Water quality troubles in the Chesapeake Bay are related to both nitrogen and phosphorus, but much less is known about the impacts of cover crops on phosphorus losses than on nitrogen losses. The main pathway for phosphorus transport from croplands to bodies of water is via surface runoff during intense rain storms or heavy snow melt. The goal of the proposed research is to provide data on how a range of cover crop practices impact the loss of phosphorus by surface runoff. We will investigate several mechanisms by which cover crops can affect the loss of phosphorus. We hypothesize that cover crops may 1) Reduce the volume of runoff water from a storm. 2) Increase the amount of rain required to start runoff from fields. 3) Reduce the concentration of P-carrying sediment in runoff water or 4) Increase the concentration P dissolved in runoff water. Phosphorus reduction might occur by uptake by the plants and phosphorus increase might occur by freezing injury that releases soluble phosphorus from cover crop tissues as well as nutrient pumping that results in stratification with greater P concentration near the soil surface. Research has already been published that compares the solubility of phosphorus in live and dead tissues from a wide range of cover crop species. What is lacking, and our research will provide, is data that shows the actual runoff volume and P concentration from single species or multi-species cover crops grow in no-till soils typical of Maryland soybean production. We will generate this data from research plots and farm fields using simulated and natural rain events during the cover crop season. We will also continue work already in progress by analyzing the various forms of phosphorus in the runoff and soil samples collected from cover crop plots in winter and early spring of 2021. Soybean yields and tissue P levels will also be measured following the cover crop treatments.

Determine effect of individual species and mixed cover crop on:
a. Runoff volume generated as percent of rainfall.
b. Time and rain volume required to cause runoff to begin.
c. Concentration of total and dissolved phosphorus in runoff water.
d. Total P load lost to runoff during a single storm and all storm in a whole season.

2. Determine effect of early interseeding establishment of multispecies cover crop on runoff volume and P content, as compared to cover crop drilled after crop harvest and no cover crop.

3. Compare effect of multispecies cover crop on runoff at different times of year:
a. Fall
b. Winter
c. Spring
d. Early summer

Update:
Phosphorus runoff from no-till soils – do cover crops make it better or worse?
August 2021 Progress Report to the Maryland Soybean Board

Being a cover crop-focused project, most of the activities will take place in fall, winter, and early spring when cover crops are likely to have the main effects on runoff from agricultural fields. The first months of this year's project were spent analyzing samples collected during the winter and spring of 2021 before the planting of soybeans and corn. Those samples have been analyzed and the results indicate that nitrogen losses in runoff are greater from fields covered with soybean residue than with corn residue but the phosphorus losses were approximately the same for both types of crop residues on average. However, in plots where a rye cover crop was grown phosphorus concentrations in the runoff were significantly lower in corn residue plots than in soybean residue plots. This result was supported by analysis of the surface 1-inch of soil in the plots in soybean residue which had higher levels of both nitrate and phosphate in soluble forms as compared to those in runoff from plots with corn residue.

For the coming season, we have established corn and soybean plots on both Sandy and silty soils. We are preparing to establish cover crops early into these crop plots by over-seeding in late August and early September. Where the slope is about 5%, we will measure runoff.

In June and July 2021, the national United Soybean Board conducted a feature interview with the project PI, Dr. Weil, which will be published on the USB website under the title “Do Cover Crops Make Phosphorus Runoff Better or Worse?” by Laura Temple.

Update:

View uploaded report

Update:
At the time of this reporting, we are reaching the end of the field runoff season which we can monitor with our mini erosion weirs. In the Fall of 2021 and winter of 2022, we deployed 24 of the erosion wears to collect runoff and sediment from plots with no cover crop, a ride cover crop, or a three-way cover crop mixture of radish - crimson clover - rye. The latter treatment is now primarily crimson clover with some rye mixed in as temperatures were cold enough this winter to completely kill the radish. Since the radish cycles more phosphorus than the other two species, this will give us a good opportunity to look for a flush of phosphorus expected after the radish winter kills. We have collected runoff from 17 rain events and anticipate being able to do possibly one more event before having to remove the runoff weirs from the field to allow planting the corn and soybeans in the plots. We have determined the sediment load by filtering the runoff through a 0.45-micron filter. The filtered samples are currently being analyzed in our lab for their nitrogen and phosphorus concentrations. This work will continue for several months before we can summarize the data.

While cover crops can provide many benefits to the farmer, the Maryland cover crop program is primarily focused on the reduction of nitrogen loading to the Chesapeake Bay. The main pathway for nitrogen losses from farm fields is via groundwater contaminated soluble nitrogen by leaching. Research, including our work sponsored by the Maryland Soybean Board, have clearly shown that cover crops can be very effective in reducing such nitrogen leaching and that their effectiveness is dependent on early cover crop establishment in fall.

Water quality troubles in the Chesapeake Bay are related to both nitrogen and phosphorus, but much less is known about the impacts of cover crops on phosphorus losses than on nitrogen losses. The main pathway for phosphorus transport from croplands to bodies of water is via surface runoff during intense rain storms or heavy snow melt. A secondary pathway in areas of poorly drained sandy soils is leaching of phosphorus to drainage ditches. There is little research on how cover crops impact phosphorus losses. Some studies that suggests that cover crops might increase soluble phosphorus at the soil surface where it would be susceptible to becoming dissolved in runoff water. In fact, cover crops can be an important tool for increasing P availability and crop yields in the phosphorus deficient soils found in many parts of the world where there has been little application of P (Hallama et al., 2019). Cover crop mechanisms that cycle P and make soil P more soluble and plant–available may also allow high productivity on Maryland farms with lower levels P fertilization. This could be part of a long term strategy to make farming more sustainable both economically and environmentally. The goal of the proposed research is to provide data on how a range of cover crop practices impact the loss of phosphorus by surface runoff. Cover crops can affect the loss of phosphorus by several, somewhat contradictory, mechanisms. Cover crops might:
1. Reduce the volume of runoff water from a storm.
2. Increase the amount of rain required to start runoff from fields.
3. Reduce the concentration of P-carrying sediment in runoff water.
4. Increase the concentration P dissolved in runoff water.
5. Reduce phosphorus in surface soil because of plant P uptake.
6. Increase P concentration by freezing injury that releases soluble phosphorus from cover crop
tissues.