What we found
Measuring a variety’s seed weight and adjusting seeding rates accordingly is extremely important when sowing because each variety differs in its seed weight (Figure 1). It was also found that growing conditions will affect seed weight. Environmental factors such as drought stress and frost can affect the size and quality of the grain.
If you are seeding at lower densities, then you will be seeding less seeds per m2 if the seed is large and this could be reduced yield potential. Further more, if your aim is to seed at a higher density for weed competition, you will be seeding less seeds than expected if the seed is large.
This is because there are less seeds in each kilogram of seed. For example, if a variety has an average seed weight of 35mg, there are 28 571 seeds per kilogram of seed sown. If a variety has an average seed weight of 45mg, there are only 22 222 seeds sown in each kilo of seed sown. This means less plants will establish.
What we did
The GRDC’s National Variety Trial (NVT) program provides wheat varietal comparisons at a location and regional level. Single site yield and grain quality data from the NVT database for the years 2012 to 2016 was used to compare seed weight of varieties relative to Mace.
What does it mean? Calculating seeding rate
Calculate seeding rate based on seed weight, target plant population and calculated germination percent. Work in terms of plants per square metre rather than kilograms per hectare (kg/ha) because seed weight varies between crops, varieties and seasons.
To determine the average seed weight, count and weigh 1000 seeds of the graded sample (note a 1000 seed weight of 40g = seed weight of 40mg). The seed rate calculation is:
Seed rate (kg/ha) = [Target plant density (plants/m2) * seed weight (mg)] / Expected establishment per cent (%)
For example, if the desired plant population is 150 plants/m2, the seed weight is 35mg and expected establishment is 80% the calculation is: 150 * 35 / 80 = 66 kg/ha. When the seed weight is 45g, 84 kg/ha of seed is suggested (Table 1).
|Average seed weight (mg)||Seed rate (kg/ha) to achieve 120 plants/m2||Seed rate (kg/ha) to achieve150 plants/m2||Seed rate (kg/ha) to achieve180 plants/m2|
The research undertaken as part of this project is made possible by the significant contributions of growers through both trial cooperation and the support of Grains Research and Development Corporation and the Department of Agriculture and Food, Western Australia. The author would like to thank them for their continued support. The National Variety Trial program is a significant project with significant outputs. Our appreciation is provided to the service providers for trial management and the NVT for access to the data.
GRDC project number: DAW00249 (Tactical wheat agronomy for the west) and NVTonline.