Co-Authored with Shane McClure and Middlesex Soil and Crop Improvement Association
Purpose:
Adequate soil phosphorus (P) and potash (K) levels are essential to produce high yielding crops. With high fertilizer prices it is important to use the fertilizer as efficiently as possible. Using starter fertilizer can be an effective way to apply fertilizer but what is the most effective rate and product to use. This trial evaluated liquid versus dry fertilizers, different rates of fertilizer, and broadcast versus in-furrow (IF). It also compared response to starter at both low and high soil testing sites.
Methods:
Replicated field scale trials were initiated at 23 locations from 2011 – 2014. The full treatment list is below:
- Check (No Starter)
- 2.5 gal/ac 6-24-6 IF
- 5 gal/ac 6-24-6 IF
- 10 gal/ac 6-24-6 IF
- 40 lbs/ac 7-34-20 IF
- 150 lbs/ac 7-34-20 IF
- 100 lbs/ac MAP IF
- 100 lbs/ac MESZ IF
- 200lbs/ 7-34-20 broadcast
Sites were planted using a 1560 JD drill (1590 boots). The broadcast treatment was applied after planting using a valmar airflow. Harvest measurements included yield, moisture, test weight, 1000 kernel weight, lodging and protein. Soil samples were taken post-harvest from the check strips.
Results:
The average yield results are summarized in table 1 sorted by the amount of P2O5 applied in the starter fertilizer application. Wheat yields responded to increasing P until reaching a maximum of 40 lbs P2O5 applied IF. Based on average data there was no response to K applied starter. This is evident by looking at the MAP and MESZ treatments which contain no starter K yet have the highest yields. Response to the broadcast treatment was very poor considering how much fertilizer was applied.
Table 1: Yield Results (3 years 23 sites)
| Treatment | Yield (bu/ac) | Gain over Check (bu/ac) | P2O5 Applied (lbs) | K2O Applied (lbs) |
| Check | 83.7 | – | 0 | 0 |
| 2.5 gal 6-24-6 IF | 86.3 | 2.6 | 7 | 1.7 |
| 5 gal 6-24-6 IF | 87.8 | 4.2 | 13 | 3.3 |
| 40lbs 7-34-20 IF | 88.5 | 4.8 | 14 | 8 |
| 10 gal 6-24-6 IF | 89.1 | 5.4 | 26 | 6.6 |
| 100lbs MESZ IF | 90.9 | 7.2 | 40 | 0 |
| 150lbs 7-34-20 IF | 90.9 | 7.2 | 51 | 30 |
| 100lbs MAP IF | 90.9 | 7.2 | 52 | 0 |
| 200lbs 7-34-20 Broadcast | 88.6 | 4.9 | 68 | 40 |
Table 2 contains the average yield data from just the locations with a low P soil test. All sites had a P value below 14 ppm with the average soil test being 10.4 ppm for P and 92.5 ppm for K. The yield response to added P was about 3 bu/ac higher at the low P testing sites then the average data from all locations. Yields still reached a maximum response with 40 lbs P2O5 applied IF.
Table 2: Low P Sites (10 Sites)
| Treatment | Yield (bu/ac) | Gain over Check (bu/ac) | P2O5 Applied |
| Check | 82.3 | – | 0 |
| 2.5 gal 6-24-6 IF | 87.7 | 5.4 | 7 |
| 5 gal 6-24-6 IF | 90.4 | 8.1 | 13 |
| 40lbs 7-34-20 IF | 90.3 | 8.0 | 14 |
| 10 gal 6-24-6 IF | 91.5 | 9.2 | 26 |
| 100lbs MESZ IF | 92.9 | 10.6 | 40 |
| 150lbs 7-34-20 IF | 93.0 | 10.6 | 51 |
| 100lbs MAP IF | 92.6 | 10.3 | 52 |
| 200lbs 7-34-20 Broadcast | 89.7 | 7.4 | 68 |
It is evident that wheat responds to starter P, but what about K? The average yield data from 7 locations with a low K soil test are summarized in table 3. All 7 sites had a K soil test below 90 ppm with the average soil test being 14 ppm for P and 69 ppm for K. At first there appears to be a response to starter K but when you take a closer look, the response is coming from the P applied in the starter treatments. The best way to discover if there is a yield response to starter K is to compare the 150lbs 7-34-20 treatment to the 100lbs MAP treatment since they both have the same rate of starter applied P. There is little yield difference between MAP which contains no K and 7-34-20 which has the highest rate of banded K. So even at the sites with a low K soil test, there is very little response to K applied starter.
