ISHS Acta Horticulturae 481: International Symposium on Growing Media and Hydroponics
MANAGING IRRIGATION BY ELECTRICAL CONDUCTIVITY |
| Authors: | T.E. Bilderback, S.L. Warren, J.H. Daniels |
| Keywords: | controlled release fertilizers, cyclic irrigation, Cotoneaster dammeri 'Skogholm' |
| Abstract:
In the nursery industry controlled release fertilizers (CRF) are a common method of supplying nutrients for container grown crops. However, nutrient solution concentrations in containers and product longevity are directly related to irrigation practices. Daily leaching of containers with high irrigation volume can shorten CRF longevity. When low conductivity readings from container leachates are compared to laboratory nutrient analyses, solution levels are also deficient. The hypothesis of this study was that adjusting weekly irrigation volume based on electrical conductivity could reduce excess and deficient nutrient levels in container solution and improve controlled release fertilizer longevity. The experiment was a randomized complete block design with 3 replications. A CRF (15-9-11 Osmocote Plus) was incorporated at five rates: (1) 5.0 g N; (2) 4.25 g N;(3) 3.5 g N; (4) 2.75 g N; (5) 2.0 g N per container. Irrigation was two daily cyclic applications for a total of 800 ml per container. Irrigation volume was reduced after 10 DAI by 30% and was maintained 15 % to 30 % lower than the initial 800 ml irrigation volume throughout the study. Irrigation volume was not reduced below 400 ml since previous studies had indicated cotoneaster growth was limited below this volume. Precipitation events reduced the influence of manipulation of irrigation volume on container EC levels. Approximately 107 cm (30 in) of rainfall was received from May 30 through October 29 which was equivalent to 30 days of irrigation. Electrical conductivity was lower than target EC of 0.85 dS/m for all fertilizer application rates for the entire study. EC reading were generally similar for all fertilizer rates. The highest EC reading during the study was 0.6 dS/m. Shoot growth increased with increasing nitrogen rate at 89 DAI and 152 DAI and root dry weight increased with increasing nitrogen rate at 89 DAI. At 152 DAI all nutrient concentration decreased as fertilizer rate decreased. Foliar N levels for ≤ 3.5 g N per container dropped below suggested levels. Plant growth and foliar nutrient levels in this study under conditions of frequent and occasionally heavy rainfall show that the 4.25 or 5.0 g N/container applications were required to maximize growth but EC levels never reach expected concentrations. | |
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