Interseeded cover crops: Evaluating nitrogen retention services provided by plant-microbe relationships

View the project final report

• 2016 annual report

Commodities

• Agronomic: corn

Practices

• Crop Production: cover crops, intercropping, nutrient cycling, organic fertilizers
• Soil Management: nutrient mineralization, soil analysis, soil microbiology

Nitrate leaching from agricultural land is not only a source of pollution affecting waterways, air quality, and biodiversity, but also represents an economic loss for farmers. Cover crops (CC) can be used to reduce nitrate leaching, however establishing a CC after a corn grain harvest can be difficult in the Northeast. One solution to this constraint is to establish a CC by interseeding into a standing corn crop. While interest in CC interseeding is growing rapidly, there is very little scientific information to document the magnitude or mechanisms of change in the nitrogen (N) cycle from this practice. The goals of this project are to experimentally test CC interseeding as a strategy to reduce N leaching in organic corn production, and to develop and deliver outreach to regional farmers regarding potential benefits and costs associated with interseeding. In a factorial field experiment, three CC treatments and three rates of fertilizer application will be examined in an organic corn grain system. CC treatments will include an interseeded ryegrass monoculture CC, and interseeded ryegrass-clover CC mixture, and a traditional cereal rye monoculture CC planted after corn grain harvest. We will quantify differences in CC- N uptake, microbial community composition, and microbial N dynamics among treatments. Additionally, we will estimate effects of CC – microbial linkages on nitrate leaching and N availability to subsequent cash crop. Results will be incorporated into outreach delivered via field days, hands-on workshops and presentations, and written materials geared towards farmers, extension personnel and agriculture professionals.  

Objective 1. Quantify differences in CC N uptake among an interseeded ryegrass monoculture (INT-Rye), interseeded ryegrass-clover mixture (INT-Mix), and a traditional cereal rye monoculture CC planted after corn grain harvest (POST).

Expected outcomes: In the fall, soil N taken up by interseeded CCs will be greater than the traditional postharvest CC because of the lengthened CC window. Soil N uptake by interseeded CCs during this critical window will increase with increasing N application rates and will be greater in INT-Rye than INT-Mix. By spring, soil N in the CC biomass will be greatest in POST, followed by INT-Rye, and then INT-Mix. However, INT-Mix will contain the most total N (atmospheric plus soil) in CC biomass.

Objective 2: Quantify potential of microbiota in interseeded systems as a N sink.

Expected outcome: In the fall, interseeding CCs will increased soil microbial biomass, relative to plots without interseeded CC, resulting in an increased microbial N sink. By spring, microbial biomass N will be similar between post-harvest and interseeded CCs.

Objective 3: Estimate effects of CC – microbial linkages on nitrate leaching.

Expected outcomes: At low N addition rates, nitrate leaching will be low and will not differ among CC strategies. At high N addition rates, nitrate leaching will be lowest in INT-Rye , intermediate in INT-Mix, and highest in POST.

Objective 4: Estimate effects of cover crop – microbial linkages on N availability to subsequent cash crop.

Expected outcomes: INT-Mix will provide the most N to the subsequent cash crop due to high N retention in plant and microbial pools that mineralize rapidly in spring after CC termination.

Objective 5: Estimate differences in soil microbial communities between interseeded and non-interseeded corn at different soil N levels.

Expected outcomes: Interseeded treatments will promote more fungal growth, shifting the ratio of bacteria to fungi in the soil. However, increased levels of soil available N may promote bacterial growth in plots fertilized with high levels of manure. We expect to see shifts in soil microbial communities among treatments that represent these patterns.

Objective 6: Make recommendations to organic grain farmers, extension agents, other researchers, and agriculture professionals in the Northeast about the potential benefits and costs associated with interseeding CCs in regards to N retention services.

Expected outcomes: Farmers, extension agents, and agriculture professionals will value information on N retention in interseeded CCs. Outreach will increase their perceived knowledge in this area and their comfort with managing N in interseeded CCs.