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  • Author or Editor: B. Krueger x
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It has been observed that overhead irrigation does not cause cracking of sweet cherries (Prunus avium l.) to the same extent as a rain of equal duration. A series of simulated rain-overhead irrigation comparisons was made to test the hypothesis that the difference observed could be due to the dissolved salt content of irrigation waters. Although the quality of the irrigation waters selected were quite high (conductivity of 0.175 millimhos/cm or less), the cracking index of cherries wetted with irrigation water was consistently less than with deionized water. The results reemphasize the marked effect of even small amounts of dissolved salts, particularly the divalent cations, on reducing cracking of sweet cherry fruits.

Open Access

The uptake efficiency of apple scions and rootstocks has not been studied in the field. Using 15N (ammonium nitrate, 1 atom % 15N) we compared nitrogen uptake efficiency of 12 rootstocks grafted to one scion (Gala) and of 20 scions on the same clonal rootstock (M.9 EMLA) in orchards located in northeastern Wisconsin. Trees were treated in either Fall or Spring 1998 with 40 g actual N per tree applied as a liquid to the soil. N uptake was assessed by measuring 15N in leaf and wood tissue taken monthly from June to Oct. 1998. Tissues were oven-dried and analized using a ratio mass spectrometer. Treatment differences were greater among scions with the same rootstocks than among rootstocks with the same scion. Total N and 15N content differences were found between roostocks and these values were inversely related to tree size.

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Nitrogen (N) uptake was compared on 10 dwarf apple rootstocks (M.9 EMLA, M.26 EMLA, M.27 EMLA, M.9 RN29, Pajam 1, Pajam 2, B.9, Mark, B.469, and M.9 T337) grafted with the same scion (`Gala') in a four year-old orchard. Trees were treated in either Spring or Fall 1998 with 40 g of soil applied actual N per tree using ammonium nitrate enriched to 1% 15N. Both percentage of N (%N) and N from fertilizer (NFF) in leaf tissue were highly affected by the rootstock and the season of N application. Generally, higher %N and NFF were observed for spring than fall applications, except for leaves collected during early June 1998. Generally, M.26 EMLA, M.27 EMLA, and M.9 RN29 were the most efficient rootstocks in N uptake for spring applied nitrogen. M.9 EMLA was most efficient late in the season following fall application. Mark was more efficient early in the season for fall applied N than spring application. However, trees on Mark rootstock had the lowest %N throughout the season regardless of the time of N application. Pajam 1 and Pajam 2 were the least efficient rootstocks in N uptake following fall N application. Rootstock also significantly affected %N and NFF of wood tissue. Generally, trees on B.469 had the highest %N in their wood regardless of the season of application. No single rootstock had consistently higher N from fertilizer in their wood tissue after spring application. At the May 1999 sampling date, M.26 EMLA had higher NFF than M.27 EMLA, Pajam 1, Pajam 2, and B.9 with a fall application. Other rootstocks were intermediate. Samples collected in August showed that Pajam 1 was the least efficient rootstock in N uptake for fall applied N compared to other rootstocks, except for Pajam 2 and B.9 that were intermediate. Leaf and wood tissue analysis showed that different rootstocks had different N uptake efficiencies throughout the season. Generally, M.26 EMLA, M.27 EMLA, M.9 RN29 and M.9 EMLA were more efficient at N uptake regardless the season of N application. Pajam 1 and Pajam 2 were the least efficient.

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Media fertility is a critical factor in the successful production of container grown plants. Fertility treatments including fertigation and slow-release fertilizers (topdressed and incorporated) were compared. Fertility treatments were studied over a two-year period on a variety of deciduous and evergreen plant materials. Plant growth was quantified based on height, volume, branching, and quality. Soil fertility levels based on leachates were followed during the study. Nutrient release for incorporated fertilizers tested was variable although less so than when the same fertilizers were topdressed. Fertility treatment effects were species-dependent. Several incorporated, slow-release fertilizers, especially those high in nitrogen (Sierra 17-6-10, Sierra High N 24-4-6, Woodace Briquettes 23-2-0, Woodace 21-4-10), show promise for use in two-year container production systems.

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A study was designed to ascertain the efficacy, water use efficiency, runoff potential, and cost effectiveness of four container irrigation systems: overhead sprinkler irrigation, in-line trickle irrigation, capillary mat with leaky hose, and sub-irrigation. Results were species dependent. Plant growth was best under capillary mat and trickle irrigation treatments, however, differences in plant growth and performance between irrigation treatments were minimal. Differences in water use, however, were quite significant. Overhead irrigation was inefficient regarding water use while capillary mat and trickle systems used much lower volumes of water. Conservative irrigation systems which maintain acceptable plant growth using less water and reduce runoff from container production areas can clearly benefit growers by reducing production and environmental costs.

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Prunes trees are believed to be relatively tolerant of water stress, and because prune fruit are dried, a low fresh to dry weight ratio of the fruit will reduce energy requirements for fruit drying and will represent an economic benefit to the grower. In previous research, we found that, under some orchard conditions, irrigation deprivation was associated with a number of economically beneficial effects, including a lower fresh to dry weight ratio of the fruit, increased return bloom, and final saleable crop yield. Analysis of these results was complicated by the effects of irrigation on alternate bearing, and the fact that tree water stress could be substantially different under different soil conditions for the same level of irrigation deprivation. Taking these factors into account, however, indicated that economic yield in prune could be maintained or increased by managing trees at a moderate level of water stress. An experiment was established to determine whether midday stem water potential could be used to guide irrigation and achieve a target level of water stress during the growing season, and whether a moderate level of water stress would be economically beneficial to prune production. By managing prune trees at a moderate level of water stress (midday stem water potential reaching about –1.5 Mpa by the end of the season) over 3 years, an average savings of 40% in applied irrigation water was obtained. Modest increases in return bloom, and an improved fruit dry to fresh weight ratio, occurred in moderately water stressed trees, although overall yield was not changed. The substantial savings in water, without reducing yield, should represent a net economic benefit to growers, depending on the price they pay for water.

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To be useful for indicating plant water needs, any measure of plant stress should be closely related to some of the known short- and medium-term plant stress responses, such as stomatal closure and reduced rates of expansive growth. Midday stem water potential has proven to be a useful index of stress in a number of fruit tree species. Day-to-day fluctuations in stem water potential under well-irrigated conditions are well correlated with midday vapor-pressure deficit, and, hence, a nonstressed baseline can be predicted. Measuring stem water potential helped explain the results of a 3-year deficit irrigation study in mature prunes, which showed that deficit irrigation could have either positive or negative impacts on tree productivity, depending on soil conditions. Mild to moderate water stress was economically beneficial. In almond, stem water potential was closely related to overall tree growth as measured by increases in trunk cross-sectional area. In cherry, stem water potential was correlated with leaf stomatal conductance and rates of shoot growth, with shoot growth essentially stopping once stem water potential dropped to between −1.5 to −1.7 MPa. In pear, fruit size and other fruit quality attributes (soluble solids, color) were all closely associated with stem water potential. In many of these field studies, systematic tree-to-tree differences in water status were large enough to obscure irrigation treatment effects. Hence, in the absence of a plant-based measure of water stress, it may be difficult to determine whether the lack of an irrigation treatment effect indicates the lack of a physiological response to plant water status, or rather is due to treatment ineffectiveness in influencing plant water status. These data indicate that stem water potential can be used to quantify stress reliably and guide irrigation decisions on a site-specific basis.

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