Deleterious Effects on Yield of Drilling Fertilizer into Established Alfalfa Stands 1

Drilling fertilizer into an established forage crop has been suggested as a means of increasing fertilizer availability. Experiments were conducted at Swift Current, Saskatchewan on an orthic Brown chernozem (aridic haploboroll) to investigate the effects of fertilizer rate and placement depth on the yield of an established dryland alfalfa ( Medicago ✕ vuriu Martyn) stand. In one experiment phosphorus fertilizer at rates of up to 64 kg P/ha was drilled‐in to depths of 0, 5, and 10 cm and in a second experiment, N fertilizer at rates of up to 200 kg N/ha was drilled‐in to the same depths. Fertilizer rate did not affect yields in either experiment and there were no interactions between depth of placement and fertilizer rate. However, in both experiments, increasing the depth of placement decreased yields between 12 and 20% in the first year and in both experiments the yield decreases persisted for 2 or more years. In a third experiment the soil 30 cm from the row of an old established stand of alfalfa was disturbed at four depths (0, 2.5, 5 and 10 cm) with a tractor‐drawn spike to simulate a fertilizer drill. A 20% decrease in yield was observed when the soil was disturbed below 2.5 cm. It is suggested that the reduced yields were a result of mechanical damage to roots and that the persistence of the effect was due to an inability of the root to regrow in the dry topsoil common to southwest Saskatchewan. It is recommended that for established alfalfa stands all fertilizer be surface applied.