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University of Dundee (1990)

Studies on mycorrhizal crop plants of the semi-arid tropics

Laing, K.M

Titre : Studies on mycorrhizal crop plants of the semi-arid tropics

Auteur : Laing, K.M

Université de soutenance : University of Dundee

Grade : Doctor of Philosophy (PhD) 1990

In this thesis, the use of relatively cheap and readily available fertilizers, namely urea, rock phosphates and organic amendments, has been examined in conjunction with the exploitation of biofertilizers such as rhizobia, free-living nitrogen-fixing bacteria and, in particular, vesicular-arbuscular mycorrhizal fungi, with the aim of improving crop yields under semi-arid tropical conditions. Work was carried out both in a glasshouse in Dundee and in the field in the Sahelian zone of Niger, West Africa.It was shown in glasshouse experiments that combinations of urea and straw producing soil C:N ratios in the range 14 to 25 were generally the most effective at increasing maize yields. The presence of urea promoted the development of mycorrhizal infection in maize plants inoculated with spores of Glomus clarum. Urea similarly increased mycorrhizal infection in inoculated chickpea plants, but caused a reduction in nodulation. Nodu-lation was, however, increased by mycorrhizal infection when urea was present at moderate levels. Mycorrhizal maize plants, grown with urea and straw amendments, tended to have higher yields than non-mycorrhizal plants when supplied with moderate levels of partially-acidulated phosphate rock (PAPR). For mycorrhizal plants, a high level of PAPR was found to be as effective as a low rate of soluble phosphate in enhancing plant growth. Further glasshouse experiments showed that application of straw to the soil surface greatly reduced water losses from the soil. Mycorrhizal infection was shown to increase the drought resistance of maize and there was some evidence that mycorrhizas also improved water utilization by the plants.It was demonstrated that on a site in Niger, spores of VA mycorrhizal fungi occurred naturally. Soil samples from a field of pearl millet showed that the long-term addition of crop residues and NPK fertilizers increased the number and infectivity of spores. These treatments also enhanced populations of free- living nitrogen-fixing bacteria (Axospirillum spp. and Axotobacter spp.). In a field experiment, introduced mycorrhizal inoculum was shown to be more effective at promoting crop growth compared with natural inoculum when added in conjunction with rock phosphate.

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