Effects of irrigation water on infiltration rate and saturated hydraulic conductivity in onion fields; a case study of ruaha mbuyuni irrigation scheme, iringa- Tanzania.
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Date
2000
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Publisher
Sokoine University of Agriculture
Abstract
A study was conducted at Ruaha Mbuyuni farmers7 managed irrigation scheme in
Iringa region to assess the effect of irrigation water on infiltration rate and hydraulic
conductivity and corresponding crop (onion) performance. The study involved
assessment of water quality and soil properties in relation to infiltration rate and
hydraulic conductivity problems, crop (onion) water requirement at different stages
and its performance under different soil types.
The results indicate that water from Lukosi river was low salinity and low sodium
water. Chemically, this water have slight effect on infiltration rate and hydraulic
conductivity. The concentration of suspended sediments were high where about
25.54 t/ha 一 42.15 t/ha of sediment were deposited in the fields over the season. This
resulted into sealing and clogging of soil pores hence reducing infiltration and
hydraulic conductivity.
The soil texture in the scheme ranged between sandy loam to heavy cracking clays
and they are neither saline nor sodic. The soils are slightly alkaline with pH ranging
from 7.4 to 7.8. The organic matter content were generally very low ranging from
1.13% to 3.05%. Due to the low organic matter content, the soils had poor structural
stability and hence easily dispersed when water is applied. Dispersion effects
resulted into reduction of infiltration rate and hydraulic conductivity.
Soil basic infiltration rate ranged from 3.75 mm/h to 52.5 mm/h while saturated
hydraulic conductivity ranged from 0.03123 m/d to 0.4236 m/d for clay and sandy loam soils respectively. Basic infiltration rate decreased for an average of 50% while
hydraulic conductivity decreased for an average of 52% - 58% over the season in all
soils. High deposition of sediment and high dispersion effect of irrigation water on
the soils were the main reasons for decreased infiltration rate and hydraulic
conductivity over the season.
The crop (onion) performance was generally low in all locations compared to the
normal yield of 35-45 t/ha and 8-10 Kg/m3 fbr yield per unit area and specific yield
respectively. Medium textured soils which had moderate infiltration and hydraulic
conductivity had better yield of 31.5t/ha while coarse texture soils with rapid
infiltration showed very poor yield of 13.3t/ha. Clay soils had better specific yield of
5Kg/m3 while sand soils showed low specific yield of 3Kg/m3. Low infiltration rates
and hydraulic conductivity resulted in water logging problems in the heavy textured
soils. Rapid infiltration in the course textured soils caused water stress to crops and
drain of plant nutrient below root zone which contributed to low yields.
It was observed that the water application depended on the available irrigation water
and not on crop water requirement. Relative water supply (RWS) ranged from 0.92
to 5.36 per crop development stage. Irrigation intervals which were far spaced was
the main reason fbr excess water application during irrigation.
It was concluded that water from Lukosi river has good quality and can be used fbr
irrigation in all types of soils with slight reduction of infiltration rate and hydraulic
conductivity.
Description
Dissertation
Keywords
water irrigation, Infiltration rate saturated hydraulic, Onion production, Ruaha mbuyuni irrigation scheme