What is the fine-grained topic of the following text: 1996) found that organic tomato Solanum lycopersicum plots containing a mulch had similar broad-leaved weed and grass biomass (6.6-10.6 g dry weight/m² and 1.3-7.3 g, respectively) to conventional plots treated with herbicide (3.0-6.0 g and 0.7-1.3 g) at 12 weeks after planting. Only return the topic.
The impact of mulch on weed and grass biomass in organic versus conventionally treated tomato plots.