Effect of diphenyl ether pre-emergence herbicides on legume cover establishment under oil palm (Elaeis guineensis Jacq.)

Two diphenyl ether pre-emergence herbicides, oxyfluorfen and nitrofluorfen, have been compared with manual weeding as a means of establishing Centrosema pubescens and Pueraria phaseoloides cover crops under Elaeis guineensis. Oxyfluorfen at 0.25 kg a.i. ha⁻¹ (a.i. = active ingredient) was the most effective treatment. Application of oxyfluorfen led to faster rates of legume establishment and higher yields of legumes. Twenty-six months after legume planting, the amount of legumes in each plot exceeded 95% of the sown area. Mineral composition of both legume shoots and litter in the oxyfluorfen treated plots was at least comparable, and usually better than that found in covers established by hand weeding.

Data on nutrient acquisition and nutrient re-cycling were obtained by comparison with plots containing naturally regenerating vegetation, fastidiously maintained bare soil, or hand-weeded legume plots in which the oil palms received extra fertilizer. These data show that legumes established by herbicide application contributed greater quantities of nutrients to the developing oil palms. This improved nutrient status led to significantly enhanced relative growth rates of the oil palms. All these benefits accrued at lower cost than the normal estate practice of hand-weeding. Thus oxyfluorfen appears to have great potential in legume cover establishment.