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In 1959 heeft de afdeling Tuinbouw van het L.E.I. een onderzoek ingesteld naar de produktiekosten van appelen en peren in Zeeland, de Betuwe en het zandgebied van Noord-Brabant en het noorden van Limburg. De uitkomsten van dit onderzoek worden in dit artikel aan een nadere beschouwing onderworpen.

Due to the increased use of dwarfing rootstocks and fertilizer experiments dressings increased from 90-120 kg N/ha in 1958 to 170-270 kg in 1965. In deciding on the quantity of nitrogen dressing its interacting effects on growth and fruit production as well as the influence of soil, weather and undergrowth were studied. Some of the experiments were carried out in pots, the others in the field.The discussions cover the availability of nitrogen in the soil and the nitrogen requirements of the trees, especially in relation to competition with a full grass cover and grass strips. The system with grass strips and mulched bare tree strips is considered a case of fertilizer placement since the soil under the grass strip is extremely low in nitrogen during the greater part of the season.

Development and ripening of pears in connection with storage - A review if the biochemical processes involved in the ripening of stored pears. Preliminary results of own investigation esp. the conversion of amylum and pectic substances by enzymes during the ripening process. The presence of pectinase could be demonstrated.

Sinds 1948 heeft geen onderzoek naar de kostprijzen van appelen on peren in de "belangrijkste productiegebieden van fruit meer plaats gehad. De snelle technische ontwikkeling in de fruitteelt gedurende de achter ons liggende jaren en het gewijzigde prijspeil hebben een algehele herziening, zowel wat de kosten als wat de opbrengsten betreft, noodzakelijk gemaakt. Hoewel de huidige ontwikkeling van de fruitteelt in Z.W. Nederland practisch geheel in de richting van intensieve beplantingen met kleine boomvormen gaat, is voor dit onderzoek de struikvormbeplanting, als zijnde het meest voorkomende plantsysteem van boomgaarden die in productie zijn, als uitgangspunt gekozen.

Germination of pear pollen markedly improved when boric acid was added to the medium. The pollen was more sensitive to boron in water than in 10 % sugar solution. Supplying weak solutions of boron to pear branches before flowering resulted in a good germination of the pollen in sugar solution without boron. Spraying apple-trees and pear-trees with boron solutions had no significant effect on fruit set, despite the pollen sensitivity to boron in vitro.The amount of boric acid in the medium determined percentage germination (saturation curve) and length of pollen tubes. Boron was not required until the tubes protruded. Temperature and sugar concentration both showed optimum values for germination. The effect of boron on germination rate was positively correlated with temperature and negatively with sugar concentration. An increase of 10°C roughly doubled this influence on germination rate. Germination was positively correlated with pollen grain number per drop, whether or not boron was present. So the mutual stimulation of the pollen was more effective with boron or with pollen from rather boron-rich branches. Pollen extracts in 10 % sugar solution with or without boron stimulated germination (also of other species).Both apple and pear pollen (and those of many other species) remained viable longest at both low humidity and temperature. In deep-freeze longevity was more than 2 years at -180°. Viability remained unchanged. Longevity would probably have been indefinite.