The influence of organic manure on Striga hermonthica (Del.) Benth. infestation in Northern Ghana

In the savannah regions of Africa intensified land use brought an increasing infestation of the parasite Striga hermonthica Del. Benth. in cereal crops. Therefore witchweed (S. hermonthica) is often described as an indicator plant for decreasing soil productivity. In Northern Ghana the interrelation of soil fertility and Striga infestation was investigated in low-infested compounds fields (0.1% affected planting holes) and highly-infested bush fields (45.5% affected planting holes). Manure application was one of the main differences between the two field types: In the compound fields organic manure was applied in 9 out of 10 years on average. The bush fields received organic manure or mineral fertiliser in 4 out of 10 years. Due to a long-term application of organic manure the contents of phosphorous, nitrogen and organic carbon were significantly higher in the compound fields. The availability of nutrients (NH4, NO3, P-Bray (I), K, Ca, Mg), the microbial biomass and the microbial activity benefited significantly by manure treatment compared to the bush fields. Fallow periods of two years were too short to maintain the soil productivity in the bush fields. Since the availability of organic manure is limited, alternative measures such as green manure application or crop rotation with legumes are required to maintain or increase the productivity of the bush fields.