Weed control and invasiveness
Mexican sunflower is a pioneering species that grows quickly and produces significant amounts of seeds. It can grow from its subterranean stolons and forms dense stands that prevent the growth of young native plants (CABI, 2014). In Thailand, it was used successfully to control Echinochloa colona in rice fields, where it increased rice tillering, leaf area and rice biomass production (Abeysekara et al., 1993). However, Mexican sunflower is considered to be invasive in some parts of Africa and Australia, and in many Pacific islands (CABI, 2014; GISD, 2012).
Crop and soil improver, soil erosion control and soil remediation
Mexican sunflower produces a nutrient-rich (N, K and P) biomass and its positive effect on subsequent rice and maize crops has been reported from Africa and Brazil (Devide, 2013; Olabode et al., 2007; Jama et al., 2000). Its abundance and adaptability, coupled with its rapid growth rate and very high vegetative matter turnover, makes it a candidate species for soil rejuvenation and improvement, as a green manure or as a major component of compost manure. Different practices have been reported: Mexican sunflower can be left to decompose on the field, or it can be turned into green manure (Olabode et al., 2007; Bot et al., 2001). In the latter case, leaves and soft twigs should be cut and chopped into small pieces before flowering and the resulting mixture evenly spread on the ground before being incorporated in the soil (Bot et al., 2001). In Kenya, Mexican sunflower green manure is profitable for high-value crops such as Brassica sp., French beans, tomatoes and Napier grass (Pennisetum purpureum) (Bot et al., 2001). In the Philippines, 1 to 2 tons of freshly chopped Mexican sunflower forage had a positive effect on a sweet potato crop (Pandosen, 1986). From the Philippines, it was also reported that Mexican sunflower could be a potential organic foliar fertilizer for rapeseed (Dela Pena et al., 2013). Mexican sunflower has a positive effect on crop yields when used in intercropping (Orwa et al., 2009).
Mexican sunflower was used to control soil erosion in the Usambara mountains of Tanzania, but it was not as effective as Napier grass or Guatemala grass (Tripsacum andersonii) (Mwango et al., 2014). In Brazil, Mexican sunflower was used for soil remediation along roadsides where heavy metals, and particularly lead, accumulate (Olivares, 2003).