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The objective of this research was to investigate the effect of EC (electric conductivity) levels of nutrient solution on the growth and yield of tomatoes under the hydroponic system. This research was conducted in a plastic house on the experimental farm of Lampung University, Lampung in Indonesia from April to July 2009. The EC treatments to nutrient solutions were S1 (1 dSm-1), S2 (2 dSm-1), S3 (3 dSm-1), S4 (4 dSm-1), and S5 (5 dSm-1) arranged in a completely randomized design with four replications. The results showed that the highest yield was under S3 (120.8 g/plant), followed by S2 (96.6 g/plant), S1 (89.7 g/plant), S4 (88.4 g/plant), and S5 (75.5 g/plant). The yields of tomato responded to EC levels of nutrient solution in the two ranges of lower and higher EC than 3 dSm-1. The yield increased as EC of nutrient solution increased from 0 to 3 dSm-1 probably, due to increase of nutrients. On the other hand, the yield decreased as the EC of nutrient solution increased from 3 to 5 dSm-1 probably, due to increase of water stress. So, it can be concluded that the salinity threshold of the tomatoes was 3 dSm-1. On the other hand, the highest SSC (soluble solid content) was recorded under S5 (7.34 brix), followed by S4 (6.93 brix), S3 (6.44 brix), S2 (6.26 brix), and S1 (6.11 brix). It means that the S5 treatment was the best quality. Among the range of treatments, treatment S3 (3 dSm-1) gave the highest yield, but lower SSC than S4 (4 dmS-1) and S5 (5 dSm-1).

The objective of this research was to investigate the effect of water stress in regulated deficit irrigation (RDI) on the yield of soybean growing on Ultisol soil. This research was conducted under plastic house on the experimental farm of Lampung Polytechnique from August to November 2004. The water stress treatments in regulated deficit irrigation were ET 1 (1.0 · ET c ), ET 2 (0.8 · ET c ), ET 3 (0.6 · ET c ), ET 4 (0.4 · ET c ) and ET 5 (0.2 · ET c ), arranged in a randomized block design with four replications. ET c means crop evapotranspiration under standard condition, which was well watered. For example, the ET 2 (0.8 · ET c ) treatment means that the amount of supplied water per a day is the same as the crop adjustment evapotranspiration (ET cadj ) with the value 0.8 of water stress coefficient (K s ). The RDI treatments were carried out just at vegetative phase and its treatments were stopped at the beginning of flowering phase, and afterwards the treatments were watered at 1.0 · ET c . The results showed that since week II, the soybean experienced stress throughout the growth period except ET 2 treatment. ET 2 treatment started to be stressed at week V and continued to be stressed until the harvest time. At the ET 3 treatment, the critical water content (h c ) of soybean was reached at week II, and the h c was 0.24 m 3 /m 3 on the average. The RDI at vegetative period significantly affected the yield. The highest yield was ET 1 (35.2 g/plant), followed by ET 2 (31.0 g/plant), ET 3 (18.1 g/plant), ET 4 (7.6 g/plant), and ET 5 (3.3 g/plant). The optimal water management of soybean with the highest yield efficiency was regulated deficit irrigation with water stress coefficient (K s ) of 0.80 for vegetative phase.

An experiment was conducted with the objective to investigate the influence of available water deficit in typical soil types on the yield and crop water requirement of soybeans in Indonesia. This research was conducted in a plastic greenhouse of the University of Lampung from June to August 2005. A factorial experiment was arranged in randomized block design with three replications. The soil type (S) was the first factor with two different soil types, Ultisol (S1), and Latosol (S2). Water deficit (D) was the second factor with five levels including D1 (0-20%), D2 (20-40%), D3 (40-60%), D4 (60-80%), and D5 (80-100%) of water deficit from the total available water (TAW). For example, D1 (0-20%) meant that water was given to maintain the available water depletion between 0% and 20% of TAW in the root zone. Yield under full irrigation in Ultisol (21.3 g/pot) was 2.3 times as much as in Latosol (9.3 g/pot). Yield efficiency (the ratio of yield to crop water requirement) in Ultisol was the greatest under deficit irrigation of 30% of available water deficit (0.0083 g/g), which was 1.26 times as much as under full irrigation (0.0066 g/g). However, yield efficiency of Latosol was the greatest under full irrigation (0.0049 g/g). Therefore, yield efficiency of soybean in Ultisol was 1.8 times as much as in Latosol.Discipline: Irrigation, drainage and reclamation Additional key words: deficit irrigation, red acid soil, soybean, yield efficiency, water stress JARQ 41 (1), 47 -52 (2007) http://www.jircas.affrc