This study evaluated the potentials of pollution due to urban agriculture to pose risk to food security in Kano, Nigeria. Two sites irrigated with industrial and domestic wastewaters at Challawa and Jakara, respectively, were sampled for soil, water, and lettuce (Lactuca sativa L.). The samples were analyzed for Pb, Cd, Cr, and Cu being metals which when present in food may pose human health hazard. The values were compared with samples from a control site not associated with wastewater at Watari. The sites were each segmented into up, mid, and downstream sectors. Results showed that the two sites and the control were contaminated with Cu (pollution indexes [PI] = 0.14, 0.16, and 0.14, respectively). Domestic wastewater site was slightly polluted (PI = 1.09) while industrial wastewater site and the control were contaminated (PI = 0.8 and 0.54, respectively) with Pb. The two sites were excessively polluted with Cd and slightly polluted with Cr. The control was contaminated with both (PI = 0.74 and 0.06 for Cd and Cr, respectively). Metal levels in the waters of the sites and the control were higher than the recommended threshold for irrigation water. There was significant positive correlation between Pb, Cr, and Cd in water and in soil; while Cu in soil and in water negatively correlated. There was high metal transfer from soil to plants at the domestic wastewater site (Metal transfer factor Pb = 1.602, Cr = 1.126, and Cu = 1.834). Plants' accumulated concentrations were also high at the domestic wastewater site (Pb = 26.21 mg/kg, Cd = 1.03 mg/kg, Cr = 28.63, and Cu = 2.66 mg/kg). The plants' metal concentrations at the domestic wastewater site exceeded the allowable limits in vegetables. The human ingestion risk was in the order of Jakara > Challawa > Watari.

A survey was conducted during dry and rainy seasons of 2011 in order to determine the phytosociological attributes of acquatic weeds of Kano-Hadeja-Nguru wetlands. Random quadrat method was adopted for the phytosociological studies. The study areas consisted of communities from Kano, Jigawa and Yobe States. In each state, six communities were randomly selected. In each community20 quadrats of 4 m 2 size were laid down and hence sum of 120 quadrats were randomly thrown for each state. Within each quadrat area, weeds were identified, counted and weed cover scores were recorded. Weeds were cut at ground level, fresh and dry weights were determined. Typha grass was the most dominant species in the wetlands of Jigawa (21.195 and 22.5%) compared to either Kano (9.345 and 5.27%) or Yobe (12.73 and12.135%) states. Weed density, weed cover scores as well as fresh and dry weight of weed samples from Kano were observed to be higher than the other two states. Morphological characteristics of Typha spp found in Kano State were taller with more leaves than the other two states. The study suggested that there is strong need to start an Integrated Typha management in the study areas.

Spatially explicit information on soil variability is relevant for agronomic decisions; however, such information is limited in the northern Guinea savanna (NGS) agroecological zone of Nigeria. This study was conducted to delineate soil nutrient management zones (MZs), based on spatial variability of soils in the smallholder maize-based farming system within the NGS. Two hundred and eighty-nine soil samples were analyzed for some physical and chemical properties. Principal component analysis (PCA) was used to aggregate the soil properties into four principal components, which accounted for about 60% of the variation in the data, and spatial variability was assessed with a semivariogram. The ordinary kriging technique was used to predict soil properties at unsampled locations, while weighted overlay analysis was conducted to delineate nutrient management zones. Results showed that total nitrogen (0.06%), available phosphorus (5.6 mg kg−1), organic carbon (0.66%), and effective cation exchange capacity (5.6 cmol(+) kg−1) are below optimal requirement for maize production. Four MZs were identifiable in the region with the highest fertility (MZ3 and MZ4) associated with the northern area but covering a relatively small part (9.1%). The differences observed in soil properties among the MZs suggest that each zone requires different agronomic management, especially in relation to fertilizer application.

Striga is one of most notorious weeds devastating crop production in the dry savannas of northern Nigeria. The weed attacks most cultivated cereals and legumes with crop losses as high as 100% when no control measure is employed. Studies conducted in the dry savannas of Nigeria indicated that Striga seedbank is strongly related to soil and climate properties. This study was conducted to model Striga hermonthica seedbank zones in the dry savannas of Nigeria based on soil and climate properties of the areas. Using multi‐stage spatial sampling, 169 soil samples were collected at the centroids of 25 × 25 km grids across the study area and analysed for physico‐chemical properties. The number of Striga seeds were counted from the soil samples using water elutriator and potassium bicarbonate method. Daily temperature, relative humidity and rainfall for each point were downloaded from Climate Hazards Group InfraRed Precipitation with Station data (CHIRPS). Minimum and maximum temperatures, and relative humidity were accessed from National Aeronautics and Space Administration (NASA POWER). Thresholds of various soil and climate variables for optimum concentration of Striga seedbank were analysed using boundary line analysis (BLA). From the BLA, optimum amount of rainfall for high Striga seedbank was 549 mm per annum. While temperature has a wide suitability range for Striga seedbank development. Principal component analysis was used to reduce dimensionality of the dataset into principal components (PCs). Seven PCs which explained 75.6% variation in the data were retained and used in the weighed overlay modelling (WOM). The weighted overlay map produced five distinct Striga seedbank zones; very low, low, moderate, high and very high. More than 60% of the study area had moderate to high Striga seedbanks. The zones vary mostly based on soil, climate and Striga seed count. The establishment of the optimum levels of the environmental factors at which Striga seedbank is favoured will assist in designing a more site‐specific Striga management. However, for scalability purpose, adoption of the Striga zoning approach can be useful.

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