Post-Sowing Review: How are your Plant Numbers Stacking Up?

Whether it happened at 1am with a coffee to keep you going or 1pm while listening to a podcast, much of the seed for this season is in the ground and working its way to the surface if it hasn’t already made it up.   

Paddock establishment surveys as part of a GRDC funded project – optimising plant establishment, undertaken by BCG in 2018 found that on average, canola was only establishing 61% of the targeted density and lentils averaged 78% establishment of the target. The project runs from 2018 – 2021 with the University of Adelaide.  

In a wheat crop it has been found that up to 60% of the potential yield is determined at sowing. Sowing too thinly, poor quality seed and uneven establishment can result in yield losses that generally can’t be overcome. 

About four weeks after sowing is a good time to check crop establishment given good growing conditions. But what are you looking for? 

Using a ruler or quadrat, you can count the number of plants established in a 1m2 area to check if target densities have been achieved. Multiple counts should be taken across a paddock to check evenness. The following table is a guide for target densities to optimise yield for the Wimmera and Mallee by crop type.  

Table 1. General guide for target plant densities to establish by crop type (plants/m2).  

Crop type Ideal plant number per m2 Wimmera/Mallee 
Barley 100-140 
Wheat 120-150 
Lentils 100-120 
Canola 30-50 
Vetch 40-60 
Beans 20-30 
Peas 40-50 

Optimal densities will change from season to season according to environment and rainfall conditions. If plant numbers aren’t reaching these densities, there could be a number of factors at play. The first, being that sowing rate may have been too low. A simple calculation to adjust sowing rate for a target density where seed size and germination are taken into account is: 

Seed weight should be calculated as an average from one thousand seeds. Expected germination can be impacted by a number of factors. These factors include: 

  • Seed quality (germination percentage and vigour) 
  • Soil moisture 
  • Seed to soil contact (impacted by soil type eg. cloddy soils and machinery eg. press wheels) 
  • Soil temperatures 
  • Disease and pests (including mice) 
  • Sowing depth 
  • Sowing speed 
  • Herbicide residues and some seed treatments 

While in farming many factors are out of our control, setting machinery up correctly when it comes to sowing and establishment can really pay off down the line. So, before packing the seeder away, have a look at your results this season, think of the issues and how they can be addressed next season.  

This month, BCG will be doing in depth assessments on bean and canola at Rupanyup as part of the project looking at seed placement and establishment numbers across a variety of sowing rates, row spacings and performance of precision and conventional seeders with these treatments. 

For more information on crop establishment and management of different crop types see GRDC grow notes publications for the Southern region

Reference: 

1 W Thomason (2004) Planting wheat: seeding rates and calibration. Virginia Cooperative Extension, http:// www.sites.ext.vt.edu/newsletter-archive/cses/2004-10/plantingwheat.html 

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