Yield and quality of mulberry (Morus alba) fertilized with nitrogen, phosphorus and potassium

The objective of this work was to determine the effect of nitrogen, phosphorus and potassium applied to the soil, on yield and bromato-logical quality of mulberry. The experiment was conducted in Costa Rica at 1542 masl, in a mulberry plantation with a population of 25000 plants/ha established in 2002. The plants were homogenized by prunning at 60 cm above the soil surface and 84 days after were harvested for the evaluation. The annual mulberry dry matter yield showed important differences between applied levels of nitrogen, phosphorus and potassium (p<0.05). The highest concentration of dry matter was observed with 112.5 kg of N/ha/year, 30 kg of P/ha/year and 225 kg K/ha/year. The highest percentage of crude protein was obtained with 112.5 kg of N/ha/year but with similar results (p>0.05) were observed when different amounts of phosphorus and potassium were applied. The concentration of neutral detergent fiber was affected (p<0.05) when the levels of nitrogen were increased and considerable variations were observed with addition of phosphorus and potassium. The different levels of NPK did not show important effects on acid detergent fiber; however, as the nitrogen levels increased the hemicelulose decreased (p<0.05), and the cellulose augmented with high levels of nitrogen and phosphorus, but decreased significantly with elevated amounts of potassium. The production of dry matter resulted highly significant (p<0.01) when nitrogen, phosphorus and potassium where applied together, but crude protein and neutral detergent fiber did not show the same pattern (p>0.05).