Interactions of soil water run-off with overhead (centre-pivot) irrigation and soil cultivations

Mahmood, G.H.T (2018) Interactions of soil water run-off with overhead (centre-pivot) irrigation and soil cultivations. Doctoral thesis, Harper Adams University.

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Actual consumption of water was addressed in this thesis by investigating how improved irrigation efficiency and use of appropriate soil cultivations would reduce irrigation water run-off, and thus reduce the actual consumption of water and lead to greater irrigation water use efficiency. The phenomenon of surface water runoff has begun to have an impact on the productivity of crops in Iraq, especially those that are irrigated by centre pivot sprinkler irrigation systems. Most of these irrigated areas are ploughed with poor tillage operations, and often without consideration of the effect of these operations on soil physical properties and crop responses. The research aims to investigate the effect of different soil tillage practices on the irrigation water runoff potential from the end section of a pre-selected centre pivot system used in Iraq. In addition, an investigation into the sprinkler nozzle outputs was conducted to quantify the uniformity of application and thus it’s potential to cause localised runoff. The optimum size of runoff test area suitable for in situ measurement in commercial fields has been identified. Based on tillage studies on sandy loam soils, subsoiling followed by mouldboard or disc ploughing resulted in higher infiltration rate and soil moisture content, lower shear strength and penetration resistance compared to gang disc harrowing, rigid tine harrowing, rotary harrowing, and no tillage which produced the lower infiltration rate and soil moisture content, higher shear strength and penetration resistance. Therefore, both mouldboard and disc ploughing methods were selected for conducting water runoff experiments. Compared to disc ploughing, mouldboard ploughing produced higher water infiltration rate, lower shear strength and soil bulk density under these experimental conditions. The results of the effect of three factors of water pressure, nozzle height and type on water distribution uniformity were found to be significant. Water distribution uniformity increased from 51% at 42 kPa (6 psi) to 91% at 103 kPa (15 psi). Similarly, water distribution uniformity increased from 58% at 0.5 m to 84% at 1.5 m nozzle height within normal wind speed. Water distribution uniformity test results were significantly affected by the rim characteristics of the catch containers and the distance between the cans. Compared with the small circular catch containers at 0.5 m spacing, the close packed larger rectangular shaped catch container produced better resolution of water distribution results under such sprinkler systems. The effect of water runoff collection sampler size (0.25 m2, 1 m2, 4 m2, and 9 m2) on the amount of water runoff under an overhead sprinkler system in field conditions was found ii to be significant. Therefore, for further experimental studies, the water runoff collection sampler selection should be considered so the most representative results of field runoff conditions can be obtained. This study showed that water runoff occurs as a result of several factors including soil preparation in combination with operating conditions of overhead sprinkler system.

Item Type: Thesis (Doctoral)
Divisions: Crop and Environment Sciences (to 31.07.20)
Depositing User: Ms Kath Osborn
Date Deposited: 10 Apr 2019 15:06
Last Modified: 10 Apr 2019 15:06

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