A comparison was made between the results of laboratory and field experiments regarding predictions of soil moisture distribution from a point source on the one hand, and those theoretically calculated by a computer simulation model (Bresler, 1975) on the other hand. A good agreement was found between computed and experimental data. When the verified model was used for predictions regarding soil water distribution under point‐source irrigation, it was found that when the same total amount of water (12 liters) was added to the soil with a 2, 4, or 8 liters/hour continuously applied trickle source, a loss of 26% of the total amount applied was affected below the 60 cm depth after 12 hours. The initial water content of the soil was adjusted to the field capacity value. Under identical conditions I liter/hour continuously applied and 2 liters/hour pulsed (intermittent) irrigation resulted in only a 12% loss. The lateral distribution of the water showed that in the first group of treatments 80% of the water in the wetted soil volume was distributed 45 and 43 cm horizontally from the point source after 12 and 24 hours respectively. In the second group of treatments the distribution was to 29 and 40 cm. Thus the second group of treatments showed a clear advantage in reducing water loss under the root zone while still not significantly affecting the horizontal distribution. The pulse treatment can therefore replace the advantageous low (1 liter/hour) discharge rate while to a large extent avoiding the difficulties of blocking of outlets by maintaining a higher (2 liter/hour) discharge rate.

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The response of'Starking Delicious' (Malus domestica Borkh.) apple trees to four N fertigation treatments in drip irrigation (50, 150, 250 and 400 kg N ha-l, supplemented with a uniform dose of 400 kg K ha-l ) was investigated in a field experiment during 6 years.Nitrate nitrogen in the soil was proportional (7-58 mg kg -1) to the applied N dose at the end of a 6 week fertigation period in the spring. At other times, the nitrate concentration in the soil was very low. Soil K decreased with depth and in the 0-30 cm soil layer it was negatively correlated with the applied N dose, before fertigation started. At the end of the spring fertigation period, higher K was found in all soil layers analyzed.Vegetative growth was correlated positively with the amount of N applied. Leaf chlorophyll and N were significantly lower only in the lowest N treatment, while increased fruit size and decreased fruit color were measured only in the higher N treatments. Yield was severely biennial. In the 'On' years crop load was heavier as less N was applied. An extremely high crop load in the lowest N treatment was followed by a reduced flower density and yield in the following season. In the 'Off years, a significantly higher yield was obtained with the 150 kg ha-~ dose. The dry weights, N, P and K contents of the above ground parts of mature apple trees were determined.

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