Wisconsin State Horticultural Society / Annual report of the Wisconsin State Horticultural Society for the year ending July 1, 1921
Vol. LI (1921)
Roberts, R. H.
Off-year apple bearing, pp. 72-78 PDF (1.8 MB)
WISCONSIN STATE HORTICULTURAL SOCIETY the one which is under-vegetative. They find the former is ex- tremely high in nitrogen, and low in carbohydrates. The other unfruitful plant is very poor in vegetation, is generally high in carbohydrates, and, as a rule, low in nitrogen. In addition to these two conditions, they had plants which were fruitful. These were plants which have conditions balanced, so to speak, between the carbohydrates and nitrogen products. In explanation of how this situation seems to fit apple trees we can call to mind several conditions with which you are already familiar. For example, the young tree before it comes into fruit is making a very strong vegetative growth and is unfruitful. Analyses show such trees have a high nitrogen content and a low carbohydrate content. We have found from analysis that a rather high carbohydrate content is necessary for blossom bud formation. That is why we are putting so much emphasis on the proposition of wood content. Blossom bud formation de- pends upon the composition of the plant, and plants that are unfruitful may be either very low in nitrogen or very high in nitrogen. We want to get that clearly in mind, because it has an important bearing upon the treatment and cultural practice which the orchard needs. The tree which is girdled becomes very fruitful. This is due to a constricting of the transporting tissue of the plants to such an extent that the carbohydrates accumulate above the girdle and conditions for blossom bud formation are created. Even the sick tree does not form blossom buds because it is trying to reproduce its kind; it forms blossom buds because it cannot help it, through the trunk or roots being injured to such an extent that there is a natural accumulation of carbohydrate products in the top, and this condition gives blossom bud formation. As growers, you are probably not much interested in the in- ternal composition of the plant. There are, however, some very good external measurements by which we can judge the condi- tion of plants, as twig length, spur length, leaf size, leaf color, color of bark, etc. The one which we want to pay special atten- tion to now is growth length, especially spur growth length. We want to discuss in detail some of the things which spurs do. We will begin by saying that some spurs are fruitful, as you know, and some are not. There is nothing new about that, but we have found that some of the unfruitful spurs are unfruitful because 73
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