the living weeds, a thick mulch covering the soil also prevents rapid drying. Soil conservationists don’t usually recommend leaving soil bare, but the conditions in spring create a quandary- the surface soil needs to dry out for tractor work. Otherwise, traffic and tillage can cause serious structural damage to soil. Besides, what if a low-residue winterkilled cover crop enables no-till planting, thereby reducing soil disturbance?
Forage radish leaves the least residue in spring, followed by phacelia. Oat (in this case in a mixture with phacelia) leaves a lot of residue in spring. Photo taken March 20, 2014.
Radish compared to winter weeds: surface and subsoil moisture
Hot off the dataloggers, data from this year show that surface soil moisture is reduced and subsoil moisture is increased after forage radish compared to winter weeds. Reduced surface soil moisture means that field operations can be carried out without as much structural damage to soil, and increased subsoil moisture means that later season crops may have more of a water reserve.
Soil moisture was monitored using Decagon capacitance sensors. Approximate winterkill date of radish is marked with line. (Data presented are average of three blocks).
Because the increased subsoil moisture is likely from water flowing down radish root channels, there is some concern over leaching losses. Planting an early season crop after forage radish is imperative to reduce N losses. Alternating shallow-rooted and deep rooted crops in a rotation may also help to minimize total N losses.
For more on cover crop effects on soil moisture, see our soil moisture page. Cover crop effects on soil temperature are discussed on the soil temperature page.
