Back Importance of uniform plant emergence in achieving greater yields and profitability

Date: 30 May 2018

As we set out to start the season, it is critical to sit back and re-evaluate what our primary goals are. For most people increased yields and/or profitability, as well as reducing the environmental impact, are ranked highest.

Factors that reduce the genetic potential of your crop will not only affect your bottom line but could indirectly influence the environmental impact. Crops are usually fertilised for a particular yield level, and failure to achieve that potential could result in excess nutrients being lost to the environment.

Even with the best paddock, hybrid, chemical, fertiliser, tillage system, planting date or density, it is still important to create an environment that allows plants to perform to their maximum potential. The crop must have a great start off the blocks and hinderance to perfect establishment means that the affected plants will never catch up, resulting in decreased yields.

Ideal plant establishment is evidenced by stands containing uniformly normal-sized plants that consistently produce one full-sized ear (see Figure 1). This is only possible if all seeds/plants are given the same opportunity to express their full potential.

Figure 1 - Ideal plant establishment resulting in uniformly sized ears.

Maize plant or ear size variability is more common than some people realise, and can usually be attributed to nonuniform emergence. Late emerging plants will struggle to compete for light, nutrients and moisture with their larger neighbours, eventually turning into small or “runt” plants which are rarely capable of producing full-sized ears (see Figure 2). Contrary to common belief that the bigger plants can compensate for the smaller neighbouring plants, the level of “flex” is usually very limited.

Figure 2 - Small ears produced on "runt" plants.

Non-uniform emergence can be attributed to a range of factors including poor seed bed preparation, soil moisture and temperature variation and seeding depth. While seeding depth can infl uence emergence timing through distance between seed placement and the soil surface, the main reason for non-uniform emergence is usually through temperature or moisture variation, particularly in cold or dry soils. Exceeding recommended planter speed can signifi cantly infl uence seeding depth variability.

In drier situations soil moisture variability is largest closer to the surface, resulting in variable emergence if seeds are planted within this zone. To ensure adequate moisture uptake to achieve uniform emergence, good seed-to-soil contact is critical (see Figure 3).

Figure 3 - Variable establishment due to poor seed to soil contact.

The standard planting depth recommendation for maize is 4–5 cm (1.5–2”). Th is allows for quick and optimum emergence rates as well as proper root system development in soils with moisture levels close to field capacity. If the 4–5 cm soil zone is drier it is best to plant deeper, particularly if no rain is forecast within a few days.

Maize can emerge from fairly deep planting depths depending on soil texture. Research shows that maize is capable of emerging as deep as 7.5–9 cm (3-3.5”) on clay soils, 10–11.5 cm (4-4.5”) on loam soils and 13–15 cm (5-6”) on sandy soils. Studies at the Rukuhia Research site (Waikato) show successful emergence for seeds planted at 20 cm depth in potting mix (peat soil).

If soil moisture is adequate within the top profi le there is no reason to plant deeper than 4-5 cm. In these conditions deeper planting can result in slower and more variable emergence, increased vulnerability to soil crusting and seedling diseases and insects.

Some people may prefer planting shallower than 4 cm to speed up emergence. Th is practice is not recommended because nodal roots develop about 1.9 cm (3/4”) below the soil surface. Shallower planting means that nodal roots are positioned either at or just below the soil surface, increasing the chance of rootless corn syndrome (see Figure 4) later in the season when hot, dry weather inhibits nodal root development.

Figure 4 - Plants displaying rootless corn syndrome courtesy of Jason Kelley, University of Arkansas.

Even though 4–5 cm (1.5–2’’) planting is the standard recommendation, the depth must be adjusted for environmental or soil conditions. It is best to plant deeper in drier conditions and stick to the recommended standards when soils moisture conditions are closer to field capacity. Provided moisture conditions are adequate, there is no benefit in planting deeper than necessary, particularly in early planting situations (cold soils). Other than moisture variability, shallow planting can also increase vulnerability of seeds to bird or rat damage.