SMALL SCALE IRRIGATION TREND ANALYSIS, SEASONAL SALT AND WATER BALANCE, AND EFFECT OF WOODASH ON QUALITY OF IRRIGATION WATER AND SALT AFFECTED SOILS IN SELECTED AREAS OF TIGRAY, NORTHERN ETHIOPIA

Abstract

Ethiopia is predominantly an agrarian country with the vast majority of its population directly or indirectly involved in agriculture that frequently affects land use change and water resources utilization. However, water resources management for irrigation agriculture was found to be poor that inevitably brought about deterioration in water quality and increased soluble salts on the irrigated fields of Tigray. Therefore, the premise of this study was to reveal the small scale irrigation (SSI) development trends, evaluate seasonal and spatial salt and water balance dynamics within the reservoir and crop root zone of irrigated fields and provide possible management intervention (using wood ash). Time-series satellite imageries that included Landsat MSS, TM, ETM+ and landsat 8 OLI, which covered the time frame between 1989 to 2015 depending on the age of selected dams, were constructed and processed using remote sensing(RS) and geographic information systems(GIS) techniques. Climatic data were used as input to the various softwares for determining the water balance; SaltMod simulation model was used for quantifying the salt balance at different soil layers for two consecutive years. Irrigation water and wood ash samples were sampled four times during each irrigation cycle in order to examine its quality and analyzed in the laboratory. Field experiments were conducted in RCBD with six (control, 75gm/l, 150gm/l, 225gm/l, 300gm/l and 375gm/l) treatments with four replications for two consecutive irrigation seasons of 2013/14 and 2014/15 in order to evaluate the effect of wood ash on soil quality and yield and yield components of maize. Plant, soil and water data were analyzed using ANOVA test at P<0.05 for determination of significant difference among the treatments. The study revealed that there were strong agreements between classified land cover classes and observed land use/land cover with greater than 85 and 80% overall accuracy and Kappa coefficient values, respectively in all selected study sites. Different trends were observed in the extent and types of land uses of the study sites. Overall, change difference (1995-2015) in Mai-dimu kebele, Dura kebele and Are-alemsegeda were by large attributed to expansion of settlement (700.20 ha,101.34 ha and 471.5a ha ), dam (124.02 ha,9 ha and 27.8 ha), and irrigated land (181.98 ha,162.45 ha and 134.01 ha ) respectively. The overall change difference (1989-2015) in Mesanu and DFM (Dideba,Felege-selam and Meseret kebeles) were mainly attributed to expansion of irrigated land (115.38 ha and134.01 ha), dam (37.26 ha and 58.23 ha) and settlement (363.26 ha and1109.16 ha) respectively. Overall, LULCC drivers (1989-2015) in all Kebeles were the expansion of settlement, expansion of dam, decreasing sizes of forest land and increased size of irrigated lands. Hence, irrigation development in the study areas have contributed to the change in land use by increasing the expansion of dam and irrigated lands. In Dideba catchment, runoff coefficient was found to be 0.18. The average annual actual and corrected potential evapotranspiration were 367.03 and 785.45 mm respectively. The simulated annual potential and actual evapotranspiration values were 1390 and 418 mm, respectively for 2013 and 1404 and 445mm, respectively for 2014. At the reservoir, the amount of water that percolates down at the base of the reservoir is 2.49 million cubic meter (MCM). The total amount of water that comes as an input to the reservoir xxiii was 3.12 MCM. Hence, the capacity of the reservoir to hold water was 0.63 MCM, which was lost through evaporation and discharging from the reservoir to the command area. According to APSIM model, the moisture content found in the 20 cm depth reached its maximum water content of 16 mm (2013) and 18 mm (2014) but it decreased with increasing depth of the profile. In saltmod, ECe of the soil do not show huge variation with depth, starting from the beginning and end of rainy season within profile pits in these two years of record. However, at the end of irrigation, ECe value increased with 3.46 dSm- and 3.04 dSm- in 2013/14 and 2014/5 respectively with the depth of 0-20 cm. Hence, salt content varies among the beginning of rainy season, the end of rain season and the end of irrigation season. Application of wood ash on irrigation water lowers the expenses of ECiw, SAR or Adj SAR severity. In addition, application of wood ash at the rate of 9.61tha-1 helped to lower down the salt concentrations in the root zone and improved the yield of maize by 1.02 t/ha in 2013/14 and 1.42 t/ha in 2014/15.. This study concludes that SSI growth trend is linear, which propelled LULC changes. Besides, the study also drew a conclusion, that salinity build up around the root zone is becoming an emerging challenge. Hence, use of a cost effective preventive method such as use of wood ash at the rate of 9.61tha-1 is appropriate. At last, the study recommends that SSI should be widened in use as it helps curbing drought effect on food security. Use of wood ashes helps to reduce the electrolyte levels of either irrigation water or soil solution that results in reducing the salt build up in the irrigated fields.