Impacts of inter-row grass cover on soil biological fertility in tomato crop in Martinique. PoS2-52

The Hemiptera Bemisia tabaci (Gennadius) species is one of the main tomato pest in Martinique, due to its role in the transmission of a variety of plant viruses (Urbino et al., 2003). One of the most effective ways to regulate its infestation in agroecology is to keep grassed inter-rows in tomato crops (Bezerra et al., 2004). This practice may have benefits for soil health such as promotion of biological activity. However, it may in some case reduce yields due to resource competition with the main crop (Singh et al., 2015). Our objective was thus to determine whether having grassed inter-rows would improve soil biological fertility in tomato crop. To do so, we monitored the biological activity in bare and grassed tomato inter-rows (spontaneous vegetation, dominated by graminoids) between plantation and flowering stage (March to May 2017) in an experimental site in Le Lamentin (Martinique, France). We used two indicators of biological fertility: lamina-bait decomposition of a labile (bean) and recalcitrant (acacia) substrate to assess soil biological activity, and bioassay to assess nutrient cycling. In line with our expectations, our results evidenced lower Bemisia tabaci densities in tomato crops with grassed than bare inter-rows (P-value = 0.04). In addition, soil biological activity was higher in grassed than bare inter-rows, with a mean increase of 23 and 68% for bean and acacia lamina-baits decomposition, respectively, for all sampling dates. Nonetheless, the biomass produced in bioassay was 31% inferior in soil from grassed than bare inter-rows, which was well reflected by crop yield differences between the two intercropping modalities. These results suggest that while grassed inter-rows may improve soil biological activity and reduce Bemisia tabaci spreading in tomato crop, the resulting soil community may have higher nutritional needs that probably led to competition with tomato growth. We conclude that good biological activity and pest control do not necessarily translate in increased yield in high inputs systems as tomato crops, at least on the short-term.