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Improving meteorological downscaling methods with artificial neural network modelsTrigo, Ricardo M. January 2000 (has links)
No description available.
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Epidemiological transition and the geography of mortality in BrazilPrata, Pedro Reginaldo dos Santos January 2000 (has links)
No description available.
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The optimization of ventilation and refrigeration in underground British coal minesAnderson, J. M. January 1985 (has links)
No description available.
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SOIL-PLANT CARBON STOCKS IN THE WEATHERLEY CATCHMENT AFTER CONVERSION FROM GRASSLAND TO FORESTRYLebenya, Relebohile Mirriam 17 May 2013 (has links)
Soil and vegetation play a vital role in the global C cycle because C exchange is affected by
both. Thus a change in land use may result in either a loss or gain of C in the soil-plant
system. This study was conducted in the Weatherley catchment in the northerly Eastern
Cape Province, a former grassland area. Approximately half of the 160 ha in the catchment
was afforested with three tree species, viz. P. elliottii, P. patula, and E. nitens in 2002.
Before afforestation, a baseline study (Le Roux et al., 2005) on soil organic matter was
conducted on the areas designated for the above mentioned tree species. Therefore, this
study was a continuation of the mentioned study with the aim to quantify the soil and
biomass C stocks (in some instances N stocks also) eight years after afforestation.
For comparable purposes the same 27 sites studied by Le Roux et al. (2005) were
investigated, viz. 25 afforested sites and two control sites. Soil samples were collected in
2010 at various depths from the 27 sites: 0-50, 0-100, 0-150, 0-200, 0-250, 0-300, 0-400, 0-
500, 0-600, 0-700, 0-800, 0-900, 0-1000, 0-1100, and 0-1200 mm and analysed for organic
C and total N as organic matter indices. At each site, three sub-samples were taken per
depth interval and mixed together to give a composite sample. The procedure was
replicated four times at each site.
At each of the 27 sites, fallen litter and undergrowth were collected simultaneously with the
soil sampling, also in four replicates. After being dried in a glasshouse, the litter was milled
and analysed for C and N contents. A year after soil and litter sampling, when trees were
eight years old, the height and diameter at breast height of 12 trees were measured at each
of the 25 afforested sites. The measured data were used to calculate the utilisable stem
volume, and hence the tree C stocks.
Afforestation of the former grassland areas influenced soil organic matter in the upper 300
mm layer, resulting in either increases or decreases in soil C stocks, N stocks and C:N
ratios. Soil C stocks decreased by 0.9 Mg ha-1 at site 235 (Katsptuit soil with grass) to 23.6
Mg ha-1 at site 232 (Katspruit soil with P. elliottii trees). The rate of decrease ranged
between 0.11 and 2.95 Mg C ha-1 yr-1. The soil C stocks increased by 0.9 Mg ha-1 at site 244
(Pinedene soil with P. patula trees) to 11.3 Mg ha-1 at site 242 (Longlands soil with P. patula
trees). The rate of increase ranged from 0.11 Mg C ha-1 yr-1 to 1.41 Mg C ha-1 yr-1. Soil C
stocks decreased significantly by 5.5 Mg ha-1, 10.0 Mg ha-1, and 12.4 Mg ha-1 for grass, E.
nitens, and P. elliottii areas, respectively. Soils under P. patula showed an increase in C
stocks of 1.9 Mg ha-1. When soils were grouped according to mapping units, drainage
classes or first subsoil (B1 or E1) horizons there was generally a significant decrease in soil C stocks due to afforestation. The soil N stocks to a large extent behaved like the soil C
stocks.
The aboveground biomass C stocks were obtained by adding the litter C stocks and the tree
C stocks together. These aboveground biomass C stocks varied from 3.71 Mg ha-1 at site
209 (Katspruit soil with grass) to 167.2 Mg ha-1 at site 246 (Pinedene soil with E. nitens
trees). On average the aboveground biomass C stocks for the 27 sites was 64.9 Mg ha-1.
