Organic amendments mitigate heterotrophic weed infestation in savannah agriculture

Abstract

The relationship between soil fertility and Striga infestation was studied in 17 lightly infested compound and 17 highly infested bush fields in 15 villages of the Tolon/Kumbungu district of north Ghana. Thirty percent of the compound fields contained Striga seeds (on average 0.4 seeds in 100 g dried soil) but emergence of the parasite was rare (0.1–6% of the planting holes). The bush fields were contaminated with 11 Striga seeds/100 g soil on average and Striga plants were observed at 45.5% (10–81%) of the planting holes. Maize in the compound fields is continuously monocropped whereas mixed cropping is common in the bush fields (e.g. maize/sorghum, maize/groundnut). Fallow periods lasted 2 years on average in bush fields and the introduction of fallow was rather exceptional and linked to local practice in compound fields. Two-year fallows were too short to maintain soil productivity in the bush fields. In the compound fields organic manure (e.g. cattle dung, in addition to continuously dispersed human faeces and compound waste) was applied in 8 out of 10 years on average. The bush fields received organic manure or mineral fertilizer in 4 out of 10 years. Due to long-term application of organic manure the contents of phosphorus, nitrogen and organic carbon were significantly higher in compound field soils. The availability of nutrients (NH 4, NO 3, P bray 1 , K, Ca, Mg), the microbial biomass and the microbial activity benefited significantly from the manure treatment compared to bush fields. The results indicated that the Striga infestation is negatively related to the total nitrogen content and microbial biomass.