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P. Parchomchuk and M. Meheriuk

Pulsed application of overtree irrigation for evaporative cooling of `Jonagold' apples (Malus domestica Borkh.) reduced visible solar injury by 15.8% (1991) and 9.4% (1992). Maximum fruit surface temperature was reduced by 8.1 °C on a day when the average surface mean of nonsprayed fruit rose to 45.6 °C. Air heated more slowly than the exposed fruit surface and was cooled only 1 to 2 °C by overtree irrigation. Cooling did not affect fruit size, firmness, or redness but reduced soluble solids concentration and increased titratable acidity. Storage breakdown was unaffected in the first year but was reduced by 6.0% in the second year.

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G.H. Neilsen, E.J. Hogue, and P. Parchomchuk

Application of high rates of P in the year of planting increased the number of flower clusters and fruit set the subsequent year on newly planted `Macspur McIntosh', `Summerland Red McIntosh', `Jonagold', and `Jonamac' apple (Malus domestica Borkh.) on dwarfing rootstock (M.26 and M.9) in three separate experiments. The effect occurred whether P was applied at rates of 36 or 48 g P/tree as granular monoammonium phosphate (11 N-23.6 P-0K) uniformly mixed with 100 or 180 liter of soil in the planting hole or at rates of 17.5 and 35 g P applied as soluble ammonium polyphosphate (10N-14.6P-0K) with the irrigation water. A leaf P concentration range between 0.20% and 0.36% was associated with the acceleration of fruiting.

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D. Neilsen, P. Parchomchuk, G.H. Neilsen, and E.J. Hogue

Direct application of fertilizers in irrigation water (fertigation) is an efficient method of supplying nutrients to fruit trees. Information is needed on the relationship between irrigation and N inputs on N availability in order to target nutrient applications to meet plant demands. Soil solution was collected from permanently installed suction lysimeters and NO3-N concentration was measured over the growing season in three experiments: 1) comparison of sprinkler irrigation + broadcast fertilizer with weekly fertigation + daily drip irrigation; 2) comparison of (NH4)2SO4 or Ca(NO3)2 as N sources under daily fertigation; and 3) comparisons of combinations of irrigation applied at either fixed rates or to meet evaporative demand and fertilizer (Ca(NO3)2) applied daily either at fixed rates or to maintain a given concentration in the fertigation solution in two soil types—loamy sand and silt loam. Trials are located in high density apple plantings of either `Gala' or `Empire' apple (Malus × domestica Borkh.) on M.9 rootstock. Nitrate-N concentration in the soil solution measured at 30 cm deep remained higher, over more of the growing season, for weekly fertigation + daily drip irrigation than for a single broadcast fertilizer application + sprinkler irrigation. With daily Ca(NO3)2 fertigation, soil solution NO3- N concentrations increased and decreased rapidly with the onset and end of fertigation respectively, remained relatively constant during the intervening period and were directly proportional to either the amount of N or the amount of irrigation water added. Daily fertigation with (NH4)2SO4 resulted in less control of NO3-N availability in the root-zone than with Ca(NO3)2, which may be problematic for precise timing of N nutrition. Except for the fixed irrigation rate applied to the loamy sand soil, soil solution NO3-N concentrations at 30 cm beneath the emitter were similar to average concentrations in the fertigating solution, for all methods of irrigation management in both soil types. Elevated NO3-N concentrations in soil solution below the root zone (75 cm deep) were detected in the loamy sand regardless of methods of N application and irrigation although there was some evidence of less leaching to this depth, under scheduled irrigation. In the silt loam soil, considerably lower concentrations of NO3-N were found beneath the root zone than at 30 cm deep for all of irrigation procedures and frequently there was insufficient water moving to 75 cm to provide sample. Tree growth in the loamy sand was less than in the silt loam soil; was limited by low application of irrigation water in 1992 and 1993; was unaffected by NO3-N concentration in the root zone, indicating that N inputs could be minimized by adding N to maintain concentrations of 75 μg·mL-1 or possibly less. Nitrogen inputs may also be reduced if fertilizer N and irrigation water could be retained within the root zone. For coarse-textured soils this will require precise additions of water and possibly soil amendments to improve water holding capacity.

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P. Parchomchuk, R.G. Berard, and C.S. Tan

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.

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G.H. Neilsen, P. Parchomchuk, W.D. Wolk, and O.L. Lau

Newly planted `Jonagold' and `McIntosh' apple (Malus domestica Borkh.) on M.26 fertigated with Ca(N03)2 showed increased early tree vigor and leaf Ca concentration but decreased leaf Mg and Mn compared to trees fertigated with urea or NH4N03. Fertigation with P increased early tree vigor, leaf and fruit P concentration, and decreased leaf Mn in the first year relative to a single planting hole application of granular P. Increased fruit Ca concentration in `Jonagold' in one year was associated with the use of Ca(N03)2 and fertigation of P. Fruit quality was generally unaffected by the experimental treatments.

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G.H. Neilsen, P. Parchomchuk, D. Neilsen, R. Berard, and E.J. Hague

`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.