The performance of three maize (Zea mays L.) hybrids, grown under two irrigation levels, was used to investigate the effects of soil moisture competition between adjacent plots, the transmission of these effects into multi-row adjacent plots and types of multi-row plots and plot borders most effective in shielding from these interplot competition effects. On the basis of grain yield, competition effects intended to the second rows of five-row plots necessitating more than five-row plots to accurately evaluate the full transmission of interplot competition effects into adjacent plots. Evaluation of genotypes in one-row plots all with the same common border row genotype to make them three-row plots would be more suitable for evaluation of relative competitiveness for soil moisture under soil moisture stress conditions compared to no border rows or border rows of the same genotype being evaluated.

Thesis (M.Sc. (Soil Science)) --University of Limpopo, 2013 / Large amount of pre-plant nitrogen (N) fertilizer results in low nutrient-use-efficiency due to poor synchrony between soil N supply and maize demand, especially during N sensitive growth stages. Optimum maize production is dependent on adequate N availability to the crop during the critical vegetative and reproductive growth stages. High N fertilizer prices and maize yield decline are the main challenges faced by the Limpopo Province farmers. The objectives of this study were to compare growth and yield of maize under conventional and site-specific N management in a dryland farming system. The study was conducted in Leeukraal, Towoomba, Ga-Marishane and Radium in the Limpopo Province, South Africa. Experimental plots were laid out in a randomized complete block design, with four replications. Phosphorus was applied through band placement using a planter in all plots at a rate of 42 kg P/ha. Hybrid maize SNK 2147 was planted on a 20 by 20 m plot with Inter-row and Intra-row spacing of 0.9 and 0.35 m respectively. Treatments consisted of 3 N management strategies as follows, (i) No N application (N0), (ii) Site-specific N at a rate ranging between 18 and 33 kg N/ha (N1) and (iii) Conventional N application at 58 kg N/ha (N2). Treatment N2 was applied at a uniform rate during maize planting. Sufficiency index as an indication for N deficiency was determined using CCM-200 for treatment N1. The sufficiency index was determined during leaf stage V6, V10 and V14, and thereafter N was applied only when needed. Data were subjected to analysis of variance through Statistical Analysis System package. Mean separation tests were computed using Duncan’s Multiple Range Test. Maize grain yield at Leeukraal of 5.2 t/ha for N1 was higher than 3.2 and 4.0 t/ha of N0 and N2, respectively. There was no difference amongst the three N management approaches on the grain yield at Towoomba. The grain yield at Ga-Marishane for N1 of 2.2 t/ha was significantly higher than 1.7 t/ha of the N0. Conventional management approach, which is a traditional approach used by farmers in the Limpopo Province, had 2.6 t/ha grain yield that was significantly higher than the N0 and N1. The maize growth and yield under N2 and N1 was compared, N1 required between 43 and 69% lesser N fertilizer as compared to N2. Therefore site-specific nutrient management approach sustains and improves growth and yield of maize using minimal inputs of N compared to conventional approach. This therefore saves input costs and avoids unnecessary environmental consequences. Key words: maize yield, nitrogen management, site-specific approach / Vlaamse Interuniveritatire Raad and Limpopo Department of Agriculture

Quality protein maize (QPM) has enhanced levels of two essential amino acids, lysine and tryptophan compared to normal maize. This makes QPM an important cereal crop in communities where maize is a staple crop. The main abiotic factor to QPM production is drought stress. Little information is available on the effect of drought stress on QPM. Therefore, the objectives of this study were to: (i) conduct diversity analysis of QPM inbred lines using morpho-agronomic and simple sequence repeat markers, (ii) screen available QPM inbred lines and F1 progeny for tolerance to seedling drought stress, (iii) determine the combining ability and type of gene action of QPM inbred lines for tolerance to seedling drought stress, grain yield and endosperm modification. The study was conducted in South Africa, at the University of Fort Hare. Morphological characterisation of 21 inbred lines was done using quantitative and qualitative traits. A randomised complete block design with three replicates was used for characterizing the inbred lines in the field. Genstat statistical software, version 12 (Genstat ®, 2009) was used for analysis of variance (ANOVA) and descriptive statistics. Analysis of variance was performed on all quantitative data for morphological traits. Data for qualitative traits was tabulated in their nominal classes. Traits that contributed most to the variation were days to anthesis, days to silking, anthesis-silking interval, plant height, number of kernel rows, ear length and grain yield. Cluster analysis grouped the inbred lines into three main clusters. The first cluster was characterised by tall and average yielding lines, while the second cluster showed the least anthesis-silking