Ed Lentz, Extension District Specialist, Agronomy
To evaluate the relationship between nitrogen rate and wheat yields.
| Cooperator: | OARDC Vegetable Farm | Soil test: | pH 6.3, P 50 ppm, |
| County: | Sandusky | K 143 ppm | |
| Nearest Town: | Fremont | Fertilizer: | 0-0-60 = 150 lbs/A |
| Drainage: | Tiled | 18-46-0 = 150 lbs/A | |
| Soil type: | Hoytville silty clay loam | Planting Date: | October 3, 2001 |
| Tillage: | No-till | Planting Rate: | 130 lb/A |
| Previous Crop: | Soybeans | Row Width: | 7.5-inch |
| Variety: | Hopewell | Herbicides: | None |
| Harvest Date: | July 15, 2002 |
Experimental design was a randomized complete block with five treatments replicated four times. Treatments were three single spring applications (80, 100, and 120 lb of nitrogen/A) at greenup; a single application at initial stem elongation (80 lb of nitrogen/A), and a split application (20 lb of nitrogen applied at greenup and 60 lb of nitrogen applied at initial stem elongation). Nitrogen treatments were applied as urea from a Gandy spreader. All plots received 20 lb of nitrogen from diammonium phosphate in Fall 2001. A John Deere 1550 Drill was used at planting. Plots were 10 feet wide and 70 feet long. The center five feet was harvested for grain yield. A combine scale and a Dickey John tester estimated grain weight and moisture, respectively. Yield was adjusted to 14% moisture. A Minolta Spad meter estimated nitrogen uptake at initial stem elongation and flowering, from 30 flag leaves and top collared leaves per plot, respectively. Head number was estimated by counting spikes in three-foot sections from three areas in each plot.
The average wheat grain yield and other agronomic traits response to split nitrogen applications are given in Table 1.
Table 1. Average Wheat Grain Yield and Other Agronomic Traits Response to Split Nitrogen Applications.
| Spring | Grain | Harvest | Spad Meter | Spad Meter | Heads |
| N Rate | Yield | Moisture | Flowering | Initial Jointing | |
| (lbs/A) | (bu/A) | (%) | (spikes/ft2) | ||
| 0/80 split | 89.8 a | 11.7 a | 45.0 a | 38.1 b | 62 |
| 20/60 split | 85.2 ab | 11.0 b | 42.1 b | 40.8 b | 65 |
| 120 | 83.5 ab | 11.4 ab | 43.6 ab | 46.0 a | 66 |
| 100 | 80.5 bc | 11.5 ab | 43.1 ab | 46.2 a | 69 |
| 80 | 73.3 c | 11.5 ab | 42.0 b | 46.0 a | 66 |
| LSD (0.05) | 9.0 | 0.6 | 2.2 | 3.4 | NS |
| F-test | 4.4 | 1.8 | 2.8 | 11.3 | <1 |
| a Means followed by the same letter in a column are not statistically different. | |||||
Applying 20 lb of nitrogen at greenup followed by 60 lb of nitrogen at initial stem elongation had larger yields than applying 80 lb of nitrogen/A at greenup. This treatment was as efficient as applying 100 lb of nitrogen at greenup. However, the largest yield was obtained by delaying spring application until initial stem elongation, and it was as efficient as applying 120 lb of nitrogen/A at greenup. The two initial elongation treatments had significantly lower nitrogen uptake at initial stem elongation (Spad meter values) than the greenup alone treatments, but the nitrogen applied as a starter in the fall and any residual soil nitrogen prevented a significant reduction in head number. Spad meter values at flowering could not explain grain yield differences. Because head numbers were similar, yield differences between the split and single application may be attributed to seeds per head or larger kernels, which were not measured in this study.
Producers prefer a split system to reduce the chance of yield reduction in nitrogen loss years. Generally, producers apply most of their nitrogen at greenup and a smaller amount at initial stem elongation in a split program. This study would suggest that the smaller amount should be applied at greenup and the larger amount at initial stem elongation. The biggest disadvantage of two applications in the spring would be the cost of the second application, which may negate any yield advantage.
The author of this report is grateful for the support provided by the OARDC staff at the Vegetable Branch.
For more information, contact:
Ed Lentz
Ohio State University Extension, Northwest District
1219 W. Main Cross St., Suite 202
Findlay, OH 45840
419-422-6106
lentz.38@osu.edu