Selected Soil Chemical Properties and Fertility Assessment in Some Traditional Irrigation Schemes of the Mpwapwa District, Tanzania

Aims: To find out the status of the major plant nutrients important for plant growth and development in selected areas in Tanzania.

Place and Duration of Study: The soil physicochemical properties survey was conducted in Msagali and Chipogolo proposed irrigation schemes, Mpwapwa District, Dodoma Region, in Tanzania during the dry season of 2003.

Methodology: Before sampling, the study areas were divided into twenty two (22) pedogeomorphic units or soil types using pedogeomorphic approach. Thirty soil samples were collected from each pedogeomorphic unit at a depth of 0 – 20 cm in a zigzag manner, bulked, homogeneously mixed, and sub-sampled to obtain a representative composite sample. The composite soil samples were sent to Selian Agricultural Research Institute (SARI), Arusha, Tanzania, for analysis of physicochemical characteristics leading to the determination of the soil fertility status by means of these major mineral elements.

Results: The results showed variations in fertility status in the selected sites of each scheme. Based on guidelines of soil mineral elements contents established elsewhere, the soils in Msagali had high pH (8.1) and excessive Na+ (6.1 cmol (+).kg-1 soil) in 30.9% of the total surveyed area (263.5 ha). Crop production in Chipogolo was slightly constrained by sodicity (ESP=9.6%) in 73.1% of the total area (130.3 ha) surveyed and very strongly (ESP =27.9%) in 55.8% of the total surveyed area in Msagali. Total N and Organic Matter (OM) were low, ranging from 0.2 to 1.0g.kg-1 and 2.3 to 11.7g.kg-1 respectively. Available P was rated as low to medium and ranged from 1.01 to 5.13 mg P.kg-1 in all sites (i.e. Msagali and Chipogolo). Mg were rated as low (1.0 to 3.2 cmol (+).kg-1 soil.) in 26.9% of the area surveyed in Chipogolo and low in 18.4% of the surveyed area in Msagali ranging from 0.6 to 6.5 cmol (+).kg-1 soil. Of the total surveyed area, 63.7% in Chipogolo and 18.4% in Msagali have low Cation Exchange Capacity (CEC) with values <12 cmol.kg-1. C:N ratio in 63.2% the total area surveyed in Chipogolo was of good quality (i.e. C:N between 8–12) suggesting ideal conditions for plant growth compared with 36.8% of the total study area in Chipogolo and all the studied sites in Msagali. The data have indicated Ca: Mg ratios to be less than the suggested guidelines in 36.8% of the total surveyed area in Chipogolo suggesting that plants would probably respond to the addition of Ca or Mg in such areas.

Conclusion: The fertility status and overall information from this study could be used in soil and fertiliser management studies to establish nutrient requirements for different crops grown in these areas