Torres Meléndez, Carlos N.

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    Balance de fósforo en vaquerías de Puerto Rico
    (2005) Torres Meléndez, Carlos N.; Ruiz López, Teodoro M.; College of Agricultural Sciences; Rodríguez Carías, Abner A.; Sotomayor Ramírez, David; Martínez Rodríguez, Gustavo A.; Latorre Acevedo, José R.; Department of Animal Science; Dávila López, Rafael F.
    On-farm phosphorus (P) balances are of importance in order to identify critical control points in P feeding and management. Phosphorus mass balances were constructed in twelve pasture-based dairy farms of Puerto Rico, using production and management data in an input-output model. The farms had a range in animal density between 1.23 to 27.50 AU/ha with a mean of 7.53 AU/ha. The range in dietary P concentrations was between 5.02 to 7.24 g P/kg DMI, with a mean of 6.16 g P/kg. The dietary P concentrations fed were not associated with higher milk yields (P>0.05) and were 87% higher than the level recommended by the NRC for the mean production levels of 18.4 kg milk/day. Manure P ranged from 9.0 to 18.5 g/kg (dry matter feces) with a mean of 13.2 g/kg. Total P excreted by dairy cows ranged from 23.9 to 36.9 kg P/cow/year with a mean of 30.3 kg P/cow/year. Manure P and excretion levels were 55% higher than those excretion levels needed to account for maintenance and milk production. High stocking rates were associated with the large aerial P surplus (R2=0.87). Soil test P (Olsen) levels showed that 87% of the paddocks (n=38) that received manure application exceed suggested agronomic critical P levels of 35 mg/kg. The on-farm mass balance showed P surpluses that ranged from 15.0 to 472.9 kg/ha/year with a mean of 156.2 kg/ha/year. Reducing the P concentration in the diet and in fertilizer and the implementation of best management practices will have the greatest and immediate impact on reducing the excess P in dairy farms of Puerto Rico that will optimize P use efficiency for eventual water-quality maintenance.