The effects in a long-term trial of minimum and reduced cultivation on wheat yields

Abstract

A trial was established at Wagga Wagga, New South Wales in 1967 to examine the value of the bipyridilium herbicides as substitutes for mechanical weed control in an extended cropping phase of a cereal/clover ley rotation. The experiment was continued for seven years and the results indicate that herbicides can successfully substitute for mechanical weed control. Direct drilling with a tined combine/seeder into a sprayed but undisturbed seed bed yielded an average of 1.97 tonnes of grain per hectare over seven years compared with 2.02 tonnes per hectare in the mechanically prepared or cultivated seed bed. The difference in yield was not significant. Direct seeding with a triple disc seeder following spraying of an undisturbed seed bed gave significantly lower yields than the other minimum tillage treatments. This minimum cultivation treatment was not successful because of poor plant establishment, possibly emphasized by restricted root growth. A reduced cultivation technique-cultivate-spray-drill-which was included in the trial over the last five years, gave comparable yields, 2.1 7 compared with 1.90 tonnes per hectare, to those obtained by conventional cultivation methods. There were no significant increases in yield with added nitrogen in a dry season, but in four out of the other six years there was significant linear increase in yield with increasing nitrogen rate. There was no significant interaction between cultivation method and applied nitrogen, indicating that neither minimum nor reduced cultivation increased the requirement for nitrogen fertilizer. The results are discussed in terms of mechanical aspects that will allow greater disturbance of the soil beneath the seed with a view to obtaining optimum root development.