A study was undertaken in order to quantify the effects of rootstock and irrigation level on the rooting pattern of fertigated apple trees. A profile trench observation method was used to map the number and location of root intersections at two planes relative to drip emitters for NP-fertigated McIntosh apple trees (Malus domestica Borkh). Four replicates of all combinations of three rootstocks (M.9, M.26 and M.7, planted in 1990) and two irrigation treatments [F1 (daily, watered to field capacity) and F2 (weekly, watered to 50% available soil water capacity, imposed in 1991)] were investigated after the 1994 growing season. Dwarfing rootstocks and F2-irrigation had lower top vigour and yield per tree. Cumulative yield efficiency was greater for trees on dwarfing rootstock but was unaffected by irrigation treatment. Root numbers per observation plane paralleled rootstock vigour, being lowest for M.9 and greatest for M.7. No effect of irrigation on root number was observed. Root distribution was affected by an interaction between rootstock and irrigation treatment with average root location moving closer to the surface and emitter for the dwarfing rootstocks M.9 and M.26 but not for M.7 under F1-irrigation. Key words: Vigour, yield, drip emitter, root number and distribution

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`Gala' apple (Malus domestica Borkh) on M.26 rootstock was subjected, in the first five growing seasons, to NP-fertigation and a factorial combination of treatments involving method and frequency of irrigation. Two types of emitters (drip or microjet) were used to apply the same quantity of water at high (daily), intermediate (about weekly) and low (about bi-weekly) irrigation frequencies. Although initial tree vigor and yield were higher for drip-fertigated trees, by the end of the study microjet fertigation produced larger trees of similar yield. These microjet fertigated trees had higher leaf P, K and Cu but lower leaf N, Mg, and Mn than drip-fertigated trees. Soil pH and extractable Mg and K concentrations were higher and extractable-P concentrations lower directly beneath microjet-emitters as a result of the larger fertigated soil volume relative to drip-emitters. High frequency irrigation improved tree growth but had less effect on leaf nutrient concentrations or soil chemical changes than lower frequency irrigation. Leaf N concentration was most affected by irrigation frequency, tending to decrease with daily irrigation.

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We have found time domain reflectrometry (TDR) to be a rapid and effective method of measuring soil water content (SWC) in microirrigated orchards, particularly in applications where many sites are monitored frequently. With simple modifications to commercially available systems, it has been possible to measure up to 100 sites per hour. TDR SWC measurements have been successfully applied for scheduling irrigation and for in situ determination of SWC characteristics. The determination of plant water use from changes in SWC of microirrigated trees, however, requires that a sufficient number of probes be used to detect the spatial distribution of water within the root zone. Due to water redistribution in the soil following an irrigation, measurements made near drip emitters depend highly on the time after irrigation that the measurement is made. It is therefore important to be consistent in the timing of SWC measurements relative to irrigation events if the effects on SWC of different irrigation management practices are to be compared.