RESPONSE OF CHICKPEA CULTIVARS TO DRYLAND MANAGEMENT IN SOUTHERN ETHIOPIA
Mengistu, Molla Assefa 1967-
Chickpea (Cicer arietinum L.) is a popular and profitable pulse crop for the southern Ethiopian region, yet, due to the lack of improved production technology the average yield of chickpea in the region is relatively low. The current research assessed the agronomic performance of chickpea cultivars as affected by seeding dates and rhizobium inoculation across agro-ecologies in southern Ethiopia. The research also examined the effect of residual nitrogen on wheat grain yield in chickpea wheat rotation. The impact of soil water deficit on nitrogen fixation and seed composition of a set of chickpea cultivars was evaluated under greenhouse conditions. Seeding date can be used as a strategy to avoid high temperatures during flowering and to reduce the effect of water deficit during pod filling. The yield and agronomic characteristics of the chickpea cultivars varied with different seeding dates. The Habru and Ejere cultivars when seeded at a mid or late seeding date tended to flower and mature early across all locations. This indicated that the plants were exposed to stress condition under late seeding resulting in a short growing period. The seeding date experiment showed a grain yield advantage under early seeding date. Growing chickpea under residual moisture immediately after the harvest of the main crop allows farmers to maximize the use of their land by double cropping. Response of chickpea cultivars to Rhizobium inoculation confirmed that the environmental factors and the host symbiont compatibility greatly affected nitrogen fixation. Despite the low total soil nitrogen concentration and the low population (< 10 μg g-1) of the native rhizobia at Wolaita, the inoculation treatment had no effect on seed yield in both 2011 and 2012 trials. This could be due to poor adaptation of the commercial strain of chickpea inoculant used in the study to the research area. It was observed that all the cultivars had small nodule number and the nodules were mostly ineffective. The chickpea cultivars had variable % Nitrogen derived from the atmosphere, ranging from 26 to 54%, regardless of inoculation treatment. The variation of % Nitrogen derived from the atmosphere was relatively high across environments. The results of the analysis of soil samples taken from the seeded plot areas indicated that soil N concentration increased from 0.16% N, before chickpea was planted, to 0.24% N after chickpea was harvested possibly due to the decomposition of the chickpea residue. The rotational benefit of chickpea was evaluated by combining with management practice like application of low rate of nitrogen fertilizer on wheat. The wheat yield grown with low rate nitrogen fertilizer after chickpea was 19 % higher than that grown on the non-fertilized plot after chickpea. Variability of chickpea cultivars in response to water deficit was examined. The accumulation of ureide and nitrate in the shoot varied across chickpea cultivars under water stress condition. The ureide concentration in leaf tissue was twice or more than its concentration in the stem indicating fast translocation of assimilate towards the sink due to stress conditions. Moisture stress reduced stem ureide concentration by 37 % and increased stem nitrate concentration by 62 % compared to control. Concentrations of eighteen different amino acids were estimated in chickpea leaves. High proline, threonine and serine in leaves may have positive effects in osmoregulation as seen in ILC 533 and CDC Chico. Twelve free amino acids were estimated in seeds of 15 cultivars grown under water deficit. The water stress treatment decreased most free amino acid concentration in the majority of the cultivars, except CDC Chico. In conclusion, increasing chickpea productivity on smallholder farms in southern Ethiopia is possible by using improved cultivars with appropriate agronomic practice, namely early seeding. Rhizobium inoculant research should test more strains (domestic or imported) to ascertain the best host-strain combination. The influence of water deficit on nitrogen fixation in chickpea indicated that cultivars varied in their accumulation of ureide and nitrate in the shoot. Screening of germplasm for improved N fixation under water stress should include measurement of leaf amino acids such as serine, proline, and threonine. Emphasis should be given to nodule and shoot ureide relationships, and root and stem nitrate concentrations during the stress period.
DegreeDoctor of Philosophy (Ph.D.)
SupervisorTar'an, Bunyamin; Bueckert, Rosalind
CommitteeBai, Yuguang; Warkentin, Tom; Shirtliffe, Steve; Walley, Fran
Copyright DateOctober 2016