Agricultural Water Management 160 (2015) 57–63 Contents lists available at ScienceDirect Agricultural Water Management journal homepage: www.elsevier.com/locate/agwat Surfactant effect on forage yield and water use efficiency for berseem clover and basil in intercropping and limited irrigation treatments F. Daneshnia a , A. Amini b , M.R. Chaichi c,∗ a Department of Agronomy and Plant Breeding, College of Agriculture and Natural Resources, University of Tehran, Iran b School of Computing, Engineering and Mathematics, University of Western Sydney, Building Y, Locked Bag 1797, Penrith, NSW 2751, Australia c College of Agriculture, California Polytechnic State University, Pomona, 3081 West Temple Avenue, Pomona, CA 91,768, USA article info Article history: Received 21 January 2015 Received in revised form 27 May 2015 Accepted 22 June 2015 Available online 14 July 2015 Keywords: Berseem clover Basil Medicinal forage Irrigation treatments Surfactant Irrigation water use efficiency (IWUE) abstract Quantifying crop response to irrigation is important for establishing effective irrigation management strategies. The present study was conducted to evaluate the response of berseem clover and basil to limited irrigation in an additive intercropping system using a surfactant. The experimental treatments were carried out in split–split plots based on a completely randomized block design with three replica- tions. The limited irrigation treatments comprised of replenishment of I 100 full irrigation, I 75 = 25% limited and I 50 = 50% limited weekly evaporation and plant water requirements which were assigned to the main plots. The planting systems of sole berseem clover and sole basil culture along with additive inter cropping of berseem clover + 50% basil were assigned to the subplots. Water treatments of control (water alone) and water + surfactant were assigned to the sub-subplots. Results show that severely limited irrigation (I 50 ) dramatically reduced the forage yield of berseem clover and basil by 19.5% compared with the control (I 100 ). The severity of the adverse effects of limited irrigation stress decreased by the surfactant application in irrigation by water + surfactant (9.5% decrement compared to full irrigation). The highest irrigation water use efficiency (2.7 kg m -3 ) was achieved in I 50 treatment with an added surfactant. The highest total dry matter yield (berseem clover + basil dry matter) (9257.9 kg ha -1 ) was obtained from additive intercropping of berseem clover 100% + basil 50% while irrigated by water + surfactant. © 2015 Elsevier B.V. All rights reserved. 1. Introduction Irrigation water use efficiency (IWUE), defined as the amount of biomass or grain produced per unit volume of applied water, pro- vides a quick and simple measure of how well the available water can be converted into grain and thereby is the basic indicator of measuring the effectiveness of water-saving in agriculture (Sekhon et al., 2010). When water resource in a crop production is a limiting factor, a proper irrigation treatment is needed to enable maximum production per unit irrigation water volume. Deficit irrigation is one way of maximizing the IWUE (Bekele and Tilahun, 2007). The main objective of deficit irrigation is to increase the IWUE of crops by reducing the amount of water in irrigation or by reducing the number of irrigation events (Kirda, 2002). In recent years, the focus is shifting towards increasing productivity efficiency within the ∗ Corresponding author. Fax: +1 909 869 5036. E-mail addresses: a.amini@uws.edu.au (A. Amini), mrchaichi@cpp.edu (M.R. Chaichi). constraints of available limited water resources. As such, deficit irrigation is becoming a possible option, i.e., in irrigating crops, reducing water requirements while minimizing the adverse effects of extreme water stress on crop yield (Garg and Dadhich, 2014). In addition, water loss by evapotranspiration is very high during the growing season in semi-arid regions. Forage crops in these envi- ronments are often subjected to the detrimental effects of high temperatures and water deficits during the spring-summer period that seriously reduce the herbage and seed production. Therefore, it is necessary to know the allowable level of transpiration defi- ciency without significant reduction in crop yield. The monetary loss due to deficit irrigation yield reduction should be smaller than the benefits gained from the saved water which in turn could be normally used for other crops under traditional irrigation practices (Kirda, 2002). Surfactant (wetting agent) application in the irrigation water increases moisture retention in soil (Leinauer, 2002). The increase in water retention under deficit irrigation treatments due to the application of surfactants can be explained by the mechanism in which the surfactant is applied. Surfactants reduce the surface http://dx.doi.org/10.1016/j.agwat.2015.06.024 0378-3774/© 2015 Elsevier B.V. All rights reserved.