Leaf water potential (') and leaf conductance (gl) were measured in the field in 20-year-old olive trees subjected to two treatments of soil water content (dry-farming and drip-irrigation). Differences between treatments of up to 0.35 MPa were observed in predawn , values. At midday, these differences were of up to 0.83 MPa. However, no significant differences between treatments were observed in gl values. Maximum gl values of about 0.77 cm S-l were found early in the morning, clossing the stomata afterwards. In just 12 hours after rewatering following the drought period, the differences between treatments on , values were reduced from 0.29 MPa to 0.14 MPa for predawn values, and from 0.64 MPa to 0.23 MPa for midday values. The recovery was virtually total at the third day after rewatering.

Additional index words: irrigation, Kjeldahl-N, drainage water, soil water content. AbstraetLosses of nitrate from an undisturbed sandy loam soil contained in two monolith lysimeters, Lo and L¡, (1 m diameter, 1.5 m deep) under com and irrigation (628 mm) were studied. The crop was fertilized with O (Lo) and 800 (L¡) kg N ha-l. Water draining was collected periodically and analysed for nitrate content during the experimental period (20)(21)(22)(23).Mean values of nitrate concentration in the drainage water were 3.1 and 41.2 mg NOrN 1-1 in Lo and Ll respectively, the latter much higher than the limit imposed by the EC for potable water (11.3 mg N l-I).Three periods were distinguished during the experiment: i) Crop season, in which the total volume of water drained was 310 and 47 mm respectively in the Lo and L l , while the nitrate 10sses were of the same order in both lysimeters ( 21 and 17 kg N ha-l , respectively); ii) Dry season, in which there was no water drainage; and iii) Rainy season, in which the total drained water was 157 and 139 mm, and the nitrate los ses 5 and 91 kg N ha-l in Lo and L¡ respectively.The greater amount of water drained in Lo is due to the lower crop development (grain yield 4.4 and 21.3 t ha-l ; total nitro gen plant uptake 69 and 400 kg N ha-l , in Lo and Ll respectively).Total nitrate losses in Ll account for 13% of the nitro gen fertilizer applied. Most of these losses occur in the rainy season.At the end of the experimental period a decrease of the soil nitrate content was observed in both lysimeters.

Tbe present work studies tbe effect of various tillaqe systems on the water infiltration in a sandy clay loam soil (Calcic Haploxeralf) from Seville province. The followinq tillaqe metbods were considered: mouldboard plouqhinq (MP), cultivator application (C) and no-tillaqe (NT). In each treatment, water infiltration was measured using both double-rinq infil trometer and rainfall simulator. Infil tration rates for MP and C treatments were siqnificantly (p=0.05 level) hiqher than for NT treatment. Tbe infiltration rates in the plouqh pan of the MP and C treatments were not siqnificantly different (p=O. 05 leve!) to those oí the consolidated zone (20 cm depth) in tbe NT treatment. For tbe different soil conditions, created witb tbe tillaqe methods used, the sorptivity parameter was calculated usinq the Philip equation.

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AbstraetMeasurements of leaf water potential ('I') and stomatal conductance to H 2 0 (g) were made in 26-year-old Manzanillo olive trees under irrigation and dry-farming conditions. On days of high water demand, the olive trees reduced water losses by closing the stomata, so preventing excessive water stress. The analysis of g values versus photosynthetically active radiation (IPAR) and vapour pressure deficit (VPD), showed that stomata were fully opened at relatively low IpARlevels, from about 500 Jlmol m-2 S-l.Also, g decreased with increasing VPD, for values of up to approximately 4 kPa. After plotting the relative extraetable soil water (REW) values against their counterparts of pre-dawn leaf water potential ('I'pd) , it was observed that 'I'pd remained eonstant for values ofREW higher than 0.4, with a mean value of -0.46 MPa.