The Effect of Leaching on Electrical Conductivity and Nitrogen in Propagation Media

Leaching of fertilizer from container substrates can rapidly occur during cutting propagation because of high applied water volume. The objective was to quantify changes in electrical conductivity (EC) and N concentration in both substrate and leachate in propagation trays. The experiment was conducted using a peat/perlite substrate with hydrated dolomitic limestone incorporated at 2.1 g L-1 of substrate, and KNO3 at 0, 0.6 or 1.2 g L-1 of substrate, resulting in three initial substrate-EC levels (0.30, 0.96 or 1.99 dS m(-1)). Two irrigation solutions were applied (deionized (DI) water or N at 200 mg L-1 derived from KNO3, with EC of 0 and 1.98 dS m-1, respectively). The experiment had 6 treatments (3 substrate-EC levels x 2 irrigation solutions) with a randomized complete block design. The substrate was placed into 128-count propagation trays, brought to container capacity (CC), and kept in the dark for complete lime reaction. Trays were then irrigated with 3.18 ml of DI water or KNO3 solution per cell 12 times over a 3-hour period. Following each irrigation, substrate and leachate EC and N concentration were analyzed. CC was 16 ml per cell, and leachate volume averaged 2.9 ml per cell and irrigation for a total of 2.23 CC. Trends in substrate-EC and leachate-EC were similar. Following irrigation with DI water, EC of the substrate containing 1.2 g KNO3 L-1 initial fertilizer charge, increased from 2.0 to 2.4 dS m(-1) after 0.36 CC leached, after which the substrate-EC decreased to a minimum of 0.1-0.3 dS m(-1) after 1.5 CC leached. When propagation trays were irrigated with KNO3 solution, substrate-EC reached a plateau at approximately 1.9 dS m(-1) regardless of the initial fertilizer charge incorporated into the substrate. When 2.23 CC were leached with DI water, 65 to 76% of incorporated fertilizer. The results emphasize the importance of minimizing leaching during irrigation to reduce runoff.