interval, and had the highest yield. Cluster three consisted of lines that were early maturing, but were the least yielding. Genetic distances between maize inbred lines were quantified by using 27 simple sequence repeat markers. The genetic distances between genotypes was computed using Roger’s (1972) genetic distances. Cluster analysis was then carried out using the neighbour-joining tree method using Power Marker software version 3.25. A dendrogram generated from the genetic study of the inbred lines revealed three groups that concurred with expectations based upon pedigree data. These groups were not identical to the groups generated using morpho-agronomic characterisation. Twenty one QPM inbred lines were crossed using a North Carolina design II mating scheme. These were divided into seven sets, each with three inbred lines. The three inbred lines in one set were used as females and crossed with three inbred lines in another set consisting of males. Each inbred line was used as a female in one set, and as a male in a second set. Sixty three hybrids (7 sets x 9 hybrids) were formed and evaluated in October 2011, using a 6x8 alpha-lattice incomplete block design with three replicates under glasshouse and optimum field conditions. A randomised complete block design with three replicates was used for the 21 parental inbred lines. Traits recorded for the glasshouse study were, canopy temperature, chlorophyll content, leaf roll, stem diameter, plant height, leaf number, leaf area, fresh and dry root and shoot weights. Data for the various traits for each environment, 25 percent (stress treatment) and 75 percent (non-stress) of field capacity, were subjected to analysis of variance using the unbalanced treatment design in Genstat statistical package Edition 12. Where varietal differences were found, means were separated using Tukey’s test. Genetic analyses for grain yield and agronomic traits were performed using a fixed effects model in JMP 10 following Residual Maximum Likelihood procedure (REML). From the results, inbred lines that were not previously classified into heterotic groups and drought tolerance categories were classified based on their total dry weight performance and drought susceptibility index. Inbred lines L18, L9, L8, L6 and L3, in order of their drought tolerance index were the best performers under greenhouse conditions and could be recommended for breeding new varieties that are tolerant to seedling drought stress. Evaluation of maize seedlings tolerant to drought stress under glasshouse conditions revealed that cross combination L18 x L11 was drought tolerant, while cross L20 x L7 was susceptible. Total dry weight was used as the major criteria for classifying F1 maize seedlings as being resistant or susceptible. General combining ability effects accounted for 67.43 percent of the genetic variation for total dry weight, while specific combining ability effects contributed 37.57 percent. This indicated that additive gene effects were more important than non-additive gene action in controlling this trait. In the field study (non-drought), the experimental design was a 6x8 alpha lattice incomplete block design with three replicates. On an adjacent field a randomised complete block design with three replicates was used to evaluate the parental inbred lines. The following variables were recorded: plant height, ear height, ears per plant, endosperm modification, days to silking and days to anthesis, anthesis-silking interval, number of kernels per row, number of rows per ear and grain yield. General analyses for the incomplete lattice block design and randomised complete block design for hybrid and inbred data respectively were performed using JMP 10 statistical software. Means were separated using the Tukey's test. Genetic analyses of data for grain yield and agronomic traits were conducted using a fixed effects model using REML in JMP 10. The importance of both GCA (51 percent) and SCA (49 percent) was observed for grain yield. A preponderance of GCA existed for ear height, days to anthesis, anthesis-silking interval, ears per plant and number of kernels per row, indicating that predominantly, additive gene effects controlled hybrid performance under optimum field conditions. The highest heritability was observed for days to silking (48.27 percent) suggesting that yield could be improved through selection for this trait. Under field conditions, variation in time to maturity was observed. This implies that these inbred lines can be recommended for utilisation in different agro-ecologies. Early maturing lines such as L18 can be used to introduce earliness in local cultivars, while early maturing single crosses such as L18 x L2, L5 x L9, L3 x L4 and L2 x L21 could be recommended for maize growers in drought prone areas such as the former Ciskei. Single crosses L18xL11, L16xL18, L8xL21 and L9xL6 had good tolerance to seedling drought stress. On the other hand, single crosses L18xL11 and L11xL13 had high grain yield and good endosperm modification. All these single crosses could be recommended for commercial production after evaluation across locations in the Eastern Cape Province. Alternatively they can be crossed with other superior inbreds to generate three or four way hybrids, which could then be evaluated for potential use by farmers in the Eastern Cape.