Decreasing phosphorus leaching and compaction of peat based growing media with clay, fiber clay and dark peat.

摘要

The ability of light colored peat to retain fertilizer phosphorus is poor. Another weakness of white peat is its compaction in long-term use. The ability of a commercial clay product, fiber clay (paper mill industry by-product), and dark peat (H 8-9 on von Post scale) to decrease P leaching and compaction of peat based substrates was studied. The materials were mixed with Finnish Sphagnum/Eriophorum white peat with H 1-3 (Wpeat), clay at 5 and 10% (v/v), and dark peat (Dpeat) and fiber clay at 30%. For better water absorption of the Wpeat+Dpeat mixture, 10% sand was added. The effect of sand was also studied. Wpeat and Dpeat were used as controls. Experiments of (1) phosphorus leaching (at 0 and 4 months) and rewettability (after 5, 10, 17 and 31 days without watering), (2) compaction follow-up (6 months), and (3) preliminary evaluation of growth properties (using Lepidium sativum) were carried out in pots in growth chamber conditions (21+or-2 degrees C). The initial structure was characterized by total pore space, air and water volume, container capacity (WHC), and volume weight. All unused media, except for Wpeat+sand, retained more P than the Wpeat. P leaching was lower from settled (4 months) than from unsettled growing media. Settled Wpeat+fiber clay reduced P leaching by 66% compared to Wpeat, whereas the value for 10% clay was 41%. Lower application rate of clay did not have a significant effect on P leaching at 4 months. Dpeat had also a quite high P retention capacity (52%), but was not significantly better than control when mixed with Wpeat. Sand and clay enhanced the rewettability of Wpeat. Dpeat most clearly reduced compaction of the growing medium. Air volume was highest and compaction reduced by half in Wpeat+fiber clay substrate. However, more research is needed before the use of fiber clay can be recommended because of high pH and EC as well as growth reduction in the cress test.