Optimising Nutrition Of Containerised Nursery Stock

Abstract

Irish peat, used as a growing medium in horticulture, tends to have a higher state of decomposition and a higher potential buffering capacity than some of the younger peats from Scandinavian or Baltic countries. Particularly where hard water, with high bicarbonate content, is used for irrigation this could be an important property in giving the peat greater stability with respect to pH levels throughout the cropping period. It may also influence the optimum rate of lime to be applied to adjust the pH prior to cropping. The effect of peat type on the performance of nursery stock plants, Azalea and Hebe in 2-litre containers, was studied when irrigated with both soft and hard water and with different rates of lime in the peat growing medium. When irrigated with hard water, the rate of pH increase was less with relatively decomposed Irish peat than with younger Baltic peats. Using Irish peat, a rate of dolomitic lime addition to the peat of 4 kg/m3 was best for Hebe when irrigated with soft water. Irrigating with hard water the lime rate could vary between 2 and 4 kg/m3 without affecting plant performance. With the Baltic peats, increasing the rate of lime addition above 2 kg/m3 tended to reduce growth of Hebe. Azalea gave better results when irrigated with soft water. In hard water areas therefore it is advisable, if possible, to collect rain water from a greenhouse roof for irrigation purposes. A zero rate of lime gave inferior results with Azalea. With hard water a rate of 1 kg/m3 was optimum. With soft water this could be increased to 2 kg/m3 without damage. New formulations of the controlled release fertiliser (CRF) have been introduced recently. An experiment was carried out to evaluate the CRFs available in Ireland for the production of containerised nursery stock over a 12 month period. The effect of rate of CRF was also studied. Experiments were also located in the Colleges of Horticulture in Warrenstown and Kildalton. All the CRFs in these experiments produced acceptable results in terms of plant performance. There were differences between the CRFs but these were not consistent between the experiments. The vigorous species Lonicera pileata and Escallonia macrantha responed positively to rates of CRF up to 8 kg/m3. The conifer, Thuja plicata gave no response to rates above 6 kg/m3. In an experiment over two seasons using 20 nursery stock species, a liquid feeding system resulted in heavier plants of most species than did one based on a controlled release fertiliser.