Weed Dynamics as Influenced by Cropping Sequence and Season in Kano River and Hadejia Valley Irrigation Project of Northern Nigeria

Weeds are the most important biotic constrains to food production in both rainfed and irrigated conditions. Six-season trials were carried out over a two-year period to evaluate the impact of various cropping sequences on weed growth, diversity and composition at the Hadejia Valley Irrigation Project (HVIP) and Kano River Irrigation Project (KRIP) in the Sudan savannah zone of Northern Nigeria. Fifty six weed species of the 71 species found throughout the study were in the maize-based sequence, 54 in the rice-based sequence, and 32 in the cowpea-based sequence. In the wet season, the cowpea-wheat-rice (CWR) rotation sequence recorded the highest biomass (231.4g m-2) whereas the cowpea-onion-rice (COR) rotation sequence recorded the lowest (165g m-2) in cold season. The cowpea-tomato-rice (CTR) rotation sequence recorded 13.4% more weeds density than cowpea-wheat-rice (CWR) and 10.4% higher weeds than cowpea-onion-rice (COR) in rainy season. Maize-wheat-fallow (MWFL) had the most weeds (250.3 m-2) while maize-wheat-cowpea (MWC) had the least (170.5 m-2) in rainy season. In terms of weed biomass, maize- tomato-fallow (MTFL) had the maximum amount (664.8g m-2) during the hot dry season, whereas maize-wheat-cowpea (MWC) had the lowest amount (411.8g m-2). The rice-wheat-maize (RWM) consistently supported more weeds during the rainy (328.87 m-2), cold (291.39 m-2), and hot (271.46 m-2) seasons. In the cold season, rice-wheat-fallow (RTF) rotation sequence showed lower weed biomass (470.1 g m-2), whereas in the hot dry season, rice-wheat-fallow (RWFL) showed the maximum weed biomass (656.3 g m-2). Rotation systems involving legumes, forage, and pasture decreased weed infestation and may be utilized as an alternative method of weed management. The conventional cereal-cereal-cereal rotation sequence encouraged weed infestation and should be discouraged.