The effects of “starter” fertilizer injection on the growth and yield of drilled vegetable crops in relation to soil nutrient status

Summary

Experiments showed that injection of liquid NPK starter fertilizers directly below the seed of several vegetable crops enhanced early growth, and often increased yield at maturity, even on a soil of high PK status in the presence of ample broadcast fertilizer. Furthermore, small amounts of starter fertilizer applied to a low PK status soil increased early season growth of some crops to a level comparable with that on an adjacent fertile soil of the same soil series subject to identical cultural practices. In a separate experiment, yields from applying starter fertilizer alone on the low PK soil gave yields which were not significantly different from those obtained with much higher levels of conventional broadcast fertilizer. The inclusion of potassium in the starter solution was beneficial on the low K soil but generally had no effect in treatments with high levels of residual K, possibly because of an associated reduction of nitrogen in the starter as K increased. The growth response of seedlings on prepared gradients of residual soil P and K, with and without NPK starter fertilizer, varied with crop but suggests that little benefit from starter applications might be expected at levels >80 μg g^–1 NaHC0₃-extractable P or >300 μg g^–1 NH₄NO₃-exchangeable K (MAFF P indices >5 in the UK fertility classification, or K indices >3). It is suggested that the use of starter fertilizer offers scope for maintaining yields with reduced fertilizer inputs on soils at lower levels of residual nutrients than currently advised for conventional dressings.