Student Research: Using a Phytometer to Assess Cover Crop Performance

Ghosts of cover crops past: quantifying the effects of cover crops on subsequent crop-weed-soil interactions

Elisabeth’s research aims to assess the effects of cover crops on agroecological processes such as weed suppression, nutrient capture, and yield response in future crops. Replicated plots of different cover crops, some common and some novel, were established at the UNH Woodman Farm last summer to evaluate these effects over the course of an entire year. These cover crops were plowed under in the spring and a uniform test crop, sorghum-sudangrass (“sudax”), was seeded over the experimental site.

This photo was taken with an unmanned aerial vehicle and shows
how the test crop responded to the previous cover crop treatments.  

The area in blue outlines the location of the previous year’s cover crop experiment. A checkerboard pattern is visible in the sudax where the different cover crop treatments were located. The area around the square was left fallow during the cover crop experiment by periodically cultivating. Notice the difference in color of the sudax growing outside of the experiment compared to where the cover crops were growing! Aerial photographs, such as this one, are proving to be great visual aids when sharing findings of our studies with growers.

We found that sudax yield was higher where legume cover crops and forage radish had been grown previously. In 2013, the study was repeated at an adjacent site.

Sudax inflorescence

Elisabeth’s favorite cover crop among those she evaluated is forage radish (Raphanus sativus var. longipinnatus, trade name “Tillage Radish”). This cover crop is an annual in our region and is very effective at competing with weeds when sown in late summer and early fall.  In our trials, forage radish suppressed weeds in the fall better than the other cover crops, and this effect carried over into the next season. Forage radish produces very long taproots that are effective at capturing nitrogen stored deep in the soil profile.  As these roots decompose in the spring, these nutrients are released for the next crop to use.

Forage radish up close

In the next few weeks we will measure yield and weed populations growing in our current test crop to verify trends we observed last year between cover crop treatments. Growers in New Hampshire have expressed interest in trying forage radish on their farms after hearing about our research – and we’ll have more to add to the discussion shortly.