Build an Optimal Nutrient Management Plan05 February 2012
Science, not speculation, is what's needed to develop a nutrient management plan, writes SFP.
The foundation for building a comprehensive plan is to know where you are and what goals you're trying to accomplish. While that plan might seem very basic, experts and farmers can agree that these two factors are the core of optimal nutrient management.
"Determining your goal by soil sampling and knowing the proper way to take a soil sample are basic things, but very important ones," says Fabian Fernandez, assistant professor of soil fertility and plant nutrition at the University of Illinois. The reason they're so important, he says, is by starting with a goal in mind, you'll be able to obtain more relevant information when you soil sample.
Step 1: Determine your goal
Farmers can have varied goals: determining the nutrient variability within a field or the fertility of the field as a whole, changing to variable-rate application, calculating the fertility for profitable crop production or just monitoring the soil over time, Fernandez says. "Soil testing is very useful to measure phosphorus (P) and Potassium (K), but there are limitations. You need to know what you want to measure."
Once you determine what to measure, it becomes much easier to decide where to take samples, Fernandez says.
Scott Odle, who farms near Linden, Ind., has a portion of his fields sampled every three years so he can decide if he needs to adjust his nutrient management plan, based on his goals. Odle uses sidedresses anhydrous ammonia on his corn, but applies a pop-up starter of 10-34-0 treated with AVAIL, mixed with an additional rate of 28% treated with NutriSphere- N, which bumps his nitrogen (N) application at planting to 40 pounds per acre.
"We have 28% on the planter and we use a pop-up, so we're using both products - AVAIL in our in furrow so we can garner any additional phosphorus that we can, and NutriSphere-N on our 28% so we can hold our N as long as we can."
Odle's goal in using both fertilizer efficiency products is simple: to keep his P available for the crop's use and to keep his early N from volatilizing or leaching. Odle likes to sidedress as late as he can, usually after V5. He says his early N application, coupled with NutriSphere-N allows him to wait as long as possible to add that supplemental N.
"By applying that nitrogen later, the N is available later, when the plant needs it," he adds.
AVAIL is a polymer that can be coated onto granular P fertilizers or mixed in with liquid P fertilizers. AVAIL helps prevent P-fixation in the soil, keeping more applied P available for plant use. NutriSphere-N protects against N leaching and volatilization by selectively inhibiting unwanted chemical reactions in the soil. Doing this keeps the nitrogen in the more stable ammonium form longer. The product can be impregnated onto dry N fertilizer or added to liquid N fertilizer.
"We're not losing N to early spring rains because we're using [NutriSphere- N]," Odle says. "It's a safety measure for me and I think it's showing a yield response, so we'll continue to use it. It lets us be aggressive and get out there and get things done. I know I have N that stays out there and P that's available."
Step 2: Choose Where to Sample
The pattern you'll use to soil sample will be determined, in part, by what you already know about a field. The more uniform you think the soil is across the entire field, the less soil samples you'll need to submit for testing. The greater the variability, the more zones there will be and the more samples you'll need. Odle is looking to pinpoint areas of variability as he sidedresses N. He, therefore, has samples taken on a 2.5-acre grid and, with areas of high variability, creates what he calls "zones within zones," stepping up his number of samples. His goal is to eventually use variable rate application on his zones.
For recommendations, consult your local Natural Resources Conservation Service (NRCS) office or university Extension agent. They can recommend sampling patterns as well as specifics on sampling techniques.
Odle has his samples taken by an independent crop consultant and says it's not something he has to spend a lot of time thinking about anymore. He knows it will be done, and he reviews the results when they come in.
Step 3: Sample Accuracy Matters
If you chose to pull the samples yourself, the challenge is accuracy, Fernandez says.
"Typically, the greatest source of inaccuracy is how the sample was collected," he adds.
