Organic cropping systems that minimize tillage and incorporate cover crops (CC) exhibit considerable ecological complexity, resulting in potential agronomic benefits and challenges. Nitrogen (N) management is a critical challenge, as nitrate leaching is not only a source of pollution affecting waterways, air quality, and biodiversity, but also represents an economic loss for farmers. An ongoing systems experiment at Pennsylvania State University is evaluating alternative strategies for reducing tillage and incorporating CCs in an organic grain system. One strategy is interseeding a CC mixture of annual ryegrass (Lolium multiflorum), orchardgrass (Dactylis glomerata L.), and winter-kill forage radish (Raphanus sativus) into a standing corn grain (Zea mays L.) crop. This approach increases the ecological complexity of the system by using nutrient and light competition to reduce weeds and leaching losses. However, it is not yet clear how this strategy will impact N dynamics. To estimate variations in N among the systems, field measurements are used to determine N supply and retention from CCs and potential N losses to the environment through leaching. Our overall goal is to explore tradeoffs in N management between an interseeded, lower biomass, multi-species CC versus a later-established, higher biomass, monoculture CC.
Results/Conclusions
Surprisingly, data from the first year of this experiment indicate that systems using an interseeded CC in corn grain may have increased N leaching during the winter and spring compared with systems using a traditional cereal rye (Secale cereal) CC in corn silage (p < 0.001). While total N content of the CC biomass in the fall did not vary substantially between systems, forage radish contained the majority of aboveground plant biomass N in interseeded systems. This plant has potential to impact winter and spring soil N dynamics because its tissues decompose rapidly after it winter kills. Additionally, systems harvested for corn grain incorporate a greater amount of plant residue into the soil than corn silage, adding potential for even more N to be mineralized from this residue and leached. The ecological complexity combined with the lack of controlled comparisons in this systems experiment make the tradeoffs between CC strategies a challenge to interpret. Further targeted research is needed to parse out mechanisms of N retention and loss resulting from using interseeded CCs in order to fully understand the impact of this ecologically-based agronomic strategy on N management.