The mixture of MBM and BWA gave the highest barley yield (Table 3.5), which was significantly higher than for MBM alone. The barley yield of the MBM and different combinations of MBM and crushed rock was at the same level as for mineral NPK. All treatments with MBM or mineral NPK gave significantly higher yields of both barley and wheat compared with the unfertilized control (treatment 1). The yield of wheat was at the same level for mineral NPK and MBM with or without K addition (Table 3.5), but there was a significantly lower yield for MBM pellets (treatment 4) and MBM plus Altagro plus Olivin compared with MBM powder alone (treatment 2).

Different additions of K did not influence the concentrations of K in the wheat grain (Table 3.6). The unfertilized control had a significantly lower concentration of N and a higher concentration of P in wheat grain than obtained for treatment with MBM plus K, Mg and S, and mineral NPK gave a significantly lower P concentra­tion than the unfertilized control. The concentrations of plant nutrients taken up in barley grain were not analyzed.

The efficiency of the N applied was high and at the same level for the treatments with MBM or mineral NPK, whereas relatively small amounts of the P and K applied were taken up in the wheat grain (Table 3.6). On the basis of the nutrient uptake in wheat, the unfertilized control had a negative balance for N, P and K, whereas addition of MBM alone caused a negative K balance (Table 3.6). All the other treatments had a positive balance of P and K. The MBM treatment lowered the amount of readily available K in the soil, but the difference from the other treatments was not statistically significant. There was no significant change in the level of nonexchangeable K (KHNO3) for any of the treatments compared with the unfertilized control. MBM plus BWA gave a significantly increased amount of readily available P compared with use of MBM pellets plus K, Mg and S and the

control. MBM plus BWA also increased the amount of readily available Ca in the soil significantly compared with the treatments with MBM, MBM pellets plus K, Mg and S and mineral NPK. The only treatment that significantly increased soil pH was the MBM plus BWA treatment. The pH increase was around 0.5 (Table 3.7).

The BWA used in this experiment had a high concentration of Ca relative to K (Ca-to-K ratio, 8.6; Table 3.3). To find ash with a stronger effect as a K fertilizer than liming material, analyses of the chemical properties of bottom ash from other plants were performed (Table 3.8). BWA Akershus (Table 3.8) had a high concen­tration of K and a low concentration of Ca (Ca-to-K ratio, 1.8) and low concen­trations of heavy metals. The wood used originated from a timber terminal at Gardermoen, where bioenergy wood from a large district in eastern Norway is collected. The ash of cereal waste had high concentrations of P and K and low concentrations of heavy metals. The analyses indicated differences in the Ca-to-K ratio between ash of spruce and ash of pine (Table 3.8). The wood used at Reinsvoll was dominated by spruce and the ash had properties similar to those of the ash of pure spruce wood.