Establishment and survival of pasture species from seeds sown on the soil surface

Abstract

Some of the factors influencing the establishment and survival of temperate pasture species when sown on the soil surface were investigated. The following were the main findings from experiments conducted in the field and in a controlled environment. (1) Both the establishment and survival of seedlings sown by broadcasting on to non-arable land can be significantly improved by a prior treatment of the site with herbicide to reduce competition from existing vegetation. (2) Providing protection for seeds by retaining dead vegetative cover, or by creating some form of surface roughness, improves establishment as it reduces desiccation and provides a more favourable moisture environment in the vicinity of the seed. (3) Uptake of water by seeds resting on the soil surface is enhanced by absorbent lime or bentonite coatings, and increased germination results. (4) Failure of radicles to penetrate the soil following germination is an important factor limiting the establishment of legumes on exposed sites, and any restraint on the movement of germinating seeds under these conditions improves the penetration of the radicle. (5) Variation between species in their ability to establish on the surface suggests that the choice of more suitable species, and selection to improve their adaptation in this respect, could also contribute a great deal to the efficiency of aerial seeding.

Planting depth effects on overdrilled seedling survival in summer

“…Seedlings classified as type (2) at emergence showed no ability to achieve root penetration and remained as just the initial shoot. Such seedlings are particularly vulnerable to poor moisture relations on the surface (Dowling et al 1971) and, without buffering by a penetrating root system tapping sub-surface water, death is rapid. Low survival and restricted root development add to the disadvantage oflower emergencewhen a coulter skims the surface (0 mm).…”

Winged coulter depth effects on overdrilled red clover seedling emergence

“…Seed lies exposed on the surface (a situation more closely resembling oversowing than overdrilling), and is dependent on surface soil water and the vapour pressure deficit at the soil-air interface for germination and emergence (McWilliam & Dowling 1970). Conditions for establishment can be more severe than for buried seed (Watkin & Vickery 1965;Evans et al 1967) particularly when rapid changes in moisture and humidity occur (Dowling et al 1971). The importance of providing a moisture retaining groove, even in moist soils, is demonstrated by the reduced emergence at 0 mm relative to 13 mm in both autumn and spring (Tables 3 and 4).…”

“…Pasture legumes such as red clover with thick radicles and epigeal development (Wellington 1970) are poorly adapted for surface germination (Campbell & Swain 1973;Dowling et al 1971). This lack of rootlet penetration can be common on the surface, especially in dry conditions.…”

Effect of seed coating on establishment and yield of grasses on a West Coast pakihi soil

“…Possible advantages of coating grass seed include increasing the uptake of moisture by the seed for germination (Dowling et al 1971), improving the nutrition of the establishing grass by supplying fertiliser from the coat, and improving the penetration of seed through vegetation to the soil surface (Hay 1973). It is difficult to envisage how any of these advantages could have aided grass establishment in this trial.…”