Abstract
A study was carried out to examine distribution of salt affected soils by types and extent in the Ndungu Agricultural Development Project (NADP) area of Tanzania. The objective was to generate information to guide salt-affected soil management for sustainable rice production. Conventional methods including use of mini-pits and profile pits, coupled with farmers’ experiences were used to characterise soil. A total of seven randomly selected soil profile pits located in major soils were dug and described. Soil was sampled from natural horizons for laboratory analysis. In addition a total of 158 topsoil (0 – 20 cm depth) composites soil samples were randomly collected from 90 sites of NADP project area for laboratory analysis. Results showed that a few blocks (block is a piece of farm of 6 to 12 acres) had high exchangeable sodium percentage and high levels of bicarbonates, indicating salt-affected soils. Soil pH, exchangeable sodium percentage (ESP), and electrical conductivity of soil paste extract (ECe) values as high as 9.06, 28.7 cmol(+)Nakg-1, and 14dSm-1 were measured. Out of 90 blocks, 10 blocks (11%) showed slight to strong salt effects. Two blocks (2%) has been abandoned, and in some cultivated blocks zero yields were recorded due to salt content. The different levels of salinity development in the project area suggest site-specific remediation and appropriate management options be developed to improve crop production. These include rehabilitation of the irrigation infrastructure, use of farmyard manure as a soil amendment and growing salt-tolerant rice varieties. Furthermore, it is important to create awareness among farmers of the problem of salt-affected soil on rice productivity.
Highlights
Salt-affected soils, where salts concentrate on the soil surface causing severe decline of crop yields, are a worldwide problem (Metternicht & Zunk, 2003; Yadava et al, 2011; Shahid & Al-Shankiti, 2013)
Results showed that a few blocks had high exchangeable sodium percentage and high levels of bicarbonates, indicating salt-affected soils
This situation was observed randomly distributed in the Ndungu Agricultural Development Project (NADP) area, but generally the detrimental effects were not evident because sands are buried in the sub-surface layers (Figure 3)
Summary
Salt-affected soils, where salts concentrate on the soil surface causing severe decline of crop yields, are a worldwide problem (Metternicht & Zunk, 2003; Yadava et al, 2011; Shahid & Al-Shankiti, 2013) Such soils are found in diverse climates but they are dominant in arid and semi-arid climates (FAO, 2000; Graaff & Patterson, 2001; Robert & Ulery, 2011; Qadir et al, 2015). The extent of salt affected soils in irrigated areas has increased in the last two decades from 45 million hectares to 62 million hectares between 1990 through 2013 (Ghassemi et al, 1995; Metternicht & Zinck, 2003; Qadir et al, 2014) These figures suggest that at global scale every day an area of about 2,000 ha of irrigated cropland is affected by varying levels of salinity (Qadir et al, 2014).
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