Best management practice turnip production: how to target a 14 tonne/ha crop on a central North Island dairy farm

Abstract

A best management protocol for growing a turnip crop was developed from published information and provided to dairy farmers intending to grow the crop. On the basis of information returned by farmers in the 2002/2003 and 2003/2004 growing seasons, the validity of the assumptions underlying the protocol were tested. Many of the returned forms were incomplete and could not be used in the analysis. Adherence to the protocol was variable as farmers interpreted the prescriptive protocol differently and applied components of the protocol as they saw fit on their property. Protocol directions for nitrogen application, soil phosphorus content and sowing rate were applied the most uniformly, providing little variation for testing the impact of these factors. Farmers who applied post-emergence herbicide and insecticide as prescribed achieved a higher (P<0.01) turnip yield (on average 12.5 t DM/ha) than those that did not (average 10.9 t DM/ha). Most of this extra yield (1.3 t of the 1.6 t DM/ha) was the result of elevated leaf yields (P<0.01) though the leaf:bulb ratio was not significantly affected by following the protocol. We cautiously conclude that following the protocol will be beneficial to farmers. The caution is based on the fact that the results reported did not originate from a controlled experiment, but from a survey where differences in factors such as farming ability and cropping experience were not adequately accounted for between treatments. Keywords: dairy farming, farmer survey, herbicide, insecticide, summer feed gap, turnip