Session 21. Soil, Plant and Water Relationships with Microirrigation
An Approximate Time-dependent Solution for Point-source Infiltration
Ph. Revol, B. E. Clothier, B. Lesaffre, G. Vachaud
Raats' (1971) steady-state theory is extended to provide an approximate analysis of the transient pattern of wetting around a point source. The axisymmetric position of the wetfront is given, as well as the profile of water content behind the wetfront. Good agreement, at short times, was obtained by comparison with the gravity-free absorption solution. This new analysis was also tested against several drip irrigation experiments in the laboratory. The agreement between the observations and predictions was good. Even the vertical elongating influence of gravity at longer times was well predicted for the sandy loam soil.
Keywords: Infiltration, Unsaturated flow, Wetting front, Gravity, Microirrigation
Abstract taken from paper found on pages 603 to 608 in Proceedings of 5th International Microirrigation Congress, April 2-6, 1995, Orlando, Florida. American Society of Agricultural Engineers, 2950 Niles Road, St. Joseph, Michigan 49085-9659, USA. Phone: 616-429-0300 FAX: 616-429-3852 EMAIL: HQ@ASAE.ORG
*******
Field Evaluation of Water and Solute Movement from a Point Source
Muluneh Yitayew and Akbar Ali Khan
An in-situ evaluation of water and solute movement from a point source was made to understand chemical and water distribution in the vadose zone. Surface wetting for three application rates (1.5, 2.0, and 2.5 liters per hour) and three applied volumes (15, 20, and 25 liters) was measured to find out the saturated water entry radius, soil water distribution, and the speed of the wetting front movement. In-situ solute distributions for three concentrations (100, 300, and 500 mg/liter of Bromide) were also measured. The results show increased concentration with increased applied solution concentration, for a depth up to 15 cm and a radial distance of about 20 cm. There was no significant difference in concentration after that. The saturated water entry radius values were 13.0, 16.5, and 19.5 centimeters, for 1.5, 2.0, and 2.5 liters per hour application rates, respectively. These values show if the application rate is more than a point infiltration rate there will be surface ponding that forms a saturated disc and this radius increased with increasing application rate. The wetting front measurements also show an increase in front speed with an increasing application rates. Mass balance results for solute reveal that the solute distributions from a point source are higher at the point of application and decrease radially also with depth. The same behavior was observed for soil water distribution.
Keywords: Microirrigation, Point source, Solute movement, Chemigation
Abstract taken from paper found on pages 609 to 614 in Proceedings of 5th International Microirrigation Congress, April 2-6, 1995, Orlando, Florida. American Society of Agricultural Engineers, 2950 Niles Road, St. Joseph, Michigan 49085-9659, USA. Phone: 616-429-0300 FAX: 616-429-3852 EMAIL: HQ@ASAE.ORG
*******
Pulsating Microirrigation for Optimal Water Use and Control in the Soil
Elisha Kenig, Ester Mor and Gideon Oron
Improved water use can be attained by employing minute microirrigation (MMI) methods whereby the water application rate is adjusted to the plants' water demand. This can be accomplished by two main methods: (a) drip irrigation with a mean minute emitter discharge in the range of 0.1 to 0.4 1/h; and (b) intermittent application using conventional micro sprinklers or sprayers, with a mean effective outlet flow in the range of 2 to 8 1/h, equivalent to conventional drippers, and wetting an area of 10 m2 to 20 m2. Both methods have an application rate which is lower by an order of magnitude than that of conventional irrigation. The reduced mean application rate is achieved by using pulsating devices at each irrigating outlet or at the head of a cluster of laterals. Field experiments were conducted to confirm the results of the efficiency of this approach.
Keywords: Microirrigation pulsating, Soil moisture control, Drip irrigation
Abstract taken from paper found on pages 615 to 620 in Proceedings of 5th International Microirrigation Congress, April 2-6, 1995, Orlando, Florida. American Society of Agricultural Engineers, 2950 Niles Road, St. Joseph, Michigan 49085-9659, USA. Phone: 616-429-0300 FAX: 616-429-3852 EMAIL: HQ@ASAE.ORG
*******
Modelling a Finite Cylindrical Trickle Source with Cylindrical Root Uptake
S. K. Agodzo, J. W. Gowing, M. A. Adey
A 2-dimensional, radial and vertical, unsaturated soil water model of a finite cylindrical trickle source with root uptake is presented. The water source was a cylindrical, porous clay pot buried in the ground. Assuming a cylindrical rooting geometry, a root growth sub-model was developed from field measurements. Model predictions agreed well with observations. Some limitations of the model are extensive data preparation, over-simplification of rooting geometry and vertical flow.
Keywords: Trickle irrigation, porous clay pot, root uptake, model
Abstract taken from paper found on pages 621 to 627 in Proceedings of 5th International Microirrigation Congress, April 2-6, 1995, Orlando, Florida. American Society of Agricultural Engineers, 2950 Niles Road, St. Joseph, Michigan 49085-9659, USA. Phone: 616-429-0300 FAX: 616-429-3852 EMAIL: HQ@ASAE.ORG
*******
Modelling of Saturated Regime as Affected by Emitter Application Rates
R. K. Gupta, R. P. Rudra, and W. T. Dickinson
The ability of analytical models to predict wetted area under a trickle source is one of the primary consideration in model selection for trickle irrigation design. The hydraulics of flow under trickle sources are complicated because of variations in the soil and trickle parameters. The flow from single, widely-spaced emitter is a case of a three-dimensional infiltration process where the water application rate controls the hydraulics and size of the wetted soil regime. In the present study, experiments were conducted to evaluate the effect of application rates on the wetted regime developed near the emitter. The effects are evaluated by the four analytical models (e.g., Philip, 1969; Wooding, 1969; Clothier et al., 1982; Howell et al., 1983) available in literature for simulation of the three-dimensional infiltration. The study shows that the hydraulics of the saturated regime is significantly affected by the emitter application rates and volume of applied water. The study indicated that the Wooding's model for flow under a ponded, circular source performed well under the experimental conditions.
Keywords: Infiltration, Trickle, Soil Physics
Abstract taken from paper found on pages 628 to 632 in Proceedings of 5th International Microirrigation Congress, April 2-6, 1995, Orlando, Florida. American Society of Agricultural Engineers, 2950 Niles Road, St. Joseph, Michigan 49085-9659, USA. Phone: 616-429-0300 FAX: 616-429-3852 EMAIL: HQ@ASAE.ORG
*******
Irrigation Water Management for Mustard Through Simulation
Rajinder Singh and Joginder Singh
Field experiments were conducted at CCS, Haryana Agricultural University Farm, Sirsa (India) to estimate optimum irrigation planning in Indian Mustard [Brassica juncea L.(Czern &Coss)cv. Prakash] so as to minimize percolation loss to groundwater. The line source sprinkler irrigation technique was adopted for creating four irrigation regimes at various crop (grown on sandy clay loam soil underlain by sandy loam) growth stages. The calibration and validation of computer simulation SWASALT model using field experimental data (1990-92) provided guidelines for adoption of efficient irrigation application at the farmers fields in mustard. The criteria for the irrigation performance with and without rainfall using water management response indicators, WMRI's viz. The relative transpiration rate, transpiration efficiency, evapotranspiration efficiency and moisture storage index were evaluated. The model study indicated that the crop yield varied linearly with increase in irrigation depth which is evident from increase in relative transpiration. It further showed that the soil profile became drier with reduced irrigation depth (soil moisture index = -0.13 to -0.23). However the relative transpiration was found to be higher (0.56 to 0.85) for a normal rainfall year as compared to a drought year (0.47 to 0.78). No percolation loss occurred with 60-mm and 100-mm irrigation depths for normal rainfall and drought years, respectively. Optimum post-sown irrigation depth under limited water availability was found to be 60 mm at crop growth stages with pre-sowing irrigation of 80 mm. The corresponding values of relative transpiration and evapotranspiration efficiency were 57 and 97 percent, respectively.
Keywords: Relative Transpiration, Evapotranspiration Efficiency, Water management response indicators, percolation loss
Abstract taken from paper found on pages 633 to 637 in Proceedings of 5th International Microirrigation Congress, April 2-6, 1995, Orlando, Florida. American Society of Agricultural Engineers, 2950 Niles Road, St. Joseph, Michigan 49085-9659, USA. Phone: 616-429-0300 FAX: 616-429-3852 EMAIL: HQ@ASAE.ORG
