Field Test: Sorghum Nitrogen Rates
A field scale replicated trial testing different fertilizer nitrogen rates on sorghum was conducted in Stanley County during the summer of 2016.
The field selected was soil sampled in March 2016 and soil test nitrate-nitrogen level was determined by a commercial soil testing lab. The soil was calculated to have 13 lbs. of available nitrate-nitrogen in the top two feet of soil. Phosphorus and potassium levels were measured at 7 (Olsen test) and 381 ppm respectively.
In addition to the standard testing procedure, the laboratory also ran the Haney suite of tests. This is a set of procedures developed by Dr. Rick Haney. It is being promoted in some areas as being able to do a better job of predicting fertilizer requirements than traditional testing procedures when no-till and cover-crop techniques are being used. The traditional and Haney test gave different recommendations for nitrogen. The yield goal was 80 bushels per acre sorghum. Using SDSU calibrations the traditional soil test levels resulted in a recommendation of 80 lbs. of additional actual nitrogen per acre. The Haney soil test recommended 40 lbs. additional actual nitrogen.
One hundred pounds of MESZ (12-40-0-10-1) was applied to the field with seed using an 1895 drill. Additional nitrogen was applied at seeding in a midrow band at four different rates. Each rate was replicated four times. The nitrogen treatments were 0, 30 lbs., 70 lbs. and 120 lbs. of actual N applied as urea. This was the same at 25 (13 lbs. in soil and 12 lbs. from MESZ), 55, 95 and 145 lbs. actual N.
Yields were measured at harvest. Average yields for each treatment are listed in Table 1. Treatment 1 which had approximately 25 lbs. of available nitrogen yielded 71 bushels per acre. Treatment 2 which had approximately 55 lbs. of available nitrogen (and matched the Haney recommendation level) yielded 78 bushels per acre. Treatment 3 which had approximately 95 lbs. of available nitrogen (and matched the SDSU recommended level of nitrogen addition) yielded 96 bushels per acre. Treatment 4 which had approximately 145 lbs. of available nitrogen yielded 95 bushels per acre.
|Table 1. Test treatment yields.|
|Treatment 1: 0 lbs. Urea *(25Lbs actual N)||71.5||a|
|Treatment 2: 65 # Urea *(55 lbs. actual N)||78.6||a|
|Treatment 3: 152 # Urea *(95 lbs. actual N)||96.6||b|
|Treatment 4: 260 # Urea *(145 lbs. actual N)||95.5||b|
|4 treatments per replicate|
|Coefficient of Variability||11.78|
|*lbs. of actual N =(soil test N+ N from MESZ+ Urea N)
Statistical analysis of yield showed that yields of treatment 1 and 2 were the same but were significantly different from treatments 3 and 4. Treatment 3 and 4 were not significantly different from each other. The traditional soil test and SDSU recommendation of 80 lbs. of additional nitrogen/acre provided optimum yield in this experiment. It should be pointed out that adding the amount recommended by the Haney procedure did produce nearly the yield goal of 80 bu./acre, but it did not optimize yield in the SD environment in 2016. It may need additional calibration to match local conditions.
Urea cost was $370/ton or $0.40/lb. actual nitrogen. The sorghum was sold for $2.75/bushel. The extra yield of 18 bushels per acre, which was produced in treatment 3 with the addition of approximately 40 lbs. of nitrogen increased gross income by $49.50/acre. The additional 40 lbs. of nitrogen cost $16.00. There was a net financial advantage of $33.50/ acre where nitrogen applications matched traditional SDSU recommendations compared to treatments where nitrogen application followed the Haney test.
Conclusions above are based on one site and one year of data.
The authors would like to thank Levi and Crystal Neuharth from Prairie Paradise Farms near Hayes, SD for their cooperation and contributions.