A DISSERTATION SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTERS OF SCIENCE IN CROPSCIENCE OF SOKOINE UNIVERSITY AGRICULTURE. MOROGORO, TANZANIA. 2016Rodents often damage crops throughout the growing season, from germination to harvest, thus making it difficult to understand its cumulative effects for crops such as rice that are able to partially compensate. This study examines response of rice yield to rat damage in farmer’s fields and simulated rat damage in irrigated and rain-fed rice (Oryza sativum L.) in Morogoro, one of Tanzania’s granary areas. The study was conducted at Hembeti village in Mvomero district from September, 2012 to July, 2013 where variety TXD 306 was used. Two field experiments; viz: farmers’ managed rice field and rodent simulation damage were conducted. The experimental design for farmer’s field study was split plot laid in Completely Randomized Design (CRD) and a split-split plot layout in a Randomized Complete Block Design (RCBD) with three replications for simulation rat damage experiment. Five damage levels (i.e. cuts at 0%, 10%, 20%, 25% and 50%) at different rice growth stages (i.e. transplanting, vegetative and maturity) and seasons (i.e. dry and wet) were carried out for later experiment. Results show that there were no significant differences in rodent abundance between seasons and crop growth stage in farmer’s managed rice fields. Mastomys natalensis was the most abundant rodent pest species while Grammomys dolichurus was found in small proportions. Higher yield was recorded during the wet season compared with the dry season. Yield loss was observed during all cropping stages for all levels of simulated rat damage for wet and dry season crops, with significant compensation noted at the transplanting stage. Damage above 10% stem cut and at vegetative and maturity stage resulted in significant reductions in rice yield. Grain yield was highly and positive correlated with number of panicles per plant and panicles m-2, filled grains per panicle, percentage grain fill and 1000 grain weight.