However, aboveground biomass C stocks averaged 69.7 Mg ha-1 for the 25 afforested sites
and only 4.8 Mg ha-1 for the two control sites. The aboveground biomass C stocks varied
significantly from 4.8 Mg C ha-1 for the grass to 41.2 Mg ha-1 for the P. elliottii and 67.3 Mg
ha-1 for the P. patula and 113.2 Mg ha-1 for the E. nitens areas. Based on the soil mapping
units, aboveground biomass C stocks varied from 45.6 Mg ha-1 for the C soil group to 83.3
Mg ha-1 for the A soil group. In the drainage class soil group, the aboveground biomass C
stocks varied significantly from 44.1 Mg ha-1 for the poorly drained soils to 81.8 Mg ha-1 for
the moderately drained soils and 74.4 Mg ha-1 for the freely drained soils. The aboveground
biomass C stocks varied significantly from 44.7 Mg ha-1 for the G horizon soils to 86.2 Mg
haâ1 for the red apedal B horizon soils. In general, the tree C stocks contributed the greatest
portion to the aboveground biomass C stocks, which in turn contributed more to the total C
stocks in the catchment. The C (undifferentiated hydromorphic), poorly drained, and G
horizon soil groups had the lowest aboveground biomass C stocks because the conditions in
these soil groups limited tree growth and hence C sequestration.
Total C stocks in the catchment before afforestation were estimated to be 7 209 Mg. After
eight years of afforestation C stocks were estimated to be 11 912 Mg. Therefore the trees
added 4 702 Mg C to the catchment, at a rate of 588 Mg C yr-1 or 3.67 Mg C ha-1 yr-1. The
rate of C sequestration in the afforested areas was 7.74 Mg ha-1 yr-1.
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YIELD AND QUALITY RESPONSE OF HYDROPONICALLY GROWN ROSE GERANIUM (Pelargonium SP.) TO CHANGES IN THE NUTRIENT SOLUTION AND SHADINGSedibe, Moosa Mahmood 17 May 2013 (has links)
This study was undertaken to determine the effect of different concentrations of phosphate, ammonium, nitrate, and sulphate as well as that of shading and moisture stress on oil yield and quality of hydroponically grown rose geranium. Five separate trials were conducted during the 2009 and 2010 growing seasons. Different concentrations of phosphate, ammonium, nitrate and sulphate were used in the first four trials, while the last study focused on the effects of shading and moisture stress on rose geranium.
The phosphate, nitrate, ammonium and sulphate trials were conducted in a greenhouse at the west campus of the University of the Free State in Bloemfontein, South Africa. Plants were grown for four months using a randomized complete block experimental design. The concentrations of phosphorus evaluated were 0.10, 0.80, 1.50 and 2.20 meq L-1. Ammonium concentrations were 0.00, 0.50, 1.00 and 1.50, nitrate concentrations were 8, 10, 12 and 14 and sulphate concentrations were 0.36, 1.90, 3.44 and 4.98 meq L-1.
Foliar drymass and oil yields increased as P concentrations were increased to 2.20 meq L-1. Both, the guaia-6,9-diene content and the citronellol:geraniol (C:G) ratio were better at the high level of phosphate indicating that the best quality oil, as required by the perfume industry is obtained with relatively high phosphate concentrations.
Plant growth as measured by the number of branches and biomass production, peaked at 10 to 12 meq L-1 nitrate concentrations. The highest chlorophyll content in the foliage was found at the nitrate concentrations of 10 and 12 meq L-1, where the best oil yield was also produced. At this nitrate level the citronellol:geraniol (C:G) ratio was slightly higher than the upper limit required for good oil quality but the geraniol and citronellylformate contents were within range for top quality oil. Height, biomass, oil yield and chlorophyll content of the leaves were not affected by ammonium, but the concentrations of plant tissue sulphur and nitrogen increased linearly with increasing concentrations of applied ammonium. Rose geranium needs to be grown at a relatively high nitrate concentration (10 to12 meq L-1) to ensure high oil yield. This application falls within the range that is used for most vegetable and ornamental crops under soilless conditions. Ammonium concentrations of up to 1.00 meq L-1 can be used without affecting yield or oil quality of rose geranium.
