In part 3 I reviewed the concept of using marginal nitrogen use efficiency and zero N check strips as tools to evaluate application rates. Now I will shift the focus to problems with overapplication, how to determine the right timing for application, and the consequences of not doing so.
The fastest way to diminish the soils’ ability to supply nitrogen naturally is to apply high doses of readily available nitrogen. This shuts down the activity of rhizobia and free-living organisms in the soil that can do the job for free. Overapplying readily available N can also interfere with the uptake of other nutrients and lead to yield drag and profit loss, just as underapplying can. Excess nitrate (an anion) in soil water can interfere with the uptake of other anions like phosphate and sulfate. The plant needs to maintain electrochemical balance, and it needs water. High nitrate concentrations in soil water can cause plant stress because the plant has a difficult time avoiding the excess.
Nitrate can also wreak havoc inside the plant if it does not have the other minerals or energy it needs to convert it to amino acids. Excess nitrate inside the plant is like a flashing neon sign for insects, saying “I’m sick, come and eat me.” This sets up a situation where a pesticide treatment may be needed, which knocks out beneficial biology that could keep pathogens in check, which leads to a downward spiral of degradation. Apply a pesticide -> kill beneficial biology -> weaken the plant’s immune system -> sick plant -> pathogen attack -> apply more pesticide. Improving nitrogen management would reduce our reliance on pesticides, and the entire system would function better. The same is true for other nutrients. Nutrient excesses can cause as many or more plant health issues as nutrient deficiencies.
We should feed the soil more like we feed ourselves and our livestock. The soil cannot properly digest months’ or years' worth of nutrients applied all at once. Adding large amounts of readily available nutrients creates imbalances, nutrient antagonisms, and leads to nutrient loss. High-salt fertilizers add insult to injury by inhibiting soil biology and creating osmotic stress in plants. There is no right time to apply too much of any nutrient.
The “right timing” paradox
Determining the ‘right timing’ of nitrogen application can be tricky. What we can say for sure is that it is most definitely not 6-9 months before the plant needs it. Fall application of nutrients for a cash crop the following year makes no sense from a plant nutrition standpoint. Corn, for example, typically uses very little nitrogen in the first month of growth. Most N demand is in midsummer. Applying it the previous fall is a recipe for guaranteed N loss, especially if the soil is bare. Most N should be put in small amounts as a sidedress or foliar spray, unless you are planting into a high C:N ratio soil or cover crop that will require a lot of N for residue decomposition.
Fall tillage and fertility applications are common because some say, “There’s not enough time to do it in the spring.” Fall cover crop establishment is uncommon because (you guessed it) “There’s not enough time to do it in the fall.” This is backwards.
Establishing a cover crop is priority one in the fall. Use living roots for bio-tillage and soil stabilization and put down nutrients at planting and in-season when plants need them. Living ground cover is especially critical on acres receiving manure from confinement operations. This is hands-down the best, most profitable use case for cover crops. This is low hanging fruit and most of it is not being picked. Industry groups should make it clear to members that cover crops and more in-season application must become part of all manure management plans and programs. Actions like this would go a long way toward addressing soil and water degradation and rebuilding public trust in agriculture.
Our current track record on voluntary conservation is dismal and we have toxic algae blooms, beach closures, and dead zones to show for it. Regulations will come if we do not take this seriously. Commodity organizations, food companies, and consumers need to demand the 6P and provide the resources to help farmers with the transition. The agricultural community needs to agree to move in unison away from practices that are clearly degrading soil and water quality.
Critics of this approach will likely argue that it would require too much labor and take too many acres to grow cover crop seed. These are features, not bugs. A more regenerative approach would create a market for desperately needed alternative crops and reduce our reliance on low-value commodity crops for revenue, not to mention all of the benefits to ecosystem health. It would open up opportunities to grow diverse, N-fixing summer cover crop mixes that could be grazed by livestock. It also creates an entirely new industry built around regenerating the soil that would provide good jobs in rural areas and opportunities for young people to get involved in agriculture.
It's also said that high-input high-yield agriculture is the only way we can ‘feed the world’. This is nonsense. Diverse, regeneratively managed farms and ranches often outproduce their conventional counterparts on a total calories per acre basis, and that food is typically higher in nutritional quality. We most certainly will not continue feeding the world with our current input-and-energy-intensive system that allows our soil to erode away to grow low value commodities that are only profitable with government support. We don’t need more bushels. We’ve been chasing that rabbit for decades and it has hollowed out the heart of rural America. We need a system that rewards the farmer, regenerates soil, revitalizes rural communities, produces healthy food, and addresses the underlying cause of soil and water quality degradation. We need to drill baby drill – with cover crops.
In the fifth and final post in this series, I’ll explain how the “right source” of fertility is probably not what you think it is, and why the old model of plant nutrient acquisition is dead and should be buried.