Expert advice

How to determine the seed sowing norm

In agricultural farms, in practice, one is able to use one of two kinds of material for sowing – the primary sowing material purchased from a producer, with a relevant level of qualification, and, what follows, of a known mass of a thousand seeds, a known ability to sprout, purity, and, very frequently, with a clear recommendation as to the sowing norm. A second, separate group is own sowing material – without qualification certificates, meaning, without predetermined quality parameters.

In case of use of own sowing material, we recommend observations and measurements that will permit the correct calculation of the sowing norm. The basic parameter that must be determined is the purity – its value tells us what is the content of contaminants (seeds of obligatory and optional weeds and parasitic plants, halves of seeds, plant parts and others). A portion of seeds foreseen for sowing needs to be prepared in such a way so that the purity would be close to norms in force. All impurities influence the quality of any treatment. The seed treatment may in fact be applied to the contaminants, instead of caryopses/ seeds. The purity may be checked by testing a sample of contaminants taken from a specific mass of sowing material, with the second stage being a calculation of their volume per a specific sample mass. E. g. if one would take 1000 g, and if contaminants make up 100 g, then purity amounts to 90%.

A further necessary parameter is the calculation of the mass of a thousand seeds – one counts a thousand seeds and then weighs them; due to the risk of errors we suggest performing several calculations, e. g. calculating 10 x 100 and averaging out the end result.

The factor most greatly influencing the sowing standard, beside purity, is the ability to sprout, or the number of seeds/ caryopses normally sprouting in a given time. Such a sample can be effectively made at home – by placing the seeds/ caryopses on a wet e. g. paper towel, selecting a specific volume – say, 50 seeds – whereby we recommend making 4-5 trials; we place the seeds at room temperature and water them as appropriate. After about a week one obtains the information of the volume of seeds that sprouted – with the next stage being determining the sprouting ability expressed as a percentage.

One last parameter remains – the determination of the volume of caryopses per square metre. It depends on such factors as the type of location and the prior crop and the time of sowing, whereby if the location is of weaker quality, if the weather conditions are worse and if sowing takes place later, the number of caryopses/ seeds should be higher. As a rule of thumb, one assumes (with these values varying for specific varieties) for winter wheat (300-450 pcs./m2); summer wheat (400-550 pcs./m2), rye (260-500 pcs./m2); winter barley (320-480 pcs./m2), summer barley (300-400 pcs./m2).

Example calculations were provided for winter wheat of the following parameters:

count per square metre – 340; purity – 90% and 100%; sprouting ability – 90.4; mass of a thousand seeds – 43.6 g, Sn – sowing norm - ?

Sn=(340×43.6x100)/90.4x90=182.2 kg/ha,

Sn=(340×43.6x100)/90.4x100=164.0 kg/ha

Appropriately purified sowing material in this case permits the reduction of the sowing norm by approx. 18 kg of unnecessary burden.