Table 3: Low K Sites (7 Sites)
| Treatment | Yield (bu/ac) | Gain over Check (bu/ac) | K2O Applied | P2O5 Applied |
| Check | 86.5 | – | 0 | 0 |
| 2.5 gal 6-24-6 IF | 88.7 | 2.1 | 1.7 | 7 |
| 5 gal 6-24-6 IF | 93.2 | 6.7 | 3.3 | 13 |
| 40lbs 7-34-20 IF | 92.3 | 5.8 | 8 | 14 |
| 10 gal 6-24-6 IF | 93.9 | 7.4 | 6.6 | 26 |
| 100lbs MESZ IF | 94.2 | 7.7 | 0 | 40 |
| 150lbs 7-34-20 IF | 95.1 | 8.5 | 30 | 51 |
| 100lbs MAP IF | 94.5 | 8.0 | 0 | 52 |
| 200lbs 7-34-20 Broadcast | 90.4 | 3.8 | 40 | 68 |
Table 4 contains yield data from selected sites with completely different soil test levels. The Lucan 2011 site had a very low P level and response to starter P was extreme. Yields increase by 18.5 bu/ac with 100lbs MAP IF compared to the check.
Response was completely different at the Fergus location which had a high P soil test level and a very low K value. Yield response was extremely variable across treatments but there is no clear response to starter K.
The Belmont site has a medium soil test for both P and K. There is still a response to starter P at this site but the response is not as significant as Lucan 2011 which had a low P soil test. There was a 3.3 bu/ac increase in yield with 100lbs MAP compared to the check.
The Lucan 2012 site had both a high P and K soil test. At this site there was very little difference between any of the treatments.
Table 4: Select Location Data
| Location | Lucan 2011 | Fergus 2012 | Belmont 2012 | Lucan 2012 |
| Check | 68.5 | 82.1 | 77.3 | 100.4 |
| 2.5 gal 6-24-6 IF | 74.4 | 79.1 | 74.3 | 100.5 |
| 5 gal 6-24-6 IF | 79.0 | 89.1 | 76.3 | 99.6 |
| 40lbs 7-34-20 IF | 82.4 | 83.4 | 81.8 | 101.8 |
| 10 gal 6-24-6 IF | 86.8 | 85.8 | 81.4 | 101.9 |
| 100lbs MESZ IF | 86.2 | 84.5 | 79.0 | 103.3 |
| 150lbs 7-34-20 IF | 86.8 | 81.1 | 80.6 | 104.3 |
| 100lbs MAP IF | 87.0 | 88.9 | 80.6 | 100.3 |
| 200lbs 7-34-20 Broadcast | 82.6 | 88.2 | 77.7 | 101.4 |
| P (ppm) | 5.8 | 34.9 | 20.3 | 56.2 |
| K (ppm) | 72.5 | 60.7 | 130.5 | 165.2 |
Summary:
This trial has shown just how important it is to have adequate P levels close to the seed to support the early growth. Adequate P levels are essential for proper root development and tillering. On average by applying 100 lbs of MAP IF wheat yields increased by 7 bu/acre. By looking at the yield response from individual sites shows an even greater response to starter P at sites with low P soil tests. As P soil test levels rise response to starter P does seem to decrease but even sites with a good P soil test (P = 20) showed a response to starter P. If your P soil test is very high (P>50) the data suggests that response to starter fertilizer may be minimal.
Starter K had little impact on yields but even though wheat does not respond to banded potash it is still important to maintain a potash soil test of 100 to support proper wheat, soybean, and corn growth.
Broadcast fertilizer yields were disappointing. Surface applying P is not an efficient way to apply P fertilizer. By banding the P fertilizer average yields were increased by 2.3 bu/ac while applying 16lbs less P2O5. Based on the results from this trial broadcast applying K to maintain soil test levels would be as efficient as banding K fertilizer.