A significant effect of sulphate on branches, height and branch:height (B:H) ratio and foliar dry mass (DM) was observed. The four sulphate concentrations showed a statistically non significant trend on yield. Based on the standards used by the perfume industry the oil of rose geranium was not of a good quality in this trial probably due to the autumn planting time.
Shading and moisture stress were used as treatments in a study conducted at the University of the Free State experimental farm during spring and summer. A split plot experimental layout was assigned using 0%, 20%, 40%, 60% and 80% shade treatments allocated to the main plots. The subplots were exposed to moisture stress levels at 0 and -0.15 MPa of osmotic pressure.
Rose geranium grew well under a shading of 40%, where plant growth parameters such as foliar fresh mass (FM), foliar dry mass (DM) and the branch:height ratio were increased. Subsequently the best oil yield was obtained at this level. Proline content was high due to excessive solar radiation at 0% shade as well as where moisture stress was induced, however, oil quality was not affected. The number of oil glands cm-2 of leaf area was not significantly affected by shading, but tended to be lower at shading levels higher than 60%. Fresh mass, DM, the ratio of branches to height and oil yield were affected by shading. Proline content gave a clear indication of stress conditions of plants at full radiation as well as moisture stress. Growers are advised to use 40% shading to grow geraniums in summer at radiation levels similar to those found in this study.
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CORRELATION BETWEEN AGRONOMIC AND ENVIRONMENTAL PHOSPHORUS ANALYSES OF SELECTED SOILSNthejane, 'Mabatho Margaret 24 May 2013 (has links)
In crop production phosphorus (P) is an essential nutrient for crop growth, and hence P
fertilization is necessary to achieve optimum yields. However, this can induces in soil a P
concentration which may contributes to eutrophication of fresh water bodies. Soil P tests are
therefore considered very useful in setting threshold values important for both agronomic and
environmental management purposes. Soil P tests developed from a water pollution protection
point unlike agronomic P tests are not easily adapted for use on a routine basis because they
are not considered, for this purpose, and this could make agronomic P tests more practical for
routine environmental P assessment also. Determination of appropriate agronomic P tests for
this purpose however, involves evaluating the potential use of the tests for environmental
purposes. Hence, the objective of this study was to review the current methods used to
determine the agronomic and environmental P status of soils, and to establish whether P
extracted from a range of soils by various agronomic and/or environmental P determination
methods are related or not.
Soil samples from the orthic A horison were collected in three cropping areas in the Free State
province, namely Jacobsdal, Bloemfontein, and Ficksburg. These samples were treated with
K2HPO4 to induce different phosphorus concentration levels and then incubated at room
temperature for three months. During incubation the samples were subjected to several wetting
and drying cycles to ensure that the applied phosphorus equilibrated. The samples were then
analysed for P using the extractants of Olsen, Bray 1, Truog, ISFEI and citric acid commonly
employed for routine analysis to establish the agronomic P status of soils. In order to establish
the environmental P status of the soils, the samples were analysed for using the extractants
calcium chloride (CaCl2) and ammonium oxalate [(NH4)2C2O4.H2O]. The latter was used to
calculate the degree of phosphorus saturation (DPSox).
The results showed significant relationships among agronomic P tests when data of individual
soils were analysed separately (r2=0.65-0.99) and, when data of all soils from a sampling area
were pooled (r2=0.52-0.87). All the relationships were significant for the Ficksburg soils
(r2â¥0.55) and for the Bloemfontein soils (r2â¥0.82) but not for the Jacobsdal soils. For the latter
soils the Truog-P correlations with Olsen-P (r2=0.44), Bray 1-P (r2=0.42) and ISFEI-P (r2=0.35)
were not significant, probably due to that they are calcareous. Significant relationships were also obtained for P extracted by the environmental P tests when
regression analysis was done for each individual soil (r2â¥0.80). However, when data of soils
from a sampling area were pooled significant relationships were obtained for Bloemfontein soils
(r2=0.92) and Ficksburg soils (r2=0.56) while Jacbosdal soils (r2=0.33) showed an insignificant
relationship. Pooling data of all soils from the three sampling areas also resulted with a lower
correlation coefficient (r2=0.40) implying a poor relationship between the environmental P tests.
