FEATURE
Preliminary results on the
impact of rehabilitation of old
potato circles in the Sandveld,
Western Cape, on soil biology
and soil seedbank
Nelmarié Saayman 1* and Craig Morris 2
Current Address: 1 Directorate: Plant Sciences, Western Cape Department of Agriculture, Elsenburg
2
ARC-API, c/o University of KwaZulu-Natal, Pietermaritzburg
T
he arid Sandveld region along
South Africa’s west coast is known
for its potato production circles
since the 1980’s. Some of these potato
production lands became economically
unviable, while others were located in
ecologically sensitive areas and were
withdrawn from the production cycle.
Eight percent, or 5 800 ha of the endan-
gered Leipoldtville Sand Fynbos veg-
etation type (FFd 2; Rebelo et al. 2006),
are under central pivot irrigation for po-
tato production and only 45% is still in a
natural state (Rouget et al. 2004). Reha-
bilitation of these abandoned lands has
become a priority. Due to years of culti-
vation and fertilization, potato produc-
tion lands have high phosphorous (P)
levels (up to 80 mg/kg) because phos-
phorous does not leach easily (Leake
undated). These high P levels will likely
inhibit the establishment of fynbos spe-
cies, which normally grows in soil with
relatively low P levels of around 8 mg/kg
(Mitchell et al. 1984; Hawkins et al. 2008).
One way to lower the soil P levels is to
plant an initial crop mixture that includes
lupines, and harvesting and removing it
at the end of the season (Hawkins et al.
2010). Lupines, like proteas, have spe-
cialised cluster roots that can mobilise P
from poorly soluble P in the soil and, in
turn, is taken up by the rapidly growing
plants (Hawkins and Cramer 2007). The
addition of annual crops in the mixture
can also initiate nutrient cycling in the
soil (Holmes and Richardson 1999).
This article addresses the question:
“Does cultivation and sowing of initial
crops have an impact on some aspects
07
Figure 1: Abandoned potato production land at the Redelinghuys site.
of the soil biology and soil seedbank
one year after cultivation?”
The study was conducted at three dif-
ferent sites in the Leipoldtville Sand
Fynbos, all on sandy soils with high soil
P levels (35-63 mg/kg). The abandoned
lands at Elands Bay and Sandberg lie
fallow since 2010 and at Redelinghuys
since 2012 (Figure 1). The long-term av-
erage annual rainfall for the area is 281
mm. The rainfall in 2017 was 50% of the
long-term average and in 2018 it was
290 mm.
At each site, shallow-tillage (to a depth
of 100 mm) with a tine-implement was
done in June 2017 and an initial crop
mixture was sown in twelve 5 × 5 m plots
following a completely randomised de-
sign. Because of the low rainfall in the
year 2017, it was repeated in May 2018.
The crop was harvested and removed in
September 2018 before seed set. The
initial crop mixture included lupines, rye
and vetch in 2017 and lupines, rye and
serradella in 2018.
In each of these plots, soil samples were
taken in May 2017 to determine the soil
seedbank composition and soil health,
using Solvita ® C and BiologEcoplate TM
Grassroots
Vol 20
No 1
March 2020