Extent of salt-affected soils and their effects in irrigated and lowland rain-fed rice growing areas of Southwestern Tanzania

Abstract

Increasing salt-affected soils have become a major abiotic constraint on rice production in lowland areas (both irrigated and rainfed) in southwestern Tanzania. Meager information on salt-affected soils distribution is available. This study was aimed at (a) establishing the salt status of salt-affected soils by type in selected irrigation schemes in the southwestern rice-growing corridor of Tanzania and (b) establishing farmers’ perceptions of the extent of the salt problem and associated crop losses in these rice irrigation schemes. Participatory diagnosis and an observation survey were conducted in the four major rice-producing regions of Katavi, Rukwa, Mbeya, and Iringa. Composite samples were collected from salt-affected hot-spot areas in 19 selected irrigation schemes and analyzed. Visual observation showed that 100 % of all surveyed irrigation schemes had symptoms of salt affected soils. However, laboratory results showed that 67 % of the schemes had salt problems. Three types of salt-affected soils (saline, sodic, and saline-sodic) with extreme salinity (4-15 dSm-1), sodicity (10-34 Sodium adsorption ratio-SAR), and high soil pH (up to 10) values recorded. Saline-sodic soil was the most common problem, followed by sodic soils. About 90 %of the surveyed irrigation schemes had inadequate irrigation infrastructures, which seems to contribute to the problem. Land loss ranged from 5 to 25 % of schemes, and yield losses ranged from 5 to 100 %. Urgent measures, including the rehabilitation of irrigation infrastructure to improve drainage systems, the use of salt-tolerant cultivars, and implementation of salt soil management options, should be taken to prevent arable land losses.