Fall manure applications are common in the dairy industry – and for good reason. Fall weather is reasonably dry, so the fields can typically handle the traffic. Labor is available for field work since you don’t have to worry about new seedings or harvesting some forage at the perfect time. And then there’s the fact that most of us have to drop the level of the pit before winter or else a messy winter becomes a whole new level of messy.
At the same time, fall is also kind of a bad time to be applying manure since you are giving the field a large dose of nutrients right before it sits fallow, exposed to the elements for several months. I don’t care where you live or how little precipitation you get over the winter, some of those nutrients are going to escape during the off-season. This is especially the case for nitrogen – which is why current Cornell recommendations consider inorganic N from fall manure to be essentially gone by springtime.
So, what’s the solution? Well, there isn’t one – at least not a perfect one. Rapid incorporation helps to prevent volatilization and surface runoff, but that still leaves a high concentration of nutrients somewhere in the upper soil profile. But what if there was a crop there to take up some of those nutrients and incorporate them into plant biomass that could last the winter? That’s exactly what researchers from the Northwest Crops and Soils program have been researching for the last several years in Alburgh, VT.
The study looked at silage corn plots with and without a rye cover crop receiving 6,000 gal/acre of manure in either the spring or the fall (pre-plant incorporated). This was done under both tilled and no-till conditions. The most recent data from the 2023 growing season showed a huge yield advantage (more than seven tons per acre at 35% dry matter) for no-till plots that had a cover crop as compared to no-till plots with fall manure alone. While no difference was detected in plots where tillage was used, there was significantly greater soil respiration measured in the fall manure plots where the rye cover crop was present. This suggests that perhaps the large amount of cover crop biomass may have caused some nutrient tie-up which hurt the corn as it initially degraded.
A word of caution here: While cover crops do typically increase corn yields, they can cause some problems if managed poorly. When incorporating large quantities of biomass before corn planting, you may need to increase the starter fertilizer rate to help the crop survive early season nutrient tie-up. However, these fields will probably require a little less late-season nitrogen, since all those stored nutrients will at some point finally become available. I would also suggest boosting the starter fertilizer rate in no-till plantings with cover crops. It does appear that the nutrient tie-up isn’t quite so bad under no-till, so this may be the winning strategy for high residue situations.
The more data I see on cover crops, the more I realize that they are a big win for the dairy industry. Whether it’s emergency forage, reducing environmental impacts, capitalizing on carbon credits, or boosting continuous corn yields, if managed properly cover crops can do it all.
— Allen Wilder