Effect of Roundup-Salt Mixtures on Weed Control and Soil Microbial Biomass Under Oil Palm

Abstract

Field experiments were conducted at Oil Palm Research Institute, Kusi from 2002 to 2004 to evaluate the effect of roundup – salt mixtures on the control of weeds and soil microbial biomass. The efficacy of roundup at 0.47 kg a.i./ha mixed with either 0.23 kg/ha of sodium chloride or 0.53 kg/ha of ammonium sulphate or 0.24 kg/ha of urea was compared with roundup at 1.44 kg a.i/ha and manual weeding. The treatments were arranged in randomized complete block design and replicated four times. The roundup and its salt mixtures effectively controlled weeds up to 3 months after treatment (MAT) in both 2002 and 2003 trials. In 2002, roundup with sodium chloride, roundup with ammonium sulphate and roundup with urea maintained a substantial weed control of 77%, 79% and 87% respectively at 3 MAT compared to the 80% and 41% weed control by roundup only
and manually weeding. By 3 MAT in 2003, the % weed control for roundup with sodium chloride, roundup with ammonium sulphate, roundup with urea, roundup only and manual weeding were 63%, 60%, 63%, 65% and 43% respectively. These weed control measures were however ineffective in the 2004 trial. The addition of ammonium sulphate or urea to roundup increased soil microbial C accumulation significantly by 115% and 650% respectively while the application of roundup with sodium chloride, roundup only and manual weeding stimulated microbial C accumulation slightly by 57%, 33% and 30% respectively. Microbial P also increased by 267%, 137%, 81%, 75% and 45%
following the application of roundup with urea, roundup with ammonium sulphate, roundup only, roundup with sodium chloride and manual weeding respectively. The use of roundup – salt mixtures reduced the annual cost of manual weeding per hectare by 76% (¢1,735,000) and annual cost of applying roundup at the labeled rate also by 47 % (¢480,000). The addition of salts to reduced rate of roundup is therefore a cost efficient strategy to control weeds in oil palm plantations.

Journal of the Ghana Science Association Vol. 9 (2) 2007: pp. 61-75