The correlation between P extracted by the agronomic tests and CaCl2-P showed positive
relationships (r2 â¥0.57) except in a few instances. Truog-P and citric acid-P showed a poor
correlation with CaCl2-P when the Jacobsdal soilsâ data were pooled (r2=0.22 and 0.35
respectively). Pooling of all soilsâ data resulted also in a poor correlation between CaCl2-P and
Truog âP (r2= 0.28). The DPSox correlated significantly with the extractable P of all agronomic
tests when the individual soilâs data were analysed separately (r2 â¥0.73). However, when data of
all soils from a sampling areas were pooled for regression analysis, all relationships were
significant for the Bloemfontein soils (r2 â¥0.70), but not for the Jacobsdal soils, and Ficksburg
soils. Pooling data of all soils from the three sites resulted with a positive relationship between
DPSox and the extractable P of all agronomic tests (r2 â¥0.50), except ISFEI (r2 â¥0.45).
The threshold values estimated for agronomic tests with regression equations from CaCl2-P
DPSox threshold values varied greatly between individual soils and even the soils groups of a
sampling area. The threshold values for all soils when based on CaCl2 implied that if the
extractable P status of cropped soils are maintained at optimum levels for Bray 1, Truog, ISFEI
and citric acid the soils may be a threat to water pollution. The opposite is true with the
estimated threshold values when based on DPSox. The results therefore showed that agronomic
tests can be used also for environmental management of P although only the Olsen test showed
the potential for developing a single threshold value for all soils.
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RESPONSE OF ONION (Allium cepa L.) TO SOWING DATE AND PLANT POPULATIONBosekeng, Gagopale 27 May 2013 (has links)
Field trials were conducted on the West Campus facility of the Department of Soil, Crop
and Climate Sciences of the University of the Free State in Bloemfontein during 2009 and
2010. The first trial during 2009 investigated the response of onion (Allium cepa L.)
cultivars to sowing date. Cultivars namely; Charlize, Jaquar, Python and South Wester
were used in 2009. Onions were sown on 31 April, 7 May and 21 May during 2009. The
second trial was conducted during 2010, where cultivar Ceres Gold was used to replace
South Wester as the latter was no-longer available in the market and sowing was done on
11 May, 25 May and 8 June. In both seasons, experiments were laid out as a randomized
complete block design with each treatment combination replicated three times. During
2009, plant population of 41 plants m-2 was used, while in 2010 plant population of 61
plants m-2 was used. Plots of 1.8 m2 were used with each plot having five rows. Each row
had fifteen plants during 2009 and twenty two plants during 2010. Before planting, soil
sampling and analysis were made, thereafter, fertilizers were applied as per soil analysis
results.
A third field trial was conducted in 2010 to evaluate the three sowing dates (11 May, 25
May and 8 June) with a combination of five plant populations (95, 83, 74, 67 and 61 plants
m-2) using one onion cultivar (âJaquarâ). The experiment was laid out as a randomized
complete bock design, with three replications having 1.8 m2 plots. In each plot there were
five rows. A bulb storage trial was also conducted under room (±25°C) and cold room
temperatures (±5°C). This was done for all field trial in both seasons.
