Nutrient management in reduced tillage systems

When tillage is reduced or eliminated, we are able to keep more nutrients in the soil.

Why is nutrient management important?

Reduced-till, no-till, and cover crops are three practices that can help you retain the nutrients in your soil. A question that I'm commonly asked in relation to these practices is, "How many pounds can I reduce my fertilizer when moving to a no-till and cover crop system?". The typical answer to this is, "it depends". With the profit margin continually being challenged on farm, we need to better understand the value of a cover crop and reduced/no-till system. We've put together an article highlighting the changes that come with implementing new soil health practices that can help you in your decision-making process. 

When we reduce or eliminate tillage, we are reducing erosion and keeping our nutrients in the field. Reducing tillage minimizes disturbance to our soil properties and the soil ecosystem. When the soil biome is not disturbed, it allows the microbial populations to build. As the soil mellows out and the biome repairs and repopulates, we'll see nutrient cycling improve.

How does organic matter impact soil health?

Soil bacteria and fungi play a big role in processing organic matter into inorganic nutrients that are readily available for plant roots. Longer-term reduced and no-till fields can see an increase in organic matter. We know that the percent of organic matter (OM) can influence the amount of nitrogen, phosphorus, and sulfur that is mineralized through the growing season. It can also influence the amount of fertilizer that you apply. The actual amount of N, P, and S is dependent on soil types and organic matter. Most agronomists reduce nitrogen by 10-30 pounds per acre for every percent of OM, depending on soil type. The NRCS and universities suggest we can expect 10-20 pounds of N, 1-2 pounds of P, and 0.5-1 pounds of S for every percent of OM per year. Reducing tillage can save thousands of dollars in fuel and add to a farm's ROI by reducing fertilizer needs.

How do cover crops influence your soil fertility?

Adding cover crops to your rotation will greatly influence your soil fertility. In general, putting cover crops to work has a whole host of great benefits including reducing erosion and increasing moisture infiltration. Some legume covers can fix nitrogen for the upcoming or current cash crop. Cover crops can also increase nutrient cycling and prevent nitrates and phosphates from leaving the field due to leaching and runoff.

Nutrient cycling is dependent on organic matter and microbial health. In order to build organic matter, you need to add biomass in the form of cover crops. With the addition of cover crops, you will not only be adding additional residue, but you will also be providing more carbon for the soil ecosystem to feed on. More carbon will increase microbial populations and diversity which, in turn, will increase mineralization (or nutrient cycling).

Cover crops can play an important role in recovering nitrates and holding phosphates that would otherwise leave the field. These nutrients can be pulled from deeper in the soil profile and brought back to the top. The cover crops provide live root systems that scavenge those nitrates and prevent leaching or denitrification. These live roots reduce erosion and keep phosphate from eroding off fields with the soil.

Another way cover crops can influence your soil's fertility is by using nitrogen-fixing legume covers. Alfalfa, clovers, field peas, and vetch are a few examples of covers that fix nitrogen for the upcoming current cash crop. Because there are so many good options, choosing cover crops should not be a quick decision. It is important to strategize in order to get the most bang for your buck. In general, cover crops can influence your ROI by providing consistent and additional amounts of nutrients throughout a cash crop season and adding protection from nutrient loss in the off-season.

Implementing nutrient management in reduced tillage systems

Does fertilizer application change when fields are transitioned to no-till or reduced-till? In a no-till field, broadcast applications that have been around for years, such as phosphate and potassium, are still adequate, especially in well-drained soils. The phosphorous and potassium will still be able to move down through the surface profile. The University of Missouri has a good article that discusses reduced-till and no-till field fertilizer management.

Other options for nutrient management include strip-till, but this isn't always necessary. Strip-till would be a better option for fertilizer applications in more poorly drained soils, compacted soils, or colder northern soils. Strip-till places the fertilizer band at a set depth and, more importantly, creates a loose root zone that allows for the strip to dry out and warm more effectively in the spring. Many planters with row cleaners do a good job of moving residue. This allows soils to continue to warm for good germination.

When it comes to nitrogen, you will want to pay attention to residue. It is important to keep the carbon-nitrogen ratio in balance as it takes nitrogen to break down carbon residue. Keeping that in mind, it is important to determine what application is going to have the least risk of N volatilization or leaching. Studies have shown that surface applied N is not as efficient, or effective, as placing nitrogen strategically below the surface on no-till fields. Universities and agronomists alike suggest using N in a starter fertilizer on no-till soils. This is necessary when planting corn into a field with heavy residue. Along with a 2x2 application at plant, a side-dress option works well in a no-till system. A side-dress application is going to reduce nitrogen loss. When determining fertility application methods, it is important to refer back to the 4R practices. There is no wrong application method if you follow the right source, the right rate, the right time, and the right place.

Soil testing regularly is going to allow you a baseline to make fertility decisions and monitor your soil's productivity. Do you soil test regularly to make sure you are making the most efficient and profitable fertilizer plan? Knowing your soil's nutrient levels allows you to use your organic matter to its full potential.