One of the frequently heard phrases over the last 15 years relating to the management of agricultural soil fertility is “the 4 R’s”. Growers hear “remember the 4R’s” when planning their soil fertility program. So, what are the 4R’s? While “R and R” may stick in our mind as representing rest and relaxation, we have to start from scratch to build the 4R’s of soil fertility.

They are Right Product, Right Rate, Right Time, and Right Place. The 4R’s of nutrient stewardship were originally intended as a response to environmental concerns and the perception that production agriculture was a significant contributor to the contamination of streams, rivers, and soils through the overuse of commercial fertilizers. This was thought to result in runoff and/or contamination of groundwater supplies by leaching though the soil profile. One of the most frequently cited issues was the phenomenon known as the Dead Zone in the Gulf of America where the Mississippi River enters the ocean. Quite a bit of the blame assigned to agriculture for these environmental issues was exaggerated and, in some cases, simply found to be inaccurate. Nevertheless, the 4R approach took hold because it is based on common sense. Today, with significantly higher fertilizer prices, the 4R’s are viewed as a tool to increase production efficiency on the farm by focusing on the agronomic justification for each aspect of a fertility budget.

Halderman farm managers work with their farm tenants to 1) be as environmentally sensitive and sustainable as possible and 2) to maximize the production of the farm as efficiently as we can. Anytime we can reduce run-off, reduce leaching and increase yields through better application techniques that is a win-win-win for the landowner, farmer and environment.

So again, what are the 4R’s?

Right Product. This simply means a product that will increase soil fertility with respect to crop yield through its use. This may be through increasing yield in the upcoming or current crop, or possibly by building a soil nutrient that is below the desired level required to support maximum crop yields. Some fertility experts would expand Right product into Right Product and Right Form. Since the form of nutrients may impact how it reacts in the soil and with the crop in a particular stage of growth but that’s getting a little deeper than we want to in this post.

Right Amount. The right amount is focused on avoiding over-application of nutrients that may then be vulnerable to runoff, leaching, or other environmental losses. Historically, some fertilizers were fairly inexpensive relative to the ‘cost’ in lost yield that results from not having enough available for the crop to access. The uncertainties inherent in predicting how big a crop will be grown in the coming year can lead farmers to over-apply since the extra cost is small compared to the potential cost of lost yield if the season allows top yields. Another aspect of the right amount determination is that it can be significantly affected by the other two R’s discussed below, timing and placement. For example, if the right product is placed closer to plant roots and is placed there just before the time in the plant’s growth cycle that it will use it, then it will be used much more efficiently. There will be less of the product that isn’t able to be accessed by the plant roots and less that may be lost in the time interval between application and plant uptake.

Right Time. Not too long ago the right time was primarily determined by logistical concerns. This meant fertilizer was most often applied between the harvest of one crop and the planting of the next. Often this was soon after harvest when the weather still allowed field work and soils were often dry, and therefore unlikely to suffer the negative effects of compaction. However, the meaning of the Right Time directive is really about applying as close to possible to the time when the crop will use the nutrient applied. As noted above, this is to minimize expected losses and reduce the amount of the nutrient that needs to be applied for the desired effect.

One example would be applying phosphorus fertilizer with the planter. Corn is most susceptible to a lack of adequate phosphorus for maximum yield between emergence and V3 (V3 might occur 2-3 weeks after planting depending on conditions). This avoids the very common issue of a high percentage of dry phosphorus that is applied immediately after harvest in the fall chemically binding with other soil components like Calcium, that will make it unavailable to plants the next spring. Another example would be nitrogen, which can also be applied with the planter. It begins to be needed by the corn plant at approximately V6. A planter application avoids the losses that can be associated with fall or winter applications through leaching or denitrification in wet springs.

Right Place. The right place used to mean which field to pull into with the fertilizer spreader. However, modern equipment and technology give us the ability to go a lot farther in pursuit of efficiency through placement. The first level of precision placement is fertilizer application based on specific areas, usually of 3-5 acres if using “grid sampling”, which arbitrarily divides the field into squares of uniform size and soil tests on that basis. Fertility applications are then tailored to the results from each portion of the grid and programmed into the spreader which adjusts rates ‘on-the-go’ as it drives through the field.

The other approach is “zone sampling”. This is usually based on creating zones in the field based on soil types or by utilizing patterns of similar yield results over multiple years. Again, soil testing is performed by zone, and the results drive fertility applications for each specific zone.

There is another level of placement precision to consider. This is placement relative to the plants. Planter application is a good example of this, so we’ll continue with the discussion from the previous paragraph on timing. In the case of phosphorus, it is considered an immobile nutrient in the soil. It doesn’t move with water as do nutrients like potassium and nitrogen. As noted above, since the key period for phosphorus uptake in corn is from emergence to V3 (V3 is usually about 6-8 inches), that means the roots of that small of plant can’t reach very far from the row. Soils have rarely warmed enough for the microbial populations that can assist plant roots in acquiring phosphorus to have established themselves by this point in the season. Efficiency can be boosted by focusing P applications directly in the furrow where the young roots can absorb from the phosphorus-rich environment in and around the furrow based on the direct application there with the planter when the furrow was created.

The same principle applies to nitrogen planter application. Placing nitrogen several inches to the side of the row and just below planting depth protects the seedling from ‘nitrogen burn’ by exposing it to the potentially damaging product too early, yet it’s close enough to boost efficiency by giving the young roots access to it when they grow into it at approximately the growth stage when it starts to be critical that it has access to N for maximum yield.

Technology and modern farm equipment/technology give us the ability to employ the 4R’s at a higher level than was practical in the past. The main motivation for most farmers is increased efficiency in today’s economic environment, i.e., more efficient use of the fertilizer applied and lower cost per bushel produced. Each farmer must base his fertility management decisions on many factors including equipment costs, labor requirements, planting logistics, and other considerations unique to their situation. For Halderman managers and client understanding the principles of the 4R’s is a necessary first step to improving farm profit, soil health, sustainability, and long-term resilience on the farm.

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