PARALLEL SESSION 4: THE SOIL ENVIRONMENT
EFFECT OF ALTERNATION TECHNIQUES OF IRRIGATION ON THE YIELD OF WHEAT
M M ABDEL-NABY1, A M EL-SAYED2, S T ABDEL-GAWAD3 and S M ABDEL-GAWAD4
1, 2, 3, Assistant Researcher, Researcher and Director, Drainage Research Institute (DRI),P O Box 13621/5, Delta Barrage (El-Kanater), Cairo, Egypt
4Professor, Faculty of Engineering, Cairo University, Egypt
>In the developing countries of the Mediterranean, the major challenge facing water planners and managers in the new millennium is that physical availability of water is fixed, while its demand will continue to increase steadily in the foreseeable future. Accordingly, the problem is how to balance between demand and supply of water under those difficult conditions. Several strategic alternatives are available for Egyptian water resources planners to satisfy the need for increasing the fresh water supply.
Studying the response of Wheat under irrigation with water of different salt concentration levels under different soil textures was the focus of this study. Leaching and alternation strategies to reduce the negative impacts of irrigation with relatively high saline water on both soil productivity and crop production were identified.
The experiment was carried out in the greenhouse of Mediterranean Agronomic Institute in Valenzano, Bari, Italy, in 1996-1997. Two types of soil were investigated, Clayey soil (CL) and Sandy Clay Loam soil (SCL). Irrigation water used in the experiment was prepared by mixing fresh water, which is used to irrigate control treatments, with sea water at certain ratios to obtain irrigation waters of 4 and 8 dS/m. In the experiment, (Triticum durum L) cv. was cultivated as an indicator plant. In both soils, under permanent saline irrigation practices, yield was generally subjected to gradual losses with gradual increments in the salt content of irrigation waters. The alternation technique under the clay soil, proved to have an effective role in reducing the damage in yield grain production under the investigated ECi values, increasing the yield production by 24 and 38% with respect to the treatment under permanent irrigation with saline water of 4.0 and 8.0 dS/m, respectively. In the case of sandy clay loam soil, its beneficial role was more noticed under irrigation with waters of relatively high salt concentration levels rather than the lower ones as the yield was improved by only 4.5% at the ECi 4.0 dS/m compared to 25% yield increase achieved with the 8.0 dS/m irrigation water.
SOIL WETTING AND SOLUTE TRANSPORT IN TRICKLE IRRIGATION SYSTEMS
K L BRISTOW1,2, C M COTE1, P J THORBURN3 and F J COOK4
1CSIRO Land and Water / 2CRC Sugar, PMB Aitkenvale, Townsville 4814 QLD, Australia
3CSIRO Tropical Agriculture / CRC Sugar, 120 Meiers Rd, Indooroopilly, QLD 4068, Australia
4CSIRO Land and Water / CRC Sugar, c/o QDNR, 80 Meiers Rd, Indooroopilly QLD 4068, Australia
Trickle irrigation/fertigation has in many instances not yielded the expected benefits, and its adoption is therefore not as widespread as it could be. One reason for this is that soil water and solute transport properties and soil profile characteristics are often not adequately incorporated in the design and management of trickle systems. In this paper we describe results of a simulation study designed to highlight the impacts of soil properties and other soil profile features (eg soil layering) on water and solute transport from buried trickle emitters (point sources). We show that (1) in sands, water and nutrients move easily downwards from the emitter and that it is difficult for water and nutrients to move upwards to wet the near surface zone if the trickle emitters are buried too deep, (2) changing the fertigation strategy for various soils to involve application of nutrients at the beginning of an irrigation cycle can help maintain larger amounts of nutrients near to and above the emitter thereby making them less susceptible to leaching losses, and (3) trickle irrigation/fertigation can work well in silts and duplex soils, even when quite different fertigation strategies are used. It is clear from the results of this study that the need to understand and account for differences in soil properties and irrigation/fertigation management strategies on solute transport is fundamental when addressing fertigation efficiency and long term sustainability of trickle systems.
A NEW WAY FOR SMALL FARM IRRIGATORS TO SAVE WATER
R J STIRZAKER,2, P A HUTCHINSON2 and M L MOSENA3
2CSIRO Land and Water, PO Box 1666, Canberra, Australia 2601
3Tompi Seleka College of Agriculture, Private Bag X9, Marble Hall, South Africa
Inefficient use of water is a problem for both the large and small farm sectors. Even in wealthy countries, the majority of farmers do not use the scheduling tools developed and promoted by the scientific community. If efficiency has eluded the large-scale sector, what technology is there to adapt for the small-farm sector? Practical experience in South Africa convinced us of the need for a new way to help small-farm irrigators to save water. We introduce a method for saving water based on the depth a wetting front penetrates during and after irrigation. A wetting front detector is buried in the root zone and gives a signal when enough water has been added to the soil. The device is a funnel-shaped object that produces liquid water when a wetting front moves through an unsaturated soil and into the funnel. Water then moves through a filter at the base of the funnel into a cavity and activates a float switch. The accuracy of this method has been demonstrated over the past three years in a range of horticultural crops and soil types. A simplified version of the detector, containing no electronic components, has been developed for the small-scale irrigation farmer. In this version a lightweight rod, floating on the water produced by convergence in the funnel, pops up out of a narrow pipe and tells the farmer the depth of the wetting front, and hence when enough water has been applied to the soil.
VARIATIONS IN WETTING PATTERNS FROM TRICKLE EMITTERS IN SOILS OF DIFFERENT TEXTURE
P J THORBURN1, FJ COOK2 and K L BRISTOW3
1CSIRO Tropical Agriculture & CRC for Sustainable Sugar Production, 120 Meiers Rd, Indooroopilly, Qld 4068, Australia
2CSIRO Land and Water, 120 Meiers Rd, Indooroopilly Qld 4068, Australia
3CSIRO Land and Water and CRC for Sustainable Sugar Production, University Rd, Townsville Qld 4814, Australia
For trickle irrigation systems to deliver improved water and nutrient use efficiency, distance between emitters and emitter flow rates must be matched to the soil's wetting characteristics and the amount and timing of water to be supplied to the crop. Dimensions of wetted soil were calculated from hydraulic properties of two groups of soils, covering a wide range of textures and soil hydraulic properties. The groups differed, however, in the extent to which hydraulic properties depended on soil texture. Wetted dimensions were determined for conditions commonly associated with daily irrigation applications in a widely spaced row crop, sugarcane, and horticultural crops. In the first group of 11 soils, which had the least expression of field structure, the wetted radius increased and depth of wetting below the emitter decreased with increasing clay content, as is commonly accepted. However, in the second group of 18 soils in which field structure was preserved, there was no such relationship between wetted dimensions and texture. For example, five soils with the same texture had as great a variation in wetting pattern as did all 11 soils in the first group, indicating the considerable impact of field structure on wetting patterns. We conclude that texture is an unreliable predictor of wetting and site-specific information is required on soil wetting or hydraulic properties to design efficient trickle irrigation systems.