Knowing how to properly sample is key to receiving good information. While there are several different methods for taking soil samples, Fernandez recommends the soil probe. The probe can be marked at the depth you want to sample, which creates more uniform sampling. In Illinois, the recommended sampling depth for P and K is 7 inches. For Odle in Indiana, recommended sample depth is 8 inches. While you can use a shovel to soil sample, Fernandez says, it's too easy to get too much soil from the surface and not enough from below the surface, which can skew your sample results.
"In a no-till field, where P and K levels get stratified, we get high concentrations on the surface," Fernandez says. "If you brush out ½ inch or ¼ inch on the surface by sweeping away what you think is residue, you're biasing the sample."
If you end up taking a sample at a shorter depth, there's a likelihood you're sampling the more nutrient-rich portion of the soil, so you'll end up applying less fertilizer than you need. The soil probe will keep a consistent diameter for every soil sample. Check with your soil lab or local Extension office to determine the right depth and recommended technique for soil sampling in your area.
Step 4: More and Less
Farmers often take too few samples to make up their representative cores. Doing so is a mistake, Fernandez says.
"Most often fewer samples made up of more cores are better than more samples made up of fewer cores," he says.
It's easier to take less cores to get each sample, but the more cores you have mixed to create each composite sample to send to the lab, the more you reduce your chance for inaccuracy. Fernandez explains if you end up taking one sample from a spot that happens to have higher fertility than the rest of the field and you mix that with only one or two other cores to give a representative sample to the lab, you have a higher chance of skewing the results than if you mixed it with six or seven cores. Each composite soil sample should be made of at least 5 cores taken within a 5- to 10-foot radius, although samples of up to 15-20 cores is better. If the composite sample is too large, the soil should be mixed thoroughly and a subsample can then be sent for analysis. This is not the place to shirk the work.
"Soil sampling the field can be hard work," Fernandez says, "But the more cores you have per sample, the more accurate your test results will be."
Step 5: Review and Repeat
Over time, patterns within fields may help pinpoint needed adjustments to your nutrient management plan. It's important to compare your results (where you are) to your goals (where you want to be) and adjust accordingly.
Odle says that his nutrient management plan has evolved over time. He added AVAIL and NutriSphere-N to his program several years ago to give him added security that the nutrients he was applying would be available when and where his crops needed them. While he plans on using those products again next year, he's sure his nutrient management plan will continue to evolve.
Plan in Progress
A proper nutrient management plan is one that is always in progress. When you're dealing with nature, there are ongoing adjustments that can be made for future years, notes Scott Odle, who farms near, Linden, Ind.
"It's imperative that we have management plans," Odle says. "Every field, every year, you have to record what you did and what you plan on doing."
Odle has a soil testing service pull samples on his ground every third year. Currently, he's pulling samples in 2.5-acre zones and creates "zones within zones" if he feels there is too much variability. Upon reviewing test results, he then decides if his nutrient management plan needs to be adjusted.
"I think we have a good management plan. We apply N when it's needed and try not to overapply," Odle says. "We are putting on the starter with the seed and 40 units of 28% with the planter. That gives us the ability to sidedress not too early but not too late. That has been very successful for us; we're not losing a lot of N to early spring rains. If there's something to be learned, it's that we lose a lot of N between applications, and if we can make better decisions and not lose that N, we will."
One way Odle is protecting N in his field is by using NutriSphere-N with his 28%. NutriSphere-N keeps N from volatilizing and leaching. Volatilization is the loss of N as free ammonia due to a lack of bonding with hydrogen in the soil. The enzyme urease is responsible for this conversion in urea.
"We're looking to hold our N as long as we can with the planter. That's where it's the most valuable; you have to have the N available when the corn needs it," Odle says. "You're never sure how much spring moisture you're going to get; and with colder, wetter conditions, you can lose that N without NutriSphere-N to keep it in place."
Odle sidedresses anhydrous after corn reaches V5 at a rate he determines by his expected yield. With the high price of fertilizer and his emphasis on being a good steward of the land, Odle wants to make sure he's putting his fertilizer exactly where his crops need it, maximizing his fertility dollars while making his nutrient management plan more efficient.