In a trial investigating response of cultivars to sowing date, better plant height, number of
leaves, bulb fresh mass, and yield were observed when sowing was done from the end of
April to the end of May. Sowing date significantly influenced bulb and neck diameters only
during 2009. Bulbs were becoming more firm as sowing date was delayed, and the
opposite was observed for bolting. Cultivar South Wester bolted more, followed by cultivar
Jaquar while other cultivars did not bolt. The shape of bulbs was not significantly
influenced by sowing date but it showed to be cultivar authentic. No split bulbs were
observed. In a trial of sowing date and plant population, significantly taller plants were obtained with
early sowing date than the two later sowing dates. Leaf production was not significantly
influenced by sowing date. Sowing date and plant population affected bulb fresh mass,
yield, bulb and neck diameters as well as firmness. Sowing date did not influence bulb
shape while plant population did. None of the bulbs bolted from this trial.
Mid-intermediate day cultivars (âSouth Westerâ and âCeres Goldâ) recorded the shortest
duration (105 days and 63 days respectively), while on average other cultivars were
stored for 126 days in 2009 and 105 days in 2010. Storage disease (black mould),
sprouting and loss of moisture from the bulbs were the contributing factors for reduction in
storage duration. These factors were promoted by both field and storage conditions. Onion producers should have adequate information on the cultivars and the production
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EVALUATION OF SELECTED INDUSTRIALLY MANUFACTURED BIOLOGICAL AMENDMENTS FOR MAIZE PRODUCTIONBaloyi, Tlangelani Cedric 27 May 2013 (has links)
The soaring prices of inorganic fertilisers among other reasons has persuaded companies to commence producing biological enhanced substances herein refers as industrially manufactured biological amendments (IMBAs) with claims that they could increase crop growth and yield, and also revitalize the soil. Such claims are often without substantial empirical agronomic data to proof the efficacy of these IMBAs.
A glasshouse pot trial was conducted during 2008/09 season to assess the effects of graded rates of nine IMBAs (Biozone, Gliogrow, Gromor, Promis, Growmax, Crop care, K-humate, Lanbac and Montys) on maize seedlings establishment and growth over six-weeks. These were assessed at 50, 75 and 100% of the recommended rates together with optimum inorganic NPK fertiliser and a control as check. The IMBAs exerted in many instances a deleterious effect on percent maize seedling emergences when applied at 100% rate. Application rates of 50 and 75% appeared sufficient amongst most IMBAs for encouraging better growth and phenological development of maize, although the most appropriate rate is dependent on the IMBA type.
Rainfed trials were conducted for three seasons (2006/07-2008/09) at four localities (Bethlehem, Bothaville, Ottosdal and Potchefstroom) to assess the effects of the same nine IMBAs used above on maize performance and on soil health in a randomised completely block design. The IMBAs were applied based on product manufactures and/or supplier recommendations along with optimum inorganic NPK rate and the unamended control as check. All trial sites were planted to one maize cultivar PAN 6479. Every season, observations on phenological growth traits, grain yield and yield components, nitrogen and phosphorus content, uptake, and agronomic use efficiency, soil chemical and microbial properties and on grain quality traits were measured.
The manure-based IMBAs like Gromor, Promis and Growmax generally raised pH (H2O) to between 6.0 and 7.0 which was not always the case with the other IMBAs that coincided with inorganic NPK fertiliser. Generally, Gromor and Gliogrow recorded most cases of significant pH increases compared to the NPK treatment. The frequency of significant increases in organic C, mineral N and extractable P were only four instances and less of all 12 potential cases in relation to the NPK check. Gromor resulted in no cases of significantly higher mineral N and extractable P than the NPK check. The IMBAs promoted higher microbial biomass-C immobilisation at 4-weeks after planting while biomass-C mineralisation was predominant at flowering and crop harvest, although it tended to decline at crop harvest. The different IMBAs exerted in many instances no significant effect on biomass-C and -P compared to the NPK check.
The IMBAs had no positive effect on maize growth and phenological traits compared with the NPK treatment. Application of Gliogrow resulted in constant reduction in plant phenological growth in the 9th leaf and silking growth stages due to poor emergence, particularly from soils with higher clay content. Gromor and Promis exerted no significant positive effect on grain yield and yield components compared to the NPK check. Despite the consistent poor stand count, Gliogrow resulted in significant increases for all the yield parameters measured than any other IMBA. Compared to the NPK check, the IMBAs resulted also in few cases of significant increases on harvest index while no positive significant effect was observed on cob length.
