Water quality problems in irrigated agriculture in Libya

Aboeltiyah Alzway, Aiad A. Akhreim (2015) Water quality problems in irrigated agriculture in Libya. PhD thesis, University of Glasgow.

Abstract

The Kufra region of south eastern Libya comprises an area about 850 km south to north, and some 500 km wide rising to 450 m above sea level. Rainfall is low and agriculture depends on irrigation. Most of the population of Kufra are private farmers who use flood irrigation from shallow wells (19-60 m), but there are co-operatives of farmers that have shared the cost of deeper wells (120 - 150 m) and sprinkler irrigation. The Kufra Agricultural Project (KAP) state farm is made up of 100 circles (farms) each having its own deep well (220 – 352 m) and rotary sprinkler.

The experimental work was conducted in three phases.
An initial study was made of soil profiles and irrigation water on 4 private and 4 state farms. An inter laboratory study compared results in the KAP and Glasgow University (GU) laboratories. The third phase was a survey of top soils, irrigation water, crop yield and questionnaires for a much larger number of farms.

Chapter 3 describes the comparison between chemical analysis results of 33 soils in the KAP and GU laboratories. There was a good level of agreement between the two laboratories. The high correlation coefficients indicate a high level of precision in both laboratories. However there were systematic differences between the two laboratories, results for EC, Ca2+, Mg2+ and Cl- were 2% to 6% lower in the KAP laboratory. There were no significant differences in the results for Na+ and K+ between the laboratories. It is important that all analyses were carried out in one laboratory, so all subsequent samples were sent to the KAP laboratory.

Chapter 4 evaluates the quality of irrigation water from 86 wells in the Kufra region in line with FAO and USDA standards for irrigated agriculture. pH, EC, Ca2+, Mg2+, Na+ and SAR were not significantly affected in state farms by well depth or age, but were significantly affected in the private farms by well depth, where the values were higher in shallow wells and significantly related to well age. There are two responses to well age related to well depth shown by two distinct lines. The shallow wells (<30 m) show a significant (p< 0.001) increase in EC, Ca2+ and Na+ and significant (p< 0.01) increase in Mg2+ as well age decreases. The deeper wells (>30 m) exhibits no significant effect of well age (p> 0.05). USDA classification indicates that the water of all the wells of private farms is unsuitable for irrigation purposes. The FAO criteria showed that all private wells had limitations on use due to salinity and SAR. (EC: 78% severe, 22% slight/moderate ; SAR: 35% severe, 65% slight/moderate)

Chapter 5 describes a survey of soil profiles from state and private farms. Irrigation lowered the salinity of the virgin soil profiles, with a clear distinction observed between the virgin and irrigated profiles for EC and water soluble Ca2+, Mg2+, Na+, K+, Cl- and SO42- in state farms, and for EC and water soluble Na+, Cl- and SO42- in private farms. In the virgin soil profiles, these parameters showed a clear decrease with depth, while in the irrigated soil profiles they were much lower in concentration and more uniform with depth. There was no clear trend with depth in irrigated soil profiles for pH, HCO3-, CaCO3%, exchangeable cations, and ESP % in the state farms and for pH, water soluble Ca2+, Mg2+and K+, CaCO3%, exchangeable cations, and ESP% in the private farms. The profile averages for pH, EC, ESP%, water soluble Na+, Cl-, HCO3- and SO42- and exchangeable sodium were significantly greater (t-test, p≤0.05) in the irrigated profiles of private farms than in KAP farms. The irrigated topsoils (0–25 cm) showed similar results except that bicarbonate and sulphate were not significantly different.
The second part of chapter 5 describes a larger survey of irrigated topsoils. This showed that the pH, EC, ESP% and exchangeable Na+ were much higher in the private farms compared to state farms soils. According to the USDA classification all state farm soils were classed as normal, while 70% of private farm soils were classed as saline alkaline, 15% normal, 10% saline and 5% alkaline. There was no significant effect of crop type on any soil parameter for state or private farms. There was no significant correlation in the combined data for state and private farms between irrigation water and soil for pH, Ca2+ and Mg2+ but there is for EC, Na+ and SAR. In all the graphs there are 2 clusters of points separating the state and private farms which masks the correlation relationship.

Chapter 6 compares the yields of alfalfa and potatoes in the state and private farms. The mean values for dry yield of alfalfa from state (6.32 t/ha) and private (3.06 t/ha) farms were significantly different (p<0.001, pooled t-test). The age of the alfalfa crop had a significant (p<0.001) positive effect on yield in the state farms, but a significant (p<0.001) negative effect in private farms. Crops on the private farms were 2 to 8 years old compared with under 2 years on the state farms. Although there were low yields at high values of water and soil parameters (private farms) and high yields at low values of water and soil parameters (state farms) plotting yield against these parameters shows 2 clusters. Looking at the private farms alone there was no significant correlation between alfalfa yield and any of the quality parameters for soil or water.
No potatoes were grown on state farms when the samples were collected, so historical data was used (average yield 40 t/ha). The mean yield of potatoes from private farms was significantly lower (p<0.001) 23.16 t/ha. None of the correlation relationships between crop yield with soil and water quality parameters for private farms was significant.
Despite the large differences in soil and irrigation water chemistry between state and private farms, there was no evidence that poor irrigation water quality or soil salinity currently limits production on private farms.

Chapter 7 describes the survey of private farmers and shows that 81% of respondents did not consider farming as a professional activity they could rely on, but rather an activity to fill their free time. The study also examined other aspects including the farmers’ education level, the farms’ age, irrigation and the impact of water salinity, types and sources of fertilisers. The study concluded that traditional agricultural systems in this region are not built on a scientific basis, or an adequate knowledge of economic feasibility. Consequently, the production rates of agricultural crops are very low.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Water quality, irrigated agriculture in Libya, shallow water, private farms
• Subjects: S Agriculture > S Agriculture (General); S Agriculture > SB Plant culture
• Colleges/Schools: College of Medical Veterinary and Life Sciences > School of Life Sciences
• Supervisor's Name: Bailey, Dr David and Flowers, Dr Hugh
• Date of Award: 2015
• Depositing User: Mr Aiad Aboeltiyah Alzway
• Unique ID: glathesis:2015-7091
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 12 Feb 2016 13:55
• Last Modified: 29 Feb 2016 12:01
• URI: https://theses.gla.ac.uk/id/eprint/7091