Commercial Potato Production and Cultural Management - The Potato: Botany, Production and Uses - page 90

Fig. 6.1. Tillage of conventional rows to disrupt weed growth. (Photo courtesy of M.J. Pavek.)

6.10 Depth of Planting

Soils should be moist but not excessively wet or
dry. If possible, pre-plant irrigation should be
used to add moisture to excessively dry soils.
Planting depths typically range from 5 to 20 cm
(measured from the top of the seed piece to the
top of the ridge/hill). Due to post-planting tillage
operations, however, final seed piece depth typic-
ally ranges from to 10 to 20 cm. In many regions,
it is common to plant shallow to encourage early
emergence. Many of the growers within these re-
gions build and shape the final hill with one or
more post-planting tillage operations. In addition
to hastened sprout emergence, shallow planting
depths may reduce at-harvest tractor horse-
power needs by minimizing harvester blade
depth. The drawbacks of shallow planting may
include lack of adequate soil moisture compared
to deeper soil, along with higher yields of under-
sized, green, and surface-exposed tubers (Pavek
and Thornton, 2009). Although deeper plant-
ing depths may provide better soil moisture and
less tuber issues, the drawbacks may include
yield reduction and disease issues due to delayed
plant emergence. The ideal planting depth bal-
ances rapid sprout emergence with the space re-
quirements of expanding and mature tubers
(Pavek and Thornton, 2009). Within limits, var-
ieties that produce large tubers and high yields
may need to be planted deeper and into a wider
hill than those that do not. Mature and rapidly
bulking tubers require a protective layer of soil

As with seed piece spacing, the ideal planting
depth is the one that helps to optimize grower
revenue. The ideal planting depth positions seed
pieces, stems, roots, and tubers in the most fa-
vorable season-long growth environment. It also
provides ample room for tubers, like those seen
in Fig. 6.2 , to expand and mature under a pro-
tective layer of soil.
Moisture and temperature differences through-
out a soil profile can influence emergence rate
strongly (Pavek and Thornton, 2009). If the soil
is adequately moist and warm (>7°C), sprouts
typically emerge more rapidly from shallower-
planted potato seed pieces. This is largely be-
cause the shallower-planted seed pieces accu-
mulate heat units quicker than deeper-planted
ones. Moreover, sprouts have less soil to travel
through prior to emerging from the soil surface.
In relatively hot, dry regions, deeper planting
depths may provide more soil moisture and less
extreme temperatures throughout the season.
Rapid emergence reduces the severity of
early season diseases like R. solani (Van Emden,
1965). Rapid emergence also hastens the plant's
ability to capture early solar radiation, which is
essential for optimizing tuber yield and dry mat-
ter (Firman and Allen, 1989). At the time of
planting, the soil temperatures at seed piece
depth should be at or above 7°C (Bohl et al ., 2003).