How Much Fertilizer Can I Save Using Cover Crops?
Although I try not to pitch cover crops as some magic bullet for cost saving, my experience shows that the answer to the question — “Do cover crops pay?” — is a resounding yes.
Often, we tend to focus on the potential for increased cash crop yields, and that may indeed occur, but probably not every season. The answer to this question is complex. It depends a lot on the field’s cropping history, its existing soil health index, the crop rotation you’re using, and the level of biological diversity you’ve been able to achieve. I’ve done controlled testing on my own farm for decades and have been surprised by how big of a difference cover crops make in my soil nutrients.
In general, your soil will have leftover nutrients hanging out in the top 24 inches, such as nitrates, which are vulnerable to leaching through groundwater and runoff. However, cover crops can forage this nitrogen and turn it into biomass that can re-release more effectively later on when your next cash crop needs it. We can capture or save nitrogen if planting scavenging cover crops like radish, annual ryegrass, triticale or cereal rye.
Radishes release nitrogen very quickly in the spring, sometimes too quickly, so mixing a winter hardy nutrient scavenging species such as cereal rye is a prudent idea. Grass cover crops like cereal rye and triticale will give up their collected nitrogen but that timetable is greatly influenced by its maturity when terminated. The more mature, the longer it will take for those nutrients to be able to be utilized by a subsequent cash crop.
Other cover crops like hairy vetch and crimson clover legumes can add nitrogen that they collect out of the very air we breathe. Not only do they “fix” their own nitrogen needs, they will capture enough to give to a follow-up nitrogen loving cash crop. If you plant your last corn into a lush cover crop of hairy vetch, you can account for up to 100 pounds of nitrogen you won’t need to buy. Getting the right mix and sequence of crops ahead of your cash crop can put you ahead of the game with needed fertilizer, which can easily offset the cost of the cover crops. We live in a volatile world with influences in fertilizer prices well out of our range of control. Take for instance the coronavirus, which threatens to impact fertilizers that have their origin in China. If we have a sustained 25% increase of fertilizer prices there won’t be enough cover crops seeds in the world to meet the demand. Farmers are primed like never before to use cover crops.
The “Biology Effect”
This is the part where I can’t tell you I quite understand everything beneficial that goes on in the soil when you use cover crops — but I can tell you it works.
Soil seems to like when a lot of different plants are grown in it. This diversity leads to synergy and benefits that are hard to pin down, but also hard to argue with. One big example for me is a study on my own farm with no added nitrogen for four years. Cover crops alone accounted for a 25% yield boost.
In general, what I’ve found is that there is a point of diminishing return when it comes to chemical fertilizers — you may be using more than you need to in the first place without seeing additional yields.
Add cover crops, and this effect increases — cover crops help make fertilizer more efficient.
I encourage you to try it out, and see what difference cover crops can make on your fertilizer inputs. It takes some observation, careful management, a few test plots in your fields to determine the amount of savings you can benefit from on your farm.