Controlled release of phosphorus fertilizers by small, frequent additions in water solution

Controlled release of P was investigated with barley plants grown on two soils. Phosphorus fertilizers (monoammonium phosphate [MAP], diammonium phosphate [DAP] and ammonium polyphosphate [APP]) were dissolved in water and were applied full dose at sowing; 1/22 dose every 2nd day and 1/4 dose each 11th day. Uptake of fertilizer P in barley was much greater when the P was applied every 2nd and 11th day compared to only the day of sowing. Key words: Barley, diammonium phosphate, monoammonium phosphate, P uptake, P yield, release of P