Treatments with Biozone, Gliogrow and Promis at 9th leaf, Gliogrow and K-humate at silking, and Biozone and K-humate at harvesting significantly increased plant N content and uptake at the respective growth stages. None of the IMBAs exerted a significant effect on the agronomic use of the applied N compared to the applied N from the NPK check, except in one case with Promis. The P content and uptake recorded at 9th leaf, silking, and harvesting increased significantly in three to four instances due to the application of Promis, Growmax and Montys. The efficiency of applied P from the IMBAs was not in one case significantly better than the applied P from the NPK check.
Application of Gliogrow, Crop care and Lanbac significantly increased thousand kernel mass in two to three cases, and milling index in two to seven cases in comparison with the NPK check. Gliogrow gave solely significantly higher percentage of >11 mm, and 10-11 mm kernels than the NPK check. Equally, Gromor gave significantly higher percentage of 8-9 mm kernels, and Growmax of 7-8 mm kernels.
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LONG-TERM EFFECTS OF TILLAGE PRACTICES ON BIOLOGICAL INDICATORS OF A SOIL CROPPED ANNUALLY TO WHEATClayton, Hannah Gudrun 27 May 2013 (has links)
Soil sustainability is a long-term goal. Although physical and chemical properties of soil
have been utilized extensively to evaluate soil quality, the application of biological
indicators is becoming more important. In order to assess soil quality, soil enzymes and
other biological parameters need to be considered.
In semi-arid Bethlehem, South Africa, samples were taken at a wheat (Triticum aestivum L.)
monoculture trial which was established in 1979 by the Agricultural Research Council-Small
Grain Institute. The treatments were: no-tillage (NT), stubble-mulch (SM), and conventional
tillage (CT); all paired with chemical weed control, the absence of burning residues, and 40
kg nitrogen ha-1 as limestone ammonium nitrate with single superphosphate as the
fertilizer sources. The study period lasted from October 2010 to October 2011 with eight
sampling times conducted over this year and two depths sampled (0-5 cm, 5-10 cm). Oat
(Avena sativa L.) was growing in the plots from the start of the study until December 2010
when it was harvested. A fallow period then lasted until the planting of wheat in August
2011 which was harvested after the end of the study period.
Potential enzyme activities were assayed for β-glucosidase, urease, acid- and alkalinephosphatase,
and dehydrogenase at all eight sampling times, along with soil texture, total
carbon, total nitrogen, Olsen-extractable phosphorus, and pH. Whole microbial community
profiling using BIOLOG EcoPlatesTM was employed at the first sampling time and
phospholipid fatty acid (PLFA) analysis for the first, third, and fifth sampling times.
It was found that NT and SM had higher values than CT across all enzymes except alkaline
phosphatase, which ranked NT higher than both SM and CT. BIOLOG EcoPlatesTM and PLFA
showed similar results across tillage treatments. Microbial biomass, estimated from both
potential dehydrogenase activities and PLFA values, was higher in NT and SM than in CT. Over the study period the values for all parameters varied but the average ranking of tillage
treatments stayed consistent. In comparing the two soil depths, soil quality was easily
shown to be higher in NT and SM in the 0-5 cm depth, but often in the 5-10 cm depth the
differences faded. Potential acid phosphatase activity was the only measured parameter
which was consistently higher in the 5-10 cm depth.
If the parameters can be used as an index of soil quality, then it can be accepted that NT
has higher quality than CT and often SM has higher quality than CT, but is not at the same
level as NT; it can then be recommended that in semi-arid South Africa, NT will enhance
soil quality under a monoculture cropping practice.
