Impacts of irrigation water quality, associated soils characteristics and on-farm practices on paddy yields

Abstract

In this study, the impacts of irrigation water quality, soil characteristics and on-farm practices on paddy yields were investigated. Standard spectroscopy and spectrometry methods were used to analyze irrigation water and irrigated soil samples. The irrigation water had sodium adsorption (SAR) values ranging from 0 to 3. The corresponding electrical conductivity (EC) values were between 0.2 and 0.7 dS/m and accounted for 14% of all samples hence posing slight to moderate infiltration problem. Neither sodium nor chloride levels were high enough to cause toxicity problems in the irrigation water. For boron, 54% of the samples was found to have moderate toxicity whereas ~14% of the samples indicated severe boron toxicity in the irrigation water. For bicarbonate, about 86 and 14% of the irrigation water indicated slight-to moderate and severe potential detrimental effect to plant growth, respectively. The trace elements Fe2+, Zn2+, Cu2+, Mn2+, B, As, Cd, Cr2+, Pb2+, Ni2+, and Al3+ in the irrigation water samples were too low to cause any harmful effect. Although soil EC (0.2 to 1.9dS/m), organic carbon (OC) (0.1 to 2.4%) and pH (6.0 to 8.5) indicated favorable levels, there were significant variations in soil Fe (2.6 to 169.5 mg/kg) and Zn (3.9 to 204.1 mg/kg). The mean value of Fe in soils was 19.8 mg/kg. Soils indicated signs of Fe-deficiency. High variabilities were also found in the total N (86 to 2155 mg/kg) content of the studied paddy soils. The levels of phosphorus (Olson P, mean 224.2 ± 149.4 mg/kg) were found to be too high compared to what is reported as normal in similar studies. There might be unsustainable and excessive application of P-containing inputs in the studied area. Furthermore, a low soil K content was observed in the analyzed soil samples. The present study recommends that regular control of irrigation water HCO3 - , EC and controlling soil pH levels as well as adoption of standard on-farm practices following of crop calendar, proper application of fertilizers. Availability of extension officers to advice farmers is highly recommended.