The Influence of Planting Rate

NDSU study compared spring wheat yield and agronomic traits of different planting rates in northeastern North Dakota

Using the correct planting rate for hard red spring wheat (HRSW) is critical to establishing plant stands that ensure optimum yields.  However, optimum planting rates can vary across growing regions. 

Bryan Hanson, agronomist at the North Dakota State University Langdon Research Extension Center, says research indicates that in southeastern Saskatchewan, a planting rate of 18-36 pounds per acre was adequate where yields are less than 20 bushels per acre, while in Alberta, where yield levels range from 38 to 51 bushels per acre, a planting rate of 90 pounds per acre gives optimum wheat yields.  In western North Dakota at Minot, Williston and Dickinson, HRSW yields were optimized at a stand rate of 1 million plants per acre at yield levels of 30 to 35 bushels per acre.

The Langdon REC conducted a planting rate study from 1991-93 to evaluate planting rate needed to obtain optimum yields of HRSW in the high-yield environment (45-60 bushels per acre) of northeastern N.D. Grandin was planted at a total of 16 locations across northeastern ND. Four planting rates, adjusted for percent germination and seed size, of 0.5, 1.0, 1.5 and 2.0 million seeds per acre were compared. Stand counts were made in each plot after emergence to determine established plant populations and percent emergence, with grain yield compared after harvest.

Yields across the 16 environments ranged from 27 bushels per acre at Devils Lake in 1993 to 75.7 bushels per acre at Cando in 1992, with an average yield of 51.7 bushels per acre. The 0.5 million seeds per acre planting rate yielded an average of 6.3 bushels per acre less than all other planting rates and was the lowest yielding in 15 of the 16 environments. Yields from the 2.0 million seeds per acre planting rate were 1.9 bushels per acre higher than yields from the 1.0 million seeds per acre planting rate. There was not a significant yield difference between the 2.0 and 1.5 million seeds per acre planting rate (Table 1).

Test weights averaged 60 lbs/bu in 1991 and 61 lbs/bu in 1992, while the 1993 test weight averaged 58.4 pounds per bushel. Test weight averaged 1 lb/bu lower for the 0.5 million seeds per acre planting rate compared to the higher planting rates and was the lowest in 13 of the 16 environments. Lower yields and test weights in 1993 resulted from fusarium head blight infections.  Percent protein did not differ with planting rate, and the effect of planting rate on plant height was non-significant. Lodging was lowest at the 0.5 million seeds per acre rate and increased as planting rates increased.

The number of days to heading from planting date was highest at the lowest planting rate, and decreased as planting rates increased. Percent emergence was highest at the lowest planting rate (Table 2). Lower percent emergence at higher planting rates may have been due to increased seed competition within the row. This same effect as been seen in other small grain planting rate studies.

Established Plant Stands Versus Yield
The relationship between established plant stand and yield was analyzed in this study to help determine the minimum number of plants per square foot needed to obtain optimum yields. The optimum yield in this study occurred at 34 plants per square foot (1.48 million plants per acre) with no significant difference in the range between 26 and 41 plants per acre). This suggests that the minimum number of established plants to obtain optimum yields would be 26 plants per square foot. No significant yield benefits would be obtained with higher established plant stands.

A producer’s goal, then, is to select a planting rate that establishes a plant stand of at least 26 plants per square foot. Percent emergence is unpredictable due to a variety of factors such as depth of planting, potential soil crusting, seedling diseases, dry seedbeds and herbicide injury. These factors can result in large differences in percent emergence that can occur from field to field, which makes selecting the best planting rate difficult.

In this study, the average percent emergence of the 1.0, 1.5 and 2.0 million seeds per acre planting rate at 16 environments was 86%. The study indicates that, generally, to obtain an established plant stand of 26 plants per square foot, a producer in northeastern N.D. should use a planting rate between 1.25 and 1.40 million pure live seeds per acre, assuming a 10-20% reduction in stand. Anticipated stand losses of greater than 10-20% would require further adjustments to planting rates.

Hanson points out that acreage of Grandin is slowly decreasing every year: Last year the variety represented just 2.7% of the total acres or 181,500 acres grown in N.D.  However, he believes that the recommendations from this study would in general still be valid for many of the varieties currently grown in northeastern N.D.

Complete details of the study can be found on the Internet at www.ag.ndsu.nodak.edu/aginfo/agreport/ar1w.htm.

Table 1.  Planting rate effect on yield, test weight and protein of Grandin HRSW across 16 enviroments in northeast North Dakota, 1991-1993. Planting Rate million seeds/acre Yield bu/acre Test Weight lbs/bu Protein % 0.5 46.9 58.3 14.8 1.0 52.2 59.1 14.8 1.5 53.2 59.3 14.8 2.0 54.1 59.5 14.9 LSD 5% 1.6 0.4 NS