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ESTABLISHING OPTIMUM PLANT POPULATIONS AND WATER USE OF AN ULTRA FAST MAIZE HYBRID (ZEA MAYS L.) UNDER IRRIGATIONYada, Gobeze Loha 18 July 2013 (has links)
For each grain production system, there is an optimum row spacing and plant density that
optimises the use of available resources, allowing the expression of maximum attainable
grain yield in that specific environment. Introduction of the ultra-fast maize hybrids raised
the question whether existing guidelines for row spacing and plant density were still
applicable. This necessitated the integration of optimum row spacing by plant density to
maintain productivity and sustainability the yields with the intention to increase water use
efficiency. Field experiments were conducted for two successive cropping seasons (2008/9
to 2009/10) at Kenilworth Experimental Station of the Department of Soil, Crop and Climate
Sciences, University of the Free State to evaluate the growth, agronomic performance,
phenological development and water use efficiency of an ultra-fast maize hybrid at varying
row spacing and plant densities under irrigation. The treatments involved in this study were
three row spacings (0.225, 0.45 and 0.90 m) and five plant densities (50 000, 75 000,
100 000, 125 000 and 150 000 plant ha-1). The treatments were arranged in a factorial
combination and laid out in a randomized complete block design (RCBD) with four
replications. The largest block was used for periodic destructive sampling for growth
analysis where a completely randomized design was adopted and replications consisted of
five (5) single plants randomly selected. Regarding soil water monitoring, twenty neutron
probe access tubes were installed prior to planting in the center of each plot in one of the
three blocks of the agronomic study. Soil water content was measured at 0.3 m intervals to
a depth of 1.8 m using a calibrated neutron probe. Measurements were made at weekly
intervals from planting to crop physiological maturity where the volumetric reading was
converted into depth of water per 1.8 m. Seasonal ET (water use) was determined by
solving the ET components of the water balance equation. From this water use efficiency
was computed as the ratio of total biomass/grain yield to seasonal ET. In each season crop
growth, agronomic, phenologic and water use efficiency parameters were measured and
the collected data were combined over seasons after carrying the homogeneity test of
variances. Growth parameters, agronomic traits, phenology and water use efficiency of
maize reacted differently to row spacing and plant density and the combination thereof.
In general a slow increase in growth parameters during establishment was followed by an
exponential increase during the vegetative phase. At the reproductive phase growth
ceased following the onset of flowering. Photosynthetic efficiency (NAR) and CGR,
averaged over row spacing, were highest at a plant density of 100 000 plants ha-1 at all
growth phases. Reducing row spacing from 0.45 to 0.225 m and a plant density below or above 100 000 plants ha-1 showed LAI outside the optimum with respect to NAR for
optimum seed yield.
Row spacing, plant density and its interaction affected yield and yield components of maize
significantly. Narrowing rows from 0.45 to 0.225 m and plant densities above
100 000 plants ha-1 as main or interaction effects led to the formation of smaller ears, a
shorter ear length and diameter, low seed mass, favored plant lodging and development of
barren plants with an obvious negative impact on grain yield. On other hand, plant densities
below 100 000 plants ha-1 were insufficient to utilise growth-influencing factors optimally.
Thus, growth analysis provided an opportunity to monitor the main effects and interaction
effects of row spacing and plant density on crop growth at different growth and
development phases.
Row spacing and plant density combinations affected the phenological development of
maize. Increasing row spacing from 0.225 to 0.90 m relatively prolonged the number of
days to anthesis and silking. Regarding anthesis-silking interval (ASI), the lowest plant
density had the shortest ASI while the higher plant densities had relatively longer ASI. Wide
row spacing coupled with low plant density increased the number of days to physiological
maturity and vice versa.
Row spacing and plant density and their interaction affected water use efficiency of maize.
Highest water use was observed at a plant density of 125 000 plants ha-1. Biomass WUE
was highest at a row spacing of 0.45 m with a plant density of 125 000 plants ha-1 while the
highest grain yield WUE recorded was at a row spacing of 0.45 m with a plant density of
100 000 plants ha-1.
The overall combined effect of row spacing and plant density revealed that a combination
of 0.45 or 0.90 m with 100 000 plants ha-1 to be the optimum for the selected ultra-fast
maize hybrid under irrigation.
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