Koksnes un zālaugu biomasas pelnu izmantošana kārklu plantācijās

"Ash composition in general
The composition of ash depended on plant species (e.g., wheat, rape, Salix) and variety, growth conditions, ash fraction (bottom ash, fly ash) and heating plant. Independent of the biofuel source, fly ash has generally higher concentrations of several heavy metals than bottom ash. Wood ash has generally higher Cd contents than straw ash.
Ash from cereal and rape straw
The composition of 79 samples of straw ash from 7 heating plants was analysed. Compared with bottom ash, Zn, Pb and Cd concentrations in fly ash were 10-90 times higher. Also the concentrations of Cu and K were higher, although to a lesser extent. With respect to heavy metals, pure fly ash is therefore not suitable as fertiliser on arable soils.
The content of Cd per unit of P in straw bottom ash was similar to that of the average in P fertilisers sold in Sweden in 1997 (0.03 g Cd kg-1 P). The Cd/´P ratio in fly ash was 0.6 g Cd kg-1 P.
The liming effect varied between 3.5 and 44 % CaO and depended mainly on the Ca content. Ash from rape straw had a higher Ca content and liming effect than that of wheat straw, and the liming effect of rape ash was more than three times higher than that of wheat ash.
Due to high K contents, straw ashes are suitable as fertiliser especially on soils low in K or to crops with a high demand for K. Since K competes with Mg with respect to plant uptake the K/Mg ratio of the soil must be considered.
Ash used as fertiliser in Salix
Ash amendments were used either to supply 24 kg P yr-1 (0.6-1.5 t ash ha-1 yr-1) or as liming agent (6 t ha-1 containing 2.0-2.9 t CaO-equivalents) in two Salix plantations, one on clay soil and one on sandy soil. Ash treatments were compared with lime and commercial fertiliser treatments. All treated plots received non-limiting doses of N fertiliser. Treatment effects were monitored during the first rotation of the crop (4-5 years).
Ash additions gave equal Salix stem mass as commercial fertilisers did. However, a lower uptake of P in the ash treatments than in treatments where superphosphate was added, indicated that the short-term availability of P in ash could be 80% of that of the easily soluble P fertiliser. Lower amounts of nutrients than those added were removed with stems.
The liming effect of ash was similar to that of slaked lime on a CaO-equivalent basis. Full effect was obtained in the year of application. Due to increased pH in the lime and ash treatments, Mn and Cd mass in stems decreased.
Amounts of Salix ash representing mere recirculation (0.6-0.7 t ha-1) supplied once during the rotation would have supplied P amounts covering the removal with stems and 50% of the CaO-equivalents corresponding to acidification.
Calculated amounts of nutrients in leaf litter exceeded the amounts required for stem growth whereas amounts of Cd recycled with leaf litter were slightly lower than those removed with the harvested stems.
Vertical distribution of plant nutrients and heavy metals in Salix
Elemental concentrations of Salix shoots increased significantly with height. It was shown for the three-year-old shoots that a slight shift in sampling point location (3-4 dm) could result in 10% change of average shoot concentration. This is mainly due to higher mineral concentration in bark than in wood tissue.
Heavy metal circulation
Net accumulation in the topsoil of Cu, Mn and Ni occurred in all ash treatments; Zn and Cd were net accumulated in the wood ash treatments and net removed in all other treatments. Higher amounts of Salix ash than representing mere recirculation resulted in net accumulation of Cd. In all, 7-16% of topsoil amounts of Cd were net accumulated in the wood ash treatments, whereas 5-8% were net removed in the controls and straw ash treatments.
The effect of ash application on soil chemistry and trace metal uptake in the Salix stand was monitored during the first rotation of the crop (4-5 years)."

Oriģināls - http://www.eeci.net/archive/biobase/B10310.html