Forage Rejuvenation with Phosphorus Fertilizer

Established forage stand productivity is seriously limited by nutrient supply in most areas of western Canada. While only limited acres of forage grass crops are fertilized, past research has shown it to be one of the most responsive crops to nitrogen (N) application. The objective of this study is to evaluate the management of dry and fluid phosphorus (P) fertilizers, applied with N, to restore the productivity of established, low-yielding forage stands.

Field studies were initiated at two locations using established forage stands that were low yielding. Fertilizer P was applied as either surface broadcast monoammonium phosphate (MAP), or surface dribbled or coulter injected ammonium polyphosphate (APP). Along with an unfertilized check and a coulter check, there was a coulter-injected N only treatment. The P was applied at either an annual rate, or three times the annual rate. All treatments received the soil test recommended rate of N, and a blanket application of potassium and sulfur. Application of N and P increased forage yields from 12 to 53% in 2003. Application of N alone always yielded less than when applied with P. Using P at three times the annual rate provided the highest forage yield, indicating that the annual rate was P-limiting at both locations. Continued use of these trial sites will help to assess the impact of annual versus one-time P application on forage yields. SK-35