Senwes Scenario December 2017 - March 2018 | Page 16

••••
T RADE N E W S
Soil health
and the impacts of conservation
INVESTIGATING THE
IMPACTS OF CONSERVA-
TION AGRICULTURE PRAC-
TICES ON SOIL HEALTH
AS KEY TO SUSTAINABLE
DRY LAND MAIZE PRO-
DUCTION SYSTEMS ON
SEMI-ARID SANDY SOILS
WITH WATER TABLES IN
THE NORTH-WESTERN
FREE STATE.

DANIE BEUKES, ANDRÉ NEL
GERRIE TRYTSMAN, MARYKE
CRAVEN, SONIA STEENKAMP
OWEN RHODE, PETRUS VAN
STADEN EN BOET VAN ZYL
T
he sandy soils of the
North-Western Free State
are known for their inherent
compaction problem, low organic
matter content and low nutrient
and water retention capability.
Research in the 1970’s led to the
implementation of the rip-on-the-
row (ROR) tillage system, which
comprised various depths of rip-
ping, mostly on the row, in com-
bination with secondary shallow
tillage practices. Actual problems
that still exist are the short-term
residual effect of ROR, poor
retention of crop residue, soil
losses and seedling damage due to
wind erosion and the impact of
14
fluctuating water tables.
A comprehensive investi-
gation based on Conservation
Agricultural (CA) principles and
practices was launched in 2016
by the Sandy Soil Development
Committee to enhance and main-
tain the productivity of these soils
in view of national food security.
The emphasis will be on: (i) poor
soil health, (ii) soil compaction,
(iii) diversifying annual crop-
ping systems to include legumes,
perennial crops and forages in
rotations, (iv) using cover crops
in conjunction with row crops,
(v) integrating livestock with
cropping systems (vi) prevalence
of crown and root rot, nematode
infestation, microbial diversity
and activity and (vii) profitability
information of various CA sys-
tems and practices.
Highlights from the
first season (2016/17)
TRIAL 1: Regenerative CA crop-live-
stock integrated system with rota-
tions of maize summer-winter diverse
ley crops (Danie Crous, Deelpan,
Kroonstad):
Growth and yield of crops:
• Dry matter (DM) yields of the
summer cover crops ranged
from 14.5 to 17.1 t ha -1 , while
DM yields of the winter cover
crops ranged from 11.3 and
16.1 t ha -1 .
• The winter cover crops gave
the highest water use efficien-
DES 2017-MRT 2018 • SENWES Scenario
cy (WUE) compared to the
summer cover crops (36.6 vs.
25.9 kg dry matter mm -1 ha -1 ),
while the monoculture maize
attained a WUE of 14.3 kg
grain mm-1 ha -1 .
Soil water studies:
• The summer cover crop mix-
ture led to a build-up of soil
organic carbon (SOC) in the
0-100 mm layer of 0.74% C
compared to, for example,
0.49% C under a grass land.
• Between rainfall events, soil
water content (SWC) quickly
approached the permanent
wilting point. SWC was much
lower under the summer cover
crop mixture compared to the
maize crop immediately after
a rain event. This is probably
due to the interception of the
rain by the closed canopy of
the former crops, followed by
evaporative losses directly from
the crop canopy. A full SWC
profile was measured on the
fallow land before planting of
the winter cover crops.
• Leaching of costly and health
threatening NO 3 -N on these
sandy soils appears to be a seri-
ous problem. Another health
threatening component was
the presence of high concen-
trations NO 2 (nitrite). Other
plant nutrients, such as PO 4 ,
K, Ca and Mg, were also pres-
ent in both water tables at all
dates of sampling.