Optimal initial stand and seeding rate can be customized by variety

Variety Specific Seeding Rates

By Dr. Jochum Wiersma,
University of Minnesota small grains specialist,
wiers002@umn.edu

The information below is a summary of research that I conducted at the Northwest Research and Outreach Center, and presented at the recent National Association of Wheat Growers’ Wheat Industry Research Forum.  I thought it would be worthwhile to present the result of my work in Prairie Grains as well.

Introduction
The University of Minnesota’s recommendation for optimum stand for hard red spring wheat cultivars is 28 to 30 plants per square foot or 1,250,000 plants per acre when planting early. If planting is delayed, seeding rates should be adjusted upwards by 1 to 2 plants per square foot each week to compensate for the shorter growing season. Based on the expected stand loss, the percentage of germination and the number of seeds per pound, a seeding rate can be calculated for each field and seed lot using the equation at the bottom of this page.

Producers, however, routinely plant spring wheat at 1.5 bushels to the acre regardless of the cultivar. Grafius (1956) described yield as a function of the number of tillers per unit area, the number of kernels per spike and weight per kernel. Subsequent research showed that each of these yield components is under genetic control and that many cultivars differ for each of the yield components.

Faris and de Pauw (1981) suggested that cultivars should be tested at a wide range of seeding rates in order to determine their optimum seeding rate. Adams (1967) described that plant development allowed compensation between yield components, thus enabling a wheat cultivar to attain maximum yield potential even if one of the yield components was below optimum. Nonetheless, an optimum stand is an important first step toward maximizing yield. The objective of this research was to determine the optimum stand and corresponding seeding rate for nine modern standard and semi-dwarf spring wheat cultivars for maximum yield for both early and delayed planting.

Materials & Methods
Nine hard red spring wheat cultivars were planted at six seeding rates using a split-split plot design with four replications combining two planting dates and six seeding rates. The experiment was repeated in 1996, 1997, and 1998 at Crookston, MN. In addition to stand counts, yield, test weight, and grain protein data was collected.  The seeding rates used ranged from 0.25 million to 2.75 million live seeds per acre planted. Planting dates used were the first week in May each year and approximately three weeks later for the delayed planting. 

Results
As the seeding rate was increased, the initial stand proportionally increased less.  In other words, a larger percentage of the healthy, live seed did not produce a seedling when the seeding rate increased.  This stand loss was as high as 30% at the highest seeding rate as shown in Table 1 for the HRSW-cultivar Verde. It is important to recognize this, as it impacts the percent stand loss estimated in calculating an optimum-seeding rate.

Table 1. Observed stand loss for the cultivar ‘Verde’ at different seedings rates. Seeding Rate   Stand     Expected Observed Loss (# x 106 / acre) (#/ft2) (#/ft2) (%) 0.25 5.7 11.2 96.5 0.75 17.2 17.4 1.2 1.25 28.7 23.6 -17.8 1.75 40.2 29.8 -25.9 2.25 51.7 36.0 -30.4

Each of the 9 cultivars showed significant linear and quadratic contrasts for yield at both planting dates. A graphical interpretation of the results is given in Figure 1. The corresponding optimum seeding rates are presented in Table 2 and Table 3.

Table 2. The optimum seeding rate and corresponding expected and realized stand for nine HRSW-cultivars to attain maximum yield when planted early. Variety Seeding Rage Stand     Expected Realized Loss   (# x 106 /acre)(lbs/acre) (#/ft2) (#/ft2) (%) Backup 1.96 128 45 33 27 Marshall 1.89 119 43 30 30 Kulm 2.05 136 47 30 36 Grandin 1.94 134 44 32 27 P2375 2.20 170 51 37 27 Nora 1.89 107 43 31 28 Gunner 2.10 132 48 35 27 Hamer 2.06 152 47 36 23 Verde 1.98 120 41 31 23

Table 3. The optimum seeding rate and corresponding expected and realized stand for nine HRSW-cultivars to attain maximum yield when planted late. Variety Seeding Rate   Stand       Expected Realized Loss   (# x 106/acre)   (lbs/acre) (#ft2) (#/ft2) (%) Backup 2.16 141 50 36 27 Marshall 2.08 131 48 33 30 Kulm 1.98 132 45 29 36 Grandin 2.25 155 52 37 27 P2375 2.08 160 48 35 27 Nora 2.02 115 46 34 28 Gunner 1.98 125 45 33 47 Hamer 2.58* 190 59 46 23 Verde 2.16* 146 50 38 23 * Contrast

Conclusion
The average realized stands support existing recommendations for optimum stands when planting early and late. The results also indicate that differences exist between cultivars, and that an optimum initial stand and corresponding seeding rate can be determined for individual cultivars. Agronomists, seed dealers and growers may want to make use of this optimum initial stand to determine seeding rates.

In addition, the results indicate that the expected stand loss is often higher than the previously assumed 10% to 15% under optimum conditions. This further stresses the need to do stand counts when wheat is in the 2 to 3 leaf stage and using the estimates for stand loss to calculate and adjust the seeding rates for particular varieties accordingly the following years.