TECHNICAL NOTES Measuring On-Farm Irrigation Efficiency with Chloride Tracing under Deficit Irrigation Zohrab Samani 1 ; Ted Sammis 2 ; Rhonda Skaggs 3 ; N. Alkhatiri 4 ; and Jose Deras 5 Abstract: Water is a limited resource in agricultural production in arid climates. Under such conditions, high irrigation efficiency can be obtained either through implementation of efficient irrigation systems such as drip or sprinkler systems or through the age-old practice of deficit irrigation with gravity systems. The method used to increase irrigation efficiency is often dictated by economic and/or social factors. In either case, the effectiveness of water management at the farm level needs to be evaluated by measuring irrigation efficiency. The objective of this study was to evaluate the irrigation efficiencies for three crops in Southern New Mexico using the chloride technique. The chloride technique is a simple method in which the natural chloride in the irrigation water is used as a tracer to estimate the leaching fraction and the irrigation efficiency at the farm level. Soil samples were collected from various fields in 15 cm increments to a depth of 180 cm at the end of the irrigation season. The samples were analyzed for moisture and chloride content. In addition to the chloride technique, on-farm irrigation efficiencies were measured using applied water, yield, and water production functions. Water production functions and yields were used to estimate total evapotranspiration while flow measurements were used to calculate the amount of applied water. The results showed that high irrigation efficiency can be accomplished using deficit irrigation. Irrigation efficiency values ranged from 83 to 98%. Irrigation efficiencies using the chloride technique were compared with efficiencies estimated from direct flow measure- ments. The differences between the two methods ranged from 2 to 11.4%. The results showed that even though the chloride technique is subject to sampling errors and simplified theoretical assumptions, it can be used to estimate on-farm irrigation efficiency with considerable accuracy. DOI: 10.1061/ASCE0733-94372005131:6555 CE Database subject headings: Irrigation systems; Farms; Agriculture; Chlorides; Water management; New Mexico. Introduction Water is a limited resource in the arid climate of southern New Mexico. The limited water supply and increasing demands have created the need to identify sources of water loss and water use as well as the economic returns from water under various conditions. Potential sources of water loss include seepage and runoff from delivery systems as well as seepage and runoff losses during on- farm irrigation practices. Irrigation systems such as drip and sprinkler irrigation are often used to increase on-farm irrigation efficiency. Even gravity systems can achieve high irrigation effi- ciency if they are designed, maintained, and managed correctly. However, gravity systems are often associated with low irrigation efficiency. A survey of irrigation systems at the national level showed that out of 25.7 million ha of irrigated land in the United States, 50% of irrigation systems used are gravity flow, 45% are sprinkler, and 5% are drip irrigation Irrigation Journal, 2001. In southern New Mexico, more than 95% of the irrigation systems are gravity flow, commonly known as surface irrigation. The major crops in the area are pecan, alfalfa and cotton, which are planted in 75% of the irrigated land. The remaining 25% is planted with vegetable crops such as onion and chile. The gener- ally mild slopes and moderate to slow water intake of soils favor basin and basin–furrow irrigation. Alfalfa and pecan com- monly use basin irrigation while cotton and vegetable crops use basin–furrow irrigation. The farmers receive water on a demand basis with a fixed allocation water right, usually 1 ha m / ha. The limited water supply has created an economic necessity for deficit irrigation, especially by commercial farmers. However, informa- tion on the efficiency of on-farm irrigation application, the level of deficit irrigation, and the economic return from water is lim- ited. The purpose of this study was to evaluate on-farm irrigation efficiencies for various crops in southern New Mexico using the chloride technique and to verify the technique using direct flow measurements. 1 Professor, Civil Engineering Dept., Box 3CE, New Mexico State Univ., Las Cruces, NM 88003 corresponding author. E-mail: zsamani@ nmsu 2 Professor, Dept. of Agronomy and Horticulture, New Mexico State Univ., Las Cruces, NM 88003. E-mail: tsammis@nmsu.edu 3 Professor, Dept. of Agricultural Economics, Box 3169, New Mexico State Univ., Las Cruces, NM 88003. E-mail: rskaggs@nmsu.edu 4 Graduate Student, Civil Engineering Dept., New Mexico State Univ., Las Cruces, NM 88003. 5 Graduate Student, Civil Engineering Dept., New Mexico State Univ., Las Cruces, NM 88003. Note. Discussion open until May 1, 2006. Separate discussions must be submitted for individual papers. To extend the closing date by one month, a written request must be filed with the ASCE Managing Editor. The manuscript for this technical note was submitted for review and possible publication on October 28, 2003; approved on October 29, 2004. This technical note is part of the Journal of Irrigation and Drainage Engineering, Vol. 131, No. 6, December 1, 2005. ©ASCE, ISSN 0733- 9437/2005/6-555–559/$25.00. JOURNAL OF IRRIGATION AND DRAINAGE ENGINEERING © ASCE / NOVEMBER/DECEMBER 2005 / 555 Downloaded 04 Nov 2009 to 128.123.105.51. Redistribution subject to ASCE license or copyright; see http://pubs.asce.org/copyright