Biomass ashes and their phosphorus fertilizing effect on different crops

The reutilization of biomass ashes in agriculture is an important issue to create nutrient cycles and to save fertilizer. To analyse the P fertilization effect of crop biomass ashes (rape meal ash (RMA), straw ash (SA), and cereal ash (CA)) in interaction with different crops, two pot experiments with a poor loamy sand deficient in P were carried out. Besides the three ash treatments, other treatments included triple superphosphate (TSP) as a high soluble P source, potassium chloride (KCl) as a high soluble K source, and a control (CON) without P and K. The main crops (maize, lupin, summer barley, and oilseed rape) were cultivated in the first experiment from April to May and the catch crops (oil radish, phacelia, italian ryegrass, and buckwheat) were cultivated in the second experiment from August to September. Plant parameters (biomass and P uptake of shoots), soil pH, different P pools of the soil (total P (Pt), water soluble P (Pw), double lactate soluble P (Pdl), oxalate soluble P (Pox)), P sorption capacity (PSC), and the degree of P saturation (DPS) were investigated. The fertilization effect of biomass ashes was comparable with that of TSP. On average of all crops, the highest P uptake (86.7 mg pot(-1)) was found after RMA application, and the lowest P uptake (66.6 mg pot(-1)) for CON. The readily bio-available soil P contents (Pw and Pdl) were significantly increased when P was supplied, regardless of whether P was given with ash or with high soluble TSP. The P fertilization effects also depended on the cultivated crops. The ash treatments resulted in highest increases of soil Pw values when combined with buckwheat cultivation. After buckwheat harvest the Pw content in the control was 8.0 mg kg(-1), and in the ash treatments between 13.9 mg kg(-1) (CA) and 15.7 mg kg(-1) (RMA). From the results of this study we conclude, that crop biomass ashes can be an adequate P source comparable to that of highly soluble commercial P fertilizer.