Prediction Of Soil Salinity Spatial Distribution And Its Management Implications For Rice Production In Magozi Irrigation Scheme, Iringa, Tanzania

EXTENDED ABSTRACT

Rice (Oryza sativa L.) plays an important role in improving household food security and national economies in Sub-Saharan Africa including Tanzania. There is an increase in annual per capita consumption of rice in Tanzania from 20.5 in 2001 to about 25 - 30 kg year-1 in 2011 coupled with an increase in population. Despite the increase in rice consumption, the current rice production in Tanzania is still as low as 2.3 t ha-1 while the potential rice yields are 4 to 10 t ha-1 in the country. Reasons for low rice production include poor agronomic practices and land degradation. Soil salinity which refers to the content of soluble salts in the soil is one of the main land degradation problems in many rice growing irrigation schemes in Tanzania. Managing soil salinity in irrigated agriculture is crucial for minimizing its negative effects and for ensuring the long-term sustainability of irrigated agriculture. To achieve this, adequate and accurate information on the magnitude and spatial distribution of soil salinity is required. The knowledge on the nature and properties of soils from pedological characterization studies is also vital in planning the best use and management of soils in crop production. Magozi Irrigation Scheme is one of the rice producing irrigation schemes with an area of 1300 ha in Iringa, Tanzania. The farmers of Magozi depend on rice production from this scheme as their main economic activity. Despite the importance of rice production in this irrigation scheme, the production yields are generally low where the average rice yields have been reported to be 3.05 t ha-1 while the potential yield in the area is 4.06 t ha-1 . There is no detailed study that has focused on addressing soil salinity problem in this irrigation scheme to understand the magnitude and its spatial distribution. This research assessed soil salinity and used GIS-based approach to predict spatial distribution of soil salinity. The study further recommends the soil, crop and irrigation management options that will contribute enhancement of sustainable rice production at Magozi Irrigation Scheme. In order to understand the nature and properties of soils in this irrigation scheme, the first specific objective was a study on pedological characterization whereby three (3) representative soil profiles namely MAG-P1, MAG-P2 and MAG-P3 were opened and characterized for their soil morphological, physical and chemical properties. The soils were then classified to the family level using USDA Soil Taxonomy and to the Tier 2 in the World Reference Base for Soil Resources (WRB). The second specific objective focused on a study to develop a linear regression model that can be used to predict electrical conductivity of the saturated paste extract (ECe) from values of electrical conductivity measured in soil to water suspension (EC1:2.5). The ECe is a globally used soil salinity index for assessing plant response to salinity. A total of 60 soil samples (45 samples for model training and 15 samples for model validation) were collected and analyzed for soil EC1:2.5, ECe and soil texture. A linear regression model relating ECe and EC1:2.5 was developed and validated for use in the next study. Lastly, the study assessed soil salinity and used GIS-based approach to predict spatial distribution of soil salinity in Magozi Irrigation Scheme. A total of 81 geo-referenced soil samples at a depth of 0 - 30 cm collected from the scheme were analyzed for soil physical and chemical properties where ECe was used as the main soil salinity index. The soil salinity spatial distribution map of the scheme based on ECe was generated using Inverse Distance Weighting (IDW) interpolation method in Geographic Information System (GIS).