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All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. A gricultural intensification through the use of high-yielding crop cultivars, chemical fertilizers and pesticides, irrigation, and mechanization has been responsible for dramatic increases in grain production in developing countries during the past three decades (Matson et al., 1998). Th ere is, however, a growing global challenge of meeting increased food demand while protecting environmental quality, and this challenge must especially be met in cropping systems that produce maize, rice (Oryza sativa L.), and wheat (Triticum aestivum L.) (Cassman et al., 2002). Th e NCP is one of the most important areas in China for cereal production, accounting for about 48% of the wheat and 39% of the maize produced in the entire country. Th e intensive farming in this region features a continuous wheat-maize cropping system, which requires careful management of soil nutrients. Intensive agriculture has dramatically increased grain production in developing countries, but yield records in the dominant food-producing regions indicate a large gap between the current and potential yields for maize (Neumann et al., 2010), which is an important crop because it contributes to food security in China. Obtaining an increased and sustainable maize yield will probably require integrated measures that could include K fertilization to maintain soil fertility. Potassium is one of the essential nutrient elements for plants; it is involved in the processes of osmoregulation and cell extension, stomatal movement, activation of enzymes, protein synthesis, photosynthesis, phloem loading, and transport and uptake (Marschner, 1995; Pettigrew, 2008). Potassium fertilization is, however, uncommon in the NCP and especially in maize production, primarily due to the relatively high soil test K as surveyed in the 1980s (National Extension Center of Agricultural Technique in China, 2004). In reality, it has oft en been reported that continuous wheat-maize cropping with unbalanced fertilization has rapidly depleted the soil available K (Jin, 1994; Liu et al., 2000; Cao et al., 2007). Many studies have focused on crop response to K fertilization as aff ected by soil properties, application methods, planting systems, etc.

The effects of potassium chloride (KCl) as a potassium (K) source in fertigation solution on growth, yield and quality of tomato (cv. Durinta) in a controlled greenhouse were compared with potassium nitrate (KNO 3 )the conventional K source for vegetable fertigation. The treatments consisted of four levels of KCl: (1) 0% KCl (100% KNO 3 ), (2) 40% KCl (40% KCl and 60% KNO 3 ), (3) 60% KCl (60% KCl and 40% KNO 3 ), and (4) 100% KCl (0% KNO 3 ) in fertigation solution in the

The effect of N and K nutrition on the salt tolerance of lettuce (Lactuca sativa L. cv. 'Salinas') and Chinese cabbage (Brassica campestris L., Pekinensis cv. Kazumi) was evaluated in three greenhouse experiments under a controlled aero-hydroponic system of cultivation. Three levels of KNO3 (1, 5 and 10 mM) were tested in all the experiments with rapidly circulated saline and nonsaline nutrient solutions. Two experiments, carried out between January and March 1989, with lettuce (Exp. I) and Chinese cabbage plants (Exp. III), consisted of two salinity levels, EC= 1.75 and 6.0 dS m-l, the former representing a nonsaline nutrient solution. In the third experiment with lettuce (Exp. II., conducted between March and May 1989), three saline nutrient solutions having EC levels of 4.7, 7.75 and 10.75 dS m-1 were compared to the nonsaline solution. The nutrient solutions were salinized with NaC1 and CaC12, in a 4:1 molar ratio. The highest yields of fresh weight of both crops were obtained from the 5 mM KNO 3 under both saline and non-saline conditions. The 10 mM treatment caused yield reduction in Chinese cabbage, probably due to a severe tipburn disorder. The relatively high fresh weight yield obtained at the lowest (1 raM) KNO 3 level can be explained by the positive effect of circulation velocity on nutrient uptake. The threshold salinity damage value for the vegetative yield of lettuce plants fed by 5 or 10 mM KNO 3 was approximately 5 dSm -1 and the yield decreased by 6.5% per unit dS m-1 above the threshold. No yield improvement due to the addition of KNO 3 occurred under highly saline conditions (Exp. II). The fresh weight of Chinese cabbage obtained from the 'saline' 1 and 5 mM KNO 3 treatments was approximately 15% lower than the 'non-saline'-treatment (Exp. III). Salinity increased tipburn and the effect was not altered by the addition of KNO 3 . No significant interaction between nutrition (KNO 3 level) and salinity was found. The application of salts increased the concentration of Na and C1 * Contribution from Institute of Soils and Water, ARO, Volcani Center, PO Box 6, Bet Dagan 50250, Israel. No. 3092-E 1990 series Offprint requests to: A Feigin in plant tissue and reduced the levels of N and K; the opposite occurred in plants fed by the medium and high levels of KNO a .The yield and quality of leaf vegetables, such as lettuce and Chinese cabbage, grown on irrigated land can be considerably influenced by water composition. This is also true for greenhouse-grown crops when saline water is used for irrigation or, when grown in soil, where a high water table or the accumulation of fertilizer residues contributes to the development of saline conditions (Sonneveld 1988). Alleviation of salt stress in leaf vegetables is important not only to prevent yield losses but also to avoid quality deterioration due to physiological disorders such as tipburn van den Ende et al. 1975).As salt damage to crops involves not only total salt effect (osmotic effect) but also specific ion effects (Lauchli and Epstein 1984) it has b...