Thesis (Ph.D. (Plant Production)) -- University of Limpopo, 2022 / Sustainable food production has been a major challenge in the era of climate change
and a growing population in the twenty-first century. However, climate change
scenarios such as extreme temperatures and fluctuations in annual precipitation
continue to pose a great threat to agricultural production systems. On the other hand,
anthropogenic activities such as conventional farming continue to contribute to climate
change through the emission of greenhouse gases while not sustaining agricultural
production. The Food and Agriculture Organization of the United Nations (FAO-UN)
developed the concept of Climate-Smart Agricultural (CSA) production with the idea
of securing food in the face of global change. No-tillage and intercropping systems are
among the traditional practices that are advocated as components of climate-smart
traditional practices, especially in the semi-arid regions of Africa like the Limpopo
Province.
Producing sorghum and cowpeas using CSA practices such as intercropping under
no-tillage is envisaged to increase productivity and soil fertility under Limpopo
Province's dryland conditions. However, there is still limited information on how grain
sorghum-cowpea intercrop will respond in terms of growth, physiological productivity,
and carbon dioxide emissions in the system, especially under no-tillage and different
growing conditions. Furthermore, more field data is required for predictions of future
scenarios using simulating crop models such as the Agricultural Production system
sImulator (APSIM). Hence, a no-till Randomized Complete Block Design (RCBD) in a
2 x 4 x 2 factorial arrangement was conducted at two locations (Syferkuil and Ofcolaco)
in the Limpopo Province during the 2018/19 and 2020/21 cropping seasons to
generate data on sorghum and cowpea growth, physiology, productivity as well as
carbon dynamics under planted and simulated intercropping system.
Leaf gaseous exchange and leaf area index (LAI) were measured on fully developed
grain sorghum and cowpea leaves in both the binary and sole cultures of sorghum and
cowpea. The CO2 measurements were taken from each plot using a GMP343 CO2
probe along with an MI70 data logger. Aboveground biomass was collected for each
crop from two plants at vegetative, flowering, physiological and harvest maturity and
oven-dried at 65 oC for 48 hours. In the 2020/21 cropping season, cowpea at Ofcolaco
failed to produce grain. Hence, only the grain yield of the 2018/19 cropping season
from Ofcolaco is presented in this thesis. Grains collected for each crop from a 2.7m2
area were taken to the laboratory to determine grain yield and yield components.
Harvest index (HI) and land equivalent ratio (LER) for each crop were also determined.
In the laboratory, the total nitrogen (%) and natural abundance of 15N (δ15N‰) were
determined using an isotope ratio mass spectrometer with an N analyzer. Growth
(biomass) and yield (grain) data obtained from APSIM were compared with data
collected from a two-year field experiment at Syferkuil. Multi-variate analysis of
variance (ANOVA) model to fit each response variable using the Statistical Analysis
System (21 SAS version 9.4). Mean separation was done where the means were
different using the least significant difference (LSD) at probability levels of p ≤ 0.05.
Intercropping system and the density of the companion crop cowpea had a significant
(p ≤ 0.05) effect on the physiological responses of sorghum and cowpea, cowpea yield
and yield components at the two experimental sites across seasons. However, grain
yield and yield components of sorghum were not affected by intercropping or the
density of cowpea. Only cultivars of sorghum were significantly different for grain yield
and yield components. At Syferkuil, Enforcer produced the highest grain yield of 4338
kg ha-1 in 2018/19, while NS5511 accumulated the highest grain yield of 2120 kg ha-1
during the 2020/21 cropping seasons. At Ofcolaco, Enforcer and Avenger were
observed to be relatively high-yielding cultivars with a mean grain yield of 2625 kg ha-
1 and 1191 kg ha-1 during the 2018/19 and 2020/21 cropping seasons, respectively. In
the 2018/19 and 2020/21 cropping seasons, respectively, cowpea accumulated about
93% and 77% more grain yield in sole compared to binary culture. At Ofcolaco, about
96% more grain yield was obtained in sole compared to binary cultures during the
2018/19 cropping season. Furthermore, cowpea accumulated over 55% and 49% of
grain yield when grown at high compared to low population density at Syferkuil and
Ofcolaco, respectively. The investigation on the impact of the intercropping system on
CO2 emissions and soil carbon stocks revealed that in 2018/19 at Syferkuil and
2020/21 at Ofcolaco, intercropping systems emitted 11% and 19% less CO2
respectively than the sole cropping systems. In both diverse agro-ecological sites, low
cowpea density consistently resulted in higher CO2 emissions than high density. The
sorghum-cowpea intercropping system significantly influenced the biological nitrogen
fixation of cowpea. Intercropping was found to improve the biological nitrogen fixation
of cowpea if a density of 74074 plants ha-1 is used. The APSIM model was able to capture the dynamics of biomass and grain yields in the sole and intercropping system
under different densities of cowpea.
The findings of this study revealed some useful insights. Firstly, biomass accumulation
depended on the cultivar in intercrop as well as the density of cowpea. Secondly,
cowpea at a density of 74074 plants ha1 was found to be a good crop to intercrop with
grain sorghum as it did not show any significant variation in terms of grain yield and
yield components of sorghum. The sorghum cultivar, Enforcer and NS5511 were the
best performing cultivars in terms of grain yields at Syferkuil and Ofcolaco. Thirdly, the
intercropping system under high cowpea density reduced CO2 emission rates while
improving soil nitrogen (N) and carbon stocks. Based on the results of this study, grain
sorghum-cowpea intercrop can be adopted as a component of a climate-smart
practice to improve crop growth, physiology, as well as productivity compared to sole
cropping. However, the grain sorghum cultivar and the density of cowpea should be
taken into consideration as they affect the productivity of the two crops. The two
seasons data generated from this study was useful in simulating the productivity of
intercropping practice using APSIM. However, more field and weather data is required
to run long-term simulations on intercropping as a component of the climate-smart
method using crop modelling techniques. / National Research Foundation (NRF), Departments of
Science and Innovation (DSI) and VLIR-IUC (Belgium)
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ul/oai:ulspace.ul.ac.za:10386/4133 |
| Date | January 2022 |
| Creators | Mogale, Tlou Elizabeth |
| Contributors | Ayisi, K. K., Munjonji, L., Kifle, Y. G. |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | xxviii, 196 leaves |
| Relation |
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