Response to NPKS strips across Oklahoma
From the fall of 2011 to about a week ago one of my grad students, Lance Shepherd, has spent A LOT of time burning up the highways and back roads of Oklahoma. Lance’s project was titled “NPKS Strips in Oklahoma winter wheat”, basically an extension of the N-Rich Strip concept. We wanted to see if we could or would find a response to added nitrogen (N), phosphorus (P), potassium (K), or sulfur (S) fertilizer on top of the farmer’s fertilizer applications. Over the two crop years lance applied NPKS strip on more than 80 fields from the Kansas border to the Red River. Of those 80+ Lance was able to collect, by hand, grain samples from 59 sites. Over the next few weeks I will be sharing some of the juicy tidbits we are gleaming from this fantastic data set.
NPKS applicator. Gandy boxes hold each fertilizer and a pto driven fan blew the fertilizer down the boom.
For the project at every site Lance collected soil samples to 18”, documented soil type and collected producer fertilizer, variety, and field history information. Over the 59 locations there were essentially 236 trials. The yield of each strip (N,P,K, and S) was compared back to a sample collected from the field, referred to as Farmer Practice. Of the 236 comparisons there were a total of 17 positive responses. Of these 17 responses seven were to N, seven to P, three to K, with no responses to S.
N-Rich strip very evident in field west of Alva. N-Rich 70 bu/ac Farmer Practice 38 bu/ac.
We are learning a great deal from these 17 locations. The biggest take home was that in most instances soil test results identified the yield limiting factors. For example of the seven responsive P locations six had either a low soil pH or low soil P index, some both. At only one site was there a response not predicted by soil test. Of all 59 harvested fields more than just six had low P or pH levels however most producers had applied enough fertilizer to reach maximum yield. For nitrogen two items proved to be the most likely reason for loss of yield, under estimated yield goal or environment conducive to N loss. As for the K responses we look at both K and chloride (Cl) as KCl, 0-0-62 potash, was applied in the K strip. Just looking at the soils data K was not low at any of the three sites. However, two sites are in sandy loam soils, which is conducive to Cl deficiencies. The lack of response to S was not surprising as soil tests indicated S was sufficient at all 80 locations were strips were applied. So again what did we learn from these plots, soil testing is key in maximizing yield and profitability and in most of the N responsive sites the N-Rich strip indicated a need for added fertilizer in February.
Placing Fertilizer with Canola at planting has positives and negatives.
With all things holding constant the last canola trials of our project should be picked up by the plot combine Thursday 6-20-13. Before the first yield results comes to my desk I can tell you that we are learning a great deal from the trials this year. In particular the DAP (18-46-0) placed with seed trail that was supported by the Oklahoma Oilseed Commission. This past year at the no-till site in Perkins, which has a low soil pH, the check plots that did not receive any fertilizer, preplant or banded, did not survive the winter. Additionally at both of our locations, Lahoma (low soil test P) and Perkins, we have documented that oil content was reduced when phosphorus was left out of the treatment.
Additionally out of the four site years, that is two locations over two years, the addition of DAP with the seed in-row reduced stand. The graph below shows just how much stand was reduced on a relative basis. Relative stand is a way to compare the DAP treated to the Check (no DAP) which we assume is 100%. So if we look at the graph below the plots were at 75% relative stand (i.e. 25% loss) at approx 5 lbs N per ac. By about 15 lbs N the stand was down to 50%.
There are a few things to keep in mind first, in the case of these trials stand loss did not always mean yield loss. Canola is a great compensatory crop, if there is open space it will grow into it. I will have to run the final yield data to get more answers. These trials were planted on 15″ rows putting down 5 lbs seed per ac, or at least that was the target rate. Many have shown that the seeding rate does not have to be that high if sown properly. I believe in a few cases we may have actually benefited from thinning the stand. However if you were planting 2.5 lbs seed per acre a small loss of stand may be a bigger yield loss. This is one of the question we will have to answer in the future.
And finally it should be noted that canola is planted on a wide range of spaces 6″,7.5″, 12″, 15″, 30″ are some of the most common. As the row width changes the amount of N placed with the seed changes. In other words if the goal is 50 lbs DAP per acre you will put twice as much in a 15″ row than you do a 7.5″ row. The Table at the bottom provide a guide for equivalent rate based on 15″ rows. For example if your target a excepted stand loss of 25% (5 lbs N according to the Figure) but you are planting on 6″ row spacing the recommendation would be apply no more than 13 lbs N per ac in the row or 72 lbs DAP/ac (13/.18)
Impact of DAP (18-46-0) placed in-row on canola stand in terms of lbs N ac-1.
Equivalent amount of N based on 15″ row spacing.
Down and Dirty with NPK 