Sorghum (Sorghum bicolor L., Moench) and pearl millet (Pennisetum americanum L., Leeke) were intercropped under soil moisture non-stress and stress at Marana, Arizona during summer 1987. Effects of soil moisture stress and inter-row competition between sorghum and pearl millet on grain yield, 50% bloom, plant height, head length, head exsertion, 1000 grain weight, and number of effective tillers were evaluated. Interplot competition significantly reduced grain yield and head exsertion of peal millet. In sorghum, only plant height was significantly different due to competition. Agronomic characters were significantly different due to the effect of soil moisture stress except head length in pearl millet and head length, 1000 seed weight, and number of effective tillers in sorghum. Sorghum growing in a neighbor plot greatly suppressed millet grain yield under soil moisture stress. Relative yield total of the cereals under intercrop was less than unity under soil moisture stress.

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Thesis (M.S.)--West Virginia University, 2002. / Title from document title page. Document formatted into pages; contains viii, 77 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 71-77).

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Experimental plots were overlaid on commercial fields of broccoli (Brassica oleraceae L. var. Italica) and cauliflower (Brassica oleraceae L. var. botrytis L.) to evaluate legume species as interseedings in vegetable production. White clover (Trifolium repens L.), red clover (T. pratense L.), yellow sweet clover (Melilotus officinalis L.), hairy vetch (Vicia villosa Roth.) and crimson clover (T. incarnatum L.) were seeded 4-5 weeks after an early planting of broccoli and a late planting of cauliflower. Crop yields, forage biomass, weed biomass and percent fall ground cover were recorded. / A dry year coupled with difficulties in applying the treatments resulted in low forage biomass. Hairy vetch yielded the most within the early broccoli planting system. High rainfall the next year resulted in high biomass yields. Over the two year study, hairy vetch and crimson clover emerged as the two most productive species. Significant effects on fall weed biomass were observed with broccoli in the second year of the study, where interseeded plots reduced weed populations by at least 66%. No evidence was seen of weed suppression by interseedings prior to harvest. Crop yields were not affected by interseedings. All interseeded treatments provided the minimum of 30% ground cover required to help reduce erosion.

The primary hypothesis of this research was that improved cowpea genotypes (selected under sole crop) could yield well in several Nigerian cropping systems, and that there were cowpea characteristics that improved overall system productivity. Cowpea lines were identified which were high yielding and stable in several management systems. Practices such as not applying insecticide and intercropping both reduced cowpea grain yield significantly. Land equivalent ratios were greater than one for all tested intercrop systems: cassava-cowpea (1.21-2.35), maize-cowpea (1.31-4.23), maize-cassava-cowpea (1.63-3.40) and millet-cowpea (1.13-6.88). Nitrogen nutrition of component crops was investigated. Line influenced both maize grain (12.5-28.4 kg ha-1) and total biomass (48.7-69.0 kg ha-1) nitrogen yield. Evidence from pot and field experiments (including $ sp{15}$N-dilution studies) indicated same-season nitrogen transfer. Light interception studies also indicated the increased light harvesting ability of early sole cowpea lines compared to early intercropped lines systems.

N-transfer from legume to grass when the two were intercropped in the field and the mechanisms of this transfer were studied. Studies involving either alfalfa-grasses or soybean-corn intercrops, were undertaken. Mycorrhizal and P-supplemented (to compensate for the lack of mycorrhizae) intercrops were compared. In these studies, the legume component of intercrops was labelled with $ sp{15}$N and any excess of the label was looked for in the associated grass plants. / There was no reversal of N transport at the legume-fungus interface. N-transfer from legume to grass must therefore, proceed via excretion of N by legume roots and subsequent uptake by grass roots. Soil microorganisms and proximity of plant root systems are important factors affecting N-transfer. Mycorrhizae enhance the transfer by increasing the absorptive efficiency of the receiver plants. / Mycorrhizal fungi enhance the competitiveness of the most mycotrophic component of the mixtures by either improving P uptake or the general nutrient balance of the plant. Mycorrhizal inoculation can decrease the level of P competition between corn and soybean by increasing the availability of P. / The observation that mycorrhizal plants differ in many regards from P-supplemented plants, emphasize the generally poor comprehension of the mycorrhizal symbiosis.

Arbuscular mycorrhizal (AM) fungi are an important component of agricultural ecosystems, and can directly influence the productivity of these systems. Unfortunately, conventional agricultural practices have been shown to adversely affect AM fungi. The use of more ecologically sustainable agricultural practices such as tree-based intercropping (TBI) may have the potential to reduce the negative impact of agricultural practices on AM fungi. The objectives of this thesis were to determine (1) if trees influence the structuring of AM fungal communities, (2) if TBI systems support a more diverse AM fungal community compared to conventional monocropping (CM) systems, and (3) if differences in AM fungal richness and composition between the two cropping systems have a functional effect on the growth of crops. Molecular analysis of the AM fungal community in the TBI system revealed 17 phylotypes that all belonged to the family Glomeraceae. Differences in richness and composition among the treatments indicated that trees had an effect on the structuring of AM fungal communities. Intercropping alleys adjacent to white ash and poplar tree rows had a significantly (P < 0.05) richer and different AM fungal community compared to intercropping alleys adjacent to Norway spruce tree rows. When comparing TBI and CM systems, AM fungal abundance was not significantly (P > 0.05) different between the two cropping systems. However, differences in both richness and community composition of AM fungi were observed between the two cropping systems. The TBI system had a significantly higher AM fungal richness and contained several taxa not found in the CM system. Controlled greenhouse experiments revealed that differences in AM fungal richness and community composition between the TBI and CM systems had no functional effect on the growth of three crops (i.e. barley, canola, and soybean). The similar growth response of crops to AM fungi from the two cropping systems may be due to the lack of functional complementarity among the AM fungi. Overall, the TBI system had a more diverse AM fungal community compared to the CM system and trees appear to be a significant factor in the structuring of these communities.

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In studies involving intercropping plant populations, the main interest is to locate the position of the maximum response or to study the response pattern. Such studies normally require many plant population levels. Thus, designs such as spacing systematic designs that minimise experimental land area are desired. Randomised block designs may not perform well as they allow few population levels which may not span the maximum or enable exploration of other features of the response surface. However, lack of complete randomisation in systematic designs may imply spatial variability (largescale and small-scale variations i.e. trend and spatial dependence) in observations. There is no correct statistical method laid out for data analysis from such designs. Given that spacing systematic designs are not well explored in literature, the main thrusts of this study are two fold; namely, to explore the use of spatial modelling techniques in analysing and modelling data from systematic designs, and to evaluate the efficiency of systematic designs used in intercropping experiments. Three classes of models for trend and error modelling are explored/introduced. These include spatial linear mixed models, semi-parametric mixed models and beta-hat models incorporating spatial variability. The reliability and precision of these methods are demonstrated. Relative efficiency of systematic designs to completely randomised design are evaluated. The analysis of data from systematic designs is shown be easily implemented. Measures of efficiency that include <pp directed measures (A and E criteria), D1 and DB efficiencies for regression parameters, and power are used. Systematic designs are shown to be efficient; on average 72% for A and E- efficiencies and 93% for D1 and DB efficiencies. Overall, these results suggest that systematic designs are suitable and reliable for intercropping plant population studies. / Thesis (M.Sc.) - University of Natal, Pietermaritzburg, 2002