Sowing depth can be used to enhance crop competitive ability. Maximum competitive ability will come from a crop sown at optimum and uniform depth to get rapid and uniform establishment. Much of the yield loss from weed competition occurs in the first few weeks of crop growth. A crop with a few days’ or one week’s head start on weeds will be significantly advantaged. Sowing healthy seed (with a high germination rate) into ideal soil moisture at the optimal depth for establishment gives the crop a competitive advantage against weeds.
Optimum sowing depth for each particular soil type and crop type will vary. Achieving an optimum and uniform sowing depth will result in synchronous emergence, benefiting crop yield and improving crop competition.
Use furrow sowing or moisture seeking techniques at sowing to establish the crop before the weeds. Moisture seeking or sowing at depth (below 5 cm) into subsurface soil moisture is a common practice in many regions where sowing rainfall is unreliable. This can be done with all pulse species and cereals, and results in improved establishment due to more favourable soil moisture for both the seed and subsequent seedlings under dry conditions. Moisture seeking ensures timely establishment of the crop ahead of the germinating weeds, giving it a competitive advantage.
An extension of moisture seeking is furrow sowing, which is the practice of sowing at depth but only returning a light cover of soil over the seed, effectively leaving it at the bottom of a seed furrow. With crops that have poor coleoptile strength, this extends the option to moisture seek long after a rainfall event while maintaining crop seedling vigour. This is only applicable when there are no significant rainfall events near sowing time.
Take care to sow seed at optimum depth. Sowing too shallowly can also result in uneven germination, with some seed being placed in dry soil and not germinating until a follow-up rain is received. Sowing too deeply can lead a crop to expend much of its stores of energy by having to push up through the soil. When such crops do emerge they are often slow growing, weak competitors, and more susceptible to disease and insect attack until they recover.
Equipment costs for independent depth control on each row will need to be considered when making row spacing decisions, and the optimal trade-off between row spacing and depth control may vary with the type of crops grown and the paddock topography.
Article: CulturalWeedControl173 (permalink) Date: 9 January 2013; 7:47